What's New
2017（July－December）
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2017.12.28
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2017.12.22
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2017.12.17
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2017.12.17
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2017.12.1
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2017.12.1
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2017.11.22
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2017.11.14
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2017.10.20
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2017.10.19
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2017.10.18
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2017.9.8
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2017.8.30
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2017.8.15
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2017.8.14
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2017.8.5
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2017.8.4
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2017.8.4
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2017.8.1
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2017.7.29
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2017.7.20
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2017.7.3
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2017.7.3
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2017.7.3
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2017.12.28
A paper demonstrating that osteoblasts differentiated from iPS cells can form oriented tissues has been published in the Journal of Biomedical Materials Research: Part A as an open access journal.
Ryosuke Ozasa, Aira Matsugaki, Yoshihiro Isobe, Taro Saku, Yun Hui-suk, Takayoshi Nakano*:
Construction of human induced pluripotent stem cell-derived oriented bone matrix microstructure by using in vitro engineered anisotropic culture model,
Journal of Biomedical Materials Research: Part A, 106 (2018), pp.360-369.
DOI: 10.1002/jbm.a.36238Abstract
Bone tissue has anisotropic microstructure based on collagen/biological apatite orientation, which plays essential roles in the mechanical and biological functions of bone. However, obtaining an appropriate anisotropic microstructure during the bone regeneration process remains a great challenging. A powerful strategy for the control of both differentiation and structural development of newly-formed bone is required in bone tissue engineering, in order to realize functional bone tissue regeneration. In this study, we developed a novel anisotropic culture model by combining human induced pluripotent stem cells (hiPSCs) and artificiallycontrolled oriented collagen scaffold. The oriented collagen scaffold allowed hiPSCs-derived osteoblast alignment and further construction of anisotropic bone matrix which mimics the bone tissue microstructure. To the best of our knowledge, this is the first report showing the construction of bone mimetic anisotropic bone matrix microstructure from hiPSCs. Moreover, we demonstrated for the first time that the hiPSCs-derived osteoblasts possess a high level of intact functionality to regulate cell alignment.Click here for this paper.
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2017.12.22
Our paper on the crystal orientation rotation mechanism in laser beam additive manufacturing of Ni₃Mo has been published in Materials & Design (Elsevier).
Shi-Hai Sun, Koji Hagihara, Takayoshi Nakano:
Effect of scanning strategy on texture formation in Ni-25 at.%Mo alloys fabricated by selective laser melting,
Materials & Design, 140 [15], (2018).Abstract
Variations in the crystallographic texture in Ni-25 at.%Mo alloys fabricated by selective laser melting with different scanning strategies were designed for the first time. Single-crystalline-like texture with a short-range order of Mo atoms can be produced via bidirectional scanning along one axis (X-scan) and bidirectional scanning with a 90° rotation in each layer (XY-scan), while only fiber texture was formed in bidirectional scanning with a 67° rotation (Rot-scan). The aligned crystal orientation along the build direction can be varied by the scanning strategy; 〈001〉 is preferred in the XY- and Rot-scan samples, while 〈101〉 is preferred in the X-scan sample. The controlling mechanisms of the texture, focusing on the preferential growth directions of the columnar cells and the following epitaxial growth, are discussed. -
2017.12.17
A collaborative study between our laboratory and Dr. Ito (Hokkaido Medical Center) and Dr. Hanawa (Tokyo Medical and Dental University), focusing on the methodology to evaluate the integrity of vertebral cages, has been published in the open access journa
Takuya Ishimoto, Katsuhisa Yamada, Hiroyuki Takahashi, Masahiko Takahata, Manabu Ito, Takao Hanawa, Takayoshi Nakano* :
Trabecular health of vertebrae based on anisotropy in trabecular architecture and collagen/apatite micro-arrangement after implantation of intervertebral fusion cages in the sheep spine,
Bone, 108 (2018), pp.25-33.
DOI : doi.org/10/1016/j.bone.2017.12.012abstract
Healthy trabecular bone shows highly anisotropic trabecular architecture and the preferential orientation of collagen and apatite inside a trabecula, both of which are predominantly directed along the cephalocaudal axis. This makes trabecular bone stiff in the principally loaded direction (cephalocaudal axis). However, changes in these anisotropic trabecular characteristics after the insertion of implant devices remain unclear. We defined the trabecular architectural anisotropy and the preferential orientation of collagen and apatite as parameters of trabecular bone health. In the present study, we analyzed these parameters after the implantation of two types of intervertebral fusion cages, open and closed box-type cages, into sheep spines for 2 and 4 months. Alteration and evolution of trabecular health around and inside the cages depended on the cage type and implantation duration. At the boundary region, the values of trabecular architectural anisotropy and apatite orientation for the closed-type cages were similar to those for isotropic conditions. In contrast, significantly larger anisotropy was found for open-type cages, indicating that the open-type cage tended to maintain trabecular anisotropy. Inside the open-type cage, trabecular architectural anisotropy and apatite orientation significantly increased with time after implantation. Assessing trabecular anisotropy might be useful for the evaluation of trabecular health and the validation and refinement of implant designs.
Click here for this paper.
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2017.12.17
Our collaborative research with Nagasaki University and Dentistry on bone quality around dental implants under stress has been published in PLoS ONE as an open access journal.
Yusuke Uto, Shinichiro Kuroshima, Takayoshi Nakano, Takuya Ishimoto, Nao Inaba, Yusuke Uchida, Takashi Sawase:
Effects of mechanical repetitive load on bone quality around implants in rat maxillae,
PLoS ONE 12, (2017), paper No: e0189893.
