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IMAI Yohsuke
Graduate School of Engineering / Department of Mechanical Engineering
Professor

Researcher basic information

■ Research Keyword
  • 混相流
  • 流体構造連成
  • 消化器
  • 微小循環
  • 計算生体流体力学
  • 数値流体力学
  • 計算力学
  • 計算バイオメカニクス
■ Research Areas
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Fluid engineering

Research activity information

■ Award
  • Dec. 2019 Asian Pacific Association for Computational Mechanics, APACM Award for Young Investigators in Computational Mechanics
    IMAI Yohsuke

  • May 2019 日本計算工学会, 第24回計算工学講演会 グラフィックスアワード優秀賞
    Japan society

  • May 2019 日本計算工学会, 第24回計算工学講演会 グラフィックスアワード特別賞（Meshman賞）
    Japan society

  • Jul. 2018 Japan Association for Computational Mechanics, JACM Fellows Award
    IMAI YOHSUKE
    Japan society

  • 17 Sep. 2017 日本機械学会, 日本機械学会計算力学部門 業績賞
    Japan society

  • 04 Dec. 2015 青葉工学振興会, 第9回青葉工学振興会賞
    Publisher

  • Jul. 2014 Dynamics of Capsules, Vesicles, and Cells in Flow, Best Poster Award
    International society

  • Apr. 2014 文部科学省, 平成26年度科学技術分野の文部科学大臣表彰 若手科学者賞
    International academic award

  • Mar. 2014 Advances in Computation Fluid-Structure Interaction and Flow Simulation, Poster Award (Second Place)
    International society

  • Aug. 2013 7th Asian Pacific Conference on Biomechanics, APCB2013 Award for Excellent Thesis
    International society

  • Mar. 2013 Journal of Biomechanical Science and Engineering, JBSE Graphics of the Year Award
    Official journal

  • Jun. 2012 日本計算工学講演会, 第17回計算工学講演会 ベストペーパーアワード
    Japan society

  • Jan. 2012 日本機械学会バイオエンジニアリング部門, 日本機械学会バイオエンジニアリング部門 瀬口賞
    Japan society

  • Nov. 2011 Journal of Biomechanical Science and Engineering, JBSE Papers of the Year Award
    Official journal

  • Jul. 2010 日本計算力学連合, JACM Award for Young Investigators in Computational Mechanics
    Publisher

  • Apr. 2010 日本機械学会, 日本機械学会奨励賞（研究）
    Publisher

  • Jan. 2010 青葉工学振興会, 第15回青葉工学研究奨励賞
    Publisher

  • Dec. 2008 International Conference on Biomedical Engineering, Young Investigator Award Merit Prize
    International society

  • Feb. 2007 財団法人手島工業教育資金団, 手島記念研究賞（博士論文賞）
    Publisher

  • Dec. 2006 第20回数値流体力学シンポジウム実行委員会, 第20回数値流体力学シンポジウム ベストCFDグラフィックス・アワード最優秀賞
    Japan society

  • Nov. 2006 日本機械学会計算力学部門, 日本機械学会第19回計算力学講演会 ビジュアリゼーションコンテスト優秀作品賞
    Japan society

  • Dec. 2005 第19回数値流体力学シンポジウム実行委員会, 第19回数値流体力学シンポジウム ベストCFDグラフィックス・アワード最優秀賞
    Japan society

  • Nov. 2005 日本機械学会計算力学部門, 日本機械学会第18回計算力学講演会 ビジュアリゼーションコンテスト最優秀作品賞
    Japan society

  • Dec. 2004 第18回数値流体力学シンポジウム実行委員会, 第18回数値流体力学シンポジウム ベストCFDグラフィックス・アワード優秀賞
    Japan society

■ Paper
  • Alexandria H. Lim, Chris Varghese, Gabrielle H. Sebaratnam, Gabriel Schamberg, Stefan Calder, Armen A. Gharibans, Christopher N. Andrews, Daphne Foong, Vincent Ho, Shunichi Ishida, Yohsuke Imai, Michelle R. Wise, Greg O’Grady
    This study evaluates gastric electrophysiology in relation to the menstrual cycle using a novel noninvasive high-resolution methodology, revealing substantial variations in gastric activity with menstrual cycling and menopause. Gastric slow-wave frequency is significantly higher in the luteal versus follicular menstrual phase. Computational modeling predicts that this difference translates to higher rates of gastric mixing and liquid emptying in the luteal phase, which is consistent with previous experimental data evaluating menstrual cycling effects on gastric emptying.
    American Physiological Society, Jul. 2024, American Journal of Physiology-Gastrointestinal and Liver Physiology, 327(1) (1), G47 - G56
    Scientific journal

  • Togo Hayashi, Hironori Takeda, Shunichi Ishida, Yohsuke Imai
    Understanding the growth-induced deformation of soft materials in viscous environments is important for a variety of problems in nature and engineering. Here, we focus on the fluid–structure interaction of a hyperelastic sheet growing in an incompressible Newtonian fluid in the Stokes flow regime. We develop a computational framework for simulating this problem, where the isogeometric boundary integral method is used with the Kirchhoff–Love shell formulation and elastic–plastic decomposition of the deformation gradient tensor. We quantify the relative effects of the growth rate, the sheet bending rigidity, and the fluid viscosity on the fold formation and development of the growing sheet. Our results suggest that the viscous resistance to in-plane deformation promotes fold formation, whereas the viscous resistance to out-of-plane deformation suppresses fold development. We also investigate the effects of the thickness and aspect ratio of the rectangular sheet. Finally, we compare the growth- and prestrain-induced deformations to find a common behavior of sheets under viscous environments.
    AIP Publishing, May 2024, Physics of Fluids, 36(5) (5)
    Scientific journal

  • Yuto Kawabata, Shunichi Ishida, Yohsuke Imai
    Effects of magnetic field applied perpendicular to a shear plane in shear flow on the deformation of a ferrofluid droplet are numerically investigated. The boundary integral method is employed to solve the two-phase Stokes flow under a uniform magnetic field. When the magnetic field is applied perpendicular to the shear plane, the deformation of the droplet in the shear plane decreases. The magnetic field causes the droplet to elongate in the y-direction, and its cross-sectional radius in shear plane decreases. Consequently, the apparent capillary number in the shear plane decreases, thereby suppressing the droplet deformation. Droplet breakup is also suppressed by imposing a magnetic field perpendicular to the shear plane, thereby increasing the critical capillary numbers. The critical capillary numbers for the magnetic Bond numbers Bo = 2.0 and 4.0 increase to approximately 110% and 130%, respectively, than those without magnetic field. Furthermore, an equation for the theoretical prediction of the droplet deformation under a magnetic field in shear flow is presented, which is based on the small deformation theory, the decrease in the cross-sectional radius, and the boundary conditions at the droplet interface. The theoretical prediction agrees well with the numerical results for the variation in the magnetic susceptibility of the droplet as well as the viscosity ratio between the external fluid and the ferrofluid droplet under a small deformation. The critical capillary numbers under a magnetic field can also be predicted by using the numerical results without a magnetic field.
    AIP Publishing, Mar. 2024, Physics of Fluids, 36(3) (3)
    Scientific journal

  • Yusuke Asai, Shunichi Ishida, Hironori Takeda, Gakuto Nakaie, Takuya Terahara, Yasutoshi Taniguchi, Kenji Takizawa, Yohsuke Imai
    Elsevier BV, Mar. 2024, Journal of Fluids and Structures, 125, 104081 - 104081
    Scientific journal

  • Hironori Takeda, Yusuke Asai, Shunichi Ishida, Yasutoshi Taniguchi, Takuya Terahara, Kenji Takizawa, Yohsuke Imai
    Elsevier BV, Jan. 2024, Journal of Fluids and Structures, 124, 104022 - 104022
    Scientific journal
    Link to Kobe Univ. Repository (Kernel)

  • SAIKI Michina, TAKEDA Hironori, KAWABATA Yuto, ISHIDA Shunichi, IMAI Yohsuke
    The Japan Society of Mechanical Engineers, 2023, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2023.34, 2B05, Japanese

  • KURIHARA Tomofumi, TAKEDA Hironori, ISHIDA Shunichi, IMAI Yohsuke
    The Japan Society of Mechanical Engineers, 2023, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2023.34, 2G09, Japanese

  • MATSUMOTO Taku, TAKEDA Hironori, ISHIDA Shunichi, IMAI Yohsuke
    The Japan Society of Mechanical Engineers, 2023, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2023.34, 1B02, Japanese

  • Rika Ebara, Shunichi Ishida, Taimei Miyagawa, Yohsuke Imai
    The amplitude and frequency of peristaltic contractions are two major parameters for assessing gastric motility. However, it is not fully understood how these parameters affect the important functions of the stomach, such as gastric mixing and emptying. This study aimed to quantify the effects of peristaltic amplitude and frequency on gastric mixing and emptying using computational fluid dynamics simulation of gastric flow with an anatomically realistic model of the stomach. Our results suggest that both the increase and decrease in peristaltic amplitude have a significant impact on mixing strength and emptying rate. For example, when the peristaltic amplitude was 1.2 times higher than normal, the emptying rate was 2.7 times faster, whereas when the amplitude was half, the emptying rate was 4.2 times slower. Moreover, the emptying rate increased more than proportionally with the peristaltic frequency. The nearest contraction wave to the pylorus and the subsequent waves promoted gastric emptying. These results suggest the importance of maintaining parameters within normal ranges to achieve healthy gastric function.
    The Royal Society, Jan. 2023, Journal of The Royal Society Interface, 20(198) (198)
    [Refereed]
    Scientific journal

  • Kohei Maeyama, Shunichi Ishida, Yohsuke Imai
    Peristaltic pumping is the primary mechanism of food transport in the human intestine. Intestinal contents are often modeled as power-law fluids with low-behavior indices ( n < 1). Peristaltic flows were studied for periodic contraction waves ([Formula: see text]) with infinitely long wavelengths ([Formula: see text]) in the Stokes flow regime ([Formula: see text]). However, the peristaltic flow generated by an isolated contraction wave with a short wavelength at nonzero Reynolds numbers is more relevant to physiological conditions. In this study, we investigated the peristaltic transport of a power-law fluid with a low behavior index of n = 0.21 at nonzero Reynolds numbers up to Re = 10, generated by a single short contraction wave. First, we investigated the analytical solution for the peristaltic transport of the power-law fluid for [Formula: see text] and [Formula: see text]. The analytical solution shows that the discharge flow rate of a power-law fluid generated by a single contraction wave is much smaller than that of a Newtonian fluid ( n = 1). Next, we investigated the peristaltic transport for [Formula: see text] 10 using the cumulant lattice Boltzmann method. The numerical results demonstrate that the discharge flow rate for the power-law fluid sharply increased owing to the inertia effect. The power-law fluid induces an asymmetric flow field with respect to the contraction wave at smaller Reynolds numbers than Newtonian fluids. The inertia effect was increased by the sharpness of the contraction wave. These results suggest that intestinal contents can be transported more quickly by an isolated contraction wave with a shorter wavelength when the contents have low consistency indices or when the contraction wave has a large propagation velocity.
    AIP Publishing, Nov. 2022, Physics of Fluids, 34(11) (11), 111911 - 111911
    [Refereed]
    Scientific journal
    Link to Kobe Univ. Repository (Kernel)

  • Haruki Yoshida, Shunichi Ishida, Taiki Yamamoto, Takayuki Ishikawa, Yuichi Nagata, Kazuhito Takeuchi, Hironori Ueno, Yohsuke Imai
    Ciliary motility disorders are known to cause hydrocephalus. The instantaneous velocity of cerebrospinal fluid (CSF) flow is dominated by artery pulsation, and it remains unclear why ciliary dysfunction results in hydrocephalus. In this study, we investigated the effects of cilia-induced surface velocity on CSF flow using computational fluid dynamics. A geometric model of the human ventricles was constructed using medical imaging data. The CSF produced by the choroid plexus and cilia-induced surface velocity were given as the velocity boundary conditions at the ventricular walls. We developed healthy and reduced cilia motility models based on experimental data of cilia-induced velocity in healthy wild-type and Dpcd-knockout mice. The results indicate that there is almost no difference in intraventricular pressure between healthy and reduced cilia motility models. Additionally, it was found that newly produced CSF from the choroid plexus did not spread to the anterior and inferior horns of the lateral ventricles in the reduced cilia motility model. These findings suggest that a ciliary motility disorder could delay CSF exchange in the anterior and inferior horns of the lateral ventricles.
    The Royal Society, Aug. 2022, Journal of The Royal Society Interface, 19(193) (193)
    [Refereed]
    Scientific journal

  • Shunichi Ishida, Ryota Matsumoto, Daiki Matsunaga, Yohsuke Imai
    American Physical Society (APS), Jun. 2022, Physical Review Fluids, 7(6) (6)
    [Refereed]
    Scientific journal
    Link to Kobe Univ. Repository (Kernel)

  • SAIKI Michina, TAKEDA Hironori, ISHIDA Shunichi, IMAI Yohsuke
    The Japan Society of Mechanical Engineers, 2022, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2022.33, 1F15, Japanese

  • MATSUMOTO Taku, TAKEDA Hironori, ISHIDA Shunichi, IMAI Yohsuke
    The Japan Society of Mechanical Engineers, 2022, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2022.33, 1F18, Japanese

  • Tomoki Oyama, Shunichi Ishida, Kohei Maeyama, Taimei Miyagawa, Yohsuke Imai
    American Physical Society (APS), Sep. 2021, Physical Review Fluids, 6(9) (9)
    [Refereed]
    Scientific journal
    Link to Kobe Univ. Repository (Kernel)

  • Tim Hsu‐Han Wang, Timothy R. Angeli, Shunichi Ishida, Peng Du, Armen Gharibans, Niranchan Paskaranandavadivel, Yohsuke Imai, Taimei Miyagawa, Thomas L. Abell, Gianrico Farrugia, Leo K. Cheng, Gregory O’Grady
    Wiley, Jan. 2021, Physiological Reports, 8(24) (24)
    [Refereed]
    Scientific journal

  • Satoshi Ii, Hiroki Kitade, Shunichi Ishida, Yohsuke Imai, Yoshiyuki Watanabe, Shigeo Wada
    The cerebral vasculature has a complex and hierarchical network, ranging from vessels of a few millimeters to superficial cortical vessels with diameters of a few hundred micrometers, and to the microvasculature (arteriole/venule) and capillary beds in the cortex. In standard imaging techniques, it is difficult to segment all vessels in the network, especially in the case of the human brain. This study proposes a hybrid modeling approach that determines these networks by explicitly segmenting the large vessels from medical images and employing a novel vascular generation algorithm. The framework enables vasculatures to be generated at coarse and fine scales for individual arteries and veins with vascular subregions, following the personalized anatomy of the brain and macroscale vasculatures. In this study, the vascular structures of superficial cortical (pial) vessels before they penetrate the cortex are modeled as a mesoscale vasculature. The validity of the present approach is demonstrated through comparisons with partially observed data from existing measurements of the vessel distributions on the brain surface, pathway fractal features, and vascular territories of the major cerebral arteries. Additionally, this validation provides some biological insights: (i) vascular pathways may form to ensure a reasonable supply of blood to the local surface area; (ii) fractal features of vascular pathways are not sensitive to overall and local brain geometries; and (iii) whole pathways connecting the upstream and downstream entire-scale cerebral circulation are highly dependent on the local curvature of the cerebral sulci.
    Jun. 2020, PLoS computational biology, 16(6) (6), e1007943, English, International magazine
    [Refereed]
    Scientific journal

  • Daiki MATSUNAGA, Yohsuke IMAI
    Last, Japan Society of Mechanical Engineers, 2020, Journal of Biomechanical Science and Engineering
    [Refereed]
    Scientific journal

  • Hiroki Kamada, Hideki Ota, Masanori Nakamura, Yohsuke Imai, Shunichi Ishida, Wenyu Sun, Ko Sakatsume, Ichiro Yoshioka, Yoshikatsu Saiki, Kei Takase
    This study investigated hemodynamic changes in the thoracic aorta and aortic arch branches before and after aortic valve replacement (AVR) by 4D-flow MRI in patients with aortic valve stenosis (AS). Thoracic 4D-flow MRI was performed in 10 AS patients before and after AVR (mean 27 ± 1.9 days). Fifteen aortic planes and 3 aortic arch branches planes were set to evaluate the mean volume flow rate in each plane during a cardiac cycle and the angle between the main flow direction in a specified plane and the axial direction of the aorta. We also focused on the distribution and magnitude of helicity density to evaluate the flow complexity. A significant increase in the volume flow rate after AVR was found in the ascending aorta (before 59.2 ± 8.7 mL/s vs after 77.3 ± 6.2 mL/s, P < 0.05) and the aortic arch branches (before 26.5 ± 2.8 mL/s vs after 35.8 ± 3.3 mL/s, P < 0.001). The flow angle significantly decreased in the ascending aorta (before 39.2 ± 2.7 degree vs after 25.2 ± 1.7°, P < 0.0001) and the arch aorta (before 19.3 ± 2.0 degree vs after 13.4 ± 0.9°, P < 0.001). The volume flow rate in the ascending aorta and the arch branches increased within 1 month after AVR, showing an increased blood supply to the upper body, including to the brain. The postoperative change was accompanied with an increased blood flow in the ascending aorta and a decreased flow complexity proximal to the arch branches.
    2020, Seminars in thoracic and cardiovascular surgery, 32(1) (1), 25 - 34, English, International magazine
    [Refereed]
    Scientific journal

  • Hiroki Ito, Daiki Matsunaga, Yohsuke Imai
    Last, Nov. 2019, Physical Review Fluids, 4, 113601, English
    [Refereed]
    Scientific journal
    Link to Kobe Univ. Repository (Kernel)

  • Naoki Takeishi, Yohsuke Imai, Shigeo Wada
    © 2019 The Japan Society of Mechanical Engineers. Studies on platelet margination have shown that the platelets can effectively marginate at the microvessel wall in a multi-file flow of red blood cells (RBCs), whereas axially migrated RBCs push platelets toward the wall. However, it is unclear whether these results can be extended to capillaries, which potentially cause a single-file line of RBCs, or a so-called bolus flow. Our previous numerical results (Takeishi and Imai, 2017) showed that microparticles with a diameter of 1 m (1-m-MPs) were captured by a bolus flow of RBCs, instead of being marginated in capillaries. Herein we perform numerical simulations to clarify whether platelets are captured or escape from the vortex-like flow structures between RBCs. We demonstrate that platelets are also captured in a capillary whose diameter is 25% larger than that of RBCs at a physiologically-relevant hematocrit (Hct 0.2), but the number of captured platelets is smaller than that of 1-m-MPs. When the capillary diameter is comparable to that of RBCs, however, many platelets flow near the wall due to an unstable bolus flow resulting in a less number of captured platelets. These results suggest that the size effect reduces platelet capture events compared to 1-m-MPs. We also investigate the effect of Hct and the non-dimensional shear rate (capillary number) on capture events. These findings may help not only to understand platelet adhesion in capillaries but also to develop therapeutic drug carriers.
    Nov. 2019, Journal of Biomechanical Science and Engineering, 14(3) (3), 18 - 00535, English
    [Refereed]
    Scientific journal

  • Jun Ohta, Shunichi Ishida, Tetsuaki Kawase, Yukio Katori, Yohsuke Imai
    Common practices to improve the ability to swallow include modifying physical properties of foods and changing the posture of patients. Here, we quantified the effects of the viscosity of a liquid bolus and patient posture on the bolus pathway and pharyngeal residue using a computational fluid dynamics simulation. We developed a computational model of an impaired pharyngeal motion with a low pharyngeal pressure and no pharyngeal adaptation. We varied viscosities from 0.002 to 1 Pa·s and postures from -15° to 30° (from nearly vertical to forward leaning). In the absence of pharyngeal adaptation, a honey-like liquid bolus caused pharyngeal residue, particularly in the case of forward-leaning postures. Although the bolus speed was different among viscosities, the final pathway was only slightly different. The shape, location, and tilting of the epiglottis effectively invited a bolus to two lateral pathways, suggesting a high robustness of the swallowing process.NEW & NOTEWORTHY Thickening agents are often used for patients with dysphagia. An increase in bolus viscosity not only reduces the risk of aspiration but also can cause a residual volume in the pharynx. Because information obtained from videofluoroscopic swallowing studies is only two-dimensional, measurement of pharyngeal residue is experimentally difficult. We successfully quantified the three-dimensional bolus pathway and the pharyngeal residual volume using computational modeling and simulation.
    Nov. 2019, American Journal of Physiology Gastrointestinal and Liver Physiology, 317(6) (6), G784 - G792, English, International magazine
    [Refereed]
    Scientific journal

  • Shunichi Ishida, Taimei Miyagawa, Gregory O'Grady, Leo K. Cheng, Yohsuke Imai
    Proper coordination of gastric motor functions is required for healthy gastric emptying. However, pyloric function may be impaired by functional disorders or surgical procedures. Here, we show how coordination between pyloric closure and antral contraction affects the emptying of liquid contents. We numerically simulated fluid dynamics using an anatomically realistic gastrointestinal geometry. Peristaltic contractions in the proximal stomach resulted in gastric emptying at a rate of 3-8 ml min-1. When the pylorus was unable to close, the emptying rate increased to 10-30 ml min-1, and instantaneous retrograde flow from the duodenum to the antrum occurred during antral relaxation. Rapid emptying occurred if the pylorus began to open during the terminal antral contraction, and the emptying rate was negative if the pylorus only opened during the antral relaxation phase. Our results showed that impaired coordination between antral contraction and pyloric closure can result in delayed gastric emptying, rapid gastric emptying and bile reflux.
    Aug. 2019, Journal of the Royal Society Interface, 16(157) (157), 20190266 - 20190266, English, International magazine
    [Refereed]
    Scientific journal
    Link to Kobe Univ. Repository (Kernel)

  • Naoki Takeishi, Marco E. Rosti, Yohsuke Imai, Shigeo Wada, Luca Brandt
    © Cambridge University Press 2019 We present a numerical analysis of the rheology of a suspension of red blood cells (RBCs) in a wall-bounded shear flow. The flow is assumed as almost inertialess. The suspension of RBCs, modelled as biconcave capsules whose membrane follows the Skalak constitutive law, is simulated for a wide range of viscosity ratios between the cytoplasm and plasma, λ = 0.1-10, for volume fractions up to φ = 0.41 and for different capillary numbers (Ca). Our numerical results show that an RBC at low Ca tends to orient to the shear plane and exhibits so-called rolling motion, a stable mode with higher intrinsic viscosity than the so-called tumbling motion. As Ca increases, the mode shifts from the rolling to the swinging motion. Hydrodynamic interactions (higher volume fraction) also allow RBCs to exhibit tumbling or swinging motions resulting in a drop of the intrinsic viscosity for dilute and semi-dilute suspensions. Because of this mode change, conventional ways of modelling the relative viscosity as a polynomial function of φ cannot be simply applied in suspensions of RBCs at low volume fractions. The relative viscosity for high volume fractions, however, can be well described as a function of an effective volume fraction, defined by the volume of spheres of radius equal to the semi-middle axis of a deformed RBC. We find that the relative viscosity successfully collapses on a single nonlinear curve independently of λ except for the case with Ca > 0.4, where the fit works only in the case of low/moderate volume fraction, and fails in the case of a fully dense suspension.
    Aug. 2019, Journal of Fluid Mechanics, 872, 818 - 848, English
    [Refereed]
    Scientific journal

  • Yohsuke Imai, Daiki Matsunaga
    Understanding the behavior of capsules in flow and the rheology of capsule suspensions is of fundamental importance for diverse problems in nature and engineering. The particle Reynolds number of capsules is often small, and the flow field is given by the boundary integral formulation of the Stokes equations. The boundary element method (BEM) based on the boundary integral formulation is thus one of the most accurate methods for simulating capsules under Stokes flow regime. A high computational cost of BEM, however, has limited its application to relatively small scale problems. We have developed a graphics process unit (GPU) computing of BEM for capsules and biological cells in Stokes flow. We have investigated rheological properties of capsules, and those of capsule suspensions using the GPU-accelerated BEM. Here, we provide an overview of our recent studies, particularly focusing on the shear viscosity of dense suspensions of capsules in simple shear flow an overshoot phenomenon of the capsule deformation in oscillating shear flow and the sedimentation of red blood cells.
    Springer Basel, 2018, Modeling and Simulation in Science, Engineering and Technology, 213 - 251, English
    In book

  • Shunichi Ishida, Akihisa Ami, Yohsuke Imai
    Cytoadhesion of red blood cells infected by Plasmodium falciparum (Pf-IRBCs) is predominantly found in postcapillary venules, rather than in arterioles. However, factors influencing this phenomenon remain unclear. Here, we conduct a systematic study using a numerical model coupling the fluid and solid mechanics of the cells and cellular environment with the biochemical ligand-receptor interaction. Our results show that, once a Pf-IRBC adheres to the vascular wall, the Pf-IRBC can withstand even arteriole shear stresses, and exhibits either rolling or firm adhesion. We also perform a simulation of the multistep process of cytoadhesion, consisting of flow, margination, capture, and rolling or firm adhesion. This multistep simulation suggests that a lower probability of contact with the vascular wall at high shear rates may diminish adherent Pf-IRBCs in the arterioles.
    CELL PRESS, Sep. 2017, BIOPHYSICAL JOURNAL, 113(5) (5), 1163 - 1172, English
    [Refereed]
    Scientific journal

  • T. Omori, H. Sugai, Y. Imai, T. Ishikawa
    Cilia-driven nodal flow is important in the determination of left-right asymmetry in the body. Several theoretical and computational models have been proposed to explain the mechanics of ciliary motion, although the full mechanism remains unknown. Here, we developed a three-dimensional nodal cilia axoneme model using a finite element-boundary element coupling method, and investigated the mechanics of nodal ciliary motion. We found that the rotational orbit was strongly dependent on the dynein activation frequency. We also investigated flow field generated by the ciliary rotation, and the flow strength decayed as r(-3) at the far field from the cilium. Our numerical results also suggest that experimentally observed tilt angle theta = 2 pi/9 is sufficiently large to make a leftward flow. These findings are helpful in better understanding ciliary motion and nodal flow. (C) 2017 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Aug. 2017, JOURNAL OF BIOMECHANICS, 61, 242 - 249, English
    [Refereed]
    Scientific journal

  • A BOUNDARY ELEMENT METHOD FOR CELLULAR SCALE PHYSIOLOGICAL FLOW PROBLEMS: PASSIVE MOTIONS OF RED BLOOD CELLS AND ACTIVE MOTIONS OF CILIA AND FLAGELLA
    Toshihiro Omori, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Yamaguchi Medal 受賞講演
    Jul. 2017, The 26th Congress of the International Society of Biomechanics (ISB 2017), English
    [Invited]

  • Naoki Takeishi, Yohsuke Imai
    Previous studies have concluded that microparticles (MPs) can more effectively approach the microvessel wall than nanoparticles because of margination. In this study, however, we show that MPs are not marginated in capillaries where the vessel diameter is comparable to that of red blood cells (RBCs). We numerically investigated the behavior of MPs with a diameter of 1 mu m in various microvessel sizes, including capillaries. In capillaries, the flow mode of RBCs shifted from multi-file flow to bolus (single-file) flow, and MPs were captured by the bolus flow of the RBCs instead of being marginated. Once MPs were captured, they rarely escaped from the vortex-like flow structures between RBCs. These capture events were enhanced when the hematocrit was decreased, and reduced when the shear rate was increased. Our results suggest that microparticles may be rather inefficient drug carriers when targeting capillaries because of capture events, but nanoparticles, which are more randomly distributed in capillaries, may be more effective carriers.
    NATURE PUBLISHING GROUP, Jul. 2017, SCIENTIFIC REPORTS, 7, 5381, English
    [Refereed]
    Scientific journal

  • Hiroki Kamada, Yohsuke Imai, Masanori Nakamura, Takuji Ishikawa, Takami Yamaguchi
    ObjectiveSIPA, which is mediated by vWF, is a key mechanism in arterial thrombosis under an abnormally high shear rate of blood flow. We investigated the influence of SIPA on thrombogenesis, focusing on alterations in blood flow at stenotic vessels. MethodsWe carried out a computer simulation of thrombogenesis in stenotic vessels at three different injury positions (ie, upstream, apex, and downstream of the stenosis) to evaluate the effect of SIPA. ResultsThe results demonstrated that thrombus volume increased downstream of the stenosis. In particular, growth was enhanced significantly as blood flow velocity and severity of stenosis increased. The influence of SIPA was induced by continuous exposure to high shear rate; thus, SIPA had a greater effect from the apex to downstream of the stenosis along the vessel wall. The asymmetry of the impact of SIPA contributed to the distribution of the thrombus. Furthermore, we found that the degree of SIPA was prolonged in a stenotic vessel with a distal injury, whereas it was moderate with thrombus growth in a nonstenosed vessel. This occurred because platelets and vWF that underwent a high shear rate around the apex were transported to the region downstream of the stenosis. ConclusionsThese results suggest that thrombus formation downstream of the stenosis is easily affected by SIPA and hemodynamics.
    WILEY, May 2017, MICROCIRCULATION, 24(4) (4), e12355, English
    [Refereed]
    Scientific journal

  • Integrated nanobiomechanics of the living system
    T. Yamaguchi, Y. Imai, T. Ishikawa
    Apr. 2017, 19th International Conference on Finite Elements in Flow Problems, English

  • RELATIONSHIP BETWEEN PERISTALTIC CONTRACTION AND GASTRIC MIXING
    Yohsuke Imai, Taimei Miyagawa, Shunichi Ishida, Takami Yamaguchi, Takuji Ishikawa
    Dec. 2016, Abstracts Book of the 16th International Conference on Biomedical Engineering, 167, English

  • DEVELOPMENT OF A BIOMECHANICAL MODEL OF CELL BEHAVIOR SUBJECTED TO CYCLIC STRETCH
    Fumiyasu Saito, Yohsuke Imai, Shunichi Ishida, Toshihiro Omori, Takuji Ishikawa
    Dec. 2016, Abstracts Book of the 16th International Conference on Biomedical Engineering, 163, English

  • A NUMERICAL ANALYSIS OF THE LATERAL MIGRATION OF FLOWING CELLS
    Stephanie Nix, Yohsuke Imai, Takuji Ishikawa
    Dec. 2016, Abstracts Book of the 16th International Conference on Biomedical Engineering, 54, English

  • Taimei Miyagawa, Yohsuke Imai, Shunichi Ishida, Takuji Ishikawa
    The relationship between gastric motility and the mixing of liquid food in the stomach was investigated with a numerical analysis. Three parameters of gastric motility were considered: the propagation velocity, frequency, and terminal acceleration of peristaltic contractions. We simulated gastric flow with an anatomically realistic geometric model of the stomach, considering free surface flow and moving boundaries. When a peristaltic contraction approaches the pylorus, retropulsive flow is generated in the antrum. Flow separation then occurs behind the contraction. The extent of flow separation depends on the Reynolds number (Re), which quantifies the inertial forces due to the peristaltic contractions relative to the viscous forces of the gastric contents; no separation is observed at low Re, while an increase in reattachment length is observed at high Re. While mixing efficiency is nearly constant for low Re, it increases with Re for high Re because of flow separation. Hence, the effect of the propagation velocity, frequency, or terminal acceleration of peristaltic contractions on mixing efficiency increases with Re.
    AMER PHYSIOLOGICAL SOC, Dec. 2016, AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY, 311(6) (6), G1114 - G1121, English
    [Refereed]
    Scientific journal

  • Numerical analysis of cell adhesion in capillary flow
    NAOKI TAKEISHI, YOHSUKE IMAI, SHUNICHI ISHIDA, TOSHIHIRO OMORI, ROGER KAMM, TAKUJI ISHIKAWA
    Nov. 2016, The 69th Annual Meetin g of The American Physical Society, Bulletin of the American Physical Society, DED 2016, 61, 72, English

  • D. Matsunaga, Y. Imai, C. Wagner, T. Ishikawa
    The reorientation phenomenon of a single red blood cell during sedimentation is simulated using the boundary element method. The cell settles downwards due to a density difference between the internal and external fluids, and it changes orientation toward a vertical orientation regardless of Bond number or viscosity ratio. The reorientation phenomenon is explained by a shape asymmetry caused by the gravitational driving force, and the shape asymmetry increases almost linearly with the Bond number. When velocities are normalised by the driving force, settling/drifting velocities are weak functions of the Bond number and the viscosity ratio, while the angular velocity of the reorientation drastically changes with these parameters: the angular velocity is smaller for lower Bond number or higher viscosity ratio. As a consequence, trajectories of the sedimentation are also affected by the angular velocity, and blood cells with slower reorientation travel longer distances in the drifting direction. We also explain the mechanism of the reorientation using an asymmetric dumbbell. From the analysis, we show that the magnitude of the angular velocity is explained by two main factors: the shape asymmetry and the instantaneous orientation angle.
    CAMBRIDGE UNIV PRESS, Nov. 2016, JOURNAL OF FLUID MECHANICS, 806, 102 - 128, English
    [Refereed]
    Scientific journal

  • Rachel Berry, Taimei Miyagawa, Niranchan Paskaranandavadivel, Peng Du, Timothy R. Angeli, Mark L. Trew, John A. Windsor, Yohsuke Imai, Gregory O'Grady, Leo K. Cheng
    High-resolution (HR) mapping has been used to study gastric slow-wave activation; however, the specific characteristics of antral electrophysiology remain poorly defined. This study applied HR mapping and computational modeling to define functional human antral physiology. HR mapping was performed in 10 subjects using flexible electrode arrays (128-192 electrodes; 16-24 cm(2)) arranged from the pylorus to mid-corpus. Anatomical registration was by photographs and anatomical landmarks. Slow-wave parameters were computed, and resultant data were incorporated into a computational fluid dynamics (CFD) model of gastric flow to calculate impact on gastric mixing. In all subjects, extracellular mapping demonstrated normal aboral slow-wave propagation and a region of increased amplitude and velocity in the prepyloric antrum. On average, the high-velocity region commenced 28 mm proximal to the pylorus, and activation ceased 6 mm from the pylorus. Within this region, velocity increased 0.2 mm/s per mm of tissue, from the mean 3.3 +/- 0.1 mm/s to 7.5 +/- 0.6 mm/s (P < 0.001), and extracellular amplitude increased from 1.5 +/- 0.1 mV to 2.5 +/- 0.1 mV (P < 0.001). CFD modeling using representative parameters quantified a marked increase in antral re-circulation, resulting in an enhanced gastric mixing, due to the accelerating terminal antral contraction. The extent of gastric mixing increased almost linearly with the maximal velocity of the contraction. In conclusion, the human terminal antral contraction is controlled by a short region of rapid high-amplitude slow-wave activity. Distal antral wave acceleration plays a major role in antral flow and mixing, increasing particle strain and trituration.
    AMER PHYSIOLOGICAL SOC, Nov. 2016, AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY, 311(5) (5), G895 - G902, English
    [Refereed]
    Scientific journal

  • Naoki Takeishi, Yohsuke Imai, Shunichi Ishida, Toshihiro Omori, Roger D. Kamm, Takuji Ishikawa
    A numerical analysis is presented of cell adhesion in capillaries whose diameter is comparable to or smaller than that of the cell. In contrast to a large number of previous efforts on leukocyte and tumor cell rolling, much is still unknown about cell motion in capillaries. The solid and fluid mechanics of a cell in flow was coupled with a slip bond model of ligand-receptor interactions. When the size of a capillary was reduced, the cell always transitioned to "bullet-like" motion, with a consequent decrease in the velocity of the cell. A state diagram was obtained for various values of capillary diameter and receptor density. We found that bullet motion enables firm adhesion of a cell to the capillary wall even for a weak ligand-receptor binding. We also quantified effects of various parameters, including the dissociation rate constant, the spring constant, and the reactive compliance on the characteristics of cell motion. Our results suggest that even under the interaction between P-selectin glycoprotein ligand-1 (PSGL-1) and P-selectin, which is mainly responsible for leukocyte rolling, a cell is able to show firm adhesion in a small capillary. These findings may help in understanding such phenomena as leukocyte plugging and cancer metastasis.
    AMER PHYSIOLOGICAL SOC, Aug. 2016, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, 311(2) (2), H395 - H403, English
    [Refereed]
    Scientific journal

  • Similarities and differences between flow mode of a leukocyte and circulating tumor cell in microvessels
    Naoki Takeishi, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2016, Summer Biomechanics, Bioengineering and Biotransport Conference, 742, English

  • Yohsuke Imai, Toshihiro Omori, Yuji Shimogonya, Takami Yamaguchi, Takuji Ishikawa
    In the past decade, numerical methods for the computational biomechanics of blood flow have progressed to overcome difficulties in diverse applications from cellular to organ scales. Such numerical methods may be classified by the type of computational mesh used for the fluid domain, into fixed mesh methods, moving mesh (boundary-fitted mesh) methods, and mesh-free methods. The type of computational mesh used is closely related to the characteristics of each method. We herein provide an overview of numerical methods recently used to simulate blood flow at macro and micro scales, with a focus on computational meshes. We also discuss recent progress in the multi-scale modeling of blood flow. (C) 2015 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Jul. 2016, JOURNAL OF BIOMECHANICS, 49(11) (11), 2221 - 2228, English
    [Refereed]
    Scientific journal

