池尾 直子 | ![]() |
イケオ ナオコ | |
大学院工学研究科 機械工学専攻 | |
助教 | |
金属工学関係 |
2020年01月 日本マグネシウム協会, 日本マグネシウム協会賞 奨励賞
2018年09月 日本金属学会, 第28回 日本金属学会奨励賞
2017年11月 一般社団法人 軽金属学会, 軽金属女性未来賞
2016年09月 日本金属学会, 第64回 日本金属学会論文賞 受賞者, Solid/Powder Clad Ti-6Al-4V Alloy with Low Young's Modulus and High Toughness Fabricated by Electron Beam Melting
学会誌・学術雑誌による顕彰
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研究論文(学術雑誌)
In this study, a Ti–6Al–4V alloy composite with uniaxial anisotropy and a hierarchical structure is fabricated using electron beam powder bed fusion, one of the additive manufacturing techniques that enable arbitrary fabrication, and subsequent heat treatment. The uniaxial anisotropic deformation behavior and mechanical properties such as Young’s modulus are obtained by introducing a unidirectional honeycomb structure. The main feature of this structure is that the unmelted powder retained in the pores of the honeycomb structure. After appropriate heat treatment at 1020◦C, necks are formed between the powder particles and between the powder particles and the honeycomb wall, enabling a stress transmission through the necks when the composite is loaded. This means that the powder part has been mechanically functionalized by the neck formation. As a result, a plateau region appears in the stress–strain curve. The stress transfer among the powder particles leads to the cooperative deformation of the composites, contributing to the excellent energy absorption capacity. Therefore, it is expected that the composite can be applied to bone plates on uniaxially oriented microstructures such as long bones owing to its excellent energy absorption capacity and low elasticity to unidirectionally suppress stress shielding.
2021年09月, Crystals, 11 (9)[査読有り]
研究論文(学術雑誌)
Metal additive manufacturing is a powerful tool for providing the desired functional performance through a three-dimensional (3D) structural design. Among the material functions, anisotropic mechanical properties are indispensable for enabling the capabilities of structural materials for living tissues. For biomedical materials to replace bone function, it is necessary to provide an anisotropic mechanical property that mimics that of bones. For desired control of the mechanical performance of the materials, we propose a novel 3D puzzle structure with cube-shaped parts comprising 27 (3 × 3 × 3) unit compartments. We designed and fabricated a Co–Cr–Mo composite structure through spatial control of the positional arrangement of powder/solid parts using the laser powder bed fusion (L-PBF) method. The mechanical function of the fabricated structure can be predicted using the rule of mixtures based on the arrangement pattern of each part. The solid parts in the cubic structure were obtained by melting and solidifying the metal powder with a laser, while the powder parts were obtained through the remaining nonmelted powders inside the structure. This is the first report to achieve an innovative material design that can provide an anisotropic Young’s modulus by arranging the powder and solid parts using additive manufacturing technology.
MDPI AG, 2021年08月16日, Crystals, 11 (8), 959 - 959[査読有り]
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研究論文(学術雑誌)
Ti-6Al-4V alloy fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF) techniques have been studied for applications ranging from medicine to aviation. The fabrication technique is often selected based on the part size and fabrication speed, while less attention is paid to the differences in the physicochemical properties. Especially, the relationship between the evolution of α, α’, and β phases in as-grown parts and the fabrication techniques is unclear. This work systematically and quantitatively investigates how L-PBF and EB-PBF and their process parameters affect the phase evolution of Ti-6Al-4V and residual stresses in the final parts. This is the first report demonstrating the correlations among measured parameters, indicating the lattice strain reduces, and c/a increases, shifting from an α’ to α+β or α structure as the crystallite size of the α or α’ phase increases. The experimental results combined with heat-transfer simulation indicate the cooling rate near the β transus temperature dictates the resulting phase characteristics, whereas the residual stress depends on the cooling rate immediately below the solidification temperature. This study provides new insights into the previously unknown differences in the α, α’, and β phase evolution between L-PBF and EB-PBF and their process parameters.