DOI:10.1371/journal.pone.0189893abstract
Greater understanding and acceptance of the new concept “bone quality”, which was pro-posed by the National Institutes of Health and is based on bone cells and collagen fibers, are required. The novel protein Semaphorin3A (Sema3A) is associated with osteoprotection by regulating bone cells. The aims of this study were to investigate the effects of mechanical loads on Sema3A production and bone quality based on bone cells and collagen fibers around implants in rat maxillae. Grade IV-titanium threaded implants were placed at 4 weeks post-extraction in maxillary first molars. Implants received mechanical loads (10 N, 3 Hz for 1800 cycles, 2 days/week) for 5 weeks from 3 weeks post-implant placement to mini-mize the effects of wound healing processes by implant placement. Bone structures, bone mineral density (BMD), Sema3A production and bone quality based on bone cells and collagen fibers were analyzed using microcomputed tomography, histomorphometry, immuno-histomorphometry, polarized light microscopy and birefringence measurement system inside of the first and second thread (designated as thread A and B, respectively), as mechanical stresses are concentrated and differently distributed on the first two threads from the implant neck. Mechanical load significantly increased BMD, but not bone volume around implants. Inside thread B, but not thread A, mechanical load significantly accelerated Sema3A production with increased number of osteoblasts and osteocytes, and enhanced production of both type I and III collagen. Moreover, mechanical load also significantly
induced preferential alignment of collagen fibers in the lower flank of thread B. These data demonstrate that mechanical load has different effects on Sema3A production and bone quality based on bone cells and collagen fibers between the inside threads of A and B. Mechanical load-induced Sema3A production may be differentially regulated by the type of bone structure or distinct stress distribution, resulting in control of bone quality around implants in jaw bones. -
2017.12.1
Our joint commentary on metal additive manufacturing with Tohoku University was published in the December issue of Matelia (mini-feature article "Frontiers of Ultra-Precision 3D Additive Manufacturing Technology for Metallic Materials").
Yuichiro Koizumi, Akihiko Chiba, Naoyuki Nomura, and Takayoshi Nakano:
Fundamentals of 3D Additive Manufacturing Technology for Metallic Materials,
Matelia, 56 [12], (2017), pp. 686-690.Click here for this PDF.
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2017.12.1
Our laboratory's paper will be published in J. Ipn. Orthop. Assoc.
Takayoshi Nakano, Takuya Ishimoto:
Effect of Mechanical Stress on Bone Matrix Orientation and Its Predictive Potential,
Journal of J. Ipn. Orthop. Assoc., 91 (2017), pp. 959-967. -
2017.11.22
At the 39th Annual Meeting of The Japanese Society for Biomaterials, Mr. Ozasa (D2) won the Journal of Materials Chemistry B Presentation Prize, and Mr. Nakanishi (M1) and Mr. Nagaishi (M1) won the Best Research Poster Award.
Journal of Materials Chemistry B Presentation Prize
〇Ryosuke Ozasa, Aira Matsugaki, Takayoshi Nakano :
Regulation of bone matrix orientation by osteoclastsExcellent Research Poster Award
〇Yohei Nakanishi, Aira Matsugaki, Kosuke Kawahara, Takafumi Ninomiya, Hiroshi Sawada, Takayoshi Nakano :
Orientation mechanism of orthotropic bone matrix by nanoperiodic structure〇Takeru Nagaishi, Ryosuke Ozasa, Machiko Kanzaki, Yasushi Sakata, Eiichi Morii, Toru Kuratani, Takayoshi Nakano :
Site dependence of anisotropic structure of vascular tunica media -
2017.11.14
A commentary written mainly by Mr. Ozasa (D2) will be published in "Kagaku Kogyo".
Ryosuke Ozasa, Takuya Ishimoto, Takayoshi Nakano :
Biofunctionalization of biomaterials from the viewpoint of bone quality,
Chemical Industry, 68 [12], (2017), pp. 891-897. -
2017.10.20
A column about Dr. Nakano appeared in the Nikkan Kogyo Shimbun.
Click here for this column.
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2017.10.19
The results of our collaborative research with Professor Hayashi at Osaka University Graduate School of Dentistry were published in Scientific Reports, a Nature publication.
K. Yagi, H. Yamamoto, R. Uemura, Y. Matsuda, K. Okuyama, T. Ishimoto, T. Nakano, M. Hayashi:
Use of PIXE/PIGE for sequential Ca and F measurements in root carious model, Scientific Reports,7 (2017), srep13450.Abstract
The progress of caries has conventionally been evaluated by checking changes in mineral density using transverse microradiography (TMR). Recent advances have seen development of a new measurement system, using in-air micro proton induced X-ray/gamma-ray emission (PIXE/PIGE). PIXE/PIGE enables analysis of distributions and concentrations of multiple mineral elements in a carious lesion. The aim of this study was to evaluate the effectiveness of PIXE/PIGE for investigating the development of root caries. In summary, we successfully established a multi-elemental sequential measuring method using in-air micro-PIXE/PIGE to identify the dynamic distributions and concentrations of Ca and F in human root dentin. The PIXE/PIGE potentially offers a useful advantageous technique for studying carious development by using as a combination with conventional techniques such as TMR and Micro-computed tomography (µCT).
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2017.10.18
A paper demonstrating that osteoblasts differentiated from iPS cells can form oriented tissues has been published in the Journal of Biomedical Materials Research: Part A as an open access journal.
Ryosuke