  • S. Nix, Y. Imai, T. Ishikawa
    Red blood cells migrate to the center of the blood vessel in a process called axial migration, while other blood cells, such as white blood cells and platelets, are disproportionately found near the blood vessel wall. However, much is still unknown concerning the lateral migration of cells in the blood; the specific effect of hydrodynamic factors such as a wall or a shear gradient is still unclear. In this study, we investigate the lateral migration of a capsule using the boundary integral method, in order to compute exactly an infinite computational domain for an unbounded parabolic flow and a semi-infinite computational domain for a near-wall parabolic flow in the limit of Stokes flow. We show that the capsule lift velocity in an unbounded parabolic flow is linear with respect to the shear gradient, while the lift velocity in a near-wall parabolic flow is dependent on the distance to the wall. Then, using these relations, we give an estimation of the relative effect of the shear gradient as a function of channel width and distance between the capsule and the wall. This estimation can be used to determine cases in which the effect of the shear gradient or wall can be neglected; for example, the formation of the cell-free layer in blood vessels is determined to be unaffected by the magnitude of the shear gradient. (C) 2015 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Jul. 2016, JOURNAL OF BIOMECHANICS, 49(11) (11), 2249 - 2254, English
    [Refereed]
    Scientific journal

  • Toshihiro Omori, Yohsuke Imai, Kenji Kikuchi, Takuji Ishikawa, Takami Yamaguchi
    Springer New York LLC, Apr. 2016, Annals of Biomedical Engineering, 44(4) (4), 1323, English

  • Yoshimichi Imai, Ryuta Kitanishi, Yoshikatsu Saiki, Atsushi Takeda, Masahiro Tachi
    Severe asphyxiating thoracic dystrophy (Jeune syndrome) is usually fatal. The authors used distraction osteogenesis in a severe case and achieved 45mm distraction of the sternum and improvement in tidal volume, lung compliance, and mean airway pressure.
    Taylor and Francis Ltd, Mar. 2016, Journal of Plastic Surgery and Hand Surgery, 50(3) (3), 180 - 183, English
    [Refereed]
    Scientific journal

  • Takuji Ishikawa, Shunsuke Kajiki, Yohsuke Imai, Toshihiro Omori
    Nutrient uptake is one of the most important factors in cell growth. Despite the biological importance, little is known about the effect of cell-cell hydrodynamic interactions on nutrient uptake in a suspension of swimming micro-organisms. In this study, we numerically investigate the nutrient uptake in an infinite suspension of squirmers. In the dilute limit, our results are in good agreement with a previous study by Magar et al. (Q. J. Mech. Appl. Maths, vol. 56, 2003, pp. 65-91). When we increased the volume fraction of squirmers, the nutrient uptake of individual cells was enhanced by the hydrodynamic interactions. The average nutrient concentration in the suspension decayed exponentially as a function of time, and the relaxation time could be scaled using the Sherwood number, the Peclet number and the volume fraction of cells. We propose a fitting function for the Sherwood number, which is useful in predicting nutrient uptake in the non-dilute regime. Furthermore, we analyse the swimming energy consumed by individual cells. The results indicate that both the energetic cost and the nutrient uptake increased as the volume fraction of cells was increased, and that the uptake per unit energy was not significantly affected by the volume fraction. These findings are important in understanding the mass transport and metabolism of swimming micro-organisms in nature and for industrial applications.
    CAMBRIDGE UNIV PRESS, Feb. 2016, JOURNAL OF FLUID MECHANICS, 789, 481 - 499, English
    [Refereed]
    Scientific journal

  • Bio-Micropump by Using A Flagellate Propulsive Force of Escherichia coli
    Kenji Kikuchi, Ryo Matsuura, Hironori Ueno, Yohsuke Imai, Noriaki Matsuki, Takami Yamaguchi, Takuji Ishikawa
    2016, The World Congress on Engineering 2016, ICSBB15, 515 - 518, English
    [Refereed]
    International conference proceedings

  • D. Matsunaga, Y. Imai, T. Yamaguchi, T. Ishikawa
    We present a numerical analysis of the rheology of a dense suspension of spherical capsules in simple shear flow in the Stokes flow regime. The behaviour of neo-Hookean capsules is simulated for a volume fraction up to phi = 0.4 by graphics processing unit computing based on the boundary element method with a multipole expansion. To describe the specific viscosity using a polynomial equation of the volume fraction, the coefficients of the equation are calculated by least-squares fitting. The results suggest that the effect of higher-order terms is much smaller for capsule suspensions than rigid sphere suspensions; for example, O(phi(3)) terms account for only 8 % of the specific viscosity even at phi = 0.4 for capillary numbers Ca >= 0.1. We also investigate the relationship between the deformation and orientation of the capsules and the suspension rheology. When the volume fraction increases, the deformation of the capsules increases while the orientation angle of the capsules with respect to the flow direction decreases. Therefore, both the specific viscosity and the normal stress difference increase with volume fraction due to the increased deformation, whereas the decreased orientation angle suppresses the specific viscosity, but amplifies the normal stress difference.
    CAMBRIDGE UNIV PRESS, Jan. 2016, JOURNAL OF FLUID MECHANICS, 786, 110 - 127, English
    [Refereed]
    Scientific journal

  • Takuji Ishikawa, Tomoyuki Tanaka, Yohsuke Imai, Toshihiro Omori, Daiki Matsunaga
    The membrane tension of some kinds of ciliates has been suggested to regulate upward and downward swimming velocities under gravity. Despite its biological importance, deformation and membrane tension of a ciliate have not been clarified fully. In this study, we numerically investigated the deformation of a ciliate swimming freely in a fluid otherwise at rest. The cell body was modelled as a capsule with a hyperelastic membrane enclosing a Newtonian fluid. Thrust forces due to the ciliary beat were modelled as torques distributed above the cell body. The effects of membrane elasticity, the aspect ratio of the cell's reference shape, and the density difference between the cell and the surrounding fluid were investigated. The results showed that the cell deformed like a heart shape, when the capillary number was sufficiently large. Under the influence of gravity, the membrane tension at the anterior end decreased in the upward swimming while it increased in the downward swimming. Moreover, gravity-induced deformation caused the cells to move gravitationally downwards or upwards, which resulted in a positive or negative geotaxis-like behaviour with a physical origin. These results are important in understanding the physiology of a ciliate's biological responses to mechanical stimuli.
    ROYAL SOC, Jan. 2016, PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, 472(2185) (2185), 20150604, English
    [Refereed]
    Scientific journal

  • Shunichi Ishida, Yohsuke Imai, Yuki Ichikawa, Stephanie Nix, Daiki Matsunaga, Toshihiro Omori, Takuji Ishikawa
    We developed a numerical model of the behavior of a red blood cell infected by Plasmodium falciparum malaria on a wall in shear flow. The fluid and solid mechanics of an infected red blood cell (Pf-IRBC) were coupled with the biochemical interaction of ligand-receptor bindings. We used the boundary element method for fluid mechanics, the finite element method for membrane mechanics, and the Monte Carlo method for ligand-receptor interactions. We simulated the behavior of a Pf-IRBC in shear flow, focusing on the effects of bond type. For slip bonds, the Pf-IRBC exhibited firm adhesion, tumbling motion, and tank-treading motion, depending on the applied shear rate. The behavior of catch bonds resembled that of slip bonds, except for a 'catch' state at high shear stress. When the reactive compliance decreased to a value in the order of 10(-2) nm, both the slip and catch bonds behaved like an ideal bond. Such bonds do not respond to the force applied to the bond, and the velocity is stabilized at a high shear rate. Finally, we compared the numerical results with previous experiments for A4- and ItG-infected cells. We found that the interaction between PfEMP1 and ICAM-1 could be a nearly ideal bond, with a dissociation rate ranging from 30 s(-1) to 100 s(-1).[GRAPHICS]
    TAYLOR & FRANCIS LTD, 2016, SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 17(1) (1), 454 - 461, English
    [Refereed]
    Scientific journal

  • Naoki Takeishi, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Quantifying the behavior of circulating tumor cells (CTCs) in the blood stream is of fundamental importance for understanding metastasis. Here, we investigate the flowmode and velocity of CTCs interactingwith red blood cells (RBCs) in various sized microvessels. The flow of leukocytes in microvessels has been described previously; a leukocyte forms a train with RBCs in small microvessels and exhibits margination in large microvessels. Important differences in the physical properties of leukocytes and CTCs result from size. The dimensions of leukocytes are similar to those of RBCs, but CTCs are significantly larger. We investigate numerically the size effects on the flow mode and the cell velocity, and we identify similarities and differences between leukocytes and CTCs. We find that a transition from train formation to margination occurs when (R-a)/t(R) approximate to 1, where R is the vessel radius, a is the cell radius, and t(R) is the thickness of RBCs, but that the motion of RBCs differs from the case of leukocytes. Our results also show that the velocities of CTCs and leukocytes are larger than the average blood velocity, but only CTCs move faster than RBCs for microvessels of R/a approximate to 1.5-2.0. These findings are expected to be useful not only for understanding metastasis, but also for developing microfluidic devices.
    AMER PHYSICAL SOC, Dec. 2015, PHYSICAL REVIEW E, 92(6) (6), 063011, English
    [Refereed]
    Scientific journal

  • K. Kyoya, D. Matsunaga, Y. Imai, T. Omori, T. Ishikawa
    Microswimmers show a variety of collective motions. Despite extensive study, questions remain regarding the role of near-field fluid mechanics in collective motion. In this paper, we describe precisely the Stokes flow around hydrodynamically interacting ellipsoidal squirmers in a monolayer suspension. The results showed that various collective motions, such as ordering, aggregation, and whirls, are dominated by the swimming mode and the aspect ratio. The collective motions are mainly induced by near-field fluid mechanics, despite Stokes flow propagation over a long range. These results emphasize the importance of particle shape in collective motion.
    AMER PHYSICAL SOC, Dec. 2015, PHYSICAL REVIEW E, 92(6) (6), 063027, English
    [Refereed]
    Scientific journal

  • Quantification of hydrodynamic factors influencing cell lateral migration
    STEPHANIE NIX, YOHSUKE IMAI, TAKUJI ISHIKAWA
    Nov. 2015, 68th Annual Meeting of the Division of Fluid Dynamics, Bulletin of the American Physical Society, DFD 2015, 60, 116, English

  • Deformable micro torque swimmer
    TAKUJI ISHIKAWA, TOMOYUKI TANAKA, TOSHIHIRO OMORI, YOHSUKE IMAI
    Nov. 2015, 68th Annual Meeting of the Division of Fluid Dynamics, Bulletin of the American Physical Society, DFD 2015, 60, 72, English

  • Rheological analysis of dense capsule suspensions – effect of volume fraction
    Daiki Matsunaga, Yohsuke Imai, Christian Wagner, Takuji Ishikawa
    Oct. 2015, The 3rd International Workshops on Advances in Computational Mechanics(IWACOM-III), 128, English

  • Graphics processing unit computing of cellular flow and adhesion in microvessels
    Yohsuke Imai, Naoki Takeishi, Shunichi Ishida, Takuji Ishikawa
    Oct. 2015, The 3rd International Workshops on Advances in Computational Mechanics(IWACOM-III), 47, English

  • Mechanics of Nodal Cilia in Early Mouse Embryo
    Toshihiro Omori, Hiroto Sugai, Yohsuke Imai, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, PS8-15, English

  • Development of a Numerical Model of Cytoskeleton Dynamics
    Fumiyasu Saito, Yohsuke Imai, Shunichi Ishida, Toshihiro Omori, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, PS3-7, English

  • Clarification of Relationship between Gastric Mixing and Movement of Wall
    Taimei Miyagawa, Yohsuke Imai, Shunichi Ishida, Takami Yamaguchi, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, PS3-6, English

  • Orientation Angle of a Single Red Blood Cell during Sedimentation
    Daiki Matsunaga, Yohsuke Imai, Christian Wagner, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, PS3-2, English

  • Hydrodynamic Interaction between the Small Microparticles and Red Blood Cells in Microchannel
    Naoki Takeishi, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, PS3-1, English

  • Swimming Behavior of a Model Ciliate near a Fluid-Air or a Fluid-Solid Interface
    Junichi Manabe, Toshihiro Omori, Yohsuke Imai, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, PS1-10, English

  • A Numerical Simulation of Cytoadhesion and Rosette Formation of Red Blood Cells Infected by Malaria
    Yohsuke Imai, Yuki Ichikawa, Shunichi Isida, Daiki Matsunaga, Stephanie Nix, Toshihiro Omori, Takami Yamaguchi, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, OS2-2, English

  • Effect of Flow Curvature on the Migration of Blood Cells
    Stephanie Nix, Yohsuke Imai, Takuji Ishikawa
    Sep. 2015, The 8th Asian-Pacific Conference on Biomechanics, OS2-1, English

  • Simulations of a swimming microorganism near an fluid-air or an fluid-solid interface
    Junichi Manabe, Toshihiro Omori, Yohsuke Imai, Takuji Ishikawa
    Sep. 2015, Computational Fluid Dynamics (CFD) in Medicine and Biology II, English

  • Separation of motile bacteria using drift force near a wall
    Takuji Ishikawa, Tatsuya Shioiri, Keiko Numayama-Tsuruta, Hironori Ueno, Yohsuke Imai, Takami Yamaguch
    Sep. 2015, Computational Fluid Dynamics (CFD) in Medicine and Biology II, English

  • H. Ueno, H. Bui, T. Ishikawa, Y. Imai, T. Yamaguchi, T. Ishikawa
    BioMed Central Ltd., Jul. 2015, Cilia, (1) (1), English
    [Refereed]
    Scientific journal

  • Cellular Scale Physiological Flow: Active Swimming Sperm Cells and Passive Flowing Red Blood Cells
    Toshihiro Omori, Takuji Ishikawa, Yohsuke Imai, Takami Yamaguchi
    Jul. 2015, 13th U.S. National Congress on Computational Mechanics, English

  • Viscosity Reduction in Bimodal Suspensions of Two Types of Capsules
    Yohsuke Imai, Hiroki Ito, Daiki Matsunaga, Toshihiro Omori, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2015, 13th U.S. National Congress on Computational Mechanics, English

  • Peclet Number Of Ciliary Transport On The Surface Of The Tracheal Lumen
    Kouki Kiyota, Hironori Ueno, Keiko Numayama-Tsuruta, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Jun. 2015, SB3C2015, 223, English

  • A Computational Study Of Red Blood Cells In Stokes Flow: From Single Cellular Mechanics To Suspension Rheology
    Toshihiro Omori, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Jun. 2015, SB3C2015, 256, English

  • Rheology of A Red Blood CEll Suspension Computing with A Boundary Element-Finite Wlement Coupled Method
    Toshihiro Omori, Yohsuke Imai, Takuji Ishikawa
    Mar. 2015, The 18th International Conference on Finite Elements in Flow Problems FEF2015, 23, English

  • Visualization of intestinal peristalsis of mosquito midgut by using micro x-ray imaging
    Kenji Kikuchi, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    2015, International Symposium on Integrated Nanobiomechanics, English
    International conference proceedings

  • Toshihiro Omori, Yohsuke Imai, Kenji Kikuchi, Takuji Ishikawa, Takami Yamaguchi
    Hemodynamics in microcirculation is important for hemorheology and several types of circulatory disease. Although hemodynamics research has a long history, the field continues to expand due to recent advancements in numerical and experimental techniques at the micro-and nano-scales. In this paper, we review recent computational and experimental studies of blood flow in microcirculation and microfluidics. We first focus on the computational studies of red blood cell (RBC) dynamics, from the single cellular level to mesoscopic multiple cellular flows, followed by a review of recent computational adhesion models for white blood cells, platelets, and malaria-infected RBCs, in which the cell adhesion to the vascular wall is essential for cellular function. Recent developments in optical microscopy have enabled the observation of flowing blood cells in microfluidics. Experimental particle image velocimetry and particle tracking velocimetry techniques are described in this article. Advancements in micro total analysis system technologies have facilitated flowing cell separation with microfluidic devices, which can be used for biomedical applications, such as a diagnostic tool for breast cancer or large intestinal tumors. In this paper, cell-separation techniques are reviewed for microfluidic devices, emphasizing recent advances and the potential of this fast-evolving research field in the near future.
    SPRINGER, Jan. 2015, ANNALS OF BIOMEDICAL ENGINEERING, 43(1) (1), 238 - 257, English
    [Refereed]
    Scientific journal

  • D. Matsunaga, Y. Imai, T. Yamaguchi, T. Ishikawa
    The deformation of a spherical capsule in oscillating shear flow is presented. The boundary element method is used to simulate the capsule motion under Stokes flow. We show that a capsule at high frequencies follows the deformation given by a leading-order prediction, which is derived from an assumption of small deformation limit. At low frequencies, on the other hand, a capsule shows an overshoot phenomenon where the maximum deformation is larger than that in steady shear flow. A larger overshoot is observed for larger capillary number or viscosity ratio. Using the maximum deformation in start-up shear flow, we evaluate the upper limit of deformation in oscillating shear flow. We also show that the overshoot phenomenon may appear when the quasi-steady orientation angle under steady shear flow is less than 9.0 degrees. We propose an equation to estimate the threshold frequency between the low-frequency range, where the capsule may have an overshoot, and the high-frequency range, where the deformation is given by the leading-order prediction. The equation only includes the viscosity ratio and the Taylor parameter under simple shear flow, so it can be extended to other deformable particles, such as bubbles and drops.
    CAMBRIDGE UNIV PRESS, 2015, JOURNAL OF FLUID MECHANICS, 762, 288 - 301, English
    [Refereed]
    Scientific journal

  • D.Matsunaga, Y.Imai, T.Omori, T.Ishikawa, T.Yamaguchi
    Although boundary element (BE) based methods are highly accurate for simulating capsule suspensions in Stokes flows, computational time has been a major issue, even when only a few capsules are simulated. We propose a full graphics processing unit (GPU) implementation of a numerical method coupling the BE method of fluid mechanics with the finite element method of membrane mechanics. In single GPU computing, the performance achieves 0.12 TFlop/s when computing one capsule (2562 nodes and 5120 elements) and 0.29 TFlop/s for two capsules. The performance increases with the number of capsules, achieving a maximum of 0.59 TFlop/s. We also implement a multi-GPU method with the data communication overlapping the computation. A weak scaling test shows perfect scalability for any number of computational nodes per GPU, indicating that the communication time is completely hidden. For a practical use of the present results, we estimate the computational time required for 10000 time steps. When we simulate one capsule and two capsules on one GPU, only 2.0 and 9.1 minutes are required to complete the simulation, respectively, and a simulation with 256 capsules on 16 GPUs takes 3.8 days.
    The Japan Society of Mechanical Engineers, Dec. 2014, Journal of Biomechanical Science and Engineering, 9(3) (3), 14-00039 - 00039-14-00039, English
    [Refereed]
    Scientific journal

  • Swimming behavior of a model microorganism at a fluid-air interface
    Junichi Manabe, Kohei Kyoya, Toshihiro Omori, Yohsuke Imai, Takuji Ishikawa
    Nov. 2014, The Sixth International Symposium on Aero Aqua Bio-mechanisms, 37, English

  • S. Nix, Y. Imai, D. Matsunaga, T. Yamaguchi, T. Ishikawa
    © 2014 American Physical Society. Lateral migration is the motion of a particle perpendicular to the direction of the surrounding flow. One of the factors leading to the lateral migration of a deformable particle in Stokes flow is the presence of a nearby wall. We numerically investigate the lateral migration of a capsule in a near-wall simple shear flow using a boundary integral method coupled with a finite element method. We find that asymmetrical deformation of the capsule induced by the wall is correlated with a reduction in the lift velocity relative to the lift velocity predicted by a far-field analytical solution. A combination of this asymmetrical deformation, which decreases the lift velocity, and an increase in the value of the capsule stresslet near the wall, which works to increase the lift velocity, leads to a migration velocity that is nearly independent of capillary number and membrane constitutive law at large deformation near the wall.
    Oct. 2014, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 90(4) (4)
    [Refereed]
    Scientific journal

  • Toshihiro Omori, Takuji Ishikawa, Yohsuke Imai, Takami Yamaguchi
    Blood is a suspension of red blood cells (RBCs) and its rheology is important when discussing the physiology of the cardiovascular system. In this study, we performed a numerical investigation of the rheological properties of an RBC suspension from the dilute to semi-dilute regime. RBCs were modelled as a capsule with a two-dimensional hyperelastic membrane. Large deformation of the thin membrane was calculated by a finite element method. Due to the small size of the RBC, fluid motion around the RBC was assumed to follow Stokes flow and was solved by a boundary element method. In the dilute limit, cell-cell interactions were omitted and the bulk stress of the suspension was calculated by the stresslet generated on a single RBC. Interestingly, the effective shear viscosity of the dilute suspension decreased with increasing viscosity of the internal liquid. In the semi-dilute regime, cells can be considered as showing pairwise interactions. The effective shear viscosity of the semi-dilute suspension shows a quadratic increase with respect to the volume fraction. These findings are important for understanding the complex phenomena of blood rheology.
    SPRINGER, Oct. 2014, COMPUTATIONAL MECHANICS, 54(4) (4), 933 - 941, English
    [Refereed]
    Scientific journal

  • S. Nix, Y. Imai, D. Matsunaga, T. Yamaguchi, T. Ishikawa
    Lateral migration is the motion of a particle perpendicular to the direction of the surrounding flow. One of the factors leading to the lateral migration of a deformable particle in Stokes flow is the presence of a nearby wall. We numerically investigate the lateral migration of a capsule in a near-wall simple shear flow using a boundary integral method coupled with a finite element method. We find that asymmetrical deformation of the capsule induced by the wall is correlated with a reduction in the lift velocity relative to the lift velocity predicted by a far-field analytical solution. A combination of this asymmetrical deformation, which decreases the lift velocity, and an increase in the value of the capsule stresslet near the wall, which works to increase the lift velocity, leads to a migration velocity that is nearly independent of capillary number and membrane constitutive law at large deformation near the wall.
    AMER PHYSICAL SOC, Oct. 2014, PHYSICAL REVIEW E, 90(4) (4), 043009, English
    [Refereed]
    Scientific journal

  • Modeling of Flow in the Stomach
    Yohsuke Imai, Ikuma Kobayashi, Taimei Miyagawa, Shunichi Ishida, Takuji Ishikawa, Takami Yamaguchi
    Sep. 2014, THE FOURTH JAPAN-SWITZERLAND WORKSHOP ON BIOMECHANICS, 102, English

  • Yohsuke Imai, Naoki Takeishi, Akihisa Ami, Takami Yamaguchi, Takuji Ishikawa
    Adhesion of cells flowing in microvessels to the vessel wall is an important process in hemostasis and immune system, and it also relates to malaria and metastasis. This process may depend on the mechanical property of cells, the size and geometry of vessels, the volume fraction of red blood cells, the shear rate, and the biochemical property of ligand-receptor interactions. We have developed a numerical model of cellular flow in microvessels to clarify the effects of these parameters. A cell is modeled as a liquid drop enclosed by a thin membrane. The finite element method for membrane mechanics is coupled with the lattice Boltzmann method for fluid mechanics. A ligand-receptor interaction model is also coupled with those methods. All the procedures are implemented in GPU computing for accelerating simulations. We simulate flow of leukocytes and circulating tumor cells, and rolling motion of malaria-infected red blood cells in microvessels.
    Japan Soc. of Med. Electronics and Biol. Engineering, Aug. 2014, Transactions of Japanese Society for Medical and Biological Engineering, 52, 45, English
    [Refereed]
    Scientific journal

  • A numerical method for simulating gastricflow
    Taimei Miyagawa, Yohsuke Imai, Takami Yamaguchi, takuji Ishikawa
    Jul. 2014, 11th World Congress on Computational Mechanics, 303, English

  • Rheological analysis of capsule suspensions containing different size capsules
    Hiroki Ito, Yohsuke Imai, Daiki Matsunaga, Toshihiro Omori, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, 11th World Congress on Computational Mechanics, 303, English

  • Rheological analysis of dense capsule suspension under simple shear flow condition
    Daiki Matsunaga, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Dyna Caps 2014, English

  • Numerical Analysis of Capsule Suspensions Containing Two Different siza Capsules
    Hiroki Ito, Yohsuke Imai, Daiki Matsunaga, Toshihiro Omori, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Dyna Caps 2014, English

  • Collective swimming of ellipoidal squimers
    Takuji Ishikawa, Kohei Kyoya, Daiki Matsunaga, Yohsuke Imai, Toshihiro Omori
    Jul. 2014, Dyna Caps 2014, English

  • Margination of large cells in microchannels
    Yohsuke Imai, Naoki Takeishi, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Dyna Caps 2014, English

  • Development of a numerical model for analysis of ciliary motions
    H. Sugai, T. Omori, Y. Imai, T. Ishikawa
    Jul. 2014, 7th WORLD CONGRESS OF BIOMECHANICS, English

  • Effect of Shear Gradient and Wall on Capsule Lateral Migration
    S. Nix, Y. Imai, T. Yamaguchi, T. Ishikawa
    Jul. 2014, 7th WORLD CONGRESS OF BIOMECHANICS, English

  • Multi-scale computational study on the formation and destruction of primary thrombus under the influence of the blood flow and red blood cells
    H. Kmada, Y. Imai, T. Ishikawa, T. Yamaguchi
    Jul. 2014, 7th WORLD CONGRESS OF BIOMECHANICS, English

  • A numerical simulation on the motion ofmalaria-infected cells in microcirculatory blood flow
    Y. Imai, A, Ami, T. Yamaguchi, T, Ishikawa
    Jul. 2014, 7th WORLD CONGRESS OF BIOMECHANICS, English

  • Numerical analysis of hydrodynamic behavior of circulating tumor cells in microchannels
    N. Takeishi, Y. Imai, T. Yamaguchi, T. Ishikawa
    Jul. 2014, 7th WORLD CONGRESS OF BIOMECHANICS, English

  • Development of an Intracellular Structure Model for Ciliary Motion Analysis
    Hiroto Sugai, Toshihiro Omori, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 17 - 18, English

  • Nutrient Uptake in a Suspension of Model Microorganisms
    Takuji Ishikawa, Shunsuke Kajiki, Yohsuke Imai, Toshihiro Omori
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 15 - 16, English

  • Capsule Lateral Migration in an Unbounded Plane Poiseuille Flow and Near-wall Shear Flow
    Stephanie Nix, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 13 - 14, English

  • Rheology of a Red Blood Cell Suspension from Dilute to Semi-dilute Regime
    Toshihiro Omori, Yohsuke Imai, Takami Imai, Takuji Ishikawa
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 11 - 12, English

  • Hydrodynamic Interction between a Circulating Tumor Cell and Blood Cells in Microcirculation
    Naoki Takeishi, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 9 - 10, English

  • Numerical Modeling of the Adhesion of Red Blood Cells Infected by Plasmodium Falciparum Malaria in Microcirculatory Blood Flow
    Yohsuke Imai, Akihisa Ami, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 7 - 8, English

  • A Numerical Analysis of Cellular Adhesion to Planar Wall Mediated by Ligand-Receptor Interactions
    Yuki Ichikawa, Yohsuke Imai, Daiki Matsunaga, Stephanie Nix, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 5 - 6, English

  • Computational Study on Thrombogenesis
    Hiroki Kamada, Yohsuke Imai, Takuji Ishikawa, Takami Ymaguchi
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 3 - 4, English

  • Shear Stress Distribution in the Stomach
    Taimei Miyagawa, Yohsuke Imai, Sunichi Ishida, Takami Yamaguchi, Takuji Ishikawa
    Jul. 2014, Internationnal Symposium on Integrated Nanobiomechanics, 1 - 2, English

  • Hironori Ueno, Khanh Huy Bui, Takuji Ishikawa, Yohsuke Imai, Takami Yamaguchi, Takashi Ishikawa
    The mechanism by which the two different heads of the ciliary outer dynein arm produce force to translocate the microtubule during beating is still unknown. In this report we use cryo-electron tomography and image processing to analyze the conformational changes and the relative abundance of each conformation of the two dynein heads from mouse respiratory cilia. In the absence of nucleotides the majority of dynein dimers are in the apo form and both heads are tightly packed, whereas they are dissociated and move independently in the presence of nucleotides. The head of the external outer arm dynein heavy chain has a diagonal shift toward both the neighboring B-tubule and the proximal end of the axoneme, while the head of the internal heavy chain shifts only longitudinally toward the proximal end. In the presence of nucleotides a significant number of the dynein dimers have two heads overlapped in the proximal shifting form or overlapped in the apo form. During ciliary bending axonemal dynein translocates microtubules by moving with short steps and two heads stay at the same position longer than cytoplasmic dynein. This demonstrates that the step of the outer arm dynein dimer is not dominated by the hand-over-hand motion, but also indicates the difference between axonemal dynein and cytoplasmic dynein. (C) 2014 Wiley Periodicals, Inc.
    WILEY-BLACKWELL, Jul. 2014, CYTOSKELETON, 71(7) (7), 412 - 422, English
    [Refereed]
    Scientific journal

  • Nutrient uptake in a suspension of model microorganisms
    Takuji Ishikawa, Shunsuke Kajiki, Yohsuke Imai, Toshihiro Omori
    Apr. 2014, COMPSAFE, 347 - 348, English

  • Rheological analysis of dense capsule suspension under Stokes flow condition
    Daiki Matsunaga, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Mar. 2014, Advances in Computational Fluid-Structure Interaction and Flow Simulation, Poster Session, English

  • Toshihiro Omori, Haruki Hosaka, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Red blood cell (RBC) deformability plays a key role in microcirculation, especially in vessels that have diameters even smaller than the nominal cell size. In this study, we numerically investigate the dynamics of an RBC in a thin micropore. The RBC is modeled as a capsule with a thin hyperelastic membrane. In a numerical simulation, we employ a boundary element method for fluid mechanics and a finite element method for membrane mechanics. The resulting RBC deformation towards the flow direction is suppressed considerably by increased cytoplasm viscosity, whereas the gap between the cell membrane and solid wall becomes smaller with higher cytoplasm viscosity. We also measure the transit time of the RBC and find that nondimensional transit time increases nonlinearly with respect to the viscosity ratio, whereas it is invariant to the capillary number. In conclusion, cytoplasmic viscosity plays a key role in the dynamics of an RBC in a thin pore. The results of this study will be useful for designing a microfluidic device to measure cytoplasmic viscosity. © 2014 American Physical Society.
    Jan. 2014, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 89(1) (1), English
    [Refereed]
    Scientific journal

  • Toshihiro Omori, Takuji Ishikawa, Yohsuke Imai, Takami Yamaguchi
    Dynamics of deformable capsules in fluid flow is great interest in chemical engineering, bioengineering, and food industry. To investigate the motion and deformation of a capsule, both the fluid mechanics of the internal and external liquids and the solid mechanics of the membrane must be solved precisely. To express the elastic behaviours of the solid membrane, two different kinds of modelling are commonly used. One is a continuum constitutive law and the other is a discrete spring network model. This study first examines the correlations between the mechanical properties of the discrete spring network model and those of continuum constitutive laws. We also derive the relationships between the spring constant and continuum properties, such as Young modulus, Poisson ratio, area dilation modulus, and shear elastic modulus. Next, we investigate the motion and deformation of a capsule in simple shear flow. Especially, we analyze the dynamics of a non-spherical capsule in shear. In the absence of inertia effect of fluid motions, a boundary element method is used to compute the internal and external Stokes flow. The results show that the orientation of a non-spherical capsule is variant under time reversal, though that of a rigid particle is invariant. Interestingly, the alignment of a non-spherical capsule over a long time duration shows a transition depending on the shear rate.
    Kluwer Academic Publishers, 2014, Lecture Notes in Computational Vision and Biomechanics, 12, 101 - 117, English
    [Refereed]
    Scientific journal

  • Toshihiro Omori, Haruki Hosaka, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Red blood cell (RBC) deformability plays a key role in microcirculation, especially in vessels that have diameters even smaller than the nominal cell size. In this study, we numerically investigate the dynamics of an RBC in a thin micropore. The RBC is modeled as a capsule with a thin hyperelastic membrane. In a numerical simulation, we employ a boundary element method for fluid mechanics and a finite element method for membrane mechanics. The resulting RBC deformation towards the flow direction is suppressed considerably by increased cytoplasm viscosity, whereas the gap between the cell membrane and solid wall becomes smaller with higher cytoplasm viscosity. We also measure the transit time of the RBC and find that nondimensional transit time increases nonlinearly with respect to the viscosity ratio, whereas it is invariant to the capillary number. In conclusion, cytoplasmic viscosity plays a key role in the dynamics of an RBC in a thin pore. The results of this study will be useful for designing a microfluidic device to measure cytoplasmic viscosity.
    AMER PHYSICAL SOC, Jan. 2014, PHYSICAL REVIEW E, 89(1) (1), 013008, English
    [Refereed]
    Scientific journal

  • Kouki Kiyota, Hironori Ueno, Keiko Numayama-Tsuruta, Tomofumi Haga, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Although we inhale air that contains many harmful substances, including, for example, dust and viruses, these small particles are trapped on the surface of the tracheal lumen and transported towards the larynx by cilia-generated flow. The transport phenomena are affected not only by the time-and space-average flow field but also by the fluctuation of the flow. Because flow fluctuation has received little attention, we investigated it experimentally in mice. To understand the origin of flow fluctuation, we first measured the distribution of ciliated cells in the trachea and individual ciliary motions. We then measured the detailed flow field using a confocal micro-PTV system. Strong flow fluctuations were observed, caused by the unsteadiness of the ciliary beat and the spatial inhomogeneity of ciliated cells. The spreading of particles relative to the bulk motion became diffusive if the time scale was sufficiently larger than the beat period. Finally, we quantified the effects of flow fluctuation on bulk flow by evaluating the Peclet number of the system, which indicated that the directional transport was an order of magnitude larger than the isotropic diffusion. These results are important in understanding transport phenomena in the airways on a cellular scale.
    AMER PHYSIOLOGICAL SOC, Jan. 2014, AMERICAN JOURNAL OF PHYSIOLOGY-LUNG CELLULAR AND MOLECULAR PHYSIOLOGY, 306(2) (2), L144 - L151, English
    [Refereed]
    Scientific journal

  • Takuji Ishikawa, Tatsuya Shioiri, Keiko Numayama-Tsuruta, Hironori Ueno, Yohsuke Imai, Takami Yamaguchi
    Separation of certain bacteria from liquids is important in the food, water quality management, bioengineering, and pharmaceutical industries. In this study, we developed a microfluidic device for the hydrodynamic separation of motile bacteria (Escherichia coli) using drift velocity. We first investigated drift tendencies of bacteria and found that cells tended to move in a spanwise direction with similar velocities regardless of the flow rate. When the drift distance was small compared to the wetted perimeter of the cross section, the cells were not separated efficiently. We then investigated the drift phenomenon in more detail using a numerical simulation. Interestingly, the drift phenomenon was observed even without a wall boundary, indicating that drift was caused mainly by the interaction of moving cells with the background shear flow. Finally, we developed a microfluidic device to separate motile bacteria from tracer particles or less motile cells. By decreasing the channel height, the device could successfully separate motile bacteria from other particles or cells with a separation efficiency of about 40%. Connecting microchannels in a series was also found to be effective, which achieved the separation efficiency of about 60%. The knowledge obtained in this study will facilitate the development of other microfluidics devices for use with bacteria.
    ROYAL SOC CHEMISTRY, 2014, LAB ON A CHIP, 14(5) (5), 1023 - 1032, English
    [Refereed]
    Scientific journal

  • Naoki Takeishi, Yohsuke Imai, Keita Nakaaki, Takami Yamaguchi, Takuji Ishikawa
    We numerically investigated margination of leukocytes at arteriole shear rate in straight circular channels with diameters ranging from 10 to 22 lm. Our results demonstrated that passing motion of RBCs effectively induces leukocyte margination not only in small channels but also in large channels. A longer time is needed for margination to occur in a larger channel, but once a leukocyte has marginated, passing motion of RBCs occurs continuously independent of the channel diameter, and leukocyte margination is sustained for a long duration. We also show that leukocytes rarely approach the wall surface to within a microvillus length at arteriole shear rate.
    American Physiological Society, 2014, Physiological Reports, 2(6) (6), e12037, English
    [Refereed]
    Scientific journal

  • A numerical analysis of a capsule containing multiple small capsules in simple shear flow
    Yuki Ichikawa, Yohsuke Imai, Daiki Matsunaga, Takami Yamaguchi, Takuji Ishikawa
    Dec. 2013, APCOM2013 & ISCM2013 Conference Handbook, 15, English

  • Numerical analysis of margination of a cancer cell in microcirculation
    N. Takeishi, Y. Imai, T. Yamaguchi, T. Ishikawa
    Dec. 2013, APCOM2013 & ISCM2013 Conference Handbook, 18, English

  • Solid particle motion in the stomach during gastric mixing
    Taimei Miyagawa, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Dec. 2013, The15th International Conference on Biomedical Enginnering, 17 - 18, English

  • Nutrient uptake in a suspension of squirmers
    Shunsuke Kajiki, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Nov. 2013, Bulletin of the American Physical Society, 58, 409, English

  • Viscoelasticity of dilute capsule suspension under Stokes flows
    Daiki Matsunaga, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Nov. 2013, Bulletin of the American Physical Society, 58, 97, English

  • Viscosity of Dense Capsule Suspension Under Simple Shear FLow Condition
    Daiki Matsunaga, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Nov. 2013, 7th East Asian Consortium on Biomedical Engineering, Proceeding Book, 80 - 81, English

  • Margination of leukocyte in different sizes of circular micro-channel
    Naoki takeishi, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Nov. 2013, 7th East Asian Consortium on Biomedical Engineering, Proceeding Book, 78 - 79, English

  • Jonathan Ferracci, Hironori Ueno, Keiko Numayama-Tsuruta, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    The importance of water-air interfaces (WAI) on microorganism activities has been recognized by many researchers. In this paper, we report a novel phenomenon: the entrapment of ciliates Tetrahymena at the WAI. We first characterized the behavior of cells at the interface and showed that the cells' swimming velocity was considerably reduced at the WAI. To verify the possible causes of the entrapment, we investigated the effects of positive chemotaxis for oxygen, negative geotaxis and surface properties. Even though the taxes were still effective, the entrapment phenomenon was not dependent on the physiological conditions, but was instead affected by the physical properties at the interface. This knowledge is useful for a better understanding of the physiology of microorganisms at interfaces in nature and in industry. © 2013 Ferracci et al.
    Oct. 2013, PLoS ONE, 8(10) (10), e75238, English
    [Refereed]
    Scientific journal