MDPI AG, 2021年07月08日, Crystals, 11 (7), 796 - 796[査読有り]
研究論文(学術雑誌)
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研究論文(学術雑誌)
PURPOSE: Develop a novel biocompatible solid fiducial marker that prevents radiopaque imaging artifacts and also maintains high imaging contrast for kilovoltage X-ray image-guided radiation therapy. METHODS: The fiducial marker was made of pure zinc. An in-house water-equivalent phantom was designed to evaluate artifacts and visibility under various simulated treatment scenarios. Image artifacts were quantitatively assessed in terms of the metal artifact index (MAI) on kilovoltage computed tomography (CT) and cone-beam CT (CBCT) scans. Marker visibility was evaluated on two types of kilovoltage planar X-ray images in terms of the contrast-to-background ratio (CBR). Comparisons with a conventional gold fiducial marker were conducted. RESULTS: Use of a zinc rather than a gold marker mitigates imaging artifacts. The MAI near the zinc marker decreased by 76, 79, and 77 % in CT, and by 77 (81), 74 (80), and 79 (85) % in CBCT full-fan (half-fan) scans, when using one-, two- and three-marker phantom settings, respectively. The high-contrast part of the zinc marker exhibited CBRs above 2.00 for 28/32 exposures under four (lung, tissue, low-density bone, and high-density bone) different simulation scenarios, making its visibility comparable to that of the gold marker (30/32 exposures with CBRs > 2.00). CONCLUSIONS: We developed a biocompatible, artifact-robust, and highly visible solid zinc fiducial marker. Although further evaluation is needed in clinical settings, our findings suggest its feasibility and benefits for kilovoltage X-ray image-guided radiation therapy.
Wiley, 2020年07月22日, Medical Physics, 47 (10), 4703 - 4710, 英語, 国際誌[査読有り]
研究論文(学術雑誌)
PURPOSE: Metallic medical devices are typically constructed from non-bioabsorbable metals that remains in the body and causes considerable complications. Particularly in the urinary tract, calculus, intractable infection, and misdiagnosis as calculus are often caused by non-bioabsorbable metals. Here, we developed a zinc-magnesium alloy as a new bioabsorbable metal and sought to evaluate the bioabsorbable behavior of zinc and zinc-magnesium alloy in a rat bladder implantation model. METHODS: We prepared zinc-magnesium alloy wires with various proportions of magnesium and investigated the strength, shape retention, formability, and absorbability of these novel materials. Then, we implanted zinc and zinc-magnesium alloy rings formed by the wires into rat bladder. Rats were euthanized at the end of the observation period, and the rings were removed for volume evaluation. Extracted bladder tissues were subjected to histological analysis. RESULTS: The strength of the zinc wire was enhanced by more than fourfold upon the addition of magnesium, without loss of ductility. Linear reduction of ring volume in urine was observed based on the concentration of magnesium within the ring. Nearly all rings were covered with a thin layer of calculus. Histological findings of the transected urinary bladder tissues did not differ among groups. CONCLUSIONS: Zinc-magnesium alloy is a promising candidate for use as a bioabsorbable medical device in the urinary tract.
2020年02月28日, World journal of urology, 39 (1), 201 - 208, 英語, 国際誌[査読有り]
研究論文(学術雑誌)
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研究論文(国際会議プロシーディングス)
BACKGROUND: The use of surgical metal clips is crucial for ligating vessels in various operations. The currently available metal clips have several drawbacks; they are permanent and interfere with imaging techniques such as computed tomography (CT) or magnetic resonance (MR) imaging and carry the potential risk of endo-clip migration. We recently developed a novel magnesium (Mg) alloy for biodegradable clips that reduces artifacts on CT imaging. This study aimed to examine the tolerance, biodegradability, and biocompatibility of the Mg alloy clips compared with those of standard titanium (Ti) clips in hepatectomy. METHODS: Thirty Wistar rats were divided into two groups based on the clip used (groups A and B). The vascular pedicle, including hepatic artery, portal vein, bile duct, and hepatic vein of the left lateral lobe, was ligated with the Ti clip in group A or the Mg alloy clip in group B, and then the left lateral lobe was removed. The rats were sacrificed at 1, 4, 12, 24, and 36 weeks after surgery. Clinical and histological evaluations were performed. Absorption rate was calculated by measuring the clip volume. RESULTS: Although the Mg alloy clips showed biodegradability over time, there were no significant differences in the serum concentration of Mg between the two groups. The remaining volume ratio of Mg alloy clips was 95.5, 94.3, 80.0, 36.2, and 16.7% at 1, 4, 12, 24, and 36 weeks, respectively. No side effects occurred. Most of the microscopic changes were similar in both groups. CONCLUSIONS: The new biodegradable Mg alloy clips are safe and feasible in vessel ligation for hepatectomy in a rat model and reduce artifacts in CT imaging compared with the standard Ti clips.