  • Hiroki Kamada, Yohsuke Imai, Masanori Nakamura, Takuji Ishikawa, Takami Yamaguchi
    Thrombogenesis results from the interaction between glycoprotein receptors and their ligands, although a thrombus is affected by multiple factors such as blood flow, platelet interactions, and changes in ligand characteristics. In this study, we propose a platelet adhesion and aggregation model, focusing on the interaction between the glycoprotein receptor and its ligand. First, we conducted thrombogenesis simulations to compare physiological and pathological conditions. The results suggested that simulations of thrombogenesis differed in distribution, volume, and stability of the thrombus based on disorders of platelet adhesion, aggregation, and the activation. For example, distribution and volume were affected by the activation of GPIIb/IIIa with a GPIb/IX/V deficiency. The thrombus was also unstable, but formed from the upstream side of the injured site, with a GPIIb/IIIa deficiency. Second, we investigated thrombogenesis enhanced by the shear-induced platelet aggregation (SIPA) mechanism. The results demonstrated that the degree of SIPA decreased gradually with thrombus growth in a straight vessel. This result suggests that SIPA is a key hemostasis mechanism in an injured healthy arteriole, although it can lead to the formation of an occlusive thrombus in stenosed vessels. (C) 2013 Elsevier Inc. All rights reserved.
    ACADEMIC PRESS INC ELSEVIER SCIENCE, Sep. 2013, MICROVASCULAR RESEARCH, 89, 95 - 106, English
    [Refereed]
    Scientific journal

  • Effect of Aeration on the Bioconvection Pattern in a Microalgae Suspension
    Y. Nonaka, H. Ueno, K. Numayama, T. Omori, Y. Imai, T. Yamaguchi, T. Ishikawa
    Aug. 2013, APCB2013 Proceedings, S12 - 002, English

  • Modeling of cytoadhesion in malaria infection
    A. Ami, Y. Imai, T. Ishikawa, T. Yamaguchi
    Aug. 2013, APCB2013 Proceedings, S4 - 3, English

  • Mechanism of capsule migration near a plane wall
    S. Nix, Y. Imai, D. Matsunaga, T. Yamaguchi, T. Ishikawa
    Aug. 2013, APCB2013 Proceedings, S4 - 020, English

  • Numerical simulation of motion of solid particles in the stomach
    T. Miyagawa, Y. Imai, T. Yamaguchi, T. Ishikawa
    Aug. 2013, APCB2013 Proceedings, S4 - 019, English

  • Margination of white blood cell in various sizes of circular micro-channel
    N. Takeishi, Y. Imai, T. Ishikawa, T. Yamaguchi
    Aug. 2013, APCB2013 Proceedings, S4 - 3, English

  • Collective Swimming of Ellipsoidal Microorganisms
    K. Kyoya, D. Matsunaga, Y. Imai, T. Yamaguchi, T. Ishikawa
    Aug. 2013, APCB2013 Proceedings, S4 - 014, English

  • Integrated Biomechanics for Physiological Flow Problems
    T. Yamaguchi, Y. Imai, T. Omori, H. Ueno, K. Numayama-Tsuruta, T. Ishikawa
    Aug. 2013, APCB2013 The7thAsian Pacific Conference on Biomechanics, ILS4 - 009, English

  • COMPUTATIONAL BIOMECHANICS ON BLOOD FLOW FROM CELLULAR TO
    T. yamaguchi, Y. Imai, T. Ishikawa
    Jun. 2013, COMPDYN 2013, S2090, English

  • T. Omori, T. Ishikawa, Y. Imai, T. Yamaguchi
    The diffusion of red blood cells (RBCs) in blood is important to the physiology and pathology of the cardiovascular system. In this study, we investigate flow-induced diffusion of RBCs in a semi-dilute system by calculating the pairwise interactions between RBCs in simple shear flow. A capsule with a hyperelastic membrane was used to model an RBC. Its deformation was resolved using the finite element method, whereas fluid motion inside and outside the RBC was solved using the boundary element method. The results show that shear-induced RBC diffusion is significantly anisotropic, i.e. the velocity gradient direction component is larger than the vorticity direction. We also found that the motion of RBCs during the interaction is strongly dependent on the viscosity ratio of the internal to external fluid, and the diffusivity decreases monotonically as the viscosity ratio increases. The scaling argument also suggests that the diffusivity is proportional to the shear rate and haematocrit, if the suspension is in a semi-dilute environment and the capillary number is invariant. These fundamental findings are useful to understand transport phenomena in blood flow. © 2013 Cambridge University Press.
    Jun. 2013, Journal of Fluid Mechanics, 724, 154 - 174, English
    [Refereed]
    Scientific journal

  • The near-wall motion of a capsule in stokes flow
    S. Nix, Y. Imai, D. Matsunaga, T. Ishikawa, T. Yamaguchi
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 52 - 53, English
    International conference proceedings

  • Simulation of nutrient uptake of a swimming model microorganism by boundary element method
    S. Kajiki, K. Kyoya, D. Matsunaga, Y. Imai, T. Yamaguchi, T. Ishikawa
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 42 - 43, English
    International conference proceedings

  • Numerical simulation of adhesion of malaria-infected red blood cells
    A. Ami, Y. Imai, T. Ishikawa, T. Yamaguchi
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 38 - 39, English
    International conference proceedings

  • Numerical analysis of swimming microorganisms by a boundary element method
    K. Kyoya, D. Matsunaga, Y. Imai, T. Yamaguchi, T. Ishikawa
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 44 - 45, English
    International conference proceedings

  • Numerical analysis of dynamics of solid particles in the stomach
    T. Miyagawa, Y. Imai, T. Ishikawa, T. Yamaguchi
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 48 - 49, English
    International conference proceedings

  • Margination of various cells in microcirculation
    N. Takeishi, Y. Imai, T. Ishikawa, T. Yamaguchi
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 36 - 37, English
    International conference proceedings

  • Gradient diffusion of red blood cells in blood flow through a Y-shape microchannel
    C. Chuang, T. Ishikawa, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 78 - 79, English
    International conference proceedings

  • A numerical analysis of complex viscosity of dilute capsule suspension
    D. Matsunaga, Y. Imai, T. Ishikawa, T. Yamaguchi
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 104 - 105, English
    International conference proceedings

  • A numerical analysis of bimodal capsule suspensions
    H. Ito, Y. Imai, D. Matsunaga, T. Ishikawa, T. Yamaguchi
    Mar. 2013, 6th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 106 - 107, English
    International conference proceedings

  • Toshihiro Omori, Takuji Ishikawa, Yohsuke Imai, Takami Yamaguchi
    Flow-induced membrane tension contributes to the release of molecules by red blood cells (RBCs), and extremely high tension may cause haemolysis. Here, we investigated the membrane tension of RBCs during pairwise interactions in simple shear flow, given that pairwise interactions form the basis of many-body interactions. RBCs were modelled as capsules with a two-dimensional hyperelastic membrane, and large deformations were solved by the finite element method. Due to the small size of the RBCs, surrounding fluid motion was estimated as a Stokes flow and solved by the boundary element method. The results showed that the maximum isotropic tension appeared around the dimple of the biconcave surface and not around the rim. A comparison of the results with solitary cases indicated that the maximum principal tension and isotropic tension were significantly increased by cell-cell interaction effects. As the volume fraction of RBCs is large under physiological conditions, as well as in blood flow in vitro, cell-cell interactions must be analysed carefully when considering mechanotransduction and haemolysis in blood flow. © 2012 Elsevier Ltd.
    Feb. 2013, Journal of Biomechanics, 46(3) (3), 548 - 553, English
    [Refereed]
    Scientific journal

  • Yohsuke Imai, Ikuma Kobayashi, Shunichi Ishida, Takuji Ishikawa, Martin Buist, Takami Yamaguchi
    We investigate flow in the stomach during gastric mixing using a numerical simulation with an anatomically realistic geometry and freesurface flow modeling. Because of momentum differences between greater and lesser curvatures during peristaltic contractions, timeaveraged recirculation is generated in the antrum, with retropulsive flow away from the pylorus and compensation flow along the greater curvature toward the pylorus. Gastric content in the distal stomach is continuously transported to the distal antrum by the forward flow of antral recirculation, and it is then mixed by the backward retropulsive flow. Hence, the content inside the antral recirculation is well mixed independently of initial location, whereas the content outside the recirculation is poorly mixed. Free-surface modeling enables us to analyze the effects of posture on gastric mixing. In the upright, prone, and right lateral positions, most of the antrum is filled with content, and the content is well mixed by antral recirculation. In contrast, in the supine and left lateral positions, most of the content is located outside antral recirculation, which results in poor mixing. The curved, twisted shape of the stomach substantially supports gastric mixing in fluid mechanical terms. © 2013 the American Physiological Society.
    2013, American Journal of Physiology - Gastrointestinal and Liver Physiology, 304(5) (5), G536 - G542, English
    [Refereed]
    Scientific journal

  • Hiroki Kamada, Yohsuke Imai, Masanori Nakamura, Takuji Ishikawa, Takami Yamaguchi
    Previous studies investigating thrombus formation have not focused on the physical interaction between red blood cells (RBCs) and thrombus, although they have been speculated that some pathological conditions such as microangiopathic hemolytic anemia (MAHA) stem from interactions between RBCs and thrombi. In this study, we investigated the mechanical influence of RBCs on primary thrombi during hemostasis. We also explored the mechanics and aggravating factors of intravascular hemolysis. Computer simulations of primary thrombogenesis in the presence and the absence of RBCs demonstrated that RBCs are unlikely to affect the thrombus height and coverage, although their presence may change microvessel hemodynamics and platelet transportation to the injured wall. Our results suggest that intravascular hemolysis owing to RBC membrane damage would be promoted by three hemodynamic factors: (1) dispersibility of platelet thrombi, because more frequent spatial thrombus formation decreases the time available for an RBC to recover its shape and enforces more severe deformation; (2) platelet thrombus stiffness, because a stiffer thrombus increases the degree of RBC deformation upon collision; and (3) vessel size and hemocyte density, because a smaller vessel diameter and higher hemocyte density decrease the room for RBCs to escape as they come closer to a thrombus, thereby enhancing thrombus-RBC interactions. (C) 2012 IPEM. Published by Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Dec. 2012, MEDICAL ENGINEERING & PHYSICS, 34(10) (10), 1411 - 1420, English
    [Refereed]
    Scientific journal

  • T. Omori, T. Ishikawa, D. Barthes-Biesel, A. -V. Salsac, Y. Imai, T. Yamaguchi
    When a red blood cell (RBC) is subjected to an external flow, it is deformed by the hydrodynamic forces acting on its membrane. The resulting elastic tensions in the membrane play a key role in mechanotransduction and govern its rupture in the case of hemolysis. In this study, we analyze the motion and deformation of an RBC in a simple shear flow and the resulting elastic tensions on the membrane. The large deformation of the red blood cell is modelled by coupling a finite element method to solve the membrane mechanics and a boundary element method to solve the flows of the internal and external liquids. Depending on the capillary number Ca, ratio of the viscous to elastic forces, we observe three kinds of RBC motion: tumbling at low Ca, swinging at larger Ca, and breathing at the transitions. In the swinging regime, the region of the high principal tensions periodically oscillates, whereas that of the high isotropic tensions is almost unchanged. Due to the strain-hardening property of the membrane, the deformation is limited but the membrane tension increases monotonically with the capillary number. We have quantitatively compared our numerical results with former experimental results. It indicates that a membrane isotropic tension O(10(-6) N/m) is high enough for molecular release from RBCs and that the typical maximum membrane principal tension for haemolysis would be O(10(-4) N/m). These findings are useful to clarify not only the membrane rupture but also the mechanotransduction of RBCs.
    AMER PHYSICAL SOC, Nov. 2012, PHYSICAL REVIEW E, 86(5) (5), 056321, English
    [Refereed]
    Scientific journal

  • Off-plane motion of a non-spherical capsule in simple shear flow
    T. Omori, T. Ishikawa, Y. Imai, T. Yamaguchi
    Nov. 2012, Bulletin of the American Physical Society 65th Annual Meeting of the APS Division of Fluid Dynamics, 331 - 331, English
    International conference proceedings

  • Measurement of ciliary flow generated on the surface of tracheal lumen
    K. Kiyota, H. Ueno, T. Ishikawa, K. Numayama-Tsuruta, Y. Imai, T. Omori, T. Yamaguchi
    Nov. 2012, Bulletin of the American Physical Society 65th Annual Meeting of the APS Division of Fluid Dynamics, 334 - 334, English
    International conference proceedings

  • Hydrodynamical entrapment of ciliates at the air-liquid interface
    J. Ferracci, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi, T. Ishikawa
    Nov. 2012, Bulletin of the American Physical Society 65th Annual Meeting of the APS Division of Fluid Dynamics, 107 - 107, English
    International conference proceedings

  • Gradient diffusion of red blood cells in blood flow through a Y-shape microchannel
    C. Chuang, T. Ishikawa, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi
    Nov. 2012, Bulletin of the American Physical Society 65th Annual Meeting of the APS Division of Fluid Dynamics, 330 - 330, English
    International conference proceedings

  • Analysis of red blood cell behavior in a narrow tube
    H. Hosaka, T. Omori, Y. Imai, T. Yamaguchi, T. Ishikawa
    Nov. 2012, Bulletin of the American Physical Society 65th Annual Meeting of the APS Division of Fluid Dynamics, 330 - 330, English
    International conference proceedings

  • 3D-PTV measurement of the phototactic movement of algae in shear flow
    T. Maeda, T. Ishikawa, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi
    Nov. 2012, Bulletin of the American Physical Society 65th Annual Meeting of the APS Division of Fluid Dynamics, 49 - 49, English
    International conference proceedings

  • Davod Alizadehrad, Yohsuke Imai, Keita Nakaaki, Takuji Ishikawa, Takami Yamaguchi
    The deformation of red blood cells in microvessels was investigated numerically for various vessel diameters, hematocrits, and shear rates. We simulated blood flow in circular channels with diameters ranging from 9 to 50 mu m, hematocrits from 20% to 45%, and shear rates from 20 to 150 s(-1) using a particle-based model with parallel computing. The apparent viscosity predicted by the simulation was in good agreement with previous experimental results. We quantified the deformation of red blood cells as a function of radial position. The numerical results demonstrated that because of the shape transition in response to local shear stress and the wall effect, the radial variation of red blood cell deformation in relatively large microvessels could be classified into three different regions: near-center, middle, and near-wall regions. Effects of the local shear stress and wall varied with vessel diameter, hematocrit, and shear rate. (C) 2012 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Oct. 2012, JOURNAL OF BIOMECHANICS, 45(15) (15), 2684 - 2689, English
    [Refereed]
    Scientific journal

  • Lateral migration of capsules in a near-wall shear flow
    S. Nix, Y. Imai, D. Matsunaga, T. Ishikawa, T. Yamaguchi
    Oct. 2012, International Computational Mechanics Symposium 2012 (USB), USB Memory, English
    International conference proceedings

  • Development of a GPU-Implemented BEM solver for biological cell suspensions
    Y. Imai, D. Matsunaga, K. Kyoya, T. Omori, T. Ishikawa, T. Yamaguchi
    Oct. 2012, International Computational Mechanics Symposium 2012, USB Memory, English
    International conference proceedings

  • GPU computing for patient-specific model of pulmonary airflow
    T. Yamaguchi, Y. Imai, T. Miki, T. Ishikawa
    Sep. 2012, Computational Modelling of Objects Represented in Images: Fundamentals, Methods and Applications, 239 - 242, English

  • Role of fluid mechanics in collective motions of bacteria
    T. Ishikawa, N. Yoshida, H. Ueno, M. Wiedeman, Y. Imai, T. Yamaguchi
    Sep. 2012, 9th International Conference on Flow Dynamics Proceedings, 732 - 733, English
    International conference proceedings

  • Computational analysis on the mechanical interaction between a thrombus and red blood cells
    H. Kamada, Y. Imai, M. Nakamura, T. Ishikawa, T. Yamaguchi
    Sep. 2012, ECCOMAS 2012 Congress Proceedings, CD-ROM, English
    International conference proceedings

  • Reorientation of a non-spherical micro-capsule in shear flow
    T. Ishikawa, T. Omori, Y. Imai, T. Yamaguchi
    Aug. 2012, Abstract Book of the 23rd International Congress of Theoretical and Applied Mechanics, 106 - 106, English
    International conference proceedings

  • Particle based simulation of microcirculation using a parallel computation
    T. Yamaguchi, Y. Imai, T. Ishikawa
    Jul. 2012, Biorheology, 49, 181 - 181, English
    International conference proceedings

  • J-J Christophe, T. Ishikawa, Y. Imai, K. Takase, M. Thiriet, T. Yamaguchi
    Pneumothorax is characterized by lung collapse and an alteration of lung geometry, resulting in alterations of the pulmonary artery blood flow. Though many clinical studies and animal experiments have investigated the effects of pneumothorax on the hemodynamics of pulmonary arteries, its precise effects remain unclear. In this patient-specific study, we investigated the effects of lung deformation and vascular resistance increases due to pneumothorax on the pulmonary blood flow during the acute phase and after recovery. Arterial geometry was extracted up to the fifth generation from computed tomography images, and reconstructed. Computational fluid dynamic analysis was performed, for an unsteady laminar flow with resistance at the outlets, in a reconstructed domain. The results demonstrated a change in flow structure during systole between the acute phase and recovery, and were associated with variations in the flow rate ratio between the right and left lungs. We observed a parabolic-like decrease of the volume flow rate ratio in the affected lung as the resistance increased. Thus, the systemic artery blood oxygenation will rely more on the unaffected lung leading to improved oxygenation of the blood under high resistance in the affected lung. These findings are significant in our understanding of ventilation function under a pneumothorax. (C) 2011 IPEM. Published by Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Jul. 2012, MEDICAL ENGINEERING & PHYSICS, 34(6) (6), 725 - 732, English
    [Refereed]
    Scientific journal

  • Hydrodynamic entrapment of ciliates at the air-liquid interface
    J. Ferracci, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi, T. Ishikawa
    Jun. 2012, Softflow 2012 – Biological Complex Fluids, 36 - 37, English
    International conference proceedings

  • Dynamics of capsules near a plane wall
    S. Nix, Y. Imai, T. Ishikawa, T. Yamaguchi
    Jun. 2012, Softflow 2012 – Biological Complex Fluids, 76 - 76, English
    International conference proceedings

  • Yohsuke Imai, Takahito Miki, Takuji Ishikawa, Takayuki Aoki, Takami Yamaguchi
    We investigated how breath holding increases the deposition of micrometer particles in pulmonary airways, compared with the deposition during inhalation period. A subject-specific airway model with up to thirteenth generation airways was constructed from multi-slice CT images. Airflow and particle transport were simulated by using GPU computing. Results indicate that breath holding effectively increases the deposition of 5 mu m particles for third to sixth generation (G3-G6) airways. After 10 s of breath holding, the particle deposition fraction increased more than 5 times for 5 mu m particles. Due to a small terminal velocity, 1 mu m particles only showed a 50% increase in the most efficient case. On the other hand, 10 mu m particles showed almost complete deposition due to high inertia and high terminal velocity, leading to an increase of 2 times for G3-G6 airways. An effective breath holding time for 5 mu m particle deposition in G3-G6 airways was estimated to be 4-6 s, for which the deposition amount reached 75% of the final deposition amount after 10 s of breath holding. (C) 2012 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Jun. 2012, JOURNAL OF BIOMECHANICS, 45(10) (10), 1809 - 1815, English
    [Refereed]
    Scientific journal

  • Energy efficiency in collective motions of swimming bacteria
    T. Ishikawa, N. Yoshida, H. Ueno, M. Wiedeman, Y. Imai, T. Yamaguchi
    May 2012, IFMBE Proceedings, World Congress on Medical Physics and Biomedical Engineering, CD-ROM, English
    International conference proceedings

  • Computational biomechanics of physiological flow
    T. Yamaguchi, T. Ishikawa, Y. Imai, H. Ueno, K. Numayama-Tsuruta, T. Omori
    Mar. 2012, Biological Flow: A Conference to Celebrate the 70th Birthday of Timothy J. Padley FRS, 38, English

  • Rheology of a dilute suspention of red blood cells in simple shear flow
    T. Omori, T. Ishikawa, Y. Imai, T. Yamaguchi
    Mar. 2012, 18th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 153 - 154, English
    International conference proceedings

  • Quantifying characteristics of blood cell at dense cellullar flow
    D. Alizadehrad, Y. Imai, T. Ishikawa, T. Yamaguchi
    Mar. 2012, 18th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 111 - 112, English
    International conference proceedings

  • Hydrodynamic entrapment of ciliates at the interface fluid-air
    J. Ferracci, T. Ishikawa, H. Ueno, K. Numayama, Y. Imai, T. Yamaguchi
    Mar. 2012, 18th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 115 - 116, English
    International conference proceedings

  • Effect of constitutive law on the lateral migration of a capsule near a wall
    S. Nix, Y. Imai, D. Matsunaga, T. Ishikawa, T. Yamaguchi
    Mar. 2012, 18th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 145 - 146, English
    International conference proceedings

  • Collective Diffusion of red blood cells from high concentration to low
    C. Chuang, T. Ishikawa, H. Ueno, K. Numayama, Y. Imai, T. Yamaguchi
    Mar. 2012, 18th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 109 - 110, English
    International conference proceedings

  • A particle model of cellular flow in microcirculation
    T. Yamaguchi, T. Ishikawa, Y. Imai
    Mar. 2012, 18th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 61 - 64, English
    International conference proceedings

  • Toshihiro Omori, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    The dynamics of a capsule and a biological cell is of great interest in chemical engineering and bioengineering. Although the dynamics of a rigid spheroid is well understood by Jeffery's theory, that of a spheroidal capsule remains unclear. In this Letter, the motion of a spheroidal capsule or a red blood cell in creeping shear flow is investigated. The results show that the orientation of a nonspherical capsule is variant under time reversal, though that of a rigid spheroid is invariant. Surprisingly, the alignment of a nonspherical capsule over a long time duration shows a transition depending on the shear rate, which can be utilized for a particle-alignment technique. These findings form a fundamental basis of the suspension mechanics of capsules and biological cells.
    AMER PHYSICAL SOC, Mar. 2012, PHYSICAL REVIEW LETTERS, 108(13) (13), 138102, English
    [Refereed]
    Scientific journal

  • Davod Alizadehrad, Yohsuke Imai, Keita Nakaaki, Takuji Ishikawa, Takami Yamaguchi
    We developed a numerical method for large-scale simulations of cellular flow in microvessels. We employed a particle method, where all blood components were modeled using a finite number of particles. Red blood cell deformation was modeled by a spring network of membrane particles. A domain decomposition method was used for parallel implementation on distributed memory systems. In a strong scaling test up to 64 CPU cores, we obtained a linear speedup with the number of CPU cores, and demonstrated that our model can simulate O(10 3) red blood cells in vessels a few tens of micrometers in diameter. For quantitative validation, we analyzed the Fåhræus effect and the formation of a cell-depleted peripheral layer. Simulations were performed for tube hematocrit ranging from 20 to 45%, and microvessel diameters from 9 to 50 μm. Our numerical results were in good agreement with previous experimental results both for the discharge hematocrit and cell-depleted peripheral layer thickness. © 2012 by JSME.
    Feb. 2012, Journal of Biomechanical Science and Engineering, 7(1) (1), 57 - 71, English
    [Refereed]
    Scientific journal

  • Radial dispersion of tracer particles through high-hematocrit blood flow within a capillary tube
    M. Saadatmand, T. Ishikawa, N. Matsuki, H. J. Abdekhodaie, Y. Imai, H. Ueno, T. Yamaguchi
    Feb. 2012, Nano-Biomedical Engineering, Imperial College Press, 134 - 143, English
    Research society

  • Tatsuya Tanaka, Takuji Ishikawa, Keiko Numayama-Tsuruta, Yohsuke Imai, Hironori Ueno, Takefumi Yoshimoto, Noriaki Matsuki, Takami Yamaguchi
    The circulating tumor cell test is used to evaluate the condition of breast cancer patients by counting the number of cancer cells in peripheral blood samples. Although microfluidic systems to detect or separate cells using the inertial migration effect may be applied to this test, the hydrodynamic forces acting on cancer cells in high hematocrit blood flow are incompletely understood. In the present study, we investigated the inertial migration of cancer cells in high hematocrit blood flow in microchannels. The maximum hematocrit used in this study was about 40%. By measuring the cell migration probability, we examined the effects of cell-cell interactions, cell deformability, and variations in cell size on the inertial migration of cancer cells in blood. The results clearly illustrate that cancer cells can migrate towards equilibrium positions up to a hematocrit level of 10%. We also performed simple scaling analysis to explain the differences in migration length between rigid particles and cancer cells as well as the effect of hematocrit on cancer cell migration. These results will be important for the design of microfluidic devices for separating cells from blood.
    SPRINGER, Feb. 2012, BIOMEDICAL MICRODEVICES, 14(1) (1), 25 - 33, English
    [Refereed]
    Scientific journal

  • Entrapment of fresh water ciliates at the interface fluid-air
    J. Ferracci, T. Ishikawa, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi
    Feb. 2012, Nano-Biomedical Engineering, Imperial College Press, 70 - 76, English
    Research society

  • Computational biomechanics of blood flow at macro- and micro-scales
    T. Yamaguchi, T. Ishikawa, Y. Imai
    Feb. 2012, Nano-Biomedical Engineering, Imperial College Press, 53 - 62, English
    Research society

  • Behavior of a spherical capsule in simple shear flow near an infinite plane
    S. Nix, Y. Imai, D. Matsunaga, T. Ishikawa, T. Yamaguchi
    Feb. 2012, Nano-Biomedical Engineering, Imperial College Press, 122 - 127, English
    Research society

  • R. Lima, R. J. Joseyphus, T. Ishikawa, Y. Imai, T. Yamaguchi
    An investigation to measure the flow behavior of magnetic nanoparticles through a 100? m microchannel is conducted. The magnetic field is applied externally by a permanent magnet and by using a micro-PTV system it was possible to measure the flow behavior of magnetic nanoparticles at different flow rates and magnetic fields through a 100?m glass capillary. A strong dependence on both magnetic and hydrodynamic force is observed on the nanoparticles fluidic paths. Based on these in vitro studies, important parameters and issues that require further understanding and investigation are point out. © 2012 Bentham Science Publishers. All rights reserved.
    Bentham Science Publishers Ltd., 2012, Single and Two-Phase Flows on Chemical and Biomedical Engineering, 600 - 612, English
    [Refereed]
    In book

  • R. Lima, T. Ishikawa, Y. Imai, T. Yamaguchi
    Over the years, various experimental methods have been applied in an effort to understand the blood flow behavior in microcirculation. Most of our current knowledge in microcirculation is based on macroscopic flow phenomena such as Fahraeus effect and Fahraeus-Linqvist effect. The development of optical experimental techniques has contributed to obtain possible explanations on the way the blood flows through microvessels. Although the past results have been encouraging, detailed studies on blood flow behavior at a microscopic level have been limited by several factors such as poor spatial resolution, difficulty to obtain accurate measurements at such small scales, optical errors arisen from walls of the microvessels, high concentration of blood cells, and difficulty in visualization of results due to insufficient computing power and absence of reliable image analysis techniques. However, in recent years, due to advances in computers, optics, and digital image processing techniques, it has become possible to combine a conventional particle image velocimetry (PIV) system with an inverted microscope and consequently improve both spatial and temporal resolution. The present review outlines the most relevant studies on the flow properties of blood at a microscale level by using past video-based methods and current micro-PIV and confocal micro-PIV techniques. Additionally the most recent computational fluid dynamics studies on microscale hemodynamics are also reviewed. © 2012 Bentham Science Publishers. All rights reserved.
    Bentham Science Publishers Ltd., 2012, Single and Two-Phase Flows on Chemical and Biomedical Engineering, 513 - 547, English
    [Refereed]
    In book

  • D. Matsunaga, Y. Imai, T. Ishikawa, T. Yamaguchi
    A capsule is a liquid drop enclosed by a thin membrane. Understanding the mechanics of capsule suspension is important in a variety of applications. However, computational time is still a barrier against successful simulations for dense suspension of capsules. We have developedan ultra-highspeed computation method based on Graphics Processing Unit (GPU) computing for simulatin gmulti-capsule flow. In the case of using single GPU, the performance achieves 1. 20 TFlops that correspondsto a 550-foldspeed up comparedwith a CPU core. We also developed an algorithm of multi GPUs that hide data communication by overlapping with computational time. Since our method enables us to simulate from one to a few hundredcapsules in a realistic computationaltime, the methodcouldbe a powerful solution for simulating the capsule suspension. © 201 WIT Press.
    2012, WIT Transactions on Modelling and Simulation, 53, 201 - 208, English
    [Refereed]
    International conference proceedings

  • S. Nix, Y. Imai, T. Ishikawa, T. Yamaguchi
    Acapsuleis definedas aliquiddropenclosedbyanelastic membrane. Thestudyof capsule behavior near a stationary surface has a numberof biological applications, such as red blood cells in the cardiovascular system. However, near-wall behavior of capsules has not been established well. In this study, we investigate the motion of initially spherical and biconcave capsules in simple shear flow near an infinite plane using a boundary integral method coupled to a finite element method. We find that the deformation of a capsule depends on its initial shape, orientation, and capillary number (Ca). However, the lift velocity of a capsule is dependent on its steady state deformation and distance from the wall. The dependence of lift velocity on deformation may help to explain phenomena such as leukocyte margination. © 201 WIT Press.
    2012, WIT Transactions on Modelling and Simulation, 53, 191 - 199
    [Refereed]
    International conference proceedings

  • Flow visualization of trace particles and Red Blood Cells in a microchannel with a diverging and converging bifurcation
    V. Leble, C. Fernandes, R. Dias, R. Lima, T. Ishikawa, Y. Imai, T. Yamaguchi
    This paper aims to investigate the effect of both diverging and converging bifurcations on the flow behaviour of Pure Water (PW) and Red Blood Cells (RBCs). A confocal micro-PTV system is used to visualize and measure the flow characteristics of the working fluids. The results show no formation of a Cell-Free Layer (CFL) around the apex of the bifurcation. In contrast, there is a clear formation of a triangular CFL just downstream of the confluence apex. As a result, this triangular CFL seems to play an important role on the in vitro blood flow characteristics at this region.
    CRC PRESS-TAYLOR & FRANCIS GROUP, 2012, COMPUTATIONAL VISION AND MEDICAL IMAGE PROCESSING: VIPIMAGE 2011, 209 - 211, English
    [Refereed]
    International conference proceedings

  • TANAKA Tatsuya, ISHIKAWA Takuji, NUMAYAMA-TSURUTA Keiko, IMAI Yohsuke, UENO Hironori, MATSUKI Noriaki, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2012, The Proceedings of the Bioengineering Conference Annual Meeting of BED/JSME, 2012(0) (0), _8F25 - 1_-_8F25-2_, Japanese
    [Refereed]
    International conference proceedings

  • SHIOIRI Tatsuya, ISHIKAWA Takuji, NUMAYAMA Keiko, UENO Hironori, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2012, The Proceedings of the Bioengineering Conference Annual Meeting of BED/JSME, 2012(0) (0), _7E41 - 1_-_7E41-2_, Japanese
    International conference proceedings

  • Stephanie Nix, Yohsuke Imai, Daiki Matsunaga, Takuji Ishikawa, Takami Yamaguchi
    AMER SOC MECHANICAL ENGINEERS, 2012, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE, PTS A AND B, CD-ROM, 839 - 840, English
    [Refereed]
    International conference proceedings

  • Kohei Kyoya, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa
    Analysis of a suspension of microorganisms is important in environmental and biomedical engineering. Previous studies had problems of high computational load in simulating many-body interaction of non-spherical swimmers. In this study, we propose a boundary element method (BEM), based on the double-layer representation, for calculating interactions of two squirmers in Stokes flow regime. By comparing the trajectories of squirmers calculated by both single- and double-layer representations, we show the accuracy of the method. The developed method has potential to deal with many-body interactions of non-spherical microorganisms.
    AMER SOC MECHANICAL ENGINEERS, 2012, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE, PTS A AND B, CD-ROM, 777 - 778, English
    [Refereed]
    International conference proceedings

  • Naoki Takeishi, Yohsuke Imai, Keita Nakaaki, Takuji Ishikawa, Takami Yamaguchi
    AMER SOC MECHANICAL ENGINEERS, 2012, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE, PTS A AND B, CD-ROM, 823 - 824, English
    [Refereed]
    International conference proceedings

  • Taimei Miyagawa, Yohsuke Imai, Ikuma Kobayashi, Takuji Ishikawa, Takami Yamaguchi
    AMER SOC MECHANICAL ENGINEERS, 2012, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE, PTS A AND B, CD-ROM, 787 - 788, English
    [Refereed]
    International conference proceedings

  • D. Matsunaga, Y. Imai, T. Ishikawa, T. Yamaguchi
    A capsule is a liquid drop enclosed by a thin membrane. Understanding the mechanics of capsule suspension is important in a variety of applications. However, computational time is still a barrier against successful simulations for dense suspension of capsules. We have developed an ultra-high speed computation method based on Graphics Processing Unit (GPU) computing for simulating multi-capsule flow. In the case of using single GPU, the performance achieves 1.20 TFlops that corresponds to a 550-fold speed up compared with a CPU core. We also developed an algorithm of multi GPUs that hide data communication by overlapping with computational time. Since our method enables us to simulate from one to a few hundred capsules in a realistic computational time, the method could be a powerful solution for simulating the capsule suspension.
    WIT PRESS, 2012, BOUNDARY ELEMENTS AND OTHER MESH REDUCTION METHODS XXXIV, 53, 201 - 208, English
    [Refereed]
    International conference proceedings

  • S. Nix, Y. Imai, T. Ishikawa, T. Yamaguchi
    A capsule is defined as a liquid drop enclosed by an elastic membrane. The study of capsule behavior near a stationary surface has a number of biological applications, such as red blood cells in the cardiovascular system. However, near-wall behavior of capsules has not been established well. In this study, we investigate the motion of initially spherical and biconcave capsules in simple shear flow near an infinite plane using a boundary integral method coupled to a finite element method. We find that the deformation of a capsule depends on its initial shape, orientation, and capillary number (Ca). However, the lift velocity of a capsule is dependent on its steady state deformation and distance from the wall. The dependence of lift velocity on deformation may help to explain phenomena such as leukocyte margination.
    WIT PRESS, 2012, BOUNDARY ELEMENTS AND OTHER MESH REDUCTION METHODS XXXIV, 53, 191 - 199, English
    [Refereed]
    International conference proceedings

  • T. Miki, X. Wang, T. Aoki, Y. Imai, T. Ishikawa, K. Takase, T. Yamaguchi
    In this paper, we propose a novel patient-specific method of modelling pulmonary airflow using graphics processing unit (GPU) computation that can be applied in medical practice. To overcome the barriers imposed by computation speed, installation price and footprint to the application of computational fluid dynamics, we focused on GPU computation and the lattice Boltzmann method (LBM). The GPU computation and LBM are compatible due to the characteristics of the GPU. As the optimisation of data access is essential for the performance of the GPU computation, we developed an adaptive meshing method, in which an airway model is covered by isotropic subdomains consisting of a uniform Cartesian mesh. We found that 4(3) size subdomains gave the best performance. The code was also tested on a small GPU cluster to confirm its performance and applicability, as the price and footprint are reasonable for medical applications.
    TAYLOR & FRANCIS LTD, 2012, COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING, 15(7) (7), 771 - 778, English
    [Refereed]
    Scientific journal

  • Tatsuya Tanaka, Takuji Ishikawa, Keiko Numayama-Tsuruta, Yohsuke Imai, Hironori Ueno, Noriaki Matsuki, Takami Yamaguchi
    The circulating tumor cell (CTC) test has recently become popular for evaluating prognosis and treatment efficacy in cancer patients. The accuracy of the test is strongly dependent on the precision of the cancer cell separation. In this study, we developed a multistage microfluidic device to separate cancer cells from a red blood cell (RBC) suspension using inertial migration forces. The device was able to effectively remove RBCs up to the 1% hematocrit (Hct) condition with a throughput of 565 mu L min(-1). The collection efficiency of cancer cells from a RBC suspension was about 85%, and the enrichment of cancer cells was about 120-fold. Further improvements can be easily achieved by parallelizing the device. These results illustrate that the separation of cancer cells from RBCs is possible using only inertial migration forces, thus paving the way for the development of a novel microfluidic device for future CTC tests.
    ROYAL SOC CHEMISTRY, 2012, LAB ON A CHIP, 12(21) (21), 4336 - 4343, English
    [Refereed]
    Scientific journal

  • Multi-GPU computing of capsule flow using boundary integral method
    D. Matsunaga, Y. Imai, T. Omori, T. Ishikawa, T. Yamaguchi
    Dec. 2011, 5th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 72 - 73, English
    International conference proceedings

  • GPU-based simulation of blood flow in complex microvessels
    K. Nakaaki, Y. Imai, T. Ishikawa, C. T. Lim, T. Yamaguchi
    Dec. 2011, 5th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 152 - 153, English
    International conference proceedings

  • Entrapment of fresh water ciliates at the interface fluid-air
    J. Ferracci, T. Ishikawa, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi
    Dec. 2011, 5th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 120 - 121, English
    International conference proceedings

  • Computation of near-wall capsule flow using boundary integral method
    S. Nix, Y. Imai, D. Matsunaga, T. Ishikawa, T. Yamaguchi
    Dec. 2011, 5th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 76 - 77, English
    International conference proceedings