2019年09月09日, BMC surgery, 19 (1), 130 - 130, 英語, 国際誌[査読有り]
研究論文(学術雑誌)
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研究論文(学術雑誌)
The present study was designed to investigate the biodegradation behavior of Mg alloy plates in the maxillofacial region. For in vitro analysis, the plates were immersed in saline solution and simulated body fluid. For in vivo, the plates were implanted into the tibia, head, back, abdominal cavity, and femur and assessed at 1, 2, and 4 weeks after implantation. After implantation, the plate volumes and the formed insoluble salt were measured via micro-computed tomography. SEM/EDX analysis of the insoluble salt and histological analysis of the surrounding tissues were performed. The volume loss of plates in the in vitro groups was higher than that in the in vivo groups. The volume loss was fastest in the abdomen, followed by the head, back, tibia, and femur. There were no statistically significant differences in the insoluble salt volume of the all implanted sites. The corrosion of the Mg alloy will be affected to the surrounding tissue responses. The material for the plate should be selected based on the characteristic that Mg alloys are decomposed relatively easily in the maxillofacial region.
2019年02月, Dental materials journal, 38 (1), 11 - 21, 英語, 国内誌[査読有り]
研究論文(学術雑誌)
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Magnesium (Mg) alloys are considered promising materials for biodegradable medical devices however, the initial effects and distribution of released Mg2+ ions following implantation are unclear. This is addressed in the present study, using two types of Mg alloys implanted into rats. An in vitro immersion test was first carried out to quantify Mg2+ ions released from the alloys at early stages. Based on these data, we performed an in vivo experiment in which large amounts of alloys were subcutaneously implanted into the backs of rats for 1, 5, 10, and 25 h. Mg2+ accumulation in organs was measured by inductively coupled plasma mass spectrometry. In vivo, blood and urine Mg2+ concentrations were higher in rats receiving the implants than in controls after 1 h however, the levels were within clinically accepted guidelines. The Mg2+ concentration in bone was significantly higher in the 25 h implanted group than in the other groups. Our results suggest that homeostasis is maintained by urinary excretion and bone accumulation of released Mg2+ ions in response to sudden changes in Mg2+ ion concentration in the body fluid in a large number of Mg alloy implants at the early stages.
Institute of Physics Publishing, 2018年03月06日, Biomedical Materials (Bristol), 13 (3), 035006, 英語[査読有り]
研究論文(学術雑誌)
A magnesium matrix composite made of Mg-1mass%Ca and 10 vol% hydroxyapatite (HAp) particles was synthesized. The alloy powder was processed by pulverization of the small blocks of the alloy ingot using a high-speed blade grinder. Unreacted composite was successfully produced by extruding the two component powders at a temperature of 538 K. In the extruded compos-ites, the grains of the magnesium matrix were equiaxed and the matrix grain size was 3.9 μm. As for the HAp particles, both thin clustering and severe agglomeration with the size of ~30 μm were observed. The Young's modulus, tensile yield strength and tensile strength of the extruded composite were 39 GPa, 101 MPa and 153 MPa, respectively. The damping capacity of the composite was higher than that of extruded magnesium. The composite also showed good forgeability at a temperature of 523 K. However, quite high impurity contents of Fe (0.130 mass%) and Ni (0.010 mass%) were introduced in the magnesium matrix of the composite, probably as a result of contamination that accumulates during the processing (pulverization) of the alloy powder.
Japan Institute of Metals (JIM), 2018年, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 82 (1), 18 - 24, 日本語[査読有り]
研究論文(学術雑誌)
Equal channel angular extrusion (ECAE) was applied to an extruded Mg-1.0mass%Ca alloy to achieve a high strength and high damping capacity. Microstructure observations revealed that the texture and local misorientation distribution depend on the ECAE temperature. ECAE at a low temperature of 260 degrees C resulted in a high average Schmid factor of basal slip and a high kernel average misorientation in the processed alloy. Consequently, the alloy processed by ECAE showed a high yield strength without sacrificing the damping capacity. (C) 2017 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE BV, 2017年08月, MATERIALS LETTERS, 201, 144 - 147, 英語[査読有り]
研究論文(学術雑誌)
Background. Operative clips used to ligate vessels in abdominal operation usually are made of titanium. They remain in the body permanently and form metallic artifacts in computed tomography images, which impair accurate diagnosis. Although biodegradable magnesium instruments have been developed in other fields, the physical properties necessary for operative clips differ from those of other instruments. We developed a biodegradable magnesium-zinc-calcium alloy clip with good biologic compatibility and enough clamping capability as an operative clip. In this study, we verified the safety and tolerability of this clip for use in canine cholecystectomy. Methods. Nine female beagles were used. We performed cholecystectomy and ligated the cystic duct by magnesium alloy or titanium clips. The chronologic change of clips and artifact formation were compared at 1, 4, 12, 18, and 24 weeks postoperative by computed tomography. The animals were killed at the end of the observation period, and the clips were removed to evaluate their biodegradability. We also evaluated their effect on the living body by blood biochemistry data. Results. The magnesium alloy clip formed much fewer artifacts than the titanium clip, and it was almost absorbed at 6 months postoperative. There were no postoperative complications and no elevation of constituent elements such as magnesium, calcium, and zinc during the observation period in both groups. Conclusion. The novel magnesium alloy clip demonstrated sufficient sealing capability for the cystic duct and proper biodegradability in canine models. The magnesium alloy clip revealed much fewer metallic artifacts in GT than the conventional titanium clip.
MOSBY-ELSEVIER, 2017年06月, SURGERY, 161 (6), 1553 - 1560, 英語[査読有り]
研究論文(学術雑誌)
Recently, biodegradable bone fixation devices have been demanded when considering the patient's quality of life (QOL). During the fracture healing, the devices must support the repeated load due to daily performance. At the same time, surface of the magnesium devices was affected by body fluid. Thus in this research, in vitro fatigue properties of biodegradable Mg-0.3at.% Ca alloy was evaluated by using simulated body fluid. Though there was fatigue limit when the test was conducted under the ambient condition, it cannot be confirmed during the test in the simulated body fluid. Inspection of fracture surface revealed that crack propagated along the grain boundary after both the fatigue tests.
SPRINGER INTERNATIONAL PUBLISHING AG, 2017年, Magnesium Technology 2017, 533 - 535, 英語[査読有り]
研究論文(国際会議プロシーディングス)
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研究論文(学術雑誌)
Biodegradable magnesium (Mg) alloys are the most promising candidates for osteosynthesis devices. However, their in vivo corrosion behaviour has not been fully elucidated. The aim of this study was to clarify the influence of the physiological environment surrounding Mg alloys on their corrosion behaviour. A Mg-1.0Al alloy with a fine-grained structure was formed into plates using titanium (Ti) as a control. These plates were implanted into the subperiosteum in the head, subcutaneous tissue of the back, and in the muscle of the femur of rats for 1, 2 and 4 weeks. The volumes of the remaining Mg alloy and of the insoluble salt deposition and gas cavities around the Mg alloy were determined by microtomography, and the volume losses were calculated. Then, the tissue response around the plates in each implantation site was examined histopathologically, and its relation to the respective volume loss was analyzed. These analyses determined that the Mg alloy was corroded fastest in the head, at an intermediate level in the back, and slowest in the femur. The insoluble salt deposition at the Mg alloy surface had no influence on the volume loss. Gas cavities formed around the Mg alloy at all implantation sites and decreased after 4 weeks. Histopathological examination revealed that the Mg alloy exhibited good biocompatibility, as was seen with Ti. In addition, vascularized fibrous capsules formed around the plates and became mature with time. Notably, the volume loss in the different anatomical locations correlated with capsule thickness. Together, our results suggest that, to facilitate the successful clinical application of Mg alloys, it will be necessary to further comprehend their interactions with specific in vivo environments.