  • Collective diffusion of red blood cells from high concentration to low
    C. Chuang, T. Ishikawa, H. Ueno, K. Numayama-Tsuruta, Y. Imai, T. Yamaguchi
    Dec. 2011, 5th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 32 - 33, English
    International conference proceedings

  • Vladimir Leble, Rui Lima, Ricardo Dias, Carla Fernandes, Takuji Ishikawa, Yohsuke Imai, Takami Yamaguchi
    In microcirculation, red blood cells (RBCs) flowing through bifurcations may deform considerably due to combination of different phenomena that happen at the micro-scale level, such as: attraction effect, high shear, and extensional stress, all of which may influence the rheological properties and flow behavior of blood. Thus, it is important to investigate in detail the behavior of blood flow occurring at both bifurcations and confluences. In the present paper, by using a micro-PTV system, we investigated the variations of velocity profiles of two working fluids flowing through diverging and converging bifurcations, human red blood cells suspended in dextran 40 with about 14% of hematocrit level (14 Hct) and pure water seeded with fluorescent trace particles. All the measurements were performed in the center plane of rectangular microchannels using a constant flow rate of about 3.0 x 10(-12) m(3)/s. Moreover, the experimental data was compared with numerical results obtained for Newtonian incompressible fluid. The behavior of RBCs was asymmetric at the divergent and convergent side of the geometry, whereas the velocities of tracer particles suspended in pure water were symmetric and well described by numerical simulation. The formation of a red cell-depleted zone immediately downstream of the apex of the converging bifurcation was observed and its effect on velocity profiles of RBCs flow has been investigated. Conversely, a cell-depleted region was not formed around the apex of the diverging bifurcation and as a result the adhesion of RBCs to the wall surface was enhanced in this region. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672689]
    AMER INST PHYSICS, Dec. 2011, BIOMICROFLUIDICS, 5(4) (4), 044120, English
    [Refereed]
    Scientific journal

  • A numerical computation on gastric mixing using GPU
    I. Kobayashi, Y. Imai, S. Ishida, T. Ishikawa, T. Yamaguchi
    Dec. 2011, 5th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 150 - 151, English
    International conference proceedings

  • Analysis of fluid flow on the surface of tracheal lumen through effective ciliary motion
    K. Kiyota, H. Ueno, T. Ishikawa, K. Numayama-Tsuruta, Y. Imai, N. Matsuki, T. Yamaguchi
    Dec. 2011, 5th East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 34 - 35, English
    International conference proceedings

  • Energy transport in a concentrated suspension of bacteria
    T. Ishikawa, N. Yoshida, H. Ueno, M. Wiedeman, Y. Imai, T. Yamaguchi
    Nov. 2011, Bulletin of the American Physical Society, DFD2011, 56, 388, English
    International conference proceedings

  • Development of GPU computing for simulating dense suspension of capsules
    Y. Imai, D. Matsunaga, T. Ishikawa, T. Yamaguchi
    Nov. 2011, 5th Shanghai Int. Conf. Biophysics and Molecular Biology Abstract Book, 125, English
    International conference proceedings

  • Swallowing simulation based on videofluorography
    S. Ishida, Y. Imai, T. Ishikawa, A. Kinjyo, N. Matsuki, T. Yamaguchi
    Sep. 2011, The International Conference on BioTribology Conference Abstracts, CD-ROM, English
    International conference proceedings

  • Modelling of red blood cell motion and deformation using particle based method
    T. Yamaguchi, Y. Imai, T. Ishikawa
    Sep. 2011, Proc. ECCOMAS SIMBIO 2011, CD-ROM, English
    International conference proceedings

  • Particle based modeling and simulation of the red blood cell infected by malaria -mechanism of the margination of the infected red blood cell
    T. Yamaguchi, T. Ishikawa, Y. Imai
    Aug. 2011, 3rd Micro and Nano Flows Conference, CD-ROM, English
    International conference proceedings

  • T. Ishikawa, N. Yoshida, H. Ueno, M. Wiedeman, Y. Imai, T. Yamaguchi
    Coherent structures appear in a concentrated suspension of swimming bacteria. While transport phenomena in a suspension have been studied extensively, how energy is transported from the individual cell scale to the larger mesoscale remains unclear. In this study, we carry out the first successful measurement of the three-dimensional velocity field in a dense suspension of bacteria. The results show that most of the energy generated by individual bacteria dissipates on the cellular scale. Only a small amount of energy is transported to the mesoscale, but the gain in swimming velocity and mass transport due to mesoscale coherent structures is enormous. These results indicate that collective swimming of bacteria is efficient in terms of energy. This paper sheds light on how energy can be transported toward smaller wave numbers in the Stokes flow regime.
    AMER PHYSICAL SOC, Jul. 2011, PHYSICAL REVIEW LETTERS, 107(2) (2), 028102, English
    [Refereed]
    Scientific journal

  • T. Ishikawa, T. Sato, G. Mohit, Y. Imai, T. Yamaguchi
    The gastrointestinal tract of humans is colonized by indigenous prokaryotic and eukaryotic microbial cells that form a complex ecological system called microbial flora. Although the microbial flora has diverse functions, its homeostasis inside the gastrointestinal tract is still largely unknown. Therefore, creating a model for investigating microbial flora in the gastrointestinal tract is important. In this study, we developed a novel numerical model to explore the transport phenomena of microbial flora in the small intestine. By simultaneously solving the flow field generated by peristalsis, the concentrations of oxygen and nutrient, and the densities of moderate anaerobes and aerobes, the effects of fluid mechanics on the transport phenomena of microbial flora are discussed. The results clearly illustrated that fluid mechanics have considerable influence not only on the bacterial population, but also on the concentration distributions of oxygen and nutrient. Especially, the flow field enhances the radial variation of the concentration fields. We also show scaling arguments for bacterial growth and oxygen consumption, which capture the main features of the results. Additionally, we investigated the transport phenomena of microbial flora in a long tube with 40 constrictions. The results showed a high growth rate of aerobes in the upstream side and a high growth rate of anaerobes in the downstream side, which qualitatively agrees with experimental observations of human intestines. These new findings provide the fundamental basis for a better understanding of the transport phenomena of microbial flora in the intestine. (C) 2011 Elsevier Ltd. All rights reserved.
    ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, Jun. 2011, JOURNAL OF THEORETICAL BIOLOGY, 279(1) (1), 63 - 73, English
    [Refereed]
    Scientific journal

  • Numerical simulation on margination of malaria-infected red blood cells in microvessels
    Y.Imai, K.Nakaaki, T.Ishikawa, T.Yamaguchi
    Jun. 2011, Proc Japan-Portugal Nano-BME Symp, 7 - 10, English
    International conference proceedings

  • Numerical simulation of cell depleted peripheral layer and red blood cells motion in microvascular blood flow
    D.Alizadehrad, Y.Imai, T.Ishikawa, T.Yamaguchi
    Jun. 2011, Proc. Japan-Portugal Nano-BME Symp, 15 - 16, English
    International conference proceedings

  • Motions of trace particles and red blood cells in a PDMS microchannel with a converging bifurcation
    V.Leble, R.Dias, R.Lima, C.Fernandes, T.Ishikawa, Y.Imai, T.Yamaguchi
    Jun. 2011, Proc. Japan-Portugal Nano-BME Symp, 29 - 30, English
    International conference proceedings

  • High performance GPU computing of capsule flow using boundary integral method
    D.Matsunaga, Y.Imai, T.Omori, T.Miki, T.Ishikawa, T.Yamaguchi
    Jun. 2011, Proc. Japan-Portugal Nano-BME Symp, 19 - 22, English
    International conference proceedings

  • Gradient diffusion of red blood cells in a Y-shape microchannel
    C.-H.Chuang, T.Ishikawa, K.Numayama-Tsuruta, Y.Imai, T.Yamaguchi
    Jun. 2011, Proc. Japan-Portugal Nano-BME Symp, 17 - 18, English
    International conference proceedings

  • Development of a microfluidic device for partial cell separation
    R.Lima, M.S.N.Oliveira, T.Yaginuma, T.Ishikawa, Y.Imai, T.Yamaguchi
    Jun. 2011, Proc. Japan-Portugal Nano-BME Symp, 49 - 50, English
    International conference proceedings

  • Computational biomechanics for respiratory and micro-circulation systems
    T.Yamaguchi, T.Ishikawa, Y.Imai
    Jun. 2011, Proc Japan-Portugal Nano-BME Symp, 1 - 4, English
    International conference proceedings

  • Analysis of ciliary motion and fluid flow on the surface of tracheal cells
    H.Ueno, T.Ishikawa, K.Gonda, K.H.Bui, T.Ishikawa, Y.Imai, K.Numayama-Tsuruta, T.Yamaguchi
    Jun. 2011, Proc. Japan-Portugal Nano-BME Symp, 11 - 14, English
    International conference proceedings

  • Computational analysis of the margination of malaria-infected red blood cells in microcirculation
    T. Yamaguchi, T. Ishikawa, Y. Imai
    May 2011, Microscale Modeling in Biomechanics and Mechanobiology Program and Abstract, English
    International conference proceedings

  • Effect of red blood cells on dynamics of microvascular blood flow
    D. Alizadehrad, Y. Imai, T. Ishikawa, T. Yamaguchi
    May 2011, Microscale Modeling in Biomechanics and Mechanobiology Program and Abstract, English
    International conference proceedings

  • Capsule flow analysis using GPU computation
    D. Matsunaga, Y. Imai, T. Omori, T. Miki, T. Ishikawa, T. Yamaguchi
    May 2011, Microscale Modeling in Biomechanics and Mechanobiology Program and Abstract, English
    International conference proceedings

  • Diffusion of red blood cells from high concentration to low in a blood flow microchannel
    C. Chugang, T. Ishikawa, K. Numayama, Y. Imai, H. Ueno, T. Yamaguchi
    May 2011, Microscale Modeling in Biomechanics and Mechanobiology Program and Abstract, English
    International conference proceedings

  • Yohsuke Imai, Keita Nakaaki, Hitoshi Kondo, Takuji Ishikawa, Chwee Teck Lim, Takami Yamaguchi
    We investigated numerically the mechanism of margination of Plasmodium falciparum malaria-infected red blood cells (Pf-IRBCs) in micro-scale blood flow. Our model illustrates that continuous hydrodynamic interaction between a Pf-IRBC in the trophozoite stage (Pf-T-IRBC) and healthy red blood cells (HRBCs) results in the margination of the Pf-T-IRBC and, thus, a longer duration of contact with endothelial cells. The Pf-T-IRBC and HRBCs first form a "train". The volume fraction of RBCs is then locally increased, to approximately 40%, and this value is maintained for a long period of time due to the formation of a long train in high-hematocrit conditions. Even in low-hematocrit conditions, the local volume fraction is instantaneously elevated to 40% and the Pf-T-IRBC can migrate to the wall. However, the short train formed in low-hematocrit conditions does not provide continuous interaction, and the Pf-T-IRBC moves back to the center of the channel. (C) 2011 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, May 2011, JOURNAL OF BIOMECHANICS, 44(8) (8), 1553 - 1558, English
    [Refereed]
    Scientific journal

  • T. Omori, T. Ishikawa, D. Barthes-Biesel, A. -V. Salsac, J. Walter, Y. Imai, T. Yamaguchi
    A capsule is a liquid drop enclosed by a solid, deformable membrane. To analyze the deformation of a capsule accurately, both the fluid mechanics of the internal and external fluids and the solid mechanics of the membrane must be solved precisely. Recently, many researchers have used discrete spring network models to express the membrane mechanics of capsules and biological cells. However, it is unclear whether such modeling is sufficiently accurate to solve for capsule deformation. This study examines the correlations between the mechanical properties of the discrete spring network model and continuum constitutive laws. We first compare uniaxial and isotropic deformations of a two-dimensional (2D) sheet, both analytically and numerically. The 2D sheet is discretized with four kinds of mesh to analyze the effect of the spring network configuration. We derive the relationships between the spring constant and continuum properties, such as the Young modulus, Poisson ratio, area dilation modulus, and shear modulus. It is found that the mechanical properties of spring networks are strongly dependent on the mesh configuration. We then calculate the deformation of a capsule under inflation and in a simple shear flow in the Stokes flow regime, using various membrane models. To achieve high accuracy in the flow calculation, a boundary-element method is used. Comparing the results between the different membrane models, we find that it is hard to express the area incompressibility observed in biological membranes using a simple spring network model.
    AMER PHYSICAL SOC, Apr. 2011, PHYSICAL REVIEW E, 83(4) (4), 041918, English
    [Refereed]
    Scientific journal

  • Novel methods for the computational biomechanics study of respiratory and micro-circulatory systems
    T. Yamaguchi, T. Ishikawa, Y. Imai
    Mar. 2011, 16th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 99 - 102, English
    International conference proceedings

  • Takahito Miki, Yohsuke Imai, Takuji Ishikawa, Shigeo Wada, Takayuki Aoki, Takami Yamaguchi
    Since abnormal fluid states in our body cause critical diseases, patient-specific computational fluid dynamics (CFD) probably become a standard diagnosis tool in the near future. The vessels in our body are multiple-branched tubes, which makes it difficult to obtain accurate solutions from conventional CFD methods. In this report, we propose a fourth-order local mesh refinement (LMR) method based on an interpolated differential operator scheme for simulating flow in multi-generation branched vessels. The proposed LMR method has the accuracy of fourth-order for three-dimensional advection and diffusion equations, respectively. We describe how to apply the LMR method to patient-specific pulmonary airflow simulations. In our method, the computational mesh size is determined locally by geometrical parameters: the diameter of airways and the distance from the airway wall. To demonstrate our method, an LMR model and a fine mesh model were compared for flow in the central airway, and there was no significant difference between results. We also show the applicability of the method to a maximum eleventh-generation airway model, where the number of computational nodes was reduced by 85% compared with the case using uniform fine meshes. Copyright (C) 2010 John Wiley & Sons, Ltd.
    WILEY-BLACKWELL, Mar. 2011, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, 27(3) (3), 424 - 435, English
    [Refereed]
    Scientific journal

  • Takuji Ishikawa, Hiroki Fujiwara, Noriaki Matsuki, Takefumi Yoshimoto, Yohsuke Imai, Hironori Ueno, Takami Yamaguchi
    Bifurcations and confluences are very common geometries in biomedical microdevices. Blood flow at microchannel bifurcations has different characteristics from that at confluences because of the multiphase properties of blood. Using a confocal micro-PIV system, we investigated the behaviour of red blood cells (RBCs) and cancer cells in microchannels with geometrically symmetric bifurcations and confluences. The behaviour of RBCs and cancer cells was strongly asymmetric at bifurcations and confluences whilst the trajectories of tracer particles in pure water were almost symmetric. The cell-free layer disappeared on the inner wall of the bifurcation but increased in size on the inner wall of the confluence. Cancer cells frequently adhered to the inner wall of the bifurcation but rarely to other locations. Because the wall surface coating and the wall shear stress were almost symmetric for the bifurcation and the confluence, the result indicates that not only chemical mediation and wall shear stress but also microscale haemodynamics play important roles in the adhesion of cancer cells to the microchannel walls. These results provide the fundamental basis for a better understanding of blood flow and cell adhesion in biomedical microdevices.
    SPRINGER, Feb. 2011, BIOMEDICAL MICRODEVICES, 13(1) (1), 159 - 167, English
    [Refereed]
    Scientific journal

  • Particle based simulation of the microvascular blood flow in the malaria infection
    T. Yamaguchi, Y. Imai, T. Ishikawa
    2011, Trends & Challenges in Computational Mechanics Program and Abstracts, 43 - 44, English
    International conference proceedings

  • R. Lima, C. S. Fernandes, R. Dias, T. Ishikawa, Y. Imai, T. Yamaguchi
    The blood flow dynamics in microcirculation depends strongly on the microvascular networks composed with short irregular vessel segments which are linked by numerous bifurcations. This paper presents the application of a confocal micro-PTV system to track RBCs through a rectangular polydimethysiloxane (PDMS) microchannel with a bifurcation. By using a confocal micro-PTV system, we have measured the effect of bifurcation on the flow behaviour of both fluorescent particles diluted in pure water and RBCs in concentrated suspensions. After performing simulations with the commercial finite element software package POLYFLOW, some experimental results were compared with the numerical results and the limitations of these simulations were outlined.
    SPRINGER-VERLAG BERLIN, 2011, COMPUTATIONAL VISION AND MEDICAL IMAGE PROCESSING: RECENT TRENDS, 19, 297 - 309, English
    International conference proceedings

  • Maryam Saadatmand, Takuji Ishikawa, Noriaki Matsuki, Mohammad Jafar Abdekhodaie, Yohsuke Imai, Hironori Ueno, Takami Yamaguchi
    Fluid particle diffusion through blood flow within a capillary tube is an important phenomenon to understand, especially for studies in mass transport in the microcirculation as well as in solving technical issues involved in mixing in biomedical microdevices. In this paper, the spreading of tracer particles through up to 20% hematocrit blood, flowing in a capillary tube, was studied using a confocal micro-PTV system. We tracked hundreds of particles in high-hematocrit blood and measured the radial dispersion coefficient. Results yielded significant enhancement of the particle diffusion, due to a micron-scale flow-field generated by red blood cell motions. By increasing the flow rate, the particle dispersion increased almost linearly under constant hematocrit levels. The particle dispersion also showed near linear dependency on hematocrit up to 20%. A scaling analysis of the results, on the assumption that the tracer trajectories were unbiased random walks, was shown to capture the main features of the results. The dispersion of tracer particles was about 0.7 times that of RBCs. These findings provide good insight into transport phenomena in the microcirculation and in biomedical microdevices. (C) 2010 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Jan. 2011, JOURNAL OF BIOMECHANICS, 44(1) (1), 170 - 175, English
    [Refereed]
    Scientific journal

  • T. Shioiri, T. Ishikawa, K. Numayama-Tsuruta, Y. Imai, H. Ueno, T. Yamaguchi
    2011, ASME 2011 6th Frontiers in Biomedical Devices Conference and Exhibition, BioMed 2011, CD-ROM, 25 - 26, English
    [Refereed]
    International conference proceedings

  • T. Tanaka, T. Ishikawa, K. Numayama-Tsuruta, Y. Imai, H. Ueno, N. Matsuki, T. Yamaguchi
    2011, ASME 2011 6th Frontiers in Biomedical Devices Conference and Exhibition, BioMed 2011, CD-ROM, 13 - 14, English
    [Refereed]
    International conference proceedings

  • HUANG Cheng-Hsi, ISHIKAWA Takuji, UENO Hironori, NUMAYAMA Keiko, IMAI Yohsuke, YAMAGUCHI Takami
    We investigated the gradient diffusion of red blood cells (RBCs) in blood flow in a microchannel. The effects of flow rates, and hematocrit (Hct) on the gradient diffusion were investigated experimentally. Under the same hematocrit condition, the gradient dispersion coefficient was increased almost linearly to the flow rate. The gradient diffusion dominated over Brownian diffusion in most of high hematocrit conditions. These findings provide useful information in understanding mass transport in small vessels.
    The Japan Society of Mechanical Engineers, 2011, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2011(0) (0), 63 - 64, English
    Research society

  • Large-scale numerical simulation of blood flow in microvessels
    D.Alizadehrad, Y.Imai, T.Ishikawa, T.Yamaguchi
    Dec. 2010, Proc. 4th East Asian Pacific Stu. Workshop Nano-Biomed. Eng, 98 - 99, English
    International conference proceedings

  • Noriaki Matsuki, Motohiro Takeda, Masahiro Yamano, Yohsuke Imai, Takuji Ishikawa, Takami Yamaguchi
    INFORMA HEALTHCARE, Nov. 2010, JOURNAL OF INTERPROFESSIONAL CARE, 24(6) (6), 738 - 741, English
    [Refereed]
    Scientific journal

  • Separation of cancer cells from blood by using a micro fluidic device
    T.Tanaka, T.Ishikawa, N.Matsuki, Y.Imai, H.Ueno, K.Numayama-Tsuruta, T.Yamaguchi
    Sep. 2010, KIST-Tohoku Joint Symp Nanobiomed Eng, 75 - 76, English
    International conference proceedings

  • Effects of rosette formation and cytoadhesion on hemodynamics in malaria infection
    K.Nakaaki, Y.Imai, H.Kondo, T.Ishikawa, C.T.Lim, T.Yamaguchi
    Sep. 2010, KIST-Tohoku Joint Symp Nanobiomed Eng, 67 - 68, English
    International conference proceedings

  • A numerical study on migration of malaria infected red blood cells
    Y.Imai, K.Nakaaki, H.Kondo, T.Ishikawa, C.T.Lim, T.Yamaguchi
    Sep. 2010, KIST-Tohoku Joint Symp Nanobiomed Eng, 15 - 16, English
    [Refereed][Invited]
    International conference proceedings

  • Parallel 3-D Code to Investigate the Pathophysiology of Malaria on Distributed Memory Systems
    D.Alizadehrad, Y.Imai, T.Ishikawa, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 581, English
    International conference proceedings

  • Micro-flow Visualization of in vitro Blood through a Microchannel with a Bifurcation and Confluence
    R.Lima, M.Oliveira, T.Ishikawa, N.Matsuki, Y.Imai, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 561, English
    International conference proceedings

  • Measuring the Cell-Free Layer in circular Microchannels
    C.Fidalgo, A.Sa, R.Lima, M.Oliveira, T.Ishikawa, Y.Imai, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 472, English
    International conference proceedings

  • Measurement of the red blood cell (RBC) dispersion in microchannels: the effect of the temperature
    D.Pinho, A.Pereira, R.Lima, T.Ishikawa, Y.Imai, T.Yamaguchi
    Aug. 2010, IFMBE Proceedings, 31, 1067 - 1070, English
    International conference proceedings

  • Effect of Membrane Modeling on the Capsule Deformation: Comparison between a Spring Network and Continuum Models
    T.Omori, T.Ishikawa, D.Barthes-Biesel, A.-V.Salsac, Y.Imai, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 470, English
    International conference proceedings

  • Effect of Adhesive Properties of Malaria-infected Red Blood Cells in Microcirculation
    K.Nakaaki, Y.Imai, H.Kondo, T.Ishikawa, C.T.Lim, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 503, English
    International conference proceedings

  • Diffusion of Fluid Particles in High Hematocrit Blood Flow in a Capillary Tube
    M.Saadatmand, T.Ishikawa, N.Matsuki, M.J.Abdekhodaie, Y.Imai, H.Ueno, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 471, English
    International conference proceedings

  • Development of a Micro Fluidic Device to Separate Cancer Cells from Blood
    T.Tanaka, T.Ishikawa, N.Matsuki, Y.Imai, H.Ueno, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 164, English
    International conference proceedings

  • A Numerical Study on the Behavior of Cells in Micro-scale Blood Flows
    Y.Matsumoto, Y.Imai, T.Ishikawa, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 471, English
    International conference proceedings

  • A Numerical Study on Fluid Motion in the Stomach
    I.Kobayashi, Y.Imai, S.Ishida, T.Ishikawa, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 575, English
    International conference proceedings

  • Analysis of Swallowing Motion based on Videofluorography
    S.Ishida, Y.Imai, A.Kinjo, N.Matsuki, T.Ishikawa, T.Yamaguchi
    Aug. 2010, 6th World Congress of Biomechanics Abstracts, 165, English
    International conference proceedings

  • Blood flow and cancer cell adhesion in a microchannel with bifurcation and confluence
    T.Ishikawa, H.Fujiwara, N.Matsuki, T.Yoshimoto, Y.Imai, H.Ueno, T.Yamaguchi
    Jul. 2010, ESB2010 Abstracts CD-ROM, English
    International conference proceedings

  • Confocal micro-flow visualization of blood cells
    R. Lima, T. Ishikawa, Y. Imai, T. Yamaguchi
    Jun. 2010, CFD2010 Proceedings (CD-ROM), English
    International conference proceedings

  • Efficient parallel code for simulating malaria infected blood flow
    D. Alizadehrad, Y. Imai, T. Ishikawa, T. Yamaguchi
    May 2010, 22nd International Conference on Parallel Computational Fluid Dynamics (ParCFD 2010) (CD-ROM), English
    International conference proceedings

  • Numerical simulation of interaction among malaria-infected red blood cells, healthy red blood cells, and endothelial cells
    Y.Imai, K.Nakaaki, H.Kondo, T.Ishikawa, C.T.Lim, T.Yamaguchi
    May 2010, Proc. 4th ECCM, CD-ROM, No.269, English
    [Refereed][Invited]
    International conference proceedings

  • Yohsuke Imai, Hitoshi Kondo, Takuji Ishikawa, Chwee Teck Lim, Takami Yamaguchi
    We propose a numerical model of hemodynamics arising from malaria infection. This model is based on a particle method, where all the components of blood are represented by the finite number of particles. A two-dimensional spring network of membrane particles is employed for expressing the deformation of malaria infected red blood cells (IRBCs). Malaria parasite within the IRBC is modeled as a rigid object. This model is applied to the stretching of IRBCs by optical tweezers, the deformation of IRBCs in shear flow, and the occlusion of narrow channels by IRBCs. We also investigate the effects of IRBCs on the theological property of blood in micro-channels. Our results indicate that apparent viscosity is drastically increased for the period from the ring stage and the trophozoite stage, whereas it is not altered in the early stage of infection. (C) 2010 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, May 2010, JOURNAL OF BIOMECHANICS, 43(7) (7), 1386 - 1393, English
    [Refereed]
    Scientific journal

  • Impact of membrane modeling in analysing deformation of a capsule:comparison between a spring network model and constitutive laws
    T.Omori, T.Ishikawa, D.Barthes-biesel, A.V.Salsac, Y.Imai, T.Yamaguchi
    May 2010, Proc. 4th ECCM, No. 781, English
    [Refereed]
    International conference proceedings

  • Noriaki Matsuki, Motohiro Takeda, Takuji Ishikawa, Aki Kinjo, Tomoaki Hayasaka, Yohsuke Imai, Takami Yamaguchi
    Few studies have examined apoptosis induced by low-voltage electric pulses (LVEPs). LVEP-induce changes in membrane potential that are below the membrane breakdown threshold and increase membrane permeability without electroporation (pore formation) through the transport of extracellular substances via phagocytosis. We demonstrated that propidium iodide uptake and apoptosis increased in accordance with the duration and number of LVEPs in B16 cells, which showed relatively good viability under mild electric field conditions. We showed that LVEP-induced apoptosis was achieved through caspase-8 and -9 activation and subsequent caspase-3 activation. Long-duration LVEPs caused only mild cell damage, such that the apoptosis ratio (apoptosis/total cell death) in electric pulse-treated cells was similar to that in non-treated control cells. To assess the relative degree of caspase dependency in LVEP-induced apoptosis, the apoptosis rate and caspase-3 activity were analyzed using a pan-caspase inhibitor (Z-VAD-FMK). Z-VAD-FMK treatment inhibited, but did not abolish. LVEP-induced apoptosis, indicating that caspases other than caspase-3 participate in this pathway. Moreover. LVEP treatment inhibited cell growth, suggesting that LVEP treatment may be a valuable anticancer therapy. Although the mechanism of LVEP-induced apoptosis remains unclear, it may be related to dysfunctional membrane transport of Ca(2+) and other extracellular substances involved in caspase activation.
    SPANDIDOS PUBL LTD, May 2010, ONCOLOGY REPORTS, 23(5) (5), 1425 - 1433, English
    [Refereed]
    Scientific journal

  • Effect of pneumothorax on morphology and hemodynamic of pulmonary artery
    J-J. Christophe, T. Ishikawa, N. Matsuki, Y. Imai, K. Takase, M. Thiriet, T. Yamaguchi
    Mar. 2010, 11th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 103 - 104, English
    International conference proceedings

  • Radial dispersion of tracer particles in blood flow in a capillary tube
    M. Saadatmand, T. Ishikawa, N. Matsuki, M. J. Abdekhodaie, Y. Imai, H. Ueno, T. Yamaguchi
    Mar. 2010, 11th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 113 - 114, English
    International conference proceedings

  • Comprehensive application of particle methods to the diseases of the blood
    T. Yamaguchi, Y. Imai, H. Kamada, K. Nakaaki, T. Ishikawa
    Mar. 2010, The 2nd Biosupercomputing symposium, 118 - 119, English
    International conference proceedings

  • Takami Yamaguchi, Takuji Ishikawa, Y. Imai, N. Matsuki, Mikhail Xenos, Yuefan Deng, Danny Bluestein
    A major computational challenge for a multiscale modeling is the coupling of disparate length and timescales between molecular mechanics and macroscopic transport, spanning the spatial and temporal scales characterizing the complex processes taking place in flow-induced blood clotting. Flow and pressure effects on a cell-like platelet can be well represented by a continuum mechanics model down to the order of the micrometer level. However, the molecular effects of adhesion/aggregation bonds are on the order of nanometer. A successful multiscale model of platelet response to flow stresses in devices and the ensuing clotting responses should be able to characterize the clotting reactions and their interactions with the flow. This paper attempts to describe a few of the computational methods that were developed in recent years and became available to researchers in the field. They differ from traditional approaches that dominate the field by expanding on prevailing continuum-based approaches, or by completely departing from them, yielding an expanding toolkit that may facilitate further elucidation of the underlying mechanisms of blood flow and the cellular response to it. We offer a paradigm shift by adopting a multidisciplinary approach with fluid dynamics simulations coupled to biophysical and biochemical transport.
    SPRINGER, Mar. 2010, ANNALS OF BIOMEDICAL ENGINEERING, 38(3) (3), 1225 - 1235, English
    [Refereed]
    Scientific journal

  • Yohsuke Imai, Kodai Sato, Takuji Ishikawa, Andrew Comerford, Tim David, Takami Yamaguchi
    ATP acts as an extracellular signaling molecule in purinergic signaling that regulates vascular tone. ATP binds purinergic P2 nucleotide receptors on endothelial cells. Understanding the mass transport of ATP to endothelial cells by blood flow is thus important to predict functional changes in aneurysmal walls. While some clinical observations indicate a difference of wall pathology between ruptured and unruptured aneurysms, no study has focused on the mass transport in aneurysms. We investigated the characteristics of ATP concentration at aneurysmal wall using a numerical model of ATP transport in aneurysms formed at arterial bends. The magnitude of ATP concentration at the aneurysmal wall was significantly smaller than that at the arterial wall. In particular, significantly low concentration was predicted at the proximal side of the aneurysmal sac. A strong correlation was revealed between the inflow flux at the aneurysmal neck and the resultant concentration at the aneurysmal wall.
    SPRINGER, Mar. 2010, ANNALS OF BIOMEDICAL ENGINEERING, 38(3) (3), 927 - 934, English
    [Refereed]
    Scientific journal

  • Computational biomechanics for investigating cardiovascular diseases
    T. Yamaguchi, H. Kondo, Y. Shimogonya, Y. Imai, N. Matsuki, T. Ishikawa
    Feb. 2010, Nano-Biomedical Engineering 2009, 41 - 50, English

  • Ishikawa T., Yoshida N., Ueno H., Matsuki N., Imai Y., Yamaguchi T.
    The Japan Society of Mechanical Engineers, 2010, The proceedings of the JSME annual meeting, 2010, 51 - 52, Japanese

  • Red Blood Cell Dispersion in 100 mu m Glass Capillaries: The Temperature Effect
    D. Pinho, A. Pereira, R. Lima, T. Ishikawa, Y. Imai, T. Yamaguchi
    The rheological behaviour of the red blood cells (RBCs) flowing in microvessels and microchannels depend on several effects, such as hematocrit (Hct), geometry, and temperature. Previous in vitro studies have measured the Hct effect on the radial dispersion (D-yy) at both diluted and concentrated suspensions of RBCs. However, according to our knowledge the effect of the temperature on RBC D-yy was never studied. Hence, the main purpose of the present work is to investigate the effect of the temperature on the RBC D-yy. In vitro human blood was pumped through a 100 mu m glass capillary and by using a confocal micro-PTV system the RBC D-yy was calculated at two different temperatures, i.e., 25 degrees C and 37 degrees C.
    SPRINGER, 2010, 6TH WORLD CONGRESS OF BIOMECHANICS (WCB 2010), PTS 1-3, 31, 1067 - +, English
    [Refereed]
    International conference proceedings

  • Takami Yamaguchi, Yosuke Imai, Takuji Ishikawa
    We developed a numerical model of blood flow in malaria infection. Our model was based on a particle method. All the components of blood were represented by finite number of particles. The membrane of red blood cells was modeled by triangular network of membrane particles. Stretch resistance and bending resistance were considered. The force generated by the deformation of membrane was substituted into the force term of Navier-Stokes equations only for membrane particles. The malaria parasite was assumed as a rigid object. Some interesting behavior of the infected and healthy red blood cells were simulated. © 2010 American Institute of Physics.
    2010, AIP Conference Proceedings, 1281, 591 - 593, English
    International conference proceedings

  • Cellular behaviours in high hematocrit blood flow in micro-channels
    T.Ishikawa, N.Matsuki, Y.Imai, H.Ueno, T. Yamaguchi
    Jan. 2010, SMART-Tohoku GCOE joint Workshop on Micro & Nano Bioenginering, 50 - 50, English
    International conference proceedings

  • Y. Imai, K. Nakaaki, H. Kondo, T. Ishikawa, C. T. Lim, T. Yamaguchi
    We develop a numerical model of hemodynamics arising from Plasmodium falciparum malaria. A free-mesh particle method is employed for simulating complex interactions among red blood cells infected by Plasmodium falciparum, healthy red blood cells, and endothelial cells. The deformability of red blood cells is expressed by a spring model. Cytoadherent and rosetting property of infected red blood cells are also modeled by using local spring models. We present the behavior of IRBCs and rosettes in shear flow, and the migration and cytoadhesion of IRBCs in micro-scale blood flow.
    SPRINGER, 2010, 6TH WORLD CONGRESS OF BIOMECHANICS (WCB 2010), PTS 1-3, 31, 1145 - +, English
    International conference proceedings

  • Jean-Joseph Christophe, Takuji Ishikawa, Noriaki Matsuki, Yohsuke Imai, Kei Takase, Marc Thiriet, Takami Yamaguchi
    Pneumothorax is characterized by lung collapse. Its effect on hemodynamics, especially on pulmonary arterial blood flow, remains unclear. This patient-specific study investigated the effects of lung deformation on pulmonary blood flow during acute phase and after recovery. Arterial geometry was extracted up to the fifth generation from computed tomography images in three patients and reconstructed. Different geometrical parameters (artery bores, area ratios, and between-branch angles) were computed. The shapes of the pulmonary trunk and its branches were affected strongly by pneumothorax. To clarify the effect of geometrical perturbations on blood flow, the Navier-Stokes equations for a steady laminar flow of Newtonian incompressible fluid were solved in a reconstructed domain. The change in flow structure between acute phase and recovery was associated with variations in flow rate ratio between the right and left lungs. This study shows, possibly for the first time, that from a patient-specific numerical test, pneumothorax has a considerable impact on pulmonary arterial morphology and hemodynamics. © 2010 by JSME.
    2010, Journal of Biomechanical Science and Engineering, 5(5) (5), 485 - 498, English
    [Refereed]
    Scientific journal

  • 和田 成生, 今井 陽介, 三木 貴仁, 石川 顕一, 鈴木 慎悟, 中村 匡徳
    (株)医学書院, Dec. 2009, 呼吸と循環, 57(12) (12), 1219 - 1227, Japanese

  • Patient specific morphological and hemodynamic analysis of pulmonary artery in the case of severe deformations of the lung
    J-J.Christophe, T.Ishikawa, N.Matsuki, Y.Imai, K.Takase, M.Thiriet, T.Yamaguchi
    Dec. 2009, 3rd East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 124 - 125, English
    International conference proceedings

  • Impact of membrane modeling on the deformation analysis of a capsule
    T.Omori, T.Ishikawa, D.Barthes-Biesel, A.V.Salsac, Y.Imai, T.Yamaguchi
    Dec. 2009, 3rd East Asian Pacific Student Workshop on Nano-Biomedical Engineering, 122 - 123, English
    International conference proceedings

  • Daisuke Hosokawa, Takuji Ishikawa, Hirohisa Morikawa, Yohsuke Imai, Takami Yamaguchi
    Background A capsule endoscope has a limited ability to obtain images of the digestive organs because its movement depends on peristaltic motion. To overcome this problem, capsule endoscopes require a propulsion system. Methods This paper proposes a propulsion system for a capsule endoscope that mimics the locomotive mechanism of snails and earthworms. The prototype crawler can elongate and contract itself longitudinally and adhere to a wall via suction cups. Results We investigated the effect of the inclination angle of the propulsion plane, the mucus viscosity between the propulsion plane and the crawler, and the stiffness of the propulsion plane on the locomotion of the prototype crawler. We found that the crawler could move on a rubber sheet and on inclined planes covered with mucus. We discussed advantages and limitations of the prototype crawler compared to the different locomotive systems developed in former studies. Conclusions We believe that the prototype crawler provides a better understanding of the propulsion mechanism for use in the gastrointestinal tract. Copyright (C) 2009 John Wiley & Sons, Ltd.
    JOHN WILEY & SONS INC, Dec. 2009, INTERNATIONAL JOURNAL OF MEDICAL ROBOTICS AND COMPUTER ASSISTED SURGERY, 5(4) (4), 471 - 478, English
    [Refereed]
    Scientific journal

  • Fluid flow analysis of the surface of tracheal ciliary cells
    H. Ueno, K. Gonda, Y. Imai, N. Matsuki, T. Ishikawa, T. Yamaguchi
    Nov. 2009, Dynein International Workshop 2009, p.11, English

  • Y. Shimogonya, T. Ishikawa, Y. Imai, N. Matsuki, T. Yamaguchi
    Nov. 2009, International Journal of Computational Fluid Dynamics, 23, 583 - 593, English
    [Refereed]
    Scientific journal