IOP PUBLISHING LTD, 2016年04月, BIOMEDICAL MATERIALS, 11 (2), 英語[査読有り]
研究論文(学術雑誌)
We measured the impact toughness of three alloys (Mg, Mg-0.3 at%Ca-0.6 at%Zn, and Mg-0.3 at%Ca-0.6 at %Al) by the impact three-point bending test The plastic deformability and impact toughness were higher in the ternary alloys than in pure Mg. The generalized stacking fault energy and grain boundary cohesive energy were estimated by first-principles calculations for Mg, binary Mg-Ca, ternary Mg-Ca-Zn, and ternary Mg-Ca-Al alloys. The calculation results agreed with the trend in the experimental results. We suggest that addition of Ca along with Zn or Al reduced plastic anisotropy and strengthened the grain boundaries, leading to higher in impact toughness of Mg alloys. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
PERGAMON-ELSEVIER SCIENCE LTD, 2016年02月, Acta Materialia, 104, 283 - 294, 英語[査読有り]
研究論文(学術雑誌)
To develop a biodegradable clip, the equivalent plastic strain distribution during occlusion was evaluated by the finite element analysis (FEA) using the material data of pure Mg. Since the PEA suggested that a maximum plastic strain of 0.40 is required to allow the Mg clips, the alloying of magnesium with essential elements and the control of microstructure by hot extrusion and annealing were conducted. Mechanical characterization revealed that the Mg-Zn-Ca alloy obtained by double extrusion followed by annealing at 673 K for 2 h possessed a fracture strain over 0.40. The biocompatibility of the alloy was confirmed here by investigating its degradation behavior and the response of extraperitoneal tissue around the Mg-Zn-Ca alloy. Small gas cavity due to degradation was observed following implantation of the developed Mg-Zn-Ca clip by in vivo micro-CT. Histological analysis, minimal observed inflammation, and an only small decrease in the volume of the implanted Mg-Zn-Ca clip confirmed its excellent biocompatibility. FEA using the material data for ductile Mg-Zn-Ca also showed that the clip could occlude the simulated vessel without fracture. In addition, the Mg-Zn-Ca alloy clip successfully occluded the renal vein. Microstructural observations using electron backscattering diffraction confirmed that dynamic recovery occurred during the later stage of plastic deformation of the ductile Mg-Zn-Ca alloy. These results suggest that the developed Mg-Zn-Ca alloy is a suitable material for biodegradable clips. Statement of significance Since conventional magnesium alloys have not exhibited significant ductility for applying the occlusion of vessels, the alloying of magnesium with essential elements and the control of microstructure by hot extrusion and annealing were conducted. Mechanical characterization revealed that the Mg-Zn-Ca alloy obtained by double extrusion followed by annealing at 673 K for 2 h possessed a fracture strain over 0.40. The biocompatibility of the alloy was confirmed by investigating its degradation behavior and the response of extraperitoneal tissue around the Mg-Zn-Ca alloy. Finite element analysis using the material data for the ductile Mg-Zn-Ca alloy also showed that the clip could occlude the simulated vessel without fracture. In addition, the Mg-Zn-Ca alloy clip successfully occluded the renal vein. Microstructural observations using electron backscattering diffraction confirmed that dynamic recovery occurred during the later stage of plastic deformation of the ductile Mg-Zn-Ca alloy. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
ELSEVIER SCI LTD, 2016年01月, ACTA BIOMATERIALIA, 29, 468 - 476, 英語[査読有り]
研究論文(学術雑誌)
Today, stent is employed to expand the narrowed tubular organ such as blood vessel, esophagus and bile duct. The major of materials used for the stent is stainless steel or Ni-Ti alloy which remains in the body permanently and prevents the second application. Accordingly, this research targets on developing the biodegradable magnesium stent. Magnesium is, however, inferior to the conventional materials in mechanical properties. Therefore, it is required to improve the mechanical properties of magnesium and design the stent considering poverty of strength and ductility. To improve the mechanical properties, strengthening by solid solution due to adding Zn and Ca and by grain refining due to doubly hot extrusion were conducted. As a result, the extruded Mg-Ca-Zn alloy showed the superior mechanical properties compared with the conventional magnesium alloys. Furthermore, finite element analysis (FEA) based on the material data was conducted to investigate mechanical performance of a stent model. As a result of the FEA, it was indicated that Mg alloy stent has sufficient ductility for expansion and strength for restenosis. Examination for expanding a fabricated stent revealed that the FEA was reasonable and the present alloy was a good candidate for the stent application.
Japan Institute of Light Metals, 2016年, Keikinzoku/Journal of Japan Institute of Light Metals, 66 (6), 312 - 317, 日本語[査読有り]
研究論文(学術雑誌)
Mechanical properties of magnesium alloys under dynamic loading are still unclear. To evaluate the impact fracture behavior of magnesium alloys, we constructed a novel impact three-point bending test apparatus using three elastic bars with Charpy standard-size specimen, and investigated the impact fracture properties of as-cast Mg-3%Al-1%Zn (hereafter denoted as AZ31) alloy. Finite element (FE) analysis were carried out to estimate the effect of inertial force of the specimen during the impact three-point bending. Based on the FE analysis, we successfully developed a small-scale apparatus for examining a quarter-size specimen, which was capable of carrying out the impact three-point bending test with minimized influence of the inertial force. Impact fracture behavior of Mg-6%Al-1%Zn-2%Ca (hereafter denoted as AZX612) alloy was estimated and compared by using small-scale apparatus. The experimental results pointed out that the AZX612 had had similar energy absorption capability to AZ31 against the dynamic loading, however, the crack propagation speed of the Ca bearing alloy was almost twice as fast as that of the AZ31 alloy.
Japan Institute of Light Metals, 2016年, Keikinzoku/Journal of Japan Institute of Light Metals, 66 (5), 258 - 265, 日本語[査読有り]
研究論文(学術雑誌)
Superplastic deformation behavior was investigated for a dual-phase Mg-Ca alloy. The elongation-to-failure reached more than 120% with the strain rate sensitivity, m, over 0.4. The activation energy required for the deformation was estimated to be 98 kJ/mol which is close to the activation energy for grain boundary diffusion in magnesium. Therefore, the superplastic deformation mechanism was suggested to be the grain boundary sliding, which is controlled by boundary diffusion.
Trans Tech Publications Ltd, 2016年, Materials Science Forum, 838-839, 256 - 260, 英語[査読有り]
研究論文(国際会議プロシーディングス)
The magnesium composites containing hydroxyapatite (HA) particles were synthesized. Unreacted Mg/HA composites were successfully fabricated by extruding the two component powders. The Young's modulus and strength of the extruded composites were lower than that of extruded magnesium, whereas the damping capacity of the composite was superior to that of extruded magnesium over the entire strain range examined. Microstructural observation of the composite containing 10 vol%HA revealed that HA agglomerates with the size of 10-15 μm were formed during the fabrication. The mechanical properties of the composites were closely associated with the HA agglomeration.
Japan Institute of Light Metals, 2016年, 軽金属, 66 (6), 318 - 323, 日本語[査読有り]
研究論文(学術雑誌)
Mechanical properties of magnesium alloys under dynamic loading are still unclear. To evaluate the impact fracture behavior of magnesium alloys, we constructed a novel impact three-point bending test apparatus using three elastic bars with Charpy standard-size specimen, and investigated the impact fracture properties of as-cast Mg-3Al-1Zn (hereafter denoted as AZ31) alloy. Finite element (FE) analysis were carried out to estimate the effect of inertial force of the specimen during the impact three-point bending. Based on the FE analysis, we successfully developed a small-scale apparatus for examining a quarter-size specimen, which was capable of carrying out the impact three-point bending test with minimized influence of the inertial force. Impact fracture behavior of Mg-6Al-1Zn-2Ca (hereafter denoted as AZX612) alloy was estimated and compared by using small-scale apparatus. The experimental results pointed out that the AZX612 had similar energy absorption capability to AZ31 against the dynamic loading, however, the crack propagation speed of the Ca bearing alloy was almost twice as fast as that of the AZ31 alloy.