  • Patient-specific blood flow analysis of pulmonary artery affected by severe deformations of the lung
    J-J.Christophe, T.Ishikawa, N.Matsuki, Y.Imai, K.Takase, M.Thiriet, T.Yamaguchi
    Nov. 2009, VIPIMAGE2009, Computational Vision and Medical Image Processing, 335 - 338, English
    [Refereed]
    International conference proceedings

  • Motions of particles and red blood cells in a bifurcation: comparison between experiments and numerical simulations
    M.Lagoela, B.Oliveira, D.Cidre, C.Fernandes, C.Balsa, R.Lima, R.Dias, T.Ishikawa, Y.Imai, T. Yamaguchi
    Nov. 2009, VIPIMAGE2009, Computational Vision and Medical Image Processing, 339 - 342, English
    [Refereed]
    International conference proceedings

  • Determination of the cell-free layer in circular PDMS microchannels
    T.Cerdeira, F.Monteiro, R.Lima, M.Oliveira, T.Ishikawa, Y.Imai, T.Yamaguchi
    Nov. 2009, VIPIMAGE2009, Computational Vision and Medical Image Processing, 357 - 360, English
    [Refereed]
    International conference proceedings

  • Simulation of rosette formation and destruction of malaria infected red blood cells
    T.Yamaguchi, Y.Imai, T.Ishikawa
    Sep. 2009, Book of Abstracts BIOENGINEERING 09, 48 - 48, English
    International conference proceedings

  • Pulmonary airflow simulation of inspiration and expiration using a patient-specific model
    T.Miki, Y.Imai, T.Ishikawa, T.Yamaguchi
    Sep. 2009, Book of Abstracts BIOENGINEERING 09, 92 - 92, English
    International conference proceedings

  • On the sensitivity of a hemodynamic index for cerebral aneurysm initiation, the GON, to flow input waveform
    Y.Shimogonya, T.Ishikawa, Y.Imai, N.Matsuki, T.Yamaguchi
    Sep. 2009, Book of Abstracts BIOENGINEERING 09, 126 - 126, English
    International conference proceedings

  • Mixing of red blood cells in high hematocrit blood flow in micro-channels
    T.Ishikawa, H.Fujiwara, R.Lima, N.Matsuki, Y.Imai, T.Yamaguchi
    Sep. 2009, Proc. 3rd Switzerland-Japan Workshop on Biomechanics 2009, 47 - 47, English
    International conference proceedings

  • Rui Lima, Takuji Ishikawa, Yohsuke Imai, Motohiro Takeda, Shigeo Wada, Takami Yamaguchi
    Developments in optical experimental techniques have helped in elucidating how blood flows through microvessels. Although initial developments were encouraging, studies on the flow properties of blood in microcirculation have been limited by several technical factors, such as poor spatial resolution and difficulty obtaining quantitative detailed measurements at such small scales. Recent advances in computing, microscopy, and digital image processing techniques have made it possible to combine a particle tracking velocimetry (PTV) system with a confocal microscope. We document the development of a confocal micro-PTV measurement system for capturing the dynamic flow behavior of red blood cells (RBCs) in concentrated suspensions. Measurements were performed at several depths through 100-mu m glass capillaries. The confocal micro-PTV system was able to detect both translational and rotational motions of individual RBCs flowing in concentrated suspensions. Our results provide evidence that RBCs in dilute suspensions (3% hematocrit) tended to follow approximately linear trajectories, whereas RBCs in concentrated suspensions (20% hematocrit) exhibited transversal displacements of about 2% from the original path. Direct and quantitative measurements indicated that the plasma layer appeared to enhance the fluctuations in RBC trajectories owing to decreased obstruction in transversal movements caused by other RBCs. Using optical sectioning and subsequent image contrast and resolution enhancement, the system provides previously unobtainable information on the motion of RBCs, including the trajectories of two or more RBCs interacting in the same focal plane and RBC dispersion coefficients in different focal planes.
    SPRINGER, Aug. 2009, ANNALS OF BIOMEDICAL ENGINEERING, 37(8) (8), 1546 - 1559, English
    [Refereed]
    Scientific journal

  • A particle based modeling and analysis of Malaria infected red blood cell in microcirculation
    T. Yamaguchi, H. Kondo, Y. Imai, N. Matsuki, H. Ueno
    Jul. 2009, 10th U.S. National Congress on Computational Mechanics Congress Program, 42 - 42, English
    International conference proceedings

  • Computational biomechanics of malaria and arterial diseases
    T. Ishikawa, Y. Imai, T. Yamaguchi
    Jul. 2009, 36th International Congress of Physiological Sciences Final Program, 143 - 143, English
    International conference proceedings

  • M. Kishimoto, T. Yoshida, T. Hayasaka, D. Mori, Y. Imai, N. Matsuki, T. Ishikawa, T. Yamaguchi
    Jul. 2009, Technology and Health Care, 17, 121 - 131, English
    [Refereed]
    Scientific journal

  • Noriaki Matsuki, Motohiro Takeda, Masahiro Yamano, Yohsuke Imai, Takuji Ishikawa, Takami Yamaguchi
    Matsuki N, Takeda M, Yamano M, Imai Y, Ishikawa T, Yamaguchi T. Effects of unique biomedical education programs for engineers: REDEEM and ESTEEM projects. Adv Physiol Educ 33: 91-97, 2009; doi: 10.1152/advan.90120.2008.-Current engineering applications in the medical arena are extremely progressive. However, it is rather difficult for medical doctors and engineers to discuss issues because they do not always understand one another's jargon or ways of thinking. Ideally, medical engineers should become acquainted with medicine, and engineers should be able to understand how medical doctors think. Tohoku University in Japan has managed a number of unique reeducation programs for working engineers. Recurrent Education for the Development of Engineering Enhanced Medicine has been offered as a basic learning course since 2004, and Education through Synergetic Training for Engineering Enhanced Medicine has been offered as an advanced learning course since 2006. These programs, which were developed especially for engineers, consist of interactive, modular, and disease-based lectures (case studies) and substantial laboratory work. As a result of taking these courses, all students obtained better objective outcomes, on tests, and subjective outcomes, through student satisfaction. In this article, we report on our unique biomedical education programs for engineers and their effects on working engineers.
    AMER PHYSIOLOGICAL SOC, Jun. 2009, ADVANCES IN PHYSIOLOGY EDUCATION, 33(2) (2), 91 - 97, English
    [Refereed]
    Scientific journal

  • H. Fujiwara, T. Ishikawa, R. Lima, N. Matsuki, Y. Imai, H. Kaji, M. Nishizawa, T. Yamaguchi
    We investigated the behavior of red blood cells (RBCs) in a microchannel with stenosis using a confocal micro-PTV system. Individual trajectories of RBCs in a concentrated suspension of up to 20% hematocrit (Hct) were measured successfully. Results indicated that the trajectories of healthy RBCs became asymmetric before and after the stenosis, while the trajectories of tracer particles in pure water were almost symmetric. The asymmetry was greater in 10% Hct than in 20% Hct. We also investigated the effect of deformability of RBCs on the cell-free layer thickness by hardening RBCs using a glutaraldehyde treatment. The results indicated that deformability is the key factor in the asymmetry of cell-free layer thickness. Therefore, the motions of RBCs are influenced strongly by the Hct, the deformability, and the channel geometry. These results give fundamental knowledge for a better understanding of blood flow in microcirculation and biomedical microdevices. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, May 2009, JOURNAL OF BIOMECHANICS, 42(7) (7), 838 - 843, English
    [Refereed]
    Scientific journal

  • Numerical simulation of inspiratory and expiratory pulmonary airflow using a patient-specific model
    T. Miki, Y. Imai, T. Ishikawa, S. Wada, T. Yamaguchi
    Apr. 2009, 10th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network CentreNano-Biomedical Engineering in the East Asian-Pacific Rim Region Jointly Organised with Fourth Asian Pacific Conf, 20 - 21, English
    International conference proceedings

  • Effect of the memberane bending stiffeness on the deformation of a red blood cell
    T. Oomori, T. Ishikawa, Dominique Barthes-Biesel, Y. Imai, T. Yamaguchi
    Apr. 2009, 10th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network CentreNano-Biomedical Engineering in the East Asian-Pacific Rim Region Jointly Organised with Fourth Asian Pacific Conf, 8 - 9, English
    International conference proceedings

  • Patient-specific pulmonary airflow simulation using cartestian adaptive mesh refinement method
    T. Miki, Y. Imai, T. Ishikawa, S. Wada, T. Yamaguchi
    Apr. 2009, 15th Int. Conf. Finite Elements in Flow Problems (FEF09) Abstracts, 37, English
    International conference proceedings

  • Numerical simulation of inpiratory and expiratory pulmonary airflow using a patient-specific model
    T. Miki, Y. Imai, T. Ishikawa, S. Wada, T. Yamaguchi
    Apr. 2009, Proc. AP Biomech 2009, 164 - 165, English
    International conference proceedings

  • Motion of individual red blood cells in a concentrated suspension flowing through micro-channels
    T. Ishikawa, H. Fujiwara, N. Matsuki, R. Lima, Y. Imai, T. Yamaguchi
    Apr. 2009, Proc. AP Biomech 2009, 102 - 103, English
    International conference proceedings

  • Motion of individual cells in high hematocrit blood flow in micro-channels
    T. Ishikawa, H. Fujiwara, N. Matsuki, R. Lima, Y. Imai, T. Yamaguchi
    Apr. 2009, Proc. ICCES'09, 244, English
    International conference proceedings

  • Modeling of the membrane bending rigidity for calculating red blood cell deformation
    T. Omori, T. Ishikawa, D. Birthes-Biesel, Y. Imai, T. Yamaguchi
    Apr. 2009, 15th Int. Conf. Finite Elements in Flow Problems (FEF09) Abstracts, 41, English
    International conference proceedings

  • Low voltage pulses can induce apoptosis
    N. Matsuki, T. Ishikawa, Y. Imai, T. Yamaguchi
    Apr. 2009, Proc. AP Biomech 2009, 154 - 155, English
    International conference proceedings

  • Hitoshi Kondo, Yohsuke Imai, Takuji Ishikawa, Ken-ichi Tsubota, Takami Yamaguchi
    Malaria-infected red blood cells (IRBCs) show various changes in mechanical properties. IRBCs lose their deformability and develop properties of cytoadherence and rosetting. To clarify how these changes advance microvascular occlusion, we need qualitative and quantitative information on hemodynamics in malaria infection, including the interaction among IRBCs, healthy RBCs, and endothelial cells. We developed a numerical model of blood flow with IRBCs based on conservation laws of fluid dynamics. The deformability and adhesive property of IRBCs were simply modeled using springs governed by Hook's law. Our model could express the basic behavior of IRBCs, including the rolling motion due to cytoadhesive interaction with endothelial cells and complex interaction with healthy RBCs. We confirmed that these types of interactions significantly increase the flow resistance, particularly when knobs develop.
    SPRINGER, Apr. 2009, ANNALS OF BIOMEDICAL ENGINEERING, 37(4) (4), 702 - 709, English
    [Refereed]
    Scientific journal

  • Effect of the membrane bending stiffness on the deformation of a red blood cell
    T. Omori, T. Ishikawa, D. Birthes-Biesel, Y. Imai, T. Yamaguchi
    Apr. 2009, Proc. AP Biomech, 196 - 197, English
    International conference proceedings

  • Computational biomechanics for investigating various diseases over micro to macro scales
    T. Yamaguchi, T. Ishikawa, Y. Imai
    Apr. 2009, Proc. ICCES'09, 10, English
    [Invited]
    International conference proceedings

  • A numerical model to study hemodynamics arising from malaria infection
    Y. Imai, H. Kondo, Y. H. Kang, T. Ishikawa, C. T. Lim, T. Yamaguchi
    Apr. 2009, Proc. ICCES'09, 96, English
    [Invited]
    International conference proceedings

  • A micro scale blood flow model to study pathology of malaria
    Y. Imai, H. Kondo, Y. H. Kang, T. Ishikawa, C. T. Lim, T. Yamaguchi
    Apr. 2009, Proc. AP Biomech 2009, 100 - 101, English
    International conference proceedings

  • Computational simulation of blood flow in pulmonary artery under respiratory disorders
    J-J. Christophe, T. Ishikawa, Y. Imai, N. Matsuki, K. Takase, T. Yamaguchi
    Mar. 2009, 9th International Symposium of Tohoku University Global COE Program, Global Nano-Biomedical Engineering Education and Research Network Centre, Nano-Biomedical Engineering in the East Asian-Pacific Rim Region, 100 - 101, English
    International conference proceedings

  • Yuji Shimogonya, Takuji Ishikawa, Yohsuke Imai, Noriaki Matsuki, Takami Yamaguchi
    We propose a new hemodynamic index for the initiation of a cerebral aneurysm, defined by the temporal fluctuations of tension/compression forces acting on endothelial cells. We employed a patient-specific geometry of a human internal carotid artery (ICA) with an aneurysm, and reconstructed the geometry of the ICA before aneurysm formation by artificially removing the aneurysm. We calculated the proposed hemodynamic index and five other hemodynamic indices (wall shear stress (WSS) at peak systole, time-averaged WSS, time-averaged spatial WSS gradient, oscillatory shear index (OSI), and potential aneurysm formation indicator (AFI)) for the geometry before aneurysm formation using a computational fluid dynamics technique. By comparing the distribution of each index at the location of aneurysm formation, we discussed the validity of each. The results showed that only the proposed hemodynamic index had a significant correlation with the location of aneurysm formation. Our findings suggest that the proposed index may be useful as a hemodynamic index for the initiation of cerebral aneurysms. (c) 2008 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Mar. 2009, JOURNAL OF BIOMECHANICS, 42(4) (4), 550 - 554, English
    [Refereed]
    Scientific journal

  • Yohsuke Imai, H. Kondo, T. Ishikawa, C. T. Lim, K. Tsubota, T. Yamaguchi
    We propose a numerical method for simulating three-dimensional hemodynamics arising from malariainfection. Malaria-infected red blood cells (IRBCs) become stiffer and develop the property of cytoadherent and resetting. To clarify the mechanism of microvascular obstruction in malaria, we need to understand the changes of hemodynamics, involving interaction between IRBC, healthy RBCs, and endothelial cells. In the proposed model, all the components of blood are represented by a finite number of particles. The membrane of RBCs is expressed by two-dimensional network. Malaria parasites inside the RBC are represented by solid objects. The motion of each particle is described by the conservation laws of mass and momentum for incompressible fluid. We examine several numerical tests, involving the stretching of IRBCs, and flow in narrow channels, to validate our model. The obtained results agree well with the experimental results. Our method would be helpful for further understandings of pathology of malaria-infection. © 2009 International Federation of Medical and Biological Engineering.
    2009, IFMBE Proceedings, 23, 2244 - 2247, English
    [Refereed]
    International conference proceedings

  • Simulation of microcirculatory disorder by malaria infection using a particle method
    T.Yamaguchi, H.Kondo, Y.Imai, T.Ishikawa
    2009, ICCB 2009, USB, 83, English
    International conference proceedings

  • Particle method simulation of red blood cells infected by malaria
    T.Yamaguchi, Y.H.Kang, H.Kondo, Y.Imai, T.Ishikawa
    2009, Med. Phys. Biomed. Eng. World Cong. 2009, CD-ROM, 131, English
    International conference proceedings

  • T. Yamaguchi, H. Kondo, Y. Imai, T. Ishikawa
    We simulated malarial microvascular blood flow disturbances by using a new particle method of biological solid-fluid interaction analysis especially developed for the analysis of malaria infection. Particle based spatial discretization and the sub time step time integration could provide us with stable computations for micro scale blood flow involving interaction with many cells. We performed numerical simulation of the stretching of infected red blood cells and the results agreed well with experimental results. Our model successfully simulated the flow of infected red blood cells into narrow channels.
    WIT PRESS/COMPUTATIONAL MECHANICS PUBLICATIONS, 2009, MODELLING IN MEDICINE AND BIOLOGY VIII, 13, 49 - +, English
    International conference proceedings

  • T. Yoshimoto, T. Ishikawa, N. Matsuki, H. Fujiwara, Y. Imai, H. Ueno, M. Takeda, T. Yamaguchi
    AMER SOC MECHANICAL ENGINEERS, 2009, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2009, PT A AND B, CD-ROM, 765 - 766, English
    [Refereed]
    International conference proceedings

  • Jean-Joseph Christophe, Takuji Ishikawa, Yohsuke Imai, Noriaki Matsuki, Kei Takase, Takami Yamaguchi
    Numerical methods are used to provide quantitative and qualitative information about effects of pulmonary disorders on blood flow. From patient's CT images, arterial geometries are extracted and compared for healthy and unhealthy conditions. We show that pulmonary artery shape is strongly affected by the pulmonary disorders, e.g., the inlet is elongated and the branches are bent. In order to clarify the effect of geometrical change on the blood flow, we performed computational simulation of blood flow in the extracted geometries.
    AMER SOC MECHANICAL ENGINEERS, 2009, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2009, PT A AND B, CD-ROM, 1037 - 1038, English
    [Refereed]
    International conference proceedings

  • T. Ishikawa, H. Fujiwara, N. Matsuki, R. Lima, Y. Imai, H. Ueno, T. Yamaguchi
    AMER SOC MECHANICAL ENGINEERS, 2009, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2009, PT A AND B, CD-ROM, 443 - 444, English
    [Refereed]
    International conference proceedings

  • N. Matsuki, M. Takede, M. Yamano, Y. Imai, T. Ishikawa, T. Yamaguchi
    AMER SOC MECHANICAL ENGINEERS, 2009, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2009, PT A AND B, CD-ROM, 479 - 480, English
    [Refereed]
    International conference proceedings

  • Yohsuke Imai, Hitoshi Kondo, Young Ho Kang, Takuji Ishikawa, Chwee Teck Lim, Takami Yamaguchi
    AMER SOC MECHANICAL ENGINEERS, 2009, PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2009, PT A AND B, CD-ROM, 331 - 332, English
    [Refereed]
    International conference proceedings

  • M. Kishimoto, T. Yoshida, T. Hayasaka, D. Mori, Y. Imai, N. Matsuki, T. Ishikawa, T. Yamaguchi
    An effective way for preventing injuries and diseases among the elderly is to monitor their daily lives. In this regard, we propose the use of a "Hyper Hospital Network", which is an information support system for elderly people and patients. In the current study, we developed a wearable system for monitoring electromyography (EMG) and acceleration using the Hyper Hospital Network plan. The current system is an upgraded version of our previous system for gait analysis (Yoshida et al. [13], Telemedicine and e-Health 13 703-714), and lets us monitor decreases in exercise and the presence of a hemiplegic gait more accurately. To clarify the capabilities and reliability of the system, we performed three experimental evaluations: one to verify the performance of the wearable system, a second to detect a hemiplegic gait, and a third to monitor EMG and accelerations simultaneously. Our system successfully detected a lack of exercise by monitoring the iEMG in healthy volunteers. Moreover, by using EMG and acceleration signals simultaneously, the reliability of the Hampering Index (HI) for detecting hemiplegia walking was improved significantly. The present study provides useful knowledge for the development of a wearable computer designed to monitor the physical conditions of older persons and patients. © 2009 - IOS Press and the authors. All rights reserved.
    2009, Technology and Health Care, 17(2) (2), 121 - 131, English
    [Refereed]
    Scientific journal

  • Y. Shimogonya, T. Ishikawa, Y. Imai, N. Matsuki, T. Yamaguchi
    Although how cerebral aneurysms initiate and grow is still unclear, haemodynamics is thought to play an important role. In order to better understand the aneurysm formation mechanism, we performed a computational analysis of aneurysm formation for a patient-specific arterial geometry. First, CFD was used to perform a pulsatile blood flow analysis and calculate a novel haemodynamic index, the gradient oscillatory number (GON). Then, using aneurysm growth model in which the proliferation of the wall was hypothesised, we performed an aneurysm formation analysis based on the GON index distribution. The result showed that a saccular cerebral aneurysm could appear based on our hypothesis for a patient-specific arterial geometry. On the other hand, a saccular aneurysm was not observed when assuming only strength degradation of the wall. Our findings have suggested that an arterial biological process, such as the proliferation of the wall, may play a vital role in saccular aneurysm formation.
    TAYLOR & FRANCIS LTD, 2009, INTERNATIONAL JOURNAL OF COMPUTATIONAL FLUID DYNAMICS, 23(8) (8), 583 - 593, English
    [Refereed]
    Scientific journal

  • Behavior of a red blood cell in a simple shear flow simulated by a boundary element method
    T. Omori, T. Ishikawa, D. Barthes-Biesel, Y. Imai, T. Yamaguchi
    Dec. 2008, GPBE/NUS-Tohoku Graduate Student Conf. Bioeng., Program & Abstract, 99 - 100, English

  • A novel hemodynamic index for the initiation of cerebral aneurysms: focusing on temporal variation of spatial wall shear stress gradient
    Y. Shimogonya, T. Ishikawa, Y. Imai, N. Matsuki, T. Yamaguchi
    Dec. 2008, GPBE/NUS-Tohoku Graduate Student Conf. Bioeng., Program & Abstract, 95 - 96, English

  • Numerical simulation of inspiratory and expiratory pulmonary airflow using a subject-specific model
    T. Miki, Y. Imai, T. Ishikawa, S. Wada, T. Yamaguchi
    Dec. 2008, GPBE/NUS-Tohoku Graduate Student Conf. Bioeng., Program & Abstract, 81 - 82, English

  • M. Okubo, Y. Imai, T. Ishikawa, T. Hayasaka, S. Ueno, T. Yamaguchi
    Nov. 2008, Int. Feder. Med. Biol. Eng. (IFMBE) Proc. (CD-ROM), 205, English

  • S. Ueno, T. Hayasaka, Y. Imai, M. Okubo, T. Ishikawa, T. Yamaguchi
    Nov. 2008, Int. Feder. Med. Biol. Eng. (IFMBE) Proc. (CD-ROM), 234, English

  • D. Hosokawa, T. Ishikawa, H. Morikawa, Y. Imai, T. Yamaguchi
    Nov. 2008, Int. Feder. Med. Biol. Eng. (IFMBE) Proc. (CD-ROM), 274, English

  • Sinbae Kim, Hiromi Nakamura, Toshihiko Yoshida, Masamichi Kishimoto, Yohsuke Imai, Noriaki Matsuki, Takuji Ishikawa, Takami Yamaguchi
    The population of most developed countries is rapidly aging, which has created a growing demand for home care. A key issue in medicine is supporting the increasing number of elderly patients, both physically and mentally. In this study, we developed a wearable computer that contained modules for measuring electrocardiograms (ECGs) and femoral artery pulse waves using an accelerometer. This system has several benefits: ( a) it can provide a database server in each patient's home; (b) its high extendibility and flexibility facilitate adaptation to a patient's needs; and ( c) it allows patients to keep their own data, thus protecting the privacy of personal information. To clarify the capabilities and reliability of the system, we applied it to 8 healthy young volunteers during states of physical and mental work. This system successfully detected clear ECGs and femoral artery pulse waves to calculate important bioinformation, including heart rate, pulse wave velocity, and the power spectral density of spontaneous beat-to-beat oscillations in the R-R interval. In this study, we proposed the way to provide an assessment of the physical and mental condition of the subject using analysis of the bio-information with respect to the physical and mental workloads. The present study provides useful knowledge for the development of a wearable computer designed to monitor the physical and mental conditions of older persons and patients.
    MARY ANN LIEBERT INC, Nov. 2008, TELEMEDICINE JOURNAL AND E-HEALTH, 14(9) (9), 939 - 945, English
    [Refereed]
    Scientific journal

  • Three-dimensional simulation of malaria-infected blood
    H. Kondo, Y. Imai, T. Ishikawa, K. Tsubota, C.T. Lim, T. Yamaguchi
    Oct. 2008, Interntional Symposium on Nano-Biomedical Engineering7th Intrnational Symposium of 2007 Tohoku University Global COE Program "Global Nano-Biomedical Engineering Education and Research Network Centre"Nano-Biomedical Engineering in the East Asian-Pacific Ri, 42 - 43, English
    International conference proceedings

  • Behavior of a red blood cell in a simple shear flow simulated by a boundary element method
    T. Omori, T. Ishikawa, D. Barthes-Biesel, Y. Imai, T. Yamaguchi
    Sep. 2008, Book of Abstracts BIOENGINEERING 08, 135 - 135, English
    International conference proceedings

  • Mixing of red blood cells in a micro-channel flow under high hematocrit conditions
    T. Ishikawa, R. Lima, H. Fujiwara, Y. Imai, N. Matsuki, T. Yamaguchi
    Sep. 2008, Bioengineering 08 Book of Abstracts, 61, English

  • Confocal micro-PTV Measurements of Blood Flow in a Circular PDMS Microchannel
    R. Lima, T. Ishikawa, H. Kaji, Y. Imai, S. Wada, M. Nishizawa, T. Yamaguchi
    Sep. 2008, Bioengineering 08 Book of Abstracts, 166, English

  • Proposal of a New Hemodynamic Index for Cerebral Aneurysm Initiation: Focusing on Temporal Fluctuation of Spatial Wall Shear Stress Gradient
    Y. Shimogonya, T. Ishikawa, Y. Imai, N. Matsuki, T. Yamaguchi
    Sep. 2008, Bioengineering 08 Book of Abstracts, 146, English

  • Noriaki Matsuki, Takuji Ishikawa, Yousuke Imai, Takami Yamaguchi
    Electroporation is used for gene transfection, drug delivery, and cell fusion. While studies have shown that high voltage electroporation induces apoptosis in. vitro, a strong electric field can lower cell survival rates. As there are no published reports which have examined apoptotic properties associate with low voltage electric charges, we demonstrated for the first time that consecutive low voltage pulses with a voltage lower than the membrane breakdown threshold of human cells can increase the membrane potential to the threshold required to induce electroporation. This led to apoptosis through caspase pathways. Moreover, necrotic cell damage was less than that caused by high voltage pulses. Therefore, low voltage electroporation can be a suitable anticancer method. (C) 2008 Elsevier Ireland Ltd. All rights reserved.
    ELSEVIER IRELAND LTD, Sep. 2008, CANCER LETTERS, 269(1) (1), 93 - 100, English
    [Refereed]
    Scientific journal

  • Yohsuke Imai, Kodai Sato, Takuji Ishikawa, Takami Yamaguchi
    To identify shortcomings in the design of conventional endovascular devices, we investigated the inflow features of untreated aneurysms at a variety of arterial bends using computational fluid dynamics. As a preliminary study, we analyzed the steady-state inflow for aneurysms created at U-shaped, twisted, and S-shaped arteries. Both the inflow pattern and inflow flux were strongly influenced by the shape of the artery and the configuration angle of the aneurysm to the artery. We revealed that the secondary flow generated in the parent artery is the dominant factor affecting the inflow. Our results suggest that the arterial geometry and secondary flow should be considered in the design of endovascular devices.
    SPRINGER, Sep. 2008, ANNALS OF BIOMEDICAL ENGINEERING, 36(9) (9), 1489 - 1495, English
    [Refereed]
    Scientific journal

  • A numerical method for simulating micro-scale blood flow in malaria infection
    Y. Imai, H. Kondo, T. Ishikawa, K. Tsubota, C. T. Lim, T. Yamaguchi
    Sep. 2008, Abstracts of Bioengineering 08, English
    [Refereed]
    International conference proceedings

  • Image-based pulmonary airflow simulation using cartesian adaptive mesh refinement method
    T. Miki, Y. Imai, M. Nakamura, C. Iwamura, T. Ishikawa, S. Wada, T. Yamaguchi
    Jul. 2008, 8th World Congress on Computational Mechanics (WCCM8) / 5th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008) (PROGRAMME, CD-ROM), 216 - 216, English
    [Refereed]
    International conference proceedings

  • Role of the hematocrit on the radial dispresion of red blood cells in glass capillaries
    R. Lima, T. Ishikawa, Y. Imai, M. Takeda, S. Wada, T. Yamaguchi
    Jul. 2008, ・16th Congress of the European Society of Biomechanics Conference Program ・Abstract 16th Congress of the European Society of Biomechanics (CD-ROM), 30 - 30, English
    International conference proceedings

  • Three-Dimensional Simulation of Blood Flow arising from Malaria Infection
    H. Kondo, Y. Imai, T. Ishikawa, K. Tsubota, C. T. Lim, T. Yamaguchi
    Jul. 2008, IACM/ECCOMAS Congress 2008 CD-ROM, MS194C, English

  • Motion of red blood cells and cell free layer distribution in a stenosed microchannel
    H.Fujiwara, T. Ishikawa, R. Lima, Y. Imai, N. Matsuki, D. Mori, T. Yamaguchi
    Jul. 2008, Journal of Biomechanics, 41, S390, English
    International conference proceedings

  • Determination of blood cells motions and interactions by a confocal micro-PTV system
    R. Lima, T. Ishikawa, Y. Imai, M. Takeda, S. Wada, T. Yamaguchi
    Jul. 2008, Journal of Biomechanics, 41, S429, English
    International conference proceedings

  • A numerical model of blood flow with malariainfected red blood cells
    Y. Imai, H. Kondo, T. Ishikawa, K. Tsubota, T. Yamaguchi
    Jul. 2008, Journal of Biomechanics, 41, S480, English
    International conference proceedings

  • Kodai Sato, Yohsuke Imai, Takuji Ishikawa, Noriaki Matsuki, Takami Yamaguchi
    We show the importance of arterial geometry in intra-aneurysmal hemodynamics. Using a new geometric parameterized saccular aneurysm model including parameters for parent artery shape and the configuration of the aneurysm in the parent artery, we performed a parametric computational fluid dynamics study. We examined lateral saccular aneurysm models with different aneurysm shapes (i.e., the ratio of aneurysm height to aneurysm neck diameter) and different configurations (i.e., the torsion angle of the aneurysm to the upstream part of the parent artery). The aneurysm lateral to the curve of the parent artery had significantly higher wall shear stress than the aneurysm inside or outside the curve of the artery, even with the same shape of the aneurysm. Our findings SUI-est the important role played by the configuration of the aneurysm relative to the parent artery in intra-aneurysmal hemodynamics. (C) 2007 IPEM. Published by Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Jul. 2008, MEDICAL ENGINEERING & PHYSICS, 30(6) (6), 774 - 782, English
    [Refereed]
    Scientific journal

  • Rui Lima, Takuji Ishikawa, Yohsuke Imai, Motohiro Takeda, Shigeo Wada, Takami Yamaguchi
    The flow properties of blood in the microcirculation depend strongly on the hematocrit (Hct). microvessel geometry. and cell properties. Previous ill vitro studies have measured the radial displacement of red blood cells (RBCs) at concentrated Suspensions using conventional microscopes. However, to measure the RBSs motion they used transparent suspensions of ghost red cells. which may have different physical properties than normal RBCs. The present Study introduces a new approach (confocal micro-PTV) to measure the motion of labeled RBCs flowing in concentrated Suspensions of normal RBCs. The ability of confocal systems to obtain thin in-focus planes allowed US to measure the radial position of individual RBCs accurately and to consequently measure the interaction between multiple labeled RBCs. All the measurements were performed in the center plane of both 50 and 100 mu m glass capillaries at Reynolds numbers (Re) front 0.003 to 0.005 using Hcts front 2% to 35%. To quantify the Motion and interaction of multiple RBCs, we used the RBC radial dispersion (D-yy). Our results clearly demonstrate that D-yy strongly depends on the Het. The RBCs exhibited higher D-yy at radial positions between 0.4 and 0.8 R and lower D-yy at locations adjacent to the wall (0.8-1 R) and around the middle of the capillary (0-0.2 R) The present work also demonstrates that D-yy tends to decrease with a decrease in the diameter. The information provided by this study not only complements previous investigations oil microhemorheology of both dilute and concentrated Suspensions of RBCs. but also shows the influence of both Hct and geometry on the radial dispersion of RBCs. This information is important for a better Understanding of blood mass transport mechanisms under both physiological and pathological conditions. (C) 2008 Elsevier Ltd. All rights reserved.
    ELSEVIER SCI LTD, Jul. 2008, JOURNAL OF BIOMECHANICS, 41(10) (10), 2188 - 2196, English
    [Refereed]
    Scientific journal

  • Multi-scale multi-physics simulations of Biological flows
    T. Yamaguchi, T. Miki, Y. Shimogonya, H. Kondo, D. Mori, Y. Imai, M. Nakamura, C. Iwamura, S. Wada, T. Ishikawa
    Jun. 2008, Int. Symp. Multi-scale Sim. Biol. Soft Mater. (MSBSM2008) Book of Abstracts, 2 - 3, English

  • The importance of proliferation of the arterial wall in formation of saccular cerebral aneurysms
    Y. Shimogonya, T. Ishikawa, Y. Imai, D. Mori, T. Yamaguchi
    Jun. 2008, Proc. ASME 2008 Summer Bioeng. Conf.CD-ROM, English

  • Pulmonary airflow simulation using subject-specific model and Cartesian adaptive mesh refinement method
    T. Miki, Y. Imai, S. Wada, T. Ishikawa, T. Yamaguchi
    May 2008, Proc. Tohoku-NUS Student Joint Symp, 16 - 17, English

  • Rui Lima, Shigeo Wada, Shuji Tanaka, Motohiro Takeda, Takuji Ishikawa, Ken-ichi Tsubota, Yohsuke Imai, Takami Yamaguchi
    Progress in microfabricated technologies has attracted the attention of researchers in several areas, including microcirculation. Microfluidic devices are expected to provide powerful tools not only to better understand the biophysical behavior of blood flow in microvessels, but also for disease diagnosis. Such microfluidic devices for biomedical applications must be compatible with state-of-the-art flow measuring techniques, such as confocal microparticle image velocimetry (PIV). This confocal system has the ability to not only quantify flow patterns inside microchannels with high spatial and temporal resolution, but can also be used to obtain velocity measurements for several optically sectioned images along the depth of the microchannel. In this study, we investigated the ability to obtain velocity measurements using physiological saline ( PS) and in vitro blood in a rectangular polydimethysiloxane (PDMS) microchannel (300 mu m wide, 45 mu m deep) using a confocal micro-PIV system. Applying this combination, measurements of trace particles seeded in the flow were performed for both fluids at a constant flow rate (Re = 0.02). Velocity profiles were acquired by successive measurements at different depth positions to obtain three-dimensional (3-D) information on the behavior of both fluid flows. Generally, the velocity profiles were found to be markedly blunt in the central region, mainly due to the low aspect ratio (h/w = 0.15) of the rectangular microchannel. Predictions using a theoretical model for the rectangular microchannel corresponded quite well with the experimental micro-PIV results for the PS fluid. However, for the in vitro blood with 20% hematocrit, small fluctuations were found in the velocity profiles. The present study clearly shows that confocal micro-PIV can be effectively integrated with a PDMS microchannel and used to obtain blood velocity profiles along the full depth of the microchannel because of its unique 3-D optical sectioning ability. Advantages and disadvantages of PDMS microchannels over glass capillaries are also discussed.
    SPRINGER, Apr. 2008, BIOMEDICAL MICRODEVICES, 10(2) (2), 153 - 167, English
    [Refereed]
    Scientific journal

  • CT image-based pulmonary airflow simulation using airway scale determined mesh
    T. Miki, Y. Imai, M. Nakamura, C. Iwamura, T. Ishikawa, S. Wada, T. Yamaguchi
    Mar. 2008, Fifth International Bio-Fluid Symposium and Workshop, 146 - 147, English

  • Some uninvestigated directions of computational fluid dynamics studies for flow
    T. Yamaguchi, T. Miki, Y. Shimogonya, H. Kondo, D. Mori, Y. Imai, M. Nakamura, C. Iwamura, S. Wada, T. Ishikawa
    Mar. 2008, Fifth International Bio-Fluid Symposium and Workshop, 65 - 66, English

  • Imai, Yohsuke, Aoki, Takayuki, Takizawa, Kenji
    The proposed scheme, which is a conservative form of the interpolated differential operator scheme (IDO-CF), can provide high accurate solutions for both compressible and incompressible fluid equations. Spatial discretizations with fourthorder accuracy are derived from interpolation functions locally constructed by both cell-integrated values and point values. These values are coupled and time-integrated by solving fluid equations in the flux forms for the cell-integrated values and in the derivative forms for the point values. The IDO-CF scheme exactly conserves mass, momentum, and energy, retaining the high resolution more than the non-conservative form of the IDO scheme. A direct numerical simulation of turbulence is carried out with comparable accuracy to that of spectral methods. Benchmark tests of Riemann problems and lid-driven cavity flows show that the IDO-CF scheme is immensely promising in compressible and incompressible fluid dynamics studies. (C) 2007 Elsevier Inc. All rights reserved.
    ACADEMIC PRESS INC ELSEVIER SCIENCE, Feb. 2008, JOURNAL OF COMPUTATIONAL PHYSICS, 227(4) (4), 2263 - 2285, English
    [Refereed]
    Scientific journal

  • SHIMOGONYA Yuji, ISHIKAWA Takuji, IMAI Yohsuke, MORI Daisuke, YAMAGUCHI Takami
    We proposed a new hemodynamic indicator for the initiation of cerebral aneurysms, defined by the temporal fluctuations of tension/compression forces acting on endothelial cells. We calculated the proposed hemodynamic indicator and other three hemodynamic quantities (time-averaged wall shear stress (WSS), time-averaged spatial WSS gradient (SWSSG), and potential aneurysm formation indicator (AFI)) for a patient-specific geometry before aneurysm formation by means of computational fluid dynamics technique. The results showed that only the proposed hemodynamic indicator had a significant correlation with the location of aneurysm formation. Our findings suggest that the proposed indicator might be a prospective hemodynamic indicator for the initiation of cerebral aneurysms.
    The Japan Society of Mechanical Engineers, 2008, The proceedings of the JSME annual meeting, 2008, 31 - 32, Japanese

  • MIKI Takahito, IMAI Yohsuke, WADA Shigeo, ISHIKAWA Takuji, YAMAGUCHI Takami
    We have numerically analyzed inspiratory and expiratory airflow using an image-based pulmonary airway model. As a result, the image-based analysis provided us with some interesting flow features, which is hardly seen in analyses using idealistic airway models. We have examined relationship between flow rate at trachea and pressure drop between trachea and peripheral airways during inspiraotry and expiratory phase. There was difference of pressure drop between inspiratory and expiratory phase even the flow rate was identical, though pressure loss due to fluid viscosity in inspiratory and expiratory phase was almost identical. Generally, pressure drop in a tube is given from summation of dynamic pressure and pressure loss due to fluid viscosity. We conclude that the difference of pressure drop was occurred due to dynamic pressure caused by the difference of cross sectional area between trachea and peripheral airways.
    The Japan Society of Mechanical Engineers, 2008, The proceedings of the JSME annual meeting, 2008, 121 - 122, Japanese

  • HOSOKAWA Daisuke, MORIKAWA Hirohisa, ISHIKAWA Takuji, IMAI Yohsuke, MORI Daisuke, YAMAGUCHI Takami
    A capsule endoscope is recently developed for the observation of the digestive system because digestive diseases particularly cancers very frequently occur and became fatal. Despite many advantages, the capsule endoscope has some limitations in the diagnosis, since it only moves passively by the peristaltic motion of the intestine. In order to overcome this problem, locomotive functions are expected to the capsule endoscope. In this study, we report a mechanical crawler system mimicking the pedal locomotion of snails for such a capsule endoscope. The crawler we developed has four joints, five segments and two suction cups. In locomotion experiments on a horizontal plane and on an inclined plane of 10 degrees, we confirmed that the developed crawler could locomote at the speed of 3 mm/s.
    The Japan Society of Mechanical Engineers, 2008, The proceedings of the JSME annual meeting, 2008, 59 - 60, Japanese

  • Microscale flow dynamics of red blood cells in a circular microchannel
    R. Lima, M. Nakamura, T. Ishikawa, S. Tanaka, M. Takeda, Y. Imai, K. Tsubota, S. Wada, T. Yamaguchi
    The blood flow dynamics in microcirculation depends strongly on the motion, deformation and interaction of RBCs within the microvessel. This paper presents the application of a confocal micro-PTV system to track RBCs through a circular polydimethysiloxane (PDMS) microchannel. This technique, consists of a spinning disk confocal microscope, high speed camera and a diode-pumped solid state (DPSS) laser combined with a single particle tracking (SPT) method. By using this system detailed motions of individual RBCs were measured at a microscale level. Our results showed that this technique can provide detailed information about microscale disturbance effects caused by RBCs in flowing blood.
    TAYLOR & FRANCIS LTD, 2008, COMPUTATIONAL VISION AND MEDICAL IMAGING PROCESSING, 53 - +, English
    [Refereed]
    International conference proceedings

  • Yuji Shimogonya, Takuji Ishikawa, Yohsuke Imai, Daisuke Mori, Noriaki Matsuki, Takami Yamaguchi
    We have performed numerical simulations to examine saccular cerebral aneurysm formation at the outer curve of a bent artery. A U-shaped arterial geometry with torsion, which was modeled on part of the human internal carotid artery, has been employed. A new numerical model was proposed to take into account proliferation as well as degradation of the arterial wall. Proliferation of the arterial wall was modeled by surface area expansion in high wall shear stress region. Based on wall shear stress distribution on the artery, we have investigated aneurysm formation for the following three conditions: (a) strength degradation of the wall, (b) proliferation of the wall, and (c) both strength degradation and proliferation of the wall. A saccular aneurysm shape was not observed when considering only arterial wall degradation up to 90%. However, the saccular shape formed when proliferation of the arterial wall was also taken into consideration. The resultant shape was consistent with clinical observations. Our findings have suggested that a saccular aneurysm may not be formed by degradation of the arterial wall alone, but also require its proliferation. © 2008, The Japan Society of Mechanical Engineers. All rights reserved.
    2008, Journal of Biomechanical Science and Engineering, 3(3) (3), 431 - 442, English
    [Refereed]
    Scientific journal

  • Tracking of red blood cells in microchannel with stenosis by confocal micro PTV system
    H. Fujiwara, T. Ishikawa, R. Lima, Y. Imai, N. Matsuki, H. Kaji, D. Mori, M. Nishizawa, T. Yamaguchi
    Dec. 2007, Proc. 7th Int. Symp. Adv. Fluid Info. & 4th Int. Symp. Transdisciplinary Fluid Integr., 56 - 57, English
    [Refereed]

  • Blood flow in microchannel with stenosis measured by a confocal micro PTV system
    H. Fujiwara, T. Ishikawa, R. Lima, Y. Imai, N. Matsuki, H. Kaji, D. Mori, M. Nishizawa, T. Yamaguchi
    Dec. 2007, Proc. 3rd Tohoku-NUS Joint Symp. Nano-Biomed. Eng. in the East Asian-Pacific Rim Region, 99 - 100, English
    [Refereed]

  • Development of respiration measurement system with conductive rubber for elderly home care
    M. Okubo, M. Kishimoto, Y. Imai, T. Ishikawa, T. Yamaguchi
    Dec. 2007, Proc. 3rd Tohoku-NUS Joint Symp. Nano-Biomed. Eng. in the East Asian-Pacific Rim Region, 47 - 48, English
    [Refereed]

  • Modeling of malaria-infected red blood cell mechanics using a particle method
    H. Kondo, Y. Imai, K. Tsubota, T. Ishikawa, T. Yamaguchi
    Dec. 2007, Proc. APCOM'07 in conjunction with EPMESC XI, CD-ROM MS22-4-2, English
    [Refereed]

  • Numerical simulation of cerebral aneurysm growth based on a hemodynamic hypothesis
    Y. Shimogonya, T. Ishikawa, Y. Imai, T. Yamaguchi
    Dec. 2007, Proc. APCOM'07 in conjunction with EPMESC XI, CD-ROM MS22-3-3, English
    [Refereed]

  • An AMR Method based on the IDO scheme for patient-specific pulmonary airflow simulation
    Y. Imai, T. Miki, T. Ishikawa, M. Nakamura, S. Wada, T. Yamaguchi
    Dec. 2007, Proc. APCOM'07 in conjunction with EPMESC XI, CD-ROM MS7-1-3, English
    [Refereed]

  • Toshihiko Yoshida, Fumio Mizuno, Tomoaki Hayasaka, Kenichi Tsubota, Yousuke Imai, Takuji Ishikawa, Takami Yamaguchi
    An aging society is a reality in developed countries. An aging population requires more health-care workers and facilities. To reduce this social problem, it is worthwhile to develop a wearable computer for elders or patients to watch over them. In this study, we developed a wearable computer, in which accelerometers were installed to detect variations of posture, falls, and gait disability. The advantages of this system include a designated database server in each patient's home, scalability and flexibility to adapt to patient's needs, and full patient access to their own information. As a first step, we adopted this system for healthy young volunteers with or without impediments to validate the system. The results show that this system can successfully detect variations in posture and falls. We also succeeded in real-time automatic gait analysis by using the Hampering Index. The present study gives useful knowledge for the development of a wearable computer to support the care of elders or other patients.
    MARY ANN LIEBERT INC, Dec. 2007, TELEMEDICINE JOURNAL AND E-HEALTH, 13(6) (6), 703 - 713, English
    [Refereed]
    Scientific journal

  • CT Image-Based Respiratory Flow Simulation by using Cartesian Adaptive Mesh Refinement Method
    T. Miki, Y. Imai, M. Nakamura, T. Ishikawa, S. Wada, T. Yamaguchi
    Nov. 2007, Proc. Int. Conf. Adaptive Modeling & Simulation, 166 - 169, English
    [Refereed]

  • A Cartesian Adaptive Mesh Refinement Method for Simulating Physiological Flows
    Y. Imai, T. Miki, T. Aoki, M. Nakamura, T. Ishikawa, S. Wada, T. Yamaguchi
    Nov. 2007, Proc. Int. Conf. Adaptive Modeling & Simulation, 128 - 131, English
    [Refereed]

  • The hydrodynamics of interactions between two swimming bacteria
    T. Ishikawa, G. Sekiya, Y. Imai, T. Yamaguchi
    Nov. 2007, Bulletin of the American Physical Society, 52, 245 - 246, English
    [Refereed]

  • Numerical Simulation of Malaria-Infected Blood Flow using a Particle Method
    H. Kondo, Y. Imai, K. Tsubota, T. Ishikawa, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S226, English
    [Refereed]

  • Measurement of Respiration by a Hyper Diaper with Conductive Rubber
    M. Okubo, M. Kishimoto, S. Kim, Y. Imai, T. Ishikawa, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S206, English
    [Refereed]

  • Monitoring Physical and Mental Workloads by a Wearable Computer
    S. Kim, H. Nakamura, M. Kishimoto, Y. Imai, N. Matsuki, T. Ishikawa, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S103, English
    [Refereed]

  • Measurement of Multi-Red Blood Cells Interactions in Blood Flow by Confocal Micro-PTV
    R. Lima, T. Ishikawa, H. Fujiwara, M. Takeda, Y. Imai, K. Tsubota, N. Matsuki, S. Wada, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S92, English
    [Refereed]

  • Observation of the Blood Flow in Microchannel with Stenosis by Confocal-Micro-PIV
    H. Fujiwara, T. Ishikawa, R. Lima, H. Kaji, N. Matsuki, Y. Imai, M. Nishizawa, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S89, English
    [Refereed]

  • Development of a Wearable System for Monitoring Health Condition
    M. Kishimoto, T. Yoshida, H. Nakamura, M. Okubo, Y. Suzuki, S. Kim, T. Hayasaka, Y. Imai, K. Tsubota, T. Ishikawa, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S84, English
    [Refereed]

  • A Simulation Model for Cerebral Aneurysm Growth based on a Hemodynamic Hypothesis
    Y. Shimogonya, T. Ishikawa, Y. Imai, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S76, English
    [Refereed]

  • CFD Study on Mass Transport to Saccular Aneurysms at Arterial Bend
    Y. Imai, K. Sato, T. Ishikawa, A. Comerford, T. David, T. Yamaguchi
    Nov. 2007, Proc. 3rd Asian Pacific Conf. Biomech., S58, English
    [Refereed]

  • CFD modeling of pulmonary airflow using IDO-AMR method
    Y. Imai, T. Miki, S. Wada, M. Nakamura, T. Ishikawa, T. Yamaguchi
    Oct. 2007, Proc. 4th Japan-Taiwan Workshop on Mech. & Aerospace Eng., 289 - 294, English
    [Refereed]

  • T. Ishikawa, G. Sekiya, Y. Imai, T. Yamaguchi
    This article evaluates the hydrodynamic interactions between two swimming bacteria precisely. We assume that each bacterium is force free and torque free, with a Stokes flow field around it. The geometry of each bacterium is modeled as a spherical or spheroidal body with a single helical flagellum. The movements of two interacting bacteria in an infinite fluid otherwise at rest are computed using a boundary element method, and the trajectories of the two interacting bacteria and the stresslet are investigated. The results show that as the two bacteria approach each other, they change their orientations considerably in the near field. The bacteria always avoided each other; no stable pairwise swimming motion was observed in this study. The effects of the hydrodynamic interactions between two bacteria on the rheology and diffusivity of a semidilute bacterial suspension are discussed.
    BIOPHYSICAL SOC, Sep. 2007, BIOPHYSICAL JOURNAL, 93(6) (6), 2217 - 2225, English
    [Refereed]
    Scientific journal

  • A fluid-solid interactions study of the pulse wave velocity in uniform arteries
    T. Fukui, Y. Imai, K. Tsubota, T. Ishikawa, S. Wada, T. Yamaguchi
    Jun. 2007, Biomechanics at micro- and nanoscale levels, World Scientific, 3, 146 - 156, English
    [Refereed]

  • Measurement of erythrocyte motions in microchannels by using a confocal micro-PTV system
    R. Lima, T. Ishikawa, M. Takeda, S. Tanaka, Y. Imai, K. Tsubota, S. Wada, T. Yamaguchi
    Jun. 2007, Proc. 2007 Summer Bioengineering Conference, CD-ROM, 175969, English

  • Wall shear stress change due to arterial wall stiffness; fluid-solid interaction study
    T. Fukui, K. H. Parker, Y. Imai, K. Tsubota, T. Ishikawa, S. Wada, T. Yamaguchi
    Jun. 2007, Proc. 2007 Summer Bioengineering Conference, CD-ROM, 176102, English

  • Image-based simulation of pulmonary airflow using multi-level voxel modeling
    Y. Imai, T. Miki, M. Nakamura, T. Ishikawa, S. Wada, T. Yamaguchi
    Jun. 2007, Proc. 2007 Summer Bioengineering Conference, CD-ROM, 176529, English

  • A simulation study on the growth of cerebral aneurysms
    Y. Shimogonya, Y. Imai, T. Ishikawa, T. Yamaguchi
    Jun. 2007, Proc. 2007 Summer Bioengineering Conference, CD-ROM, 176106, English

  • Effects of arterial geometry on inflow rate into cerebral aneurysms on curved arteries
    Y. Imai, K. Sato, T. Ishikawa, T. Yamaguchi
    Jun. 2007, Proc. 2007 Summer Bioengineering Conference, CD-ROM, 176556, English

  • T. Fukui, K.H. Parker, Y. Imai, K. Tsubota, T. Ishikawa, S. Wada, T. Yamaguchi
    The distribution of wall shear stress (WSS) in arteries is affected by both blood and wall motion. Most studies have ignored wall motion by assuming that the artery wall is rigid. To investigate the influence of wall motion we have solved the coupled fluid-solid problem in a straight homogeneous tube. The inlet boundary condition of the tube was given as a pulse of velocity imposed at the inlet of the tube upon a steady flow of Reynolds number 1000. A commercial code (Radioss, Altair Engineering) was used to solve the fluid-solid interactions. Two kinds of waves are generated on the wall by the pulse imposed in the inlet flow; a wave of longitudinal motion of the wall (the longitudinal wave) and a wave of radial motion of the wall (the elastic wave). The ends of the vessel are assumed to be fixed which results in the reflection of both waves. The longitudinal wall motion reduces the relative speed of the blood, reducing WSS by up to 0.5 Pa. The largest effect of wall motion occurs when the longitudinal and elastic waves coincide, where the peak WSS is reduced by 1.0 Pa, which is a significant fraction of the observed WSS. Thus we can say that the effect of wall motion is important in considering physiological response of arterial wall to the blood flow.
    The Japan Society of Mechanical Engineers, May 2007, Journal of Biomechanical Science and Engineering, 2(2) (2), 58 - 68, English
    [Refereed]
    Scientific journal

  • Yohsuke Imai, Takayuki Aoki, Magdi Shoucri
    Two explicit schemes for the numerical solution of the shallow-water equations are examined. The directional-splitting fractional-step method permits relatively large time steps without an iterative process by using a treatment based on the characteristics of the governing equations. The interpolated differential operator (IDO) scheme has fourth-order accuracy in time and space by using a Hermite interpolation function covering local domains, and accurate results are obtained with coarse meshes. It is shown that the two schemes are very efficient for hydrostatic meteorological models from the viewpoints of numerical accuracy and central processing unit time, and the fact that they are explicit makes them suitable for computers with parallel architecture.
    AMER METEOROLOGICAL SOC, Mar. 2007, JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY, 46(3) (3), 388 - 395, English
    [Refereed]
    Scientific journal

  • 64チャンネルマルチスライスCTを用いた肺気道形態の計測
    三木 貴仁, 中村 匡徳, 須田 祐司, 田村 弦, 今井 陽介, 石川 拓司, 山口 隆美, 和田 成生
    CT画像から形態を定量的に計測するためのアルゴリズムを確立すると共に、最新の医療用64チャンネルマルチスライスCT装置を用いて、気管から細部の気道までを撮影し、得られたCT画像から肺気道形態の計測を試みた。アルゴリズムを実際の気道形態計測に適用する際にはファントムを用い実験を行った。ファントムはアクリル製の板で、直径0.5〜4.5mmの穴を0.5mm間隔で開けたものを用いた。アルゴリズムを用いて穴の直径を求めたところ、直径1.0mm以上の穴については全ての穴において計測値が設計値を10%程度上回る結果となった。また0.5mmの穴についてはCT画像が不鮮明で穴直径を求めることができなかった。58歳男の肺について形態計測を行ったが今回の方法で第14世代迄の気道を抽出することができた。
    (一社)呼吸研究, Feb. 2007, 呼吸, 26(2Suppl.) (2Suppl.), S7 - S10, Japanese

  • A Fluid-Solid Interaction Study of the Pulse Wave Velocity in Uniform Arteries
    T. Fukui, Kim. H. Parker, Y. Imai, K. Tsubota, T. Ishikawa, S. Wada, T. Yamaguchi
    Jan. 2007, Proc. Final Symp. Tohoku University 21st Century of Excellence Program, 919 - 927, English
    [Refereed]

  • MIKI Takahito, IMAI Yohsuke, NAKAMURA Masanori, ISHIKAWA Takuji, WADA Shigeo, YAMAGUCHI Takami
    We have developed a new method for respiratory computational fluid dynamics (CFD) simulation using realistic airway models extracted from multi-slice computed tomography (CT) images. Pulmonary airway is multi-scale tube, which is one of the difficulties in respiratory simulation. In the viewpoint of CFD, mesh size must be refined to capture airflow in the small airways. Therefore adaptive mesh refinement (AMR) method based on Interpolated Differential Operator (IDO) scheme is applied to respiratory simulation model. Mesh size is determined by the diameter of the airways in the local domain to maintain accuracy for CFD simulation and adjust computational time. As a result of CFD analysis, we have confirmed accuracy of our new AMR adopted airflow simulation in spite of the number of computational nodes decreased 75%.
    The Japan Society of Mechanical Engineers, 2007, The proceedings of the JSME annual meeting, 2007, 271 - 272, Japanese

  • KISHIMOTO Masamichi, Yoshida Toshihiko, NAKAMURA Hiromi, Okubo Masahiko, SUZUKI Yuta, HAYASAKA Tomoaki, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    To solve an aging problem in the society, it is important that the aged people are encouraged to be independent and spend healthy life. We have proposed the concept of the Hyper Hospital, which is the information support system for patients. In the Hyper Hospital, some units analyze their vital data, and patient's family who lives in the distance, the neighborhood and their doctor share the analyzed data through computer network to know their health condition. In this paper, we present a wearable platform for monitoring health condition. This platform sends the analyzed biomedical signal of a patient to a database server in his/her house. We developed a sensor module to acquire EMG that informs weakening of muscular strength by an underexercise or disease such as a hemiplegia. We confirmed that the sensor module works well with storage module and analysis module through some experiment. We also developed a database server for collecting data from any other sensor module and processing the data from each module separately. The proposed system will be expected monitoring health condition of the elderly.
    The Japan Society of Mechanical Engineers, 2007, The proceedings of the JSME annual meeting, 2007, 57 - 58, Japanese

  • SHIMOGONYA Yuji, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The mechanism of the growth of cerebral aneurysm has not yet been understood. We focus on biological reactions in addition to purely mechanical process. We propose a simulation model to express the assumption that surface areas of the arterial wall are increased locally where wall shear stress value is much higher. We applied the model to a U-shaped artery with torsion. The resultant shape was consistent with clinical observations. It is concluded that it is necessary to consider biological reactions to understand the growth of the cerebral aneurysm.
    The Japan Society of Mechanical Engineers, 2007, The proceedings of the JSME annual meeting, 2007, 91 - 92, Japanese

  • IMAI Yohsuke, SATO Kodai, ISHIKAWA Takuji, YAMAGUCHI Takami
    This paper focuses on inflow into an aneurysm from its parent artery. Understandings of the inflow are required in designing endovascular devices such as coils and stents. A parametric computational fluid dynamics study of the inflow is performed for saccular cerebral aneurysms at a variety of arterial bends. Numerical results show that the inflow rate is strongly influenced by parent arterial geometry because secondary flow momentum in the parent artery determines the inflow. We also present that the shape of an aneurysm little affects the inflow rate.
    The Japan Society of Mechanical Engineers, 2007, The proceedings of the JSME annual meeting, 2007, 89 - 90, Japanese

  • Kondo Hitoshi, Tsubota Ken-ichi, Imai Yohsuke, Ishikawa Takuji, Yamaguchi Takami
    Malaria is one of the most serious diseases for all around the world. It is thought that severe symptoms are caused by microvasucular occlusions of parasitized red blood cells (PRBC) that have adhesive property and low deformability. However, the detailed mechanisms of the vascular occlusion caused by red blood cells are still not clear. In this study, the malaria-infected blood is modeled by particles. The adhesive property of PRBC is expressed by local spring. The result shows that the PRBC interacts with some healthy RBCs and move downstream keeping attachment to the vessel wall. This phenomenon induces the high resistance to the flow, which is likely to lead to microvascular obstruction in lower shear flow.
    The Japan Society of Mechanical Engineers, 2007, The proceedings of the JSME annual meeting, 2007, 87 - 88, Japanese

  • T. Yamaguchi, T. Ishikawa, K. Tsubota, Y. Imai, D. Mori, N. Matsuki
    Variations in both spatial and temporal scales must be considered to fully understand cardiovascular diseases. Given these considerations, we investigated the cardiovascular system from the micro- to macroscale using computational biomechanics. This paper presents our findings on mass transport in cerebral aneurysms, platelet aggregation in blood flow, and a particle method for computing microcirculation. Ultimately, these models will help to clarify the biological phenomena surrounding disease processes and will provide a framework for integrating future developments in understanding macro- and microscale biomechanics.
    World Scientific Publishing Co., Jan. 2007, Biomechanics at Micro- and Nanoscale Levels, 4, 130 - 140, English
    [Refereed]
    In book

  • Effect of Aneurysmal Geometry on the Distribution of ATP Concentration
    K. Sato, Y. Imai, T. Ishikawa, A. Comerford, T. David, T. Yamaguchi
    Jan. 2007, The 9th Int. Symp. Future Med. Eng. based on Bio-nanotech., 128 - 129, English
    [Refereed]

  • Tracking Red Blood Cells in a Circular PDMS Microchannel using a Confocal Micro-PIV System
    R. Lima, T. Ishikawa, S. Tanaka, M. Takeda, Y. Imai, K. Tsubota, S. Wada, T. Yamaguchi
    Jan. 2007, The 9th Int. Symp. Future Med. Eng. based on Bio-nanotech., 126 - 127, English
    [Refereed]

  • Numerical Simulation on the Growth of Saccular Aneurysm
    Y. Shimogonya, Y. Imai, T. Ishikawa, T. Yamaguchi
    Jan. 2007, The 9th Int. Symp. Future Med. Eng. based on Bio-nanotech., 94 - 95, English
    [Refereed]

  • T. Ishikawa, N. Kawabata, Y. Imai, K. Tsubota, T. Yamaguchi
    The blood flow in a large artery is commonly analyzed by means of constitutive equations. However, it is not appropriate to use these equations for small arteries because of the heterogeneity of the blood. In this study, we use a bead-spring model for an erythrocyte to simulate a low-hematocrit blood flow in a small artery with a stenosis. The flow field is solved using Euler coordinates, whereas the motion of the erythrocyte is solved using Lagrangian coordinates (two-way coupling). The results show that the erythrocytes are considerably deformed around the stenosis and that the separated region downstream of the stenosis is weakened by the erythrocytes.
    The Japan Society of Mechanical Engineers, Jan. 2007, Journal of Biomechanical Science and Engineering, 2(1) (1), 12 - 22, English
    [Refereed]
    Scientific journal

  • Development of a wearable watch over system for patients home with an accelerometer
    T. Yoshida, H. Nakamura, M. Kishimoto, F. Mizuno, T. Hayasaka, K. Tsubota, Y. Imai, T. Ishikawa, T. Yamaguchi
    Dec. 2006, Proc. 2nd Tohoku-NUS Joint Symp. Future Nano-med. Bioeng. in the East Asian Region as the 8th Int. Symp. Future Med. Eng. Based on Bio-nanotech., 120 - 121, English
    [Refereed]

  • Numerical analysis of ATP transport in aneurysms
    K. Sato, Y. Imai, T. Ishikawa, A. Comerford, T. David, T. Yamaguchi
    Dec. 2006, Proc. 2nd Tohoku-NUS Joint Symp. Future Nano-med. Bioeng. in the East Asian Region as the 8th Int. Symp. Future Med. Eng. Based on Bio-nanotech., 118 - 119, English
    [Refereed]

  • Monitoring physical and mental workloads by wearable system for elderly home care
    H. Nakamura, T. Yoshida, Y. Imai, T. Ishikawa, T. Yamaguchi
    Dec. 2006, Proc. 2nd Tohoku-NUS Joint Symp. Future Nano-med. Bioeng. in the East Asian Region as the 8th Int. Symp. Future Med. Eng. Based on Bio-nanotech., 122 - 123, English
    [Refereed]

  • Development of a wearable system for an quantification measurment of human motions in daily life
    M. Kishimoto, H. Nakamura, T. Yoshida, F. Mizuno, T. Hayasaka, Y. Imai, K. Tsubta, T. Ishikawa, T. Yamaguchi
    Dec. 2006, Proc. 15th Int. Conf. Mechanics in Medicine and Biology, 187 - 188, English
    [Refereed]

  • Computer simulation of effects of deformabilities of red blood cells on blood flow using particle method
    K. Tsubota, S. Wada, Y. Imai, T. Ishikawa, T. Yamaguchi
    Dec. 2006, Proc. 15th Int. Conf. Mechanics in Medicine and Biology, 422 - 423, English
    [Refereed]

  • An adaptive mesh refinement method for CFD analysis of arterial blood flow
    Y. Imai, T. Aoki, T. Ishikawa, K. Tsubota, T. Yamaguchi
    Dec. 2006, Proc. 15th Int. Conf. Mechanics in Medicine and Biology, 80 - 81, English
    [Refereed]

  • Numerinal simulation of a low Hematocrit blood flow in a small artery with stenosis
    T. Ishikawa, N. Kawabata, Y. Imai, K. Tsubota, T. Yamaguchi
    Dec. 2006, Proc. 15th Int. Conf. Mechanics in Medicine and Biology, 420 - 421, English
    [Refereed]

  • T. Yamaguchi, T. Ishikawa, K. Tsubota, Y. Imai, M. Nakamura, T. Fukui
    Over the past few decades, a large number of novel numerical methods have been proposed to analyze blood flows and to understand the relationship between vascular diseases and hemodynamics. In this paper, we review recent computational fluid dynamics studies on macroscale hemodynamics such as blood flow in the heart and large arteries, microscale blood flows in small vessels in which blood is assumed to be a suspension of red blood cells in plasma, and single red blood cell motions in an induced flow field. The advantages and disadvantages of numerical methods are discussed, and current trends in these research fields are introduced.
    The Japan Society of Mechanical Engineers, Oct. 2006, Journal of Biomechanical Science and Engineering, 1(1) (1), 29 - 50, English
    [Refereed]
    Scientific journal

  • Yohsuke Imai, Takayuki Aoki
    The numerical accuracy of the Interpolated Differential Operator (IDO) scheme is studied with Fourier analysis for the solutions of Partial Differential Equations (PDEs): advection, diffusion, and Poisson equations. The IDO scheme solves governing equations not only for physical variable but also for first-order spatial derivative. Spatial discretizations are based on Hermite interpolation functions with both of them. In the Fourier analysis for the IDO scheme, the Fourier coefficients of the physical variable and the first-order derivative are coupled by the equations derived from the governing equations. The analysis shows the IDO scheme resolves all the wavenumbers with higher accuracy than the fourth-order Finite Difference (FD) and Compact Difference (CD) schemes for advection equation. In particular, for high wavenumbers, the accuracy is superior to that of the sixth-order Combined Compact Difference (CCD) scheme. The diffusion and Poisson equations are also more accurately solved in comparison with the FD and CD schemes. These results show that the IDO scheme guarantees highly resolved solutions for all the terms of fluid flow equations. (c) 2006 Elsevier Inc. All rights reserved.
    ACADEMIC PRESS INC ELSEVIER SCIENCE, Sep. 2006, JOURNAL OF COMPUTATIONAL PHYSICS, 217(2) (2), 453 - 472, English
    [Refereed]
    Scientific journal

  • Y. Imai, T. Aoki
    Aug. 2006, Computational Mechanics, 38(3) (3), 211 - 224, English
    [Refereed]
    Scientific journal

  • Y Imai, T Aoki
    The Interpolated Differential Operator (IDO) scheme on collocated grids provides fourth-order discretizations for all the terms of the fluid flow equations. However, computations of fluid flows on collocated grids are not guaranteed to produce accurate solutions because of the poor coupling between velocity vector and scalar variables. A stable coupling method for the IDO scheme oil collocated grids is proposed, where a new representation of first-order derivatives is adopted. It is important in deriving the representation to refer to the variables at neighboring grid points, keeping fourth-order truncation error. It is clear that accuracy and stability are drastically improved for shallow water equations in comparison with the conventional IDO scheme. The effects of the stable coupling are confirmed in incompressible flow calculations for DNS of turbulence and a driven cavity problem. The introduction of a rational function into the proposed method makes it possible to calculate shock waves with the initial conditions of extreme density and pressure jumps. (c) 2005 Elsevier Inc. All rights reserved.
    ACADEMIC PRESS INC ELSEVIER SCIENCE, Jun. 2006, JOURNAL OF COMPUTATIONAL PHYSICS, 215(1) (1), 81 - 97, English
    [Refereed]
    Scientific journal

  • Y Imai, T Aoki
    An Interpolated Differential Operator (IDO) scheme using a new interpolation function is proposed. The gradient of the dependent variable is calculated at the position shifted by a half grid size from that of the physical value. A fourth-order Hermite-interpolation function is constructed locally using both the value and the gradient defined at staggered positions. The numerical solutions for the Poisson, diffusion, advection and wave equations have fourth-order accuracy in space. In particular, for the Poisson and diffusion equations, the Gradient-Staggered (G-S) IDO scheme shows better accuracy than the original IDO scheme. As a practical application, the Direct Numerical Simulation (DNS) for two-dimensional isotropic homogeneous turbulence is examined and a comparable result with that of the original IDO scheme is obtained. The G-S IDO scheme clearly contributes to high-accurate computations for solving partial differential equations in computational mechanics.
    JAPAN SOC MECHANICAL ENGINEERS, Nov. 2004, JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING, 47(4) (4), 681 - 689, English
    [Refereed]
    Scientific journal

  • 今井陽介, 青木尊之, 布施智之, 池平博夫
    We have developed a numerical method on Cartesian grid for image-based blood flow simulation. Cartesian grid has advantages for grid generation for the complex and moving boundary problems. Interpolated Differential Operator (IDO) scheme with Local Mesh Refinement method are effectively introduced for blood flow simulations. In order to simulate flow interacting with elastic vessel on Cartesian grid, a new technique INTERGRID has been developed and it is shown that the simulation of fluid-structure interaction problems that structure does not displace over the resolution of grid is carried out.
    The Japan Society of Mechanical Engineers, Sep. 2004, Transactions of the Japan Society of Mechanical Engineers, Series A, 70(697) (697), 1232 - 1239, Japanese
    [Refereed]
    Scientific journal

■ MISC
  • 細胞膜の拡大による樹状突起スパインのアイソジオメトリック解析—An isogeometric analysis of dendritic spine morphogenesis induced
    芥川 侑真, 林 桃郷, 竹田 宏典, 石田 駿一, 今井 陽介
    東京 : 日本計算工学会, Jun. 2024, 計算工学講演会論文集 = Proceedings of the Conference on Computational Engineering and Science / 日本計算工学会 編, 29, 1286 - 1290, Japanese

  • アイソジオメトリック境界要素法による超弾性体シートの沈降挙動解析—An analysis of sedimentation of a hyperelastic sheet using isogeometric boundary element method
    舩越 啓樹, 竹田 宏典, 石田 駿一, 今井 陽介
    東京 : 日本計算工学会, Jun. 2024, 計算工学講演会論文集 = Proceedings of the Conference on Computational Engineering and Science / 日本計算工学会 編, 29, 1228 - 1230, Japanese

  • 弾性管の蠕動運動により生じる管内流れのアイソジオメトリック境界要素解析—Isogeometric boundary element analysis of flow driven by peristaltic motion of an elastic tube
    竹田 宏典, 栗原 睦典, 石田 駿一, 今井 陽介
    東京 : 日本計算工学会, Jun. 2024, 計算工学講演会論文集 = Proceedings of the Conference on Computational Engineering and Science / 日本計算工学会 編, 29, 1225 - 1227, Japanese

  • 粘性流体との相互作用による薄膜の変形の流体構造連成解析—A fluid-structure interaction analysis of the thin film deformation due to interaction with
    林 桃郷, 竹田 宏典, 石田 駿一, 今井 陽介
    東京 : 日本計算工学会, Jun. 2024, 計算工学講演会論文集 = Proceedings of the Conference on Computational Engineering and Science / 日本計算工学会 編, 29, 1231 - 1236, Japanese

  • An isogeometric analysis of dendritic spine morphogenesis induced by cell membrane expansion
    芥川侑真, 林桃郷, 竹田宏典, 石田駿一, 今井陽介
    2024, 計算工学講演会論文集(CD-ROM), 29

  • 粘性流体中で成長する薄膜の変形のアイソジオメトリック解析—An isogeometric analysis of deformation of a growing thin menbrane in a viscous fluid
    林 桃郷, 竹田 宏典, 石田 駿一, 今井 陽介
    東京 : 日本計算工学会, May 2023, 計算工学講演会論文集 = Proceedings of the Conference on Computational Engineering and Science / 日本計算工学会 編, 28, 761 - 766, Japanese

  • Large scale parallel computing of cerebral circulation
    石田駿一, 北出宏紀, 伊井仁志, 今井陽介, 和田成生
    2019, 計算工学講演会論文集(CD-ROM), 24

  • Development of whole-scale cerebral blood flow simulator
    石田駿一, 北出宏紀, 伊井仁志, 今井陽介, 和田成生
    2019, バイオエンジニアリング講演会講演論文集(CD-ROM), 32nd

  • Modeling of cerebrovasculature network and numerical simulation of whole-scale cerebral circulation
    石田駿一, 北出宏紀, 伊井仁志, 今井陽介, 和田成生
    2019, 日本機械学会計算力学講演会論文集(CD-ROM), 32nd

  • FLUID-STRUCTURE INTERACTIONS OF NODAL CILIA AXONEME
    Toshihiro Omori, Hiroto Sugai, Yohsuke Imai, Takuji Ishikawa
    Sep. 2018, 8th International Conference on Fluid Mechanics (ICFM8), S10BM0-04, English
    [Refereed]
    Summary international conference

  • 太田 淳, 石田 駿一, 川瀬 哲明, 香取 幸夫, 今井 陽介
    (一社)日本耳鼻咽喉科学会, Apr. 2018, 日本耳鼻咽喉科学会会報, 121(4) (4), 569 - 569, Japanese

  • 嚥下の3D数値流体力学シミュレーションの開発と検討
    太田淳, 石田駿一, 川瀬哲明, 香取幸夫, 今井陽介
    2018, 日本嚥下医学会抄録(Web), 41st

  • Takami Yamaguchi, Takuji Ishikawa, Yohsuke Imai
    Integrated Nano-Biomechanics provides an integrated look into the rapidly evolving field of nanobiomechanics. The book demystifies the processes in living organisms at the micro- and nano-scale through mechanics, using theoretical, computational and experimental means. The book develops the concept of integrating different technologies along the hierarchical structure of biological systems and clarifies biomechanical interactions among different levels for the analysis of multi-scale pathophysiological phenomena. With a focus on nano-scale processes and biomedical applications, it is shown how knowledge obtained can be utilized in a range of areas, including diagnosis and treatment of various human diseases and alternative energy production. This book is based on collaboration of researchers from a unique combination of fields, including biomechanics, computational mechanics, GPU application, electron microscopy, biology of motile micro-organisms, entomological mechanics and clinical medicine. The book will be of great interest to scientists and researchers involved in disciplines, such as micro- and nano-engineering, bionanotechnology, biomedical engineering, micro- and nano-scale fluid-mechanics (such as in MEMS devices), nanomedicine and microbiology, as well as industries such as optical devices, computer simulation, plant based energy sources and clinical diagnosis of the gastric diseases.
    Elsevier, 01 Jan. 2018, Integrated Nano-Biomechanics, 1 - 297, English
    Others

  • Modeling the cerebral vasculature for numerical simulation in whole scale cerebral blood flow circulation
    北出宏紀, 伊井仁志, 今井陽介, 石田駿一, 和田成生
    2018, 日本機械学会バイオフロンティア講演会講演論文集(CD-ROM), 29th

  • 実形状モデルを用いた胃内流動の数値計算
    石田駿一, 宮川泰明, O’GRADY Gregory, CHENG Leo K., 今井陽介
    2018, 数値流体力学シンポジウム講演論文集(CD-ROM), 32nd

  • 胃内容物の撹拌・排出の数値シミュレーション
    石田駿一, 宮川泰明, O’GRADY Gregory, CHENG Leo K., 今井陽介
    2018, バイオエンジニアリング講演会講演論文集(CD-ROM), 31st

  • Numerical analysis of gastric mixing and emptying
    石田駿一, 宮川泰明, O’GRADY Gregory, CHENG Leo K., 今井陽介
    2018, 日本機械学会計算力学講演会論文集(CD-ROM), 31st

  • 胃から十二指腸への食物排出の数値計算
    今井陽介, 石田駿一, 宮川泰明, O’GRADY Gregory, CHENG Leo K.
    2017, 計算工学講演会論文集(CD-ROM), 22

  • 胃における蠕動運動と流れの関係についての一考察
    宮川泰明, 石田駿一, 今井陽介
    2017, 日本機械学会計算力学講演会論文集(CD-ROM), 30th