JAPAN INST METALS, 2016年, MATERIALS TRANSACTIONS, 57 (11), 1872 - 1879, 英語[査読有り]
研究論文(学術雑誌)
Today, there is a demand for bio-stapler which gradually degraded in the body and disappeared after healing from the medical field. Magnesium is noted as the material with biodegradability and biocompatibility. However, compared with the current material, magnesium have too poor mechanical properties to apply to the stapler. Therefore, it is necessary to improve its mechanical properties. It is known that addition of Ca improves the strength and corrosion resistance. To investigate the effect of alloying element on formability of Mg-Ca alloys, the generalized stacking fault energy was estimated by first-principles calculations for binary Mg-Ca, ternary Mg-Ca-Na, ternary Mg-Ca-K and ternary Mg-Ca-Sr alloys. We suggest that addition of Na, K or Sr reduced plastic anisotropy of binary Mg-Ca alloys.
一般社団法人 日本機械学会, 2016年, M&M材料力学カンファレンス, 2016 (0), PS - 41, 日本語[査読有り]
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A clad structure that consists of solid and powder parts was created from powdered Ti-6Al-4V utilizing electron beam melting (EBM) technique by a single process. The input energy density required to melt the raw powder material was controlled by changing the scan speed of the electron beam from 100 to 2000 mm/s. The finished products showed several types of structures: a dense solid, a periodic layered (clad) structure made up of a solid part and an unmelted powder part, and almost full powder. The products with the clad structure showed a combination of low Young's modulus and high toughness as characterized by the presence of a stress plateau in the stress-strain curve. Both of these qualities are necessary for feasibility as implant materials used in orthopedic fields. We conclude that the products developed in this study could be useful as bone implants in terms of the mechanical similarity to bones, despite needing only an single EBM process for fabrication.
JAPAN INST METALS, 2015年, Materials Transactions, 56 (5), 755 - 758, 英語[査読有り]
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Weight reduction is effective for improving fuel efficiency of automobiles. Although magnesium is widely recognized as the lightest structural metal, applications for the automobile are limited because of the relatively low ductility, toughness, impact resistance and fatigue resistance. The aim of this research was to evaluate the impact energy absorption capability of a magnesium alloy pipe by a numerical simulation. First of all, finite element (FE) analysis of impact compression of magnesium alloy pipes was performed to design the shape of anvils for a dynamic compression experiment. The compression tests were conducted at a high strain rate on two Mg alloys, AZ31 and Mg-0.6Y, to examine the deformation response. The load-displacement data obtained were compared with the results of FE analysis to validate the simulation. The FE analysis revealed that the AZ31 pipe fractured at an early stage of deformation, while the Mg-0.6Y pipe fractured at about 90% compressed. As a result, Mg-0.6Y pipe exhibited lower yield strength, but a higher absorption energy capability than AZ31 pipe due to a weakened basal texture.
JAPAN INST METALS, 2014年04月, 日本金属学会誌, 78 (4), 142 - 148, 日本語[査読有り]
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Recently, more attention has been devoted to porous implants to avoid stress-shielding effects and facilitate anchor effects. In addition, our previous research revealed that uniaxially aligned pores promoted early recovery of bone tissue with high bone quality similar to that of intact bone. In this study, Ti-based implant materials with uniaxially aligned pores were fabricated using the electron beam melting (EBM) method with 2 types of grid spacing, 0.5 and 1.0 mm. Although grid spacing was varied, the constituent phase and microstructure of the products were homogenous regardless of the grid spacing. Uniaxially aligned pores were created when the grid spacing was 1.0 mm, whereas almost solid structures with random pores were formed when the grid spacing was 0.5 mm. Young's modulus of the products with the grid spacing of 1.0 mm was 34 GPa this value is close to that of the bone. It is concluded that the porous material with aligned pores is suitable as a bone implant to reduce stress-shielding effects and to induce bone regeneration with good bone quality. © (2012) Trans Tech Publications, Switzerland.
2012年, Advanced Materials Research, 409, 142 - 145, 英語[査読有り]
研究論文(国際会議プロシーディングス)
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研究論文(学術雑誌)
New cylindrical bone implants containing elongated pores interconnected as open pores were fabricated by an electron beam melting (EBM) method using Ti-6mass%Al-4mass%V ELI powder (mean particle diameter, 65 mu m). New bone formation in the elongated pores of the implant and preferential arrangement of biological apatite c-axis were confirmed along the long bone axis by microbeam X-ray diffraction. Bone mass and preferential degree of biological apatite c-axis, which were considered a bone quality parameter, decreased with the distance from the edge of the implant along the longitudinal bone axis because of a stress-shielding effect. Although clear interconnections between new bones appeared through the implant with elongated pores parallel to the bone axis, the defective portion was not covered with new bone in the absence of the new implant.
IRON STEEL INST JAPAN KEIDANREN KAIKAN, 2011年, ISIJ INTERNATIONAL, 51 (2), 262 - 268, 英語[査読有り]
研究論文(学術雑誌)
研究論文(国際会議プロシーディングス)
New cylindrical bone implants containing elongated pores interconnected as open pores were fabricated by an electron beam melting (EBM) method from Ti-6 mass% Al-4 mass% V ELI powders of 65 mu m in mean diameter. New bone formed in the elongated pores of implant and preferential arrangement of biological apatite c-axis were confirmed along the long bone axis by the microbeam X-ray diffraction method. Bone mass and preferential degree of biological apatite c-axis as a bone quality parameter decreased with the distance from the edge of implant along the longitudinal bone axis because of a stress shielding effect. However, clear interconnection of new bone appeared through the implant with elongated pores parallel to the bone axis, while the defected portion was not recovered with new bone without the new implant.
IRON STEEL INST JAPAN KEIDANREN KAIKAN, 2010年09月, TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN, 96 (9), B42 - B48, 日本語[査読有り]
研究論文(学術雑誌)
Our group focused on the preferential degree of biological apatite (BAp) c-axis, an important bone quality parameter based on the microstructural anisotropy in intact, pathological, and regenerated bones. The preferential degree of the BAp c-axis strongly depends on the bone position, in vivo stress distribution, bone growth, degree of pathology and regeneration, activity of bone cells, gene defect, etc. We attempted to challenge clarification of the BAp preferential alignment formation mechanism and control the degree of BAp orientation by using an anisotropic biomaterial design to develop suitable distribution of the BAp c-axis orientation.
TRANS TECH PUBLICATIONS LTD, 2010年, PRICM 7, PTS 1-3, 654-656, 2212 - +, 英語[査読有り]
研究論文(国際会議プロシーディングス)
チタン製インプラントの創製を目指し、新規積層造形法を利用したポーラス材料の開発および力学機能制御因子の解明を試みた。
大阪工研協会, 2013年12月, 科学と工業 = Science and industry, 87 (12), 428 - 432, 日本語記事・総説・解説・論説等(学術雑誌)
その他
Bone tissue is predominantly composed of biological apatite (BAp) crystals and collagen (Col) fibers, which shows hierarchical structure at various scale levels. Therefore, to design and develop implants suitable for bone replacement, both bone mineral density (BMD) and bone anisotropic microstructure should be investigated. From the viewpoint of materials scientific study, the bone microstructure based on the orientation degree of BAp c-axis which is dependent upon the bone portion, turnover, cell arrangement, etc., was clarified in intact, pathological and regenerated bones. For the analysis of BAp orientation, the microbeam X-ray diffraction method is quite effective on the basis of crystallography of anisotropic hexagonal BAp crystal. Moreover, this method is applicable even to a small region of several 10 μm or more on a side. Therefore, advanced design of implants for bone replacement should take into account anisotropic bone microstructure containing preferential alignment of BAp/Col.
Springer Japan, 2013年01月01日, Progress in Advanced Structural and Functional Materials Design, 155 - 167, 英語The present work was aimed at understanding the stress shielding caused by hip joint implantation into a femur by using a human cadaver with a cementless hip implant. In particular, bone quality was assessed from the standpoint of preferential c axis orientation of biological apatite (BAp). Comparing the implanted side to the non implanted side, a finite element analysis (PEA) indicated that artificial hip joint implantation had a significant stress shielding on the femur. The results also showed a remarkable decrease in the degree of preferential BAp orientation as well as bone loss in Haversial canal in the medial proximal femur. This is the first report showing a reduction in the degree of preferential BAp orientation due to a stress shielding after artificial hip joint implantation. Since preferential BAp orientation is an important parameter for determining bone mechanical function, these findings should be taken into account in future artificial hip joint designs, especially those involving the stem component.
JAPAN INST METALS, 2012年07月, JOURNAL OF THE JAPAN INSTITUTE OF METALS, 76 (7), 468 - 473, 日本語その他
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