  • 胃壁の運動機能と胃内容物攪拌の関係
    宮川泰明, 今井陽介, 石田駿一, 山口隆美, 石川拓司
    2017, バイオエンジニアリング講演会講演論文集(CD-ROM), 29th

  • 胃内部の固体粒子挙動の数値計算
    石田駿一, 今井陽介, 宮川泰明, 石川拓司
    2017, バイオエンジニアリング講演会講演論文集(CD-ROM), 29th

  • A Numerical Analysis of Cell Adhesion in Microcirculation
    武石 直樹, 今井 陽介, カム ロジャー, 石川 拓司
    日本計算工学会, May 2016, 計算工学講演会論文集 Proceedings of the Conference on Computational Engineering and Science, 21, 4p, Japanese

  • 2E32 Numerical Analysis Concerning the Reorientation Phenomenon of Sedimenting Red Blood Cell
    Matsunaga Daiki, Imai Yohsuke, Wagner Christian, Ishikawa Takuji
    When keeping blood inside a static tube, it is well known that the red blood cells (RBCs) start to sediment downward due to the density difference between inner fluid and the outer fluid plasma. In present work, we numerically investigate the orientation angle of settling RBCs. First, we confirm that the RBCs change its orientation toward vertical angle as also reported in previous experimental studies. Secondly, we find that this reorientation is faster for a red blood cell with higher Bond number or lower viscosity ratio. In this report, we also discuss how this reorientation speed would impact the overall trajectories of the RBCs.
    The Japan Society of Mechanical Engineers, 09 Jan. 2016, バイオエンジニアリング講演会講演論文集, 2016(28) (28), "2E32 - 1"-"2E32-4", Japanese

  • 2E24 Clarification of the hydrodynamic factors influencing blood cell lateral migration
    NIX Stephanie, IMAI Yohsuke, ISHIKAWA Takuji
    In the blood, cells are observed to move perpendicular to the direction of the blood flow in a process called lateral migration. This lateral migration occurs due to several hydrodynamic factors, such as the presence of the vessel wall, the applied Poiseuille flow within the vessel, and cell-cell interactions. However, the effect of these factors has not been well understood. Thus, using the boundary integral method, we have been numerically investigating the effect of the wall and the effect of the curvature of the applied flow on the lateral migration of a single cell. We have shown that the effect of the wall on cell lateral migration is dominant relative to the effect of the flow curvature, even at large distances between the cell and the wall. We have also derived a semi-analytical equation representing the relative effects of the wall and flow curvature, which allows us to predict the migration velocity in slit flows or microvessels. Our results can also be used to develop simplified models, based on the position of the cell within the vessel, for biophysical phenomena such as cell margination and axial migration.
    The Japan Society of Mechanical Engineers, 09 Jan. 2016, バイオエンジニアリング講演会講演論文集, 2016(28) (28), "2E24 - 1"-"2E24-4", English

  • 1C46 Numerical simulation of a swimming ciliate near a water-air or a water-wall interface
    MANABE Junichi, OMORI Toshihiro, IMAI Yohsuke, ISHIKAWA Takuji
    Swimming behavior of microorganism near an interface is important to understand how to prevent bio-film formation, which can be a cause of medical instrument pollution. Recently, we found that a ciliate can be trapped at a water-air interface, though swims away from a water-wall interface. We conducted numerical simulation of swimming microorganism near an interface from hydrodynamic perspective, to reveal the entrapment mechanism. By mimicking microorganism shape in detail, our microorganism model reproduced entrapment phenomena for the first time in the world. We concluded that shape of a ciliate dominates the entrapment phenomena.
    The Japan Society of Mechanical Engineers, 09 Jan. 2016, バイオエンジニアリング講演会講演論文集, 2016(28) (28), "1C46 - 1"-"1C46-5", Japanese

  • 1E11 Numerical simulation of cell adhesion in microchannels
    TAKEISHI Naoki, IMAI Yohsuke, YAMAGUCHI Takami, Kamm Roger D., ISHIKAWA Takuji
    We numerically investigate the velocity of an adherent cell in various sizes of microchannels. The velocity drastically decreases as decreasing the size of microchannels. When the channel size becomes smaller, the motion of the adherent cell changes from a "rolling motion" to a "bullet motion", where the cell rotates on side wall in rolling motion, while the cell adhere its circular arc to the wall in bullet motion. Larger adhesion force is generated in rear parts of rolling cell, and existed bonds experience rupturing with higher probability because of slip bond. Because cell cannot move forward unless the ligand-receptor bonds in rear parts rupture, frequent rupturing allows the rolling cell to move faster than the cell exhibiting bullet motion. As getting smaller in channel diameter, the surface area attached to the wall is larger and then the number of ligand-receptor bonds is larger for smaller microchannels, resulting in a lower velocity. Our numerical model allows us to investigate the effect of various parameters on adherent cell velocity.
    The Japan Society of Mechanical Engineers, 09 Jan. 2016, バイオエンジニアリング講演会講演論文集, 2016(28) (28), "1E11 - 1"-"1E11-5", Japanese

  • 195 Numerical simulation of a sperm cell swimming in a viscoelastic fluid
    SHIMOMURA Eisaku, OMORI Toshihiro, IMAI Yhosuke, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 2016, 講演論文集, 2016(51) (51), 187 - 188, Japanese

  • 蠕動運動と胃内容物攪拌の関係
    宮川泰明, 今井陽介, 石田駿一, 山口隆美, 石川拓司
    2016, バイオエンジニアリング講演会講演論文集(CD-ROM), 28th

  • Iwasaki Yuwa, Imai Yohsuke, Kikuchi Kenji, Numayama-Tsuruta Keiko, Shigeta Shunsuke, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 2016, The Proceedings of Conference of Tohoku Branch, 2016(0) (0), 191 - 192, Japanese

  • B212 A numerical simulation of cytoskeletal dynamics
    SAITO Fumiyasu, IMAI Yohsuke, ISHIDA Shunichi, OMORI Toshihiro, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 01 Oct. 2015, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2015(26) (26), 123 - 124, Japanese

  • PS8-15 Mechanics of nodal cilia in early mouse embryo(PS8: Poster Short Presentation VIII,Poster Session)
    Omori Toshihiro, Sugai Hiroto, Imai Yohsuke, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 16 Sep. 2015, Proceedings of the ... Asian Pacific Conference on Biomechanics : emerging science and technology in biomechanics, 2015(8) (8), 366 - 366, English

  • PS8-14 Visualization of intestinal peristalsis of mosquito midgut by using micro X-ray imaging(PS8: Poster Short Presentation VIII,Poster Session)
    Kikuchi Kenji, Imai Yohsuke, Numayama-Tsuruta Keiko, Yamaguchi Takami, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 16 Sep. 2015, Proceedings of the ... Asian Pacific Conference on Biomechanics : emerging science and technology in biomechanics, 2015(8) (8), 365 - 365, English

  • PS3-7 DEVELOPMENT OF A NUMERICAL MODEL OF CYTOSKELETON DYNAMICS(PS3: Poster Short Presentation III,Poster Session)
    Saito Fumiyasu, Imai Yohsuke, Ishida Shunichi, Omori Toshihiro, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 16 Sep. 2015, Proceedings of the ... Asian Pacific Conference on Biomechanics : emerging science and technology in biomechanics, 2015(8) (8), 268 - 268, English

  • PS3-1 Hydrodynamic behavior of small particles in a microchannel(PS3: Poster Short Presentation III,Poster Session)
    Takeishi Naoki, Imai Yohsuke, Yamaguchi Takami, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 16 Sep. 2015, Proceedings of the ... Asian Pacific Conference on Biomechanics : emerging science and technology in biomechanics, 2015(8) (8), 262 - 262, English

  • Capsule lateral migration : shear gradient vs. wall
    Nix Stephanie, Imai Yohsuke, Ishikawa Takuji
    日本計算工学会, Jun. 2015, 計算工学講演会論文集 Proceedings of the Conference on Computational Engineering and Science, 20, 3p, English

  • 1A15 A numerical simulation of rolling and adhesion of red blood cells infected by malaria
    ICHIKAWA Yuki, IMAI Yohsuke, MATSUNAGA Daiki, NIX Stephanie, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2015, バイオエンジニアリング講演会講演論文集, 2015(27) (27), 11 - 12, Japanese

  • 1A16 Numerical Simulation of the Nodal Ciliary Motion Driven by the Dynein Motor Protein
    SUGAI Hiroto, Omori Toshihiro, IMAI Yohsuke, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 08 Jan. 2015, バイオエンジニアリング講演会講演論文集, 2015(27) (27), 13 - 14, Japanese

  • 1A12 Behavior of tracer particles in capsule suspensions : the effect of size of tracer particles
    ITO Hiroki, IMAI Yohsuke, MATSUNAGA Daiki, Omori Toshihiro, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 08 Jan. 2015, バイオエンジニアリング講演会講演論文集, 2015(27) (27), 5 - 6, Japanese

  • 1D35 Rheology of a red blood cell suspension in a simple shear flow
    OMORI Toshihiro, ISHIKAWA Takuji, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2015, バイオエンジニアリング講演会講演論文集, 2015(27) (27), 165 - 166, Japanese

  • 胃内のせん断応力の数値解析
    宮川泰明, 今井陽介, 石田駿一, 山口隆美, 石川拓司
    2015, バイオエンジニアリング講演会講演論文集, 27th

  • 胃内容物攪拌の数値計算:胃壁の運動の影響
    宮川泰明, 今井陽介, 石田駿一, 山口隆美, 石川拓司
    2015, 計算工学講演会論文集(CD-ROM), 20

  • A112 Numerical Simulation of the Ciliary Motion Driven by the Motor Protein
    SUGAI Hiroto, OMORI Toshihiro, IMAI Yohsuke, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 02 Oct. 2014, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2014(25) (25), 21 - 22, Japanese

  • A111 A numerical simulation of a microorganism behavior near an interface
    Manabe Junichi, Kyouya Kouhei, Omori Toshihiro, Imai Yohsuke, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 02 Oct. 2014, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2014(25) (25), 19 - 20, Japanese

  • Numerical analysis of dense capsule suspension with changing volume fraction
    松永 大樹, 今井 陽介, 山口 隆美
    日本計算工学会, Jun. 2014, 計算工学講演会論文集 Proceedings of the Conference on Computational Engineering and Science, 19, 4p, Japanese

  • 2G34 A simulation of nutrient uptake in a suspension of squirmers
    KAJIKI Shunsuke, IMAI Yohsuke, Yamaguchi Takami, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 539 - 540, Japanese

  • 1G43 A numerical simulation of the cytoadhesion of malaria-infected red blood cells using a ligand-receptor interaction model
    AMI Akihisa, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 245 - 246, Japanese

  • 1G44 A numerical analysis of the behavior of cancer cells related to hematogenous metastasis in microvasculature
    TAKEISHI Naoki, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 247 - 248, Japanese

  • 1G33 A numerical simulation of motion of food in the stomach
    MIYAGAWA Taimei, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 235 - 236, Japanese

  • 2E15 Numerical analysis of a red blood cell flowing through a micro flow channel
    OMORI Toshihiro, ISHIKAWA Takuji, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 439 - 440, Japanese

  • 2E22 Mechanism of the non-linear response of viscosity to volume fraction in dense capsule suspension
    MATSUNAGA Daiki, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 445 - 446, Japanese

  • 2E21 A numerical simulation of capsule behavior in a near-wall shear flow
    Nix Stephanie, IMAI Yohsuke, MATSUNAGA Daiki, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 443 - 444, Japanese

  • 167 気液界面における微生物の遊泳シミュレーション
    眞鍋 隼一, 京谷 浩平, 今井 陽介, 大森 俊宏, 石川 拓司
    一般社団法人日本機械学会, 2014, 講演論文集, 2014(49) (49), 131 - 132, Japanese

  • J027014 Simulation of nutrient uptake by swimming microorganisms in a suspension
    KAJIKI Shunsuke, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    Little is known about the mass transport in microbial suspension in previous studies. The aim of this study is to analyze the effect of the swimming motion on the nutrient uptake. We modeled a microorganism as a squirmer and calculated its locomotion by boundary element method . Moreover we simulated the nutrient uptake by tracking nutrient particles. The results show that the nutrient uptake is strongly affected by the swimming mode of a microorganism.
    The Japan Society of Mechanical Engineers, 08 Sep. 2013, Mechanical Engineering Congress, Japan, 2013, "J027014 - 1"-"J027014-4", Japanese

  • J027011 A Numerical Simulation of Collective Swimming of Microorganisms
    KYOYA Kohei, MATSUNAGA Daiki, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    Microorganisms play a vital role in many biological, medical and engineering phenomena. Some recent research efforts have demonstrated the importance of biomechanics in understanding certain aspects of microorganism behaviors such as locomotion and collective motions of cells. Previous studies had problems of high computational load in simulating many-body interaction of swimmers. In this study, we propose a boundary element method, based on the double-layer representation, for calculating interactions of many-body swimmers in Stokes flow regime. We use Graphic Processing Unit (GPU) to speed up the computation. We then analyze interactions of 100 swimmers.
    The Japan Society of Mechanical Engineers, 08 Sep. 2013, Mechanical Engineering Congress, Japan, 2013, "J027011 - 1"-"J027011-4", Japanese

  • 102 A Numerical Analysis of Bimodal Capsule Suspensions
    ITO Hiroki, IMAI Yohsuke, MATSUNAGA Daiki, ISHIKAWA Takuji, YAMAGUCH Takami
    The Japan Society of Mechanical Engineers, 15 Mar. 2013, 講演論文集, 2013(48) (48), 8 - 9, Japanese

  • 2B14 Rheological analysis of capsule suspension using boundary element method
    MATSUNAGA Daiki, IMAI Yohsuke, ISHIKAWA Takuji, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2013, バイオエンジニアリング講演会講演論文集, 2013(25) (25), 299 - 300, Japanese

  • 2E02 Analysis of Red Blood Cell Behavior in a Narrow Tube
    HOSAKA Haruki, OMORI Toshihiro, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2013, バイオエンジニアリング講演会講演論文集, 2013(25) (25), 387 - 388, Japanese

  • 2B19 A numerical analysis of the cell migration in microcirculatory blood flow
    TAKEISHI Naoki, IMAI Yohsuke, NAKAAKI Keita, ISHIKAWA Takuji, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2013, バイオエンジニアリング講演会講演論文集, 2013(25) (25), 307 - 308, Japanese

  • 1D04 Numerical analysis of swimming model microorganisms by GPU
    KYOYA Kohei, MATSUNAGA Daiki, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 08 Jan. 2013, バイオエンジニアリング講演会講演論文集, 2013(25) (25), 117 - 118, Japanese

  • MAEDA Tatsuyuki, ISHIKAWA Takuji, UENO Hironori, NUMAYAMA-TSURUTA Keiko, IMAI Yosuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2013, The Proceedings of the Bioengineering Conference Annual Meeting of BED/JSME, 2013(0) (0), 111 - 112, Japanese

  • KIYOTA Koki, UENO Hironori, ISHIKAWA Takuji, NUMAYAMA Keiko, IMAI Yohsuke, OMORI Toshihiro, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2013, The Proceedings of the Bioengineering Conference Annual Meeting of BED/JSME, 2013(0) (0), 609 - 610, Japanese

  • NONAKA Yuki, UENO Hironori, NUMAYAMA Keiko, OMORI Toshihiro, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    Bioconvection patterns are often observed in microalgae suspensions of randomly, but on average upwardly, swimming microalgae which are little denser than water. When we culture microalgae in the laboratory, we usually add aeration for mixing the culture fluid and supplying oxygen and carbon dioxide. However, the effect of aeration on the bioconvection pattern and the transport phenomena in the suspension is unclear. In this study, we investigated bioconvection pattern in a suspension of Chlamydomonas reinhardtii under the condition with aeration. Bioconvection pattern in a cylindrical container was visualized by red illumination, and white light for phototaxis could be added from above. Small bubbles were injected by a needle connected to a syringe. Observation of bioconvection patterns of microalgae suspension with aeration showed three kinds of flow patterns depending on the bubble flow rate. When there was no bubble flow, conventional bioconvection was dominant. When flow rate was low, observed pattern in the cylindrical container was split into two flow regions, where the bioconvection and the bubble flow were dominant respectively. When flow rate was high, bubble flow became dominant and no clear bioconvection was observed. Such changes in the bioconvection pattern have not been reported before. These findings are important to understand the transport phenomena in algae suspensions in engineering settings.
    The Japan Society of Mechanical Engineers, 2013, The Proceedings of Mechanical Engineering Congress, Japan, 2013(0) (0), _J027013 - 1-_J027013-4, Japanese

  • NONAKA Yuki, UENO Hirinori, NUMAYAMA Keiko, OMORI Toshihiro, IMAI Yosuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 2013, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2013(0) (0), 45 - 46, Japanese

  • NONAKA Yuki, UENO Hironori, NUMAYAMA-TSURUTA Keiko, OMORI Toshihiro, IMAI Yosuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 2013, The Proceedings of Conference of Tohoku Branch, 2013(0) (0), 10 - 11, Japanese

  • 計算生体力学シミュレーションによるミクロからマクロスケールの生体機能の解析
    山口 隆美, 今井 陽介, 水野 文雄, 大森 俊宏, 上野 裕則, 沼山 恵子, 石川 拓司
    バイオメカニズム学会, Dec. 2012, バイオメカニズム学術講演会予稿集, 33回, 33 - 34, Japanese

  • 806 Numerical simulation of dynamics of solid particles in the stomach
    MIYAGAWA Taimei, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Oct. 2012, The Computational Mechanics Conference, 2012(25) (25), 9 - 10, Japanese

  • 807 Numerical analysis of swimming model microorganisms by a boundary element method based on the double-layer representation
    KYOYA Kohei, MATSUNAGA Daiki, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 06 Oct. 2012, The Computational Mechanics Conference, 2012(25) (25), 11 - 12, Japanese

  • 803 Numerical simulation of adhesive phenomena of Pf-T-IRBC and the endothelial cells
    AMI Akihisa, IMAI Yohsuke, NAKAAKI Keita, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Oct. 2012, The Computational Mechanics Conference, 2012(25) (25), 3 - 4, Japanese

  • A107 Simulation of nutrient uptake by a swimming model microorganism
    Kajiki Shunsuke, Kyoya Kohei, Matsunaga Daiki, Imai Yohsuke, Yamaguchi Takami, Ishikawa Takuji
    The Japan Society of Mechanical Engineers, 04 Oct. 2012, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2012(23) (23), 13 - 14, Japanese

  • ストークス流れ中の非球形カプセルの配向現象
    石川拓司, 大森俊宏, 今井陽介, 山口隆美
    01 Sep. 2012, 京都大学数理解析研究所講究録, (1808) (1808), 121 - 126, Japanese
    Introduction research institution

  • Development of a numerical model for micro-scale blood flow simulation using GPU computing
    武石 直樹, 今井 陽介, 中秋 慶太
    日本計算工学会, May 2012, 計算工学講演会論文集 Proceedings of the Conference on Computational Engineering and Science, 17, 4p, Japanese

  • Numerical Analysis of a Red Blood Cells in Simple Shear Flow
    大森 俊宏, 石川 拓司, 今井 陽介
    日本計算工学会, May 2012, 計算工学講演会論文集 Proceedings of the Conference on Computational Engineering and Science, 17, 4p, Japanese

  • Development of a multi GPU implementation of a boundary integral method for capsule flow
    松永 大樹, 今井 陽介, 石川 拓司
    日本計算工学会, May 2012, 計算工学講演会論文集 Proceedings of the Conference on Computational Engineering and Science, 17, 4p, Japanese

  • 111 Simulation of mass absorption of swimming model microorganisms by a boundary element method
    KAJIKI Shunsuke, MATSUNAGA Daiki, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 13 Mar. 2012, 講演論文集, 2012(47) (47), 28 - 29, Japanese

  • 110 Numerical analysis of swimming model microorganisms by a boundary element method
    Kyoya Kohei, MATSUNAGA Daiki, IMAI Yohsuke, YAMAGUCHI Takami, ISHIKAWA Takuji
    The Japan Society of Mechanical Engineers, 13 Mar. 2012, 講演論文集, 2012(47) (47), 26 - 27, Japanese

  • 113 Numerical analysis of adhesive phenomena of malaria-infected red blood cells
    AMI Akihisa, IMAI Yohsuke, NAKAAKI Keita, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2012, 講演論文集, 2012(47) (47), 32 - 33, Japanese

  • 109 Analysis of Red Blood Ce11 Deformation in Flow Field Using a Boundary Element Method
    Hosaka Haruki, Ishikawa Takuji, Omori Toshihiro, Imai Yohsuke, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2012, 講演論文集, 2012(47) (47), 24 - 25, Japanese

  • 212 Development of a numerical model for blood flow in microvessels using GPGPU computing
    Takeishi Naoki, IMAI Yohsuke, NAKAAKI Keita, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2012, 講演論文集, 2012(47) (47), 230 - 231, Japanese

  • 8G24 A 3-dimensional computation on gastric mixing using GPU.
    KOBAYASHI Ikuma, IMAI Yosuke, ISHIDA Shunichi, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Jan. 2012, バイオエンジニアリング講演会講演論文集, 2012(24) (24), "8G24 - 1"-"8G24-2", Japanese

  • 8F34 Development of a numerical model of microcirculatory blood flow in malaria infection based on GPU
    NAKAAKI Keita, IMAI Yohsuke, ISHIKAWA Takuji, Lim Chwee Teck, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Jan. 2012, バイオエンジニアリング講演会講演論文集, 2012(24) (24), "8F34 - 1"-"8F34-2", Japanese

  • 8F13 Development of a GPU computing platform for accurate simulations of large-scale cellular flow
    IMAI Yohsuke, MATSUNAGA Daiki, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Jan. 2012, バイオエンジニアリング講演会講演論文集, 2012(24) (24), "8F13 - 1"-"8F13-2", Japanese

  • 7H22 A fast simulation of pulmonary airflow and inhaled particles by GPU
    IMAI Yohsuke, MIKI Takahito, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Jan. 2012, バイオエンジニアリング講演会講演論文集, 2012(24) (24), "7H22 - 1"-"7H22-2", Japanese

  • 固体成分を含む胃内容物の攪拌の数値シミュレーション
    宮川泰明, 今井陽介, 小林生馬, 石川拓司, 山口隆美
    2012, 日本機械学会東北支部総会・講演会講演論文集, 47th

  • 胃内部の固体粒子運動の数値シミュレーション
    宮川泰明, 今井陽介, 石川拓司, 山口隆美
    2012, 日本機械学会計算力学講演会論文集(CD-ROM), 25th

  • 2306 A numerical computation on gastric mixing
    KOBAYASHI Ikuma, IMAI Yohsuke, ISHIDA Shunichi, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Oct. 2011, The Computational Mechanics Conference, 2011(24) (24), 642 - 643, Japanese

  • 2305 Numerical simulation of swallowing based on videofluorography
    ISHIDA Shunichi, IMAI Yohsuke, ISHIKAWA Takuji, KINJO Aki, MATSUKI Noriaki, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Oct. 2011, The Computational Mechanics Conference, 2011(24) (24), 639 - 641, Japanese

  • 2308 A fast simulation of capsule motion in flow by GPU computing
    IMAI Yohsuke, MATSUNAGA Daiki, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Oct. 2011, The Computational Mechanics Conference, 2011(24) (24), 646 - 647, Japanese

  • 2307 Development of GPU simulation of microcirculatory blood flow
    NAKAAKI Keita, IMAI Yohsuke, ISHIKAWA Takuji, Lim Chwee Teck, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Oct. 2011, The Computational Mechanics Conference, 2011(24) (24), 644 - 645, Japanese

  • B112 Development of GPU computing method for capsule suspension
    MATSUNAGA Daiki, IMAI Yohsuke, OMORI Toshihiro, MIKI Takahito, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Oct. 2011, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2011(22) (22), 61 - 62, Japanese

  • 184 Numerical simulation of red blood cell flow in micro vessels : effects of endothelial cell geometry
    FUJIWARA Masaki, IMAI Yohsuke, NAKAAKI Keita, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 15 Mar. 2011, 講演論文集, 2011(46) (46), 170 - 171, Japanese

  • 9G-17 Numerical simulation of swallowing based on videofluorography
    ISHIDA Shunichi, IMAI Yohsuke, ISHIKAWA Takuji, KINJO Aki, MATSUKI Noriaki, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 07 Jan. 2011, バイオエンジニアリング講演会講演論文集, 2010(23) (23), 559 - 560, Japanese

  • 9G-16 Development of a computational fluid dynamics model of gastric mixing
    IMAI Yohsuke, KOBAYASHI Ikuma, ISHIDA Shunichi, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 07 Jan. 2011, バイオエンジニアリング講演会講演論文集, 2010(23) (23), 557 - 558, Japanese

  • 9E-08 Numerical analysis of cell behavior in blood flow
    MATSUMOTO Yoshihiro, IMAI Yohsuke, ALIZADEHRAD Davod, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 07 Jan. 2011, バイオエンジニアリング講演会講演論文集, 2010(23) (23), 389 - 390, Japanese

  • SHIOIRI Tatsuya, ISHIKAWA Takuji, NUMAYAMA Keiko, IMAI Yohsuke, UENO Hironori, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2011, The Proceedings of Conference of Tohoku Branch, 2011(0) (0), 166 - 167, Japanese

  • YOSHIMOTO Takefumi, ISHIKAWA Takuji, NUMAYAMA Keiko, MATSUKI Noriaki, TANAKA Tatsuya, UENO Hironori, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2011, The Proceedings of the Bioengineering Conference Annual Meeting of BED/JSME, 2010(0) (0), 487 - 488, Japanese

  • MAEDA Tatsuyuki, ISHIKAWA Takuji, NUMAYAMA Keiko, IMAI Yosuke, UENO Hironori, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2011, The Proceedings of Conference of Tohoku Branch, 2011(0) (0), 176 - 177, Japanese

  • A107 Changes in blood flow caused by adhesive properties of malaria-infected red blood cells
    NAKAAKI Keita, IMAI Yohsuke, KONDO Hitoshi, ISHIKAWA Takuji, Teck Lim Chwee, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 11 Nov. 2010, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2010(21) (21), 13 - 14, Japanese

  • A108 Effects of content volume on the flow in a stomach
    KOBAYASHI Ikuma, IMAI Yohsuke, ISHIDA Shunichi, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 11 Nov. 2010, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2010(21) (21), 15 - 16, Japanese

  • 164 Numerical simulation of gastric mixing by particle method
    KOBAYASHI Ikuma, IMAI Yohsuke, ISIDA Shunichi, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 12 Mar. 2010, 講演論文集, 2010(45) (45), 128 - 129, Japanese

  • 192 Three-dimensional simulation of behavior of malaria infected red blood cell in blood flow
    NAKAAKI Keita, IMAI Yohsuke, KONDO Hitoshi, ISHIKAWA Takuji, Teck Lim Chwee, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 12 Mar. 2010, 講演論文集, 2010(45) (45), 184 - 185, Japanese

  • 196 Basic Study for Bio-micropump by using Escherichia coli
    Matsuura Ryo, Ishikawa Takuji, Ueno Yusuke, Imai Yohsuke, Matsuki Noriaki, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 12 Mar. 2010, 講演論文集, 2010(45) (45), 192 - 193, Japanese

  • 193 Measurement of mesoscopic flow structure in a suspension of Escherichia coli by using micro-PIV system
    YOSHIDA Naoto, ISHIKAWA Takuji, UENO Yusuke, MATSUKI Noriaki, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 12 Mar. 2010, 講演論文集, 2010(45) (45), 186 - 187, Japanese

  • 194 Behavior of cancer cells flowing in microchannels
    TANAKA Tatsuya, ISHIKAWA Takuji, MATSUKI Noriaki, IMAI Yohsuke, UENO Yusuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 12 Mar. 2010, 講演論文集, 2010(45) (45), 188 - 189, Japanese

  • 0205 Effects of adhesion property of malaria infected red blood cells on blood flows
    IMAI Yohsuke, NAKAAKI Keita, KONDo Hitoshi, KANG Young Ho, ISHIKAWA Takuji, LIM Chwee Teck, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2010, バイオエンジニアリング講演会講演論文集, 2009(22) (22), 14 - 14, Japanese

  • 0625 Patient-specific morphological and blood flow analysis of pulmonary artery in the case of severe deformations of the lung
    CHRISTOPHE Jean-Joseph, ISHIKAWA Takuji, IMAI Yohsuke, MATSUKI Noriaki, TAKASE Kei, THIRIET Marc, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2010, バイオエンジニアリング講演会講演論文集, 2009(22) (22), 280 - 280, Japanese

  • 0513 Computation biomechanics of transport phenomenon in the small intestine
    SATO Takuya, ISHIKAWA Takuji, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2010, バイオエンジニアリング講演会講演論文集, 2009(22) (22), 270 - 270, Japanese

  • 1005 Monitoring system of water content in a body by bioimpedance method
    WATANABE Aya, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2010, バイオエンジニアリング講演会講演論文集, 2009(22) (22), 169 - 169, Japanese

  • 0914 Development of a mobile toilet system for elderly
    Ueno Sozo, IMAI Yohsuke, Hayasaka Tomoaki, Mizuno Fumio, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 08 Jan. 2010, バイオエンジニアリング講演会講演論文集, 2009(22) (22), 156 - 156, Japanese

  • TANAKA Tatsuya, ISHIKAWA Takuji, MATSUKI Noriaki, IMAI Yohsuke, UENO Hironori, NUMAYAMA-TSURUTA Keiko, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 2010, The Proceedings of the JSME Conference on Frontiers in Bioengineering, 2010(0) (0), 105 - 106, Japanese

  • B210 Patient-specific study on pulmonary blood now in the case of severe deformations of the lung
    CHRISTOPHE Jean-Joseph, ISHIKAWA Takuji, IMAI Yohsuke, MATSUKI Noriaki, THIRIET Marc, TAKASE Kei, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Nov. 2009, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2009(20) (20), 111 - 112, English

  • B209 Effect of anti-cancer drug on the rheological property of cancer cells
    YOSHIMOTO Takefumi, ISHIKAWA Takuji, MATSUKI Noriaki, IMAI Yohsuke, UENO Hironori, TAKEDA Motohiro, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Nov. 2009, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2009(20) (20), 109 - 110, Japanese

  • B106 Motion analysis of bolus and epiglottis based on VF images
    ISHIDA Shunichi, IMAI Yohsuke, MATSUKI Noriaki, KINJO Aki, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Nov. 2009, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2009(20) (20), 39 - 40, Japanese

  • 2001 Development of a three-dimensional model of hemodynamics arising from malaria infection
    IMAI Yohsuke, KONDO Hitoshi, Ho Kang Young, ISHIKAWA Takuji, Teck Lim Chwee, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 10 Oct. 2009, The Computational Mechanics Conference, 2009(22) (22), 544 - 545, Japanese

  • 変形機構を有する室内飛行船の開発
    広瀬量平, 今井陽介, 石川拓司, 山口隆美
    Oct. 2009, ブイヤント航空, 37, 81 - 88, Japanese
    Introduction other

  • K-014 Development of a mobile toilet system for solitary elderly people
    Ueno Sozo, Imai Yohsuke, Hayasaka Tomoaki, Ishikawa Takuji, Yamaguchi Takami
    Forum on Information Technology, 20 Aug. 2009, 情報科学技術フォーラム講演論文集, 8(3) (3), 555 - 556, Japanese

  • 151 Airship type watch-over system cruising in a house with occasional deformation
    HIROSE Ryohei, ISHIKAWA Takuji, IMAI Yhousuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2009, 講演論文集, 2009(44) (44), 100 - 101, Japanese

  • 187 The relationship between cancer cell deformability and its metastasis
    YOSHIMOTO Takefumi, ISHIKAWA Takuji, MATSUKI Noriaki, FUJIWARA Hiroki, IMAI Yhousuke, UENO Hironori, TAKEDA Motohiro, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2009, 講演論文集, 2009(44) (44), 168 - 169, Japanese

  • 198 Flow analysis of digested material in the small intestine
    SATO Takuya, ISHIKAWA Takuji, SHIMOGONYA Yuji, IMAI Yosuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2009, 講演論文集, 2009(44) (44), 188 - 189, Japanese

  • 188 Basic study on monitoring system of water content in a body for elderly people
    WATANABE Aya, IMAI Yhousuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2009, 講演論文集, 2009(44) (44), 170 - 171, Japanese

  • 190 A study on the mechanism of swallowing using videofluorography
    Ishida Shunichi, Imai Yhousuke, Matsuki Noriaki, Kinjo Aki, Ishikawa Takuji, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2009, 講演論文集, 2009(44) (44), 174 - 175, Japanese

  • 189 Quantification of mechanical stimulus to induce avoiding reaction of Paramecium
    Ishiguro Takashi, Ishikawa Takuji, Matsuki Noriaki, Ueno Hironori, Imai Yhousuke, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2009, 講演論文集, 2009(44) (44), 172 - 173, Japanese

  • 199 Development of a numerical model of rosettes in malaria infection
    KANG Yongho, IMAI Yosuke, KONDO Hitoshi, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 13 Mar. 2009, 講演論文集, 2009(44) (44), 190 - 191, Japanese

  • 439 Development of a mobile toilet robot
    Ueno Sozo, IMAI Yohsuke, Hayasaka Tomoaki, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 22 Jan. 2009, バイオエンジニアリング講演会講演論文集, 2008(21) (21), 411 - 412, Japanese

  • 434 Development of respiration monitoring system for home-care
    OKUBO Masahiko, IMAI Yohsuke, ISHIKAWA Takuji, HAYASAKA Tomoaki, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 22 Jan. 2009, バイオエンジニアリング講演会講演論文集, 2008(21) (21), 401 - 402, Japanese

  • 215 Measurement of blood flow through bifurcation and confluence of microchannel with confocal micro-PIV system
    FUJIWARA Hiroki, ISHIKAWA Takuji, MATSUKI Noriaki, YOSHIMOTO Takefumi, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 22 Jan. 2009, バイオエンジニアリング講演会講演論文集, 2008(21) (21), 87 - 88, Japanese

  • B412 An automatic inhaler control system based on respiration monitoring
    OKUBO Masahiko, IMAI Yohsuke, ISHIKAWA Takuji, HAYASAKA Tomoaki, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 22 Sep. 2008, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2008(19) (19), 153 - 154, Japanese

  • B203 Behavior of a Red Blood Cell in a Simple Shear Flow Simulated by a Boundary Element Method
    OMORI Toshihiro, ISHIKAWA Takuji, BARTHES-BIESEL Dominique, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 22 Sep. 2008, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2008(19) (19), 47 - 48, Japanese

  • B209 A Locomotive System Mimicking Pedal Locomotion of Snails for the Capsule Endoscope
    HOSOKAWA Daisuke, ISHIKAWA Takuji, MORIKAWA Hirohisa, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 22 Sep. 2008, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2008(19) (19), 58 - 59, Japanese

  • 1G3-2 Development of a mobile toilet system
    Ueno Sozo, IMAI Yohsuke, Hayasaka Tomoaki, ISHIKAWA Takuji, YAMAGUCHI Takami
    A number of elderly people have a difficulty in going to the toilet by themselves. They sometimes wear an adult diaper but it makes the elderly uncomfortable and unsanitary. Moreover, their pride is injured by wearing the diaper. A portable toilet is also used for the elderly requiring assistance to the toilet. The portable toilet is not a sufficient solution because it is also uncomfortable and unsanitary for them. We propose a mobile toilet system for solving this problem. The concept of the proposed system is as follows. The toilet waits for calling signal from the elderly at standby room. When the calling signal is received, the toilet autonomously goes to the bedroom and approaches the elderly. After excreting, the toilet returns to the standby room and automatically disposes feces. This system is also equipped with analyzing function of feces for monitoring their health condition. We have developed a prototype of the toilet.
    The Japan Society of Mechanical Engineers, 17 Sep. 2008, The JSME Symposium on Welfare Engineering, 2008, 176 - 177, Japanese

  • 1G2-2 Development of respiration monitoring system for home-care patients of respiratory diseases
    OKUBO Masahiko, IMAI Yohsuke, ISHIKAWA Takuji, HAYASAKA Tomoaki, YAMAGUCHI Takami
    A number of patients are suffering from respiratory diseases, such as dyspnea, sleep apnea syndrome (SAS), asthma and chronic obstructive pulmonary disease (COPD). These patients can be supported by early detection of symptom and administration of milder treatment. However, it is a serious burden for them and their family to care for their respiratory conditions in daily life. We propose a new home-care system for such patients. The system is an automatic inhaler control system based on continuous respiration monitoring. We employ a mask-type unit to install a measurement sensor for respiration together with an inhaler. Respiration is monitored using a thermocouple in the mask. Respiratory rate is measured by counting peaks of temperature change due to expiration and inspiration. The error of respiratory rate at rest in sitting posture was within 2% between the measurement and the reference. Based on the monitored data, the inhaler can be controlled automatically. Moreover, the information of respiration can be shared with family, hospital, and local supporters at a long distance through a computer network.
    The Japan Society of Mechanical Engineers, 17 Sep. 2008, The JSME Symposium on Welfare Engineering, 2008, 164 - 165, Japanese

  • Availability of Adaptive Mesh Refinement method for the analysis of pulmonary airflow
    MIKI Takahito, IMAI Yohsuke, WADA Shigeo, IWAMURA Chihiro, ISHIKAWA Takuji, YAMAGUCHI Takami
    日本計算工学会, 19 May 2008, Proceedings of the conference on computational engineering and science, 13(2) (2), 827 - 830, Japanese

  • A three-dimensional model of malaria-infected blood flow
    KONDO Hitoshi, IMAI Yohsuke, ISHIKAWA Takuji, TSUBOTA Ken-ichi, LIM C. T., YAMAGUCHI Takami
    日本計算工学会, 19 May 2008, Proceedings of the conference on computational engineering and science, 13(2) (2), 533 - 536, Japanese

  • 126 Development of the self-propelled intelligent toilet
    UENO Sozo, KISHIMOTO Masamichi, HAYASAKA Tomoaki, MORI Daisuke, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 15 Mar. 2008, 講演論文集, 2008(43) (43), 53 - 54, Japanese

  • 608 Measurement of physical load by a wearable thermometer system
    SUZUKI Yuta, KISHIMOTO Masamichi, MORI Daisuke, IMAI Yohsuke, MATSUKI Noriaki, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 24 Jan. 2008, バイオエンジニアリング講演会講演論文集, 2007(20) (20), 219 - 220, Japanese

  • 101 Measurement of the blood flow in a microchannel with stenosis by confocal-micro-PTV system
    Rui Lima
    The Japan Society of Mechanical Engineers, 24 Jan. 2008, バイオエンジニアリング講演会講演論文集, 2007(20) (20), 1 - 2, Japanese

  • 105 DISPERSION OF RED BLOOD CELLS IN MICROCHANNELS : A CONFOCAL MICRO-PTV ASSESSMENT
    LIMA RUI, ISHIKAWA TAKUJI, IMAI YOHSUKE, FUJIWARA HIROKI, TAKEDA MOTOHIRO, MATSUKI NORIAKI, WADA SHIGEO, YAMAGUCHI TAKAMI
    The Japan Society of Mechanical Engineers, 24 Jan. 2008, バイオエンジニアリング講演会講演論文集, 2007(20) (20), 9 - 10, English

  • 210 Interactions between two swimming bacteria
    Ishikawa Takuji, Sekiya Go, Imai Yohsuke, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 24 Jan. 2008, バイオエンジニアリング講演会講演論文集, 2007(20) (20), 57 - 58, Japanese

  • 118 Numerical Simulation of Saccular Aneurysm Formation in a Realistic Cerebral Artery Model
    SHIMOGONYA Yuji, ISHIKAWA Takuji, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 24 Jan. 2008, バイオエンジニアリング講演会講演論文集, 2007(20) (20), 35 - 36, Japanese

  • 2304 Multiscale modeling of pulmonary airway system
    WADA Shigeo, NAKAMURA Masanori, MIKI Takahito, IMAI Yohsuke
    The Japan Society of Mechanical Engineers, 25 Nov. 2007, The Computational Mechanics Conference, 2007(20) (20), 189 - 190, Japanese

  • 303 Application of a High-Order AMR Method to Pulmonary Airflow Simulations
    IMAI Yohsuke, MIKI Takahito, ISHIKAWA Takuji, NAKAMURA Masanori, WADA Shigeo, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 25 Nov. 2007, The Computational Mechanics Conference, 2007(20) (20), 583 - 584, Japanese

  • 2211 A Simulation Study on Saccular Cerebral Aneurysm Formation Considering Biological Reactions
    SHIMOGONYA Yuji, ISHIKAWA Takuji, IMAI Yohsuke, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 25 Nov. 2007, The Computational Mechanics Conference, 2007(20) (20), 341 - 342, Japanese

  • B208 Development of respiration measurement unit with wearable system
    OKUBO Masahiko, KISHIMOTO Masamichi, IMAI Yohsuke, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 05 Oct. 2007, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2007(18) (18), 127 - 128, Japanese

  • Blood Cell Motions and Interactions in Microchannels
    LIMA Rui, ISHIKAWA Takuji, FUJIWARA Hiroki, TAKEDA Motohiro, IMAI Yohsuke, TSUBOTA Ken-ichi, WADA Shigeo, YAMAGUCHI Takami
    01 Jul. 2007, 可視化情報学会誌 = Journal of the Visualization Society of Japan, 27, 141 - 142, English

  • Numerical simulation of cerebral aneurysm growth considering arterial adaptation
    下權谷 祐児, 今井 陽介, 石川 拓司
    日本計算工学会, May 2007, Proceedings of the conference on computational engineering and science, 12(1) (1), 213 - 216, Japanese

  • 421 An adaptive mesh refinement method for numerical analysis of pulmonary airflow
    MIKI Takahito, IMAI Yohsuke, NAKAMURA Masanori, ISHIKAWA Takuji, YAMAGUCHI Takami, WADA Shigeo
    The Japan Society of Mechanical Engineers, 06 Jan. 2007, バイオエンジニアリング講演会講演論文集, 2006(19) (19), 140 - 141, Japanese

  • 331 Meso-scale structure in a concentrated suspension of micro-organisms
    Ishikawa Takuji, Pedley T.J., Imai Yohsuke, Tsubota Ken-ichi, Yamaguchi Takami
    The Japan Society of Mechanical Engineers, 06 Jan. 2007, バイオエンジニアリング講演会講演論文集, 2006(19) (19), 318 - 319, Japanese

  • 237 Numerical analysis of ATP transport in blood vessels
    SATO Kodai, IMAI Yohsuke, ISHIKAWA Takuji, COMERFORD Andrew, DAVID Tim, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 06 Jan. 2007, バイオエンジニアリング講演会講演論文集, 2006(19) (19), 298 - 299, Japanese

  • A101 Development of a wearable system for an quantification measurement of human motions in daily life
    KISHIMOTO Masamichi, NAKAMURA Hiromi, YOSHIDA Toshihiko, MIZUNO Fumio, HAYASAKA Tomoaki, IMAI Yohsuke, TSUBOTA Ken-ichi, ISHIKAWA Takuji, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 10 Nov. 2006, Proceedings of the ... JSME Conference on Frontiers in Bioengineering, 2006(17) (17), 3 - 4, Japanese

  • 527 The effect of arterial wall movement on the wall shear stress by a fluid-solid interaction computational study
    FUKUI Tomohiro, PARKER Kim H., IMAI Yohsuke, TSUBOTA Ken-ichi, ISHIKAWA Takuji, WADA Shigeo, YAMAGUCHI Takami
    The Japan Society of Mechanical Engineers, 02 Nov. 2006, The Computational Mechanics Conference, 2006(19) (19), 499 - 500, Japanese

■ Books And Other Publications
  • Frontiers in Computational Fluid-Structure Interaction and Flow Simulation: A Numerical Analysis of Rheology of Capsule Suspensions Using a GPU-Accelerated Boundary Element Method
    Yohsuke Imai, Daiki Matsunaga
    Joint work, Springer, Nov. 2018, English
    Scholarly book

  • Integrated Nano-Biomechanics: 3.2 Gastric Motility and Flow in the Stomach
    Yohsuke Imai
    Joint work, Elsevier, Jul. 2018, English
    Scholarly book

  • Integrated Nano-Biomechanics: 3.1 Dynamics of Swallowing
    Yohsuke Imai
    Joint work, Elsevier, Jul. 2018, English
    Scholarly book

  • Integrated Nano-Biomechanics: 2.3 Cell Adhesion in Microvessels
    Yohsuke Imai
    Joint work, Elsevier, Jul. 2018, English
    Scholarly book

  • Integrated Nano-Biomechanics
    Takami Yamaguchi, Takuji Ishikawa, Yohsuke Imai
    Joint editor, Elsevier, Jul. 2018, English
    Scholarly book

  • Visualization and Simulation of Complex Flows in Biomedical Engineering
    R.Lima, Y.Imai, T.Ishikawa, M.S.N.Oliveira
    Joint editor, Springer, 2014, English
    Scholarly book

■ Lectures, oral presentations, etc.
  • Computation of complex physiological flows
    Yohsuke Imai
    Osaka University MEI-Center Summer School 2019, Aug. 2019, English, Suita, Japan, International conference
    [Invited]
    Invited oral presentation

  • Development of a numerical model of whole-scale cerebral circulation
    Shunichi Ishida, Hiroki Kitade, Satoshi Ii, Naoki Takeishi, Yoshiyuki Watanabe, Yohsuke Imai, Shigeo Wada
    29th International Symposium on Cerebral Blood Flow, Metabolism, and Function, Jul. 2019, English, Yokohama, Japan, International conference
    Poster presentation

  • Modeling cerebral vasculatures for analysis of the whole cerebral circulation
    Hiroki Kitade, Satoshi Ii, Shunichi Ishida, Yohsuke Imai, Shigeo Wada
    6th International Conference on Computational and Mathematical Biomedical Engineering, Jun. 2019, English, Sendai, Japan, International conference
    Poster presentation

  • Hemorheology of dense suspension of red blood cells in a wall-bounded shear flow
    Naoki Takeishi, Marco E. Rosti, Yohsuke Imai, Shigeo Wada, Luca Brandt
    71st Annual Meeting of the APS Division of Fluid Dynamics, Nov. 2018, English, Atlanta, USA, International conference
    Oral presentation

  • Relationship between gastric wall motility and mixing of liquid foods in the stomach
    Taimei Miyagawa, Shunichi Ishida, Gregory O'Grady, Leo Cheng, Yohsuke Imai
    8th World Congress on Biomechanics, Jul. 2018, English, Dublin, Ireland, International conference
    Poster presentation

  • Perioperative hemodynamic changes in the patient with pulmonary arterial hypertension by use of thoracic 4D-flow MRI
    Hiroki Kamada, Hideki Ota, Yohsuke Imai, Kei Takase
    8th World Congress on Biomechanics, Jul. 2018, English, Dublin, Ireland, International conference
    Poster presentation

  • Numerical simulation of cytoadhesion of red blood cells infected by Plasmodium falciparum
    Shunichi Ishida, Akihisa Ami, Yohsuke Imai
    8th World Congress on Biomechanics, Jul. 2018, English, Dublin, Ireland, International conference
    Invited oral presentation

  • Effect of internal viscosity on suspension rheology of red blood cells
    Naoki Takeishi, Marco E. Rosti, Yohsuke Imai, Shigeo Wada, Luca Brandt
    Joint Meeting of the European Society for Clinical Hemorheology and Microcirculation, the International Society of Clinical Hemorheology, and the International Society of Biorheology, Jul. 2018, English, Krakow, Porland, International conference
    Oral presentation

  • Cell adhesion during bullet and rolling motion in capillaries
    Naoki Takeishi, Yohsuke Imai, Roger Kamm
    8th World Congress on Biomechanics, Jul. 2018, English, Dublin, Ireland, International conference
    Invited oral presentation

  • 微小循環の血液の流れを計算する
    IMAI YOHSUKE
    日本機械学会2018年度年次大会, 2018, Japanese, 吹田, Domestic conference
    Invited oral presentation

  • 体の中の流れを計算する
    IMAI YOHSUKE
    第14回東北大学REDEEMシンポジウム, 2018, Japanese, 東京, Domestic conference
    Invited oral presentation

  • 体の中の複雑な流れを計算する
    IMAI YOHSUKE
    第90回バイオメクフォーラム, 2018, Japanese, 豊中, Domestic conference
    Invited oral presentation

  • 胃の中の流れを計算する
    IMAI YOHSUKE
    第50回生物機械システム研究会, 2018, Japanese, 豊中, Domestic conference
    Invited oral presentation

■ Research Themes
  • 流体構造生化学連成解析によるニューロンの移動モードと大脳皮質形成の力学の解明
    今井 陽介, 林 周宏, 滝沢 研二
    日本学術振興会, 科学研究費助成事業, 基盤研究(A), 神戸大学, 05 Apr. 2021 - 31 Mar. 2024
    哺乳類の大脳皮質深部で誕生した神経細胞（ニューロン）は，三種類の移動モードを駆使して脳表層に到着し，インサイドアウトと呼ばれる六層構造の大脳皮質を形成する． 本研究の目的は，流体構造生化学連成解析とイン・ビボ細胞実験の統合的な手法によって，ニューロンの移動モードの変化とインサイドアウト構造の形成メカニズムを力学に基づいて明らかにすることである．そのための基盤計算技術として，細胞膜の固体力学，細胞質と細胞外の液体の流体力学，細胞接着タンパクと細胞骨格タンパクの生化学反応を連成するトランススケール流体構造生化学連成解析手法を開発する． ２０２１年度は，ニューロンの先導突起の挙動を再現できるトランススケール流体構造生化学連成解析手法の基礎を構築した．生体組織の成長理論をヒントに，局所的な生体膜の面積増加と薄膜の力学を連成する手法を開発した．非一様有理Ｂスプライン（ＮＵＲＢＳ）関数を用いて高次に表現した曲面に対し，細胞膜に対する代表的な構成則であるスカラックのひずみエネルギー関数（Skalak et al., Biophys. J., 1973）とヘルフリッヒの曲げエネルギー関数（Helfrich, Zeitschrift fur Naturforschung C, 1973）を弱形式で記述し，アイソジオメトリック解析を適用した．マッシュルーム形状の先導突起や長く伸びた先導突起を再現することに成功し，さらに，これらの先導突起の形状を記述する理論解を導出した．

  • 薄く時間変化する生体建築部材の流体構造連成解析ーからだ建築のCAEの方法
    今井 陽介
    日本学術振興会, 科学研究費助成事業, 学術変革領域研究(A), 神戸大学, 10 Sep. 2021 - 31 Mar. 2023
    生体の組織を構成する建築部材は，多くの場合，繊維と膜と液体であり，例えば，上皮組織の管腔構造などが作られる．これらの建築部材に共通する特徴は，薄い構造であること，部材の数や形が時間変化すること，流体の中で建築作業が進行することである．本研究の目的は，生体建築部材から作られる生体組織のコンピュータ支援エンジニアリング（ＣＡＥ）の手法を開発することである．具体的には，建築部材の変形，成長，結合の変化を考慮して生体構造力学を数理モデル化し，Ｔ－スプライン曲面理論に基づくアイソジオメトリック解析を応用する流体構造連成計算手法を開発する．これを用いて，イン・ビボ実験で得られている螺旋形状の血管形成の再現を試みる． ２０２１年度は，生体建築部材の流体構造連成解析手法として，Ｔースプライン曲面理論に基づくアイソジオメトリック流体構造連成解析のフレームワークを開発した．この手法は曲面の高次表現に特徴があり，薄い構造の曲げ変形を高精度に計算することができる．管腔構造の生体組織に対し，成長を伴う管壁の構造力学を生体組織の成長理論とキルヒホッフ・ラブシェルを用いて定式化している．現在，この手法を用いて，血管を模擬した管腔構造に対する簡易的なパラメトリック解析を実施している．管腔構造が一次元的，二次元的，三次元的に座屈変形するパターンが得られており，それぞれの座屈変形パターンに至る条件を検討し，メカニズムを明らかにしようとしているところである．

  • 腹部大動脈瘤の拡大速度を規定する病理組織学的因子に関する前向きコホート研究
    濱田 庸, 後藤 均, 赤松 大二朗, 今井 陽介, 菅原 宏文, 権田 幸祐
    日本学術振興会, 科学研究費助成事業, 基盤研究(C), 東北大学, 01 Apr. 2019 - 31 Mar. 2023
    昨年度に報告した通り現状ではコロナウイルス感染拡大により、研究計画遂行に大きな支障が生じている。今年度は遅れを取り戻すべく、昨年度と同様に大動脈瘤の拡大速度を規定する病理組織学的因子を解析するため、大動脈瘤血流シミレーション技術の確立と習得、大動脈瘤症例の瘤径の継時的変化の観察、また、大動脈瘤壁の組織サンプルの蓄積、得た技術をもとにした大動脈瘤破裂症例の血流シミレーション等を行う予定であった。しかしながら、今年度も引き続いてコロナ感染は拡大に歯止めがかからず、数回の波も出現した。研究代表者が所属するのが大規模医療機関である事から、大動脈瘤血流シミレーションソフトを開発する予定であった神戸大学との共同研究が、人的交流を含めて困難である状況は変わっていない。それゆえ、現在に至るまでもシミレーションの基盤を確立する段階に至っていない。オンラインミーティングを活用もしているものの、オンラインではその特性からプライバシーに配慮した患者データのやり取りには限界があり、それを元にしたシミレーションデモは行っているものの、数名程度にとどまっている。また、引き続きコロナウイルス感染症の影響で、そもそも大動脈瘤の新規受診症例が減少していることは変わりなく、また、ICU病床・手術室の利用制限も同様であるため、大動脈瘤手術症例の蓄積を行う事が困難である事にも変わりがない。したがって今年度も研究実績は、残念ながらほぼ得られていない。コロナウイルス感染症は収束の糸口が若干見えてきた感があるが、残りの研究期間を考えると、現時点で当初予定していた研究遂行は非常に困難であると言わざるを得ない。従って、次年度最終年度を迎えるにあたり、研究期間の延長申請を行う事を考えている。

  • Fluid-Structure Interaction Modeling of Heart Valves and Red Blood Cells
    滝沢 研二, 今井 陽介
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Waseda University, 01 Apr. 2018 - 31 Mar. 2023
    心臓弁の開閉に伴い、その内側を流れる赤血球を含む血液は1)流速3 m/sから急激に静止する強い非定常性、2)弁尖同士に挟まれるという 特異性がある。そのため、実験での観測が極めて困難であり、従来の数値計算でも再現できない。従って、弁の開閉やそれに伴う血流動態といった物理の解明には至っていない。本研究では、心臓の弁近傍の血流動態の解明に向け、流体構造連成解析手法を拡張する。具体的には、弁を 含む流体構造連成問題、高速流れ中の赤血球挙動、心臓弁開閉時の赤血球挙動の数値計算手法を順に構築する。統合した手法を用い、赤血球が 弁の開閉時にどのように振る舞うかを詳細に再現することで、血流動態を明らかにする。これにより、心臓弁の機能を損なう疾患の予防・治療 方法に、力学的視点から新たな指針を提示することを目的としている。
    本研究では、心臓弁の開閉が起こるようなトポロジー変化が起きる空間を占める流体を、物体適合格子を用いて計算する手法を構築している。この方法は従来の信頼のある解析手法を損なうことなく同時にトポロジー変化も考慮できる方法で、トポロジー変化に特化した手法に比べ信頼性が高い。この方法による計算から、弁が閉じる際に流速は必ずしも徐々に小さくなるわけではないことが示されており、開閉時に生じる速度境界層を捉えることの重要性などがわかる。この事実から、他手法では議論しにくい開閉近傍の現象解明を数値計算により検証ができるようになっている。また赤血球を含む流体解析は多く場合、その影響度合いの高い毛細血管のような低速の箇所であるが、本研究では速度の高い領域での赤血球挙動を議論するために、Navier-Stokes方程式に基づく流体と赤血球の連成問題について取り組んでいる。

  • An integrated analysis of biomechanics of cytokinesis: in vitro experiment and computer simulation
    Imai Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Challenging Research (Exploratory), Kobe University, 30 Jul. 2020 - 31 Mar. 2022
    In cells, two talins form a homodimer, connecting to each other at the C-terminus dimerization domain. We hypothesized that an alteration in the talin dimer structure changes the dynamics of cytokinesis. To test the hypothesis, we performed a three-dimensional time-lapse imaging of MDA-MB-231 cells, expressing talin-GFP which forms heterodimers with endogenous talin. We show that the cytokinesis orientation was changed to more oblique rather than horizontal by expressing talin-GFP.

  • ニューロンの四つの移動モードの数理・計算モデルの開発
    今井 陽介
    日本学術振興会, 科学研究費助成事業, 新学術領域研究(研究領域提案型), 神戸大学, 01 Apr. 2019 - 31 Mar. 2021
    本研究課題の目的は，大脳新皮質を構成する興奮性ニューロンの四つの移動モードに対する数理モデルを開発し，大脳新皮質の形成過程を数値解析するための基盤技術を構築することである．大脳新皮質のインサイドアウト構造の形成にはリーリンと呼ばれる分子が必要であり，リーリンはニューロンの四つの移動モード全ての制御に関わっていることが分かっている．ここでは，リーリンによる細胞骨格分子，細胞接着分子の制御に着目し，その効果を細胞骨格分子の重合・脱重合速度の変化，あるいは細胞接着分子の結合・離脱速度の変化としてモデル化する．大規模な数値解析によってこれらのパラメータの変化とニューロンの形態・挙動の変化の関係を力学法則に基づき定量的に理解する．ここでは，細胞を一様な非圧縮の粘弾性体と仮定し，細胞外部の粘性流体との流体構造連成問題としてモデル化した．細胞接着分子のリガンドレセプタ結合にはスリップボンドモデルを採用し，モンテカルロ法を用いて計算した．細胞表面にリガンド，細胞外部の足場にレセプタを分布させ，これらの結合による接着力を埋め込み境界法を用いて流体構造連成計算と連立した．ニューロンのモデルにほとんど同じ物性値を設定し，繊維のネットワーク状の足場とロッド状の足場にそれぞれ配置した．繊維のネットワーク状の足場に配置したニューロンは多極性移動でみられるような挙動を示した．一方，ロッド状の足場に配置したニューロンはロコモーションでみられるような挙動を示した．これらの結果から，多極性移動からロコモーションへの移動モードの変化では，細胞接着の足場となる細胞環境の変化が主な要因であり，細胞の力学特性や生化学特性の変化は二次的な効果となる可能性が示唆された．

  • Development of computational biomechanics of the gastrointestinal system
    Imai Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), 01 Apr. 2017 - 31 Mar. 2021
    We developed a numerical model of gastric flow using computational fluid dynamics, medical imaging, and electrophysiology. We showed that impaired coordination between antral contraction and pyloric closure can result in delayed gastric emptying and bile reflux. We also found that slow wave velocity changed with interstitial cells of Cajal loss and aging, resulting in changes in emptying rate.

  • Upgrading Microbial Biomechanics
    Ishikawa Takuji
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Tohoku University, 01 Apr. 2017 - 31 Mar. 2021
    By using an original method that carefully builds up physical laws from the nanoscale to the macroscale, we have clarified the behavior and biological functions of sperm, microalgae, ciliates, E. coli, yeast, and other organisms under mechanical environments. We succeeded in analyzing through the scale hierarchy from the movement of ciliary axonemes driven by molecular motors, synchronization of flagellar movement, swimming and biological responses of ciliates with many flagella, two-body interactions and cooperative swimming, rheology and diffusion properties as a continuum, cell growth and accumulation, and so on. These results were published in a total of 48 peer-reviewed journal articles, including two in PNAS, one in Science Adv, and six in J Fluid Mech. In addition, 8 press releases were issued to widely publicize the research results.

  • Physiological fluid mechanics of intestine
    Imai Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Challenging Research (Exploratory), Kobe University, 29 Jun. 2018 - 31 Mar. 2020
    We have developed a numerical model of “Rectosigmoid brake”. We constructed a geometry model of the large intestine based on medical imaging data. We gave retrograde waves to the geometry model, where the waves initiated at the rectosigmoid, and travelled along the sigmoid colon. We applied the cumulant lattice Boltzmann method and the adaptive subdomain method for computational fluid dynamics simulation. We showed that pressure at the rectum was decreased by the retrograde waves.

  • The recurrent laryngeal nerve search system to detect nerve saltatory conduction by magnetic stimulation in esophageal cancer surgery
    SHIMIZU Kazuo
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Tohoku University, 01 Apr. 2016 - 31 Mar. 2019
    A reliable method is required for the search of recurrent laryngeal nerve during esophagectomy. We found the following new findings using the sciatic nerve of the small animals such as rat and rabitt. First, the occurrence interval of saltatory conduction is about 45 mm. Second, it is possible to distinguish conduction between nerve or other tissue by performing continuous pulse stimulation using the firing characteristics of Na+ channel in the Ranvier's constriction. Unfortunately, even using the lock-in amplifier, it could not detect the firing of the Na+ channel in the Ranvier's constriction by magnetic sensor. In addition, it could not realize the saltatory conduction by continuous pulse stimulation using magnetism. However, a new finding was obtained that the saltatory conduction was occurred jumping over several Ranvier's constriction.

  • Advances in cell suspension mechanics based on the hierarchy structure
    Ishikawa Takuji
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Tohoku University, 01 Apr. 2014 - 31 Mar. 2017
    In this project, we have succeeded to construct a world leading ‘cell suspension mechanics based on the hierarchy structure’ by combining experiment, theory and numerical simulation. We have clarified many phenomena from nano to macro scale using various cells such as algae, bacteria and blood. Then, the obtained knowledge was utilized to develop devices for engineering and biomedical use. The results have been published as 30 peer review journal papers.

  • Integrated nano-biomechanics
    YAMAGUCHI Takami, ISHIKAWA Takuji, UENO Hironori, MIZUNO Fumio, OMORI Toshihiro, MATSUKI Noriaki, TANAKA Tetsu, SHIMOGONYA Yuji, NIX Stephanie, NUMAYAMA Keiko, IMAI Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Specially Promoted Research, Tohoku University, 2013 - 2017
    We have established integrated nano-biomechanics by modeling multi-scale physical and biomedical phenomena from the molecular level. By using the established model, we succeeded to numerically simulate various diseases, such as an infectious disease, and developed novel methodologies for medical diagnosis and treatments based on quantitative predictions. Besides, we developed biochips to separate or detect cancer cells and bacteria. These findings have been published as 50 peer reviewed journal papers.

  • 実験的に抽出された分子反応パラメータを導入したマラリア感染赤血球モデルの開発
    今井 陽介
    日本学術振興会, 科学研究費助成事業, 新学術領域研究(研究領域提案型), 東北大学, 01 Apr. 2014 - 31 Mar. 2016
    マラリアに感染した赤血球は膜表面に接着タンパクを発現する．この分子反応の発現によりマラリア感染赤血球は微小血管内に接着し，周囲の赤血球を巻き込んだ組織レベルの微小循環障害を引き起こす． 細胞の力学と生化学を連立する計算力学モデルを開発し，接着分子の生化学特性とマラリア感染赤血球挙動の関係に対する大規模パラメトリック計算を実施した．まず単体のマラリア感染赤血球挙動の計算を実施し，次に，多数の正常赤血球と相互作用する微小循環内の挙動を計算することで総合的に検討を行った．血管内皮細胞上にTSPやCD36がレセプタとして存在している場合，マラリア感染赤血球は定常接着をすると報告されているが，このような定常接着は離脱頻度が1/s以下の場合に生じることを明らかにした．またレセプタとしてICAM-1が存在する場合，マラリア感染赤血球は回転運動をすることが知られているが，ICAM-1は結合に作用する力にほとんど依存しない結合特性を有することを明らかにした． また，開発した計算力学モデルをより一般的なカプセル懸濁液のレオロジー解析や白血球・腫瘍細胞の流動・接着の問題に応用した．マラリアと同様，白血球の接着は生体防御において，腫瘍細胞の接着はがん転移において重要な過程であり，古くから血管壁面の「Rolling」や定常接着が調べられてきた．我々はセレクチンを発現した毛細血管内の細胞挙動を計算し，毛細血管径が細胞径より小さくなると，細胞は管の中央を移動する「Bullet」挙動を示すことを明らかにした．このときリガンド‐レセプタ結合によって細胞の移動速度は著しく減少し，レセプタ密度が十分低い領域においても定常接着とみなせるような速度となることを示した．

  • A numerical study of functional dyspepsia
    Imai Yohsuke, MIYAGAWA Taimei
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Challenging Exploratory Research, Tohoku University, 01 Apr. 2014 - 31 Mar. 2016
    To understand the relationship between the peristaltic contraction and the flow in the stomach, we have developed a numerical model of gastric flow. This model is based on a multi-phase flow modeling, an anatomically realistic geometry of the stomach, and a parametric model of peristaltic contractions. Antral recirculation is generated in the stomach. Our result shows that when peristaltic wave velocity increases, the strength of antral recirculation increases, resulting in enhancement of gastric mixing. We also show that mixing strength per one contraction becomes lower when the initiation period of peristaltic contractions is shorter.

  • Computational biomechanics of interactions between cells and their environment in microcirculation
    IMAI Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (A), Tohoku University, 01 Apr. 2012 - 31 Mar. 2015
    We developed a graphics processing unit computing method for simulating cellular flows in microcirculation. Fluid mechanics of plasma and cytoplasm is coupled with solid mechanics of membrane, and ligand-receptor bindings for cell adhesion. We quantified the deformation of red blood cells and the rheology of red blood cell suspension. We also analyzed margination, rolling motion and firm adhesion of white blood cells and circulating tumor cells in microcirculatory blood flows.

  • 生体流れに関わる疾患の診断・治療・予防のための計算ナノバイオメカニクスの新展開
    山口 隆美, 大森 俊宏, 沼山 恵子, 今井 陽介, 上野 裕則
    日本学術振興会, 科学研究費助成事業, 基盤研究(S), 東北大学, 31 May 2011 - 31 Mar. 2014
    平成25年度（平成25年4月1日～平成25年4月25日）の研究内容は，細胞スケールにおける生体力学および分子生物学の融合を目指したシミュレーション技術の開発であり，主な成果は以下のとおりである． (1) 平成24年度に開発した細胞の接着に関連するligand-receptor結合の計算力学モデルについて，これを格子ボルツマン法と有限要素法に基づく流体－膜連成計算手法へと導入し，血小板血栓形成，マラリア感染赤血球の血管内皮細胞上の回転運動，がん細胞の血管内皮細胞への接着を対象としたシミュレーション手法の開発に着手した． (2) 平成24年度にクライオ電子線トモグラフィー法を用いて解明した気管繊毛の三次元内部構造を考慮し，ダイニン分子の滑り運動に由来する個々の気管繊毛の運動と，これによって駆動される周囲の流れ場の連成シミュレーション手法の開発に着手した． (3) 平成24年度までに赤血球の希薄・準希薄懸濁液を対象として，境界要素法と有限要素法に基づく流体－膜連成計算手法を開発し，循環器のマクロスケールの解析で必要となる粒子応力テンソル，自己拡散テンソルを算出している．これを赤血球濃厚懸濁液へと拡張するため，細胞濃厚懸濁液を対象とした大規模GPUシミュレーション手法の開発に着手した． (4) 平成24年度に開発した実形状の胃に対する液体食物流動（食物攪拌）の計算力学モデルについて，これを相の異なる液体や固体運動を連成する手法へと改良し，様々な食物および胃液などの流動を解析するための計算力学モデルの開発に着手した．

  • Large-scale simulations for gas-liquid two-phase flow-structure interaction using GPU supercomputer
    AOKI Takayuki, KOBAYASHI Hiromichi, IMAI Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Tokyo Institute of Technology, 01 Apr. 2011 - 31 Mar. 2014
    In spite of unknown complex dynamics of two-phase flows including gas-liquid interfaces, it is hard to study them with high spatial resolution by numerical computation due to quit less efficiency of parallel computing. By using a large number of GPUs equipped with high computational performance, we have developed a numerical simulator of gas-liquid two-phase flows with high resolution by introducing a new CLSVOF (Coupled Level Set with Volume of Fluid) method, a Pressure Poisson solver of Multi-grid preconditioned BiCGSTAB and IBM (Immersed Boundary Method). In order to get high parallel scalability, an overlapping technique between computation and communication is indispensable.

  • Development of computational biomechanics of gastric mixing
    IMAI Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (B), Tohoku University, 2008 - 2010
    We developed a computational fluid dynamics model of gastric mixing. Moving wall condition of antral contraction wave and free-surface condition of gastric gas were given as boundary conditions of the numerical model. We investigated the effects of physiological conditions such as the viscosity and volume of food bolus and the antral contraction wave pattern on the mixing efficiency and fluid stress in the stomach.

  • Computational nano-biomechanics for the diagnosis, treatment, and prevention of diseases of blood, circulatory, and digestive organs
    YAMAGUCHI Takami, ISHIKAWA Takuji, IMAI Yohsuke, MORI Daisuke, MATSUKI Noriaki, MIZUNO Fumio
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (S), Tohoku University, 2007 - 2010
    We have developed computational nano-biomechanics for the diagnosis, treatment, and prevention of diseases of blood, circulatory, and digestive organs. We proposed a novel hemodynamic index to predict the initiation of cerebral aneurysms. A numerical model of microvascular blood flow was developed for simulating microvascular occlusion in malaria infection, and thrombogenesis. A model of swimming microorganisms was also developed for analyzing intestinal flora.

  • Development of Multi-Purpose CFD Core using Multi-Moment Scheme
    AOKI Takayuki, UTSUMI Takayuki, IMAI Yohsuke, KOBAYASHI Hiromichi
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Tokyo Institute of Technology, 2007 - 2009
    次世代の流体解析(CFD)において、流体方程式を格子点上の値、線積分平均値、面積分、体積積分平均値を従属変数として解く多モーメント手法が高精度かつ安定な計算を行うために有効である。直交格子に適合細分化格子法を導入することで解像度制御を行い、保存形IDO法による圧縮性流体計算、非圧縮性流体計算、乱流計算、多相流計算などの様々な流体問題に適用できる高性能な計算コアを開発する。

  • 消化管内容物輸送シミュレータによる消化器系疾患の病態生理研究
    今井 陽介
    日本学術振興会, 科学研究費助成事業, 若手研究(スタートアップ), 東北大学, 2006 - 2007
    消化管内ガス,食塊,消化液の混相流問題では,領域によって解像するべき流れのスケールが大きく異なる.例えば気相・液相の界面において適切な格子サイズを用いなければ,界面近傍の解が拡散的になる.さらに蠕動運動によって生じる胃壁の移動境界や将来的に導入する食塊の粒子成分の近傍などにおいても同様に,局所的に高解像度の格子が要求される.任意領域の格子解像度を局所的に変化させるAdaptive Mesh Refinement(AMR)法はこのための有望な解決法であるが,粗い格子と細かい格子の境界において流体変数の補間や非等間隔の離散化が必要となるため,2次精度までの手法しか報告されていなかった.Interpolated Differential Operator(IDO)法を適用し,3次元Navier-Stokes方程式に対して4次精度の定式化を行い,医用画像ベースの生体内流動問題に適用し,本手法によって高精度なマルチスケール解析が可能であることを確認した.AMR法を用いた場合,非圧縮性流体の半陰的解法に必要となる圧力のPoisson方程式の係数行列が著しく不規則になるため収束性が悪化する.IDO法の係数行列は非対称な疎行列であるが,従来の差分法と同様,Algebraic Multi-grid(AMG)法を適用することでこれを改善できることを確認した.胃内部の食塊流動問題へ適用するための界面追跡および捕獲法として,Constrained Interpolated Profile-Conservative Semi-Lagrangian3(CIP-CSL3)法およびTangent of Hyperbola for Interface Capturing(THINC)法をIDO法に適合させた,Semi-Lagrange法であるこれらの手法をEuler法として定式化し,記述が簡易になる一方で従来の方法と同等または優れた界面捕獲法となりえることを確認した.2次元の胃内部食塊流動問題に適用し,消化管内ガスの影響に関する基礎的知見を得た.

  • Mechanism of the formation, destruction, and movement of thrombi responsible for ischemia of vital organs
    YAMAGUCHI Takami, WADA Shigeo, TSUBOTA Ken-ichi, ISHIKAWA Takuji, IMAI Yohsuke
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Tohoku University, 2004 - 2006
    We investigated multi-scale behaviors of the formation, destruction, and movement of thrombi under blood flow that are responsible for ischemia of vital organs by using computer simulation and in vitro experiments based on biomechanics. We carried out computer simulations based on a Stokesian Dynamics method and a particle method to characterize the relationships between physiological and fluid mechanical factors in platelet aggregation under blood flow. We determined the relationships between deformation of red blood cells and apparent blood flow resistance. The result indicated that interactions among blood cells play a pivotal role in blood flow properties. It was also shown that biological/mechanical interactions among different types of blood cells determine thrombogenesis process. We established an in vitro quantitative measurement of blood flow through micro channel with micro PIV system, and obtained a spatiotemporal velocity fluctuation in blood flow that depends on hemaetocrit values. This indicated that mechanical interaction among blood cells governs blood flow properties. We proposed a large-scale computer simulation model of flow of red blood cells with the Earth Simulator, and established mathematical formulae of blood flow that can explain hierarchical mechanical behaviors of blood flows from the scale of blood cells (jam) to large vessel (cm). We also developed an integrated computer model of the left ventricle and the aorta, and demonstrated that the model is practically useful in detailed evaluation of the vortex and stagnation, which greatly affects thrombogenesis, in heart and large arteries.

  • Study on Mechanisms of the Development of Cardiovascular and Cerebrovascular Diseases
    YAMAGUCHI Takami, ISHIKAWA Takuji, TSUBOTA Ken-ichi, IMAI Yohsuke, WADA Shigeo
    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research on Priority Areas, Tohoku University, 2003 - 2006
    Human cardiovascular system is always under the integrated nervous and Humoral control of the whole body, i.e., in homeostasis. Multiple feedback mechanisms with mutual interactions among systems, organs, and even tissues provide integrated control of the entire body. These control mechanisms have different spatial coverage, from the micro- to macroscale, and different time constants, from nanoseconds to decades. Based on this consideration, we investigated the cardiovascular system over micro to macro levels by using conjugated computational mechanics analyzing fluid and solid interactions in the research project. We studied blood flow in the aorta with beating left ventricle as a power source, ATP transport in a cerebral artery with aneurysm, the progress of cerebral aneurysm due to adaptation of arterial wall, the blood flow considering more than 16 thousands of red blood cells' motion, and platelets aggregation in blood flow using a particle method developed for the purpose. The aortic blood flow showed independence from the intraventricular vortices formation downstream from the aortic arch, where the three dimensional configuration of the aorta determined the global flow structure. Transport and distribution of ATP molecule was found to be strongly dependent on the relative position of aneurysms to the mother arteries. The particle method developed in the present study showed its potential to represent the microscale aggregation process of the platelet in the blood flow. In considering clinical applications, however, one needs to include more about biological complexities in the analysis of blood flow, especially with respect to disease processes. A disease is not just a failure of machine. It is an outcome of complex interactions among multi-layered systems and subsystems. We expect that biological phenomena, including disease processes, will be clarified in the future by integrating new understandings of macroscale and microscale hemodynamics.

■ Industrial Property Rights
  • 数値計算方法，プログラムおよび記録媒体
    青木尊之, 今井陽介
    特願2005-142404, 16 May 2005, 国立大学法人東京工業大学, 特開2006-318355, 24 Nov. 2006
    Patent right

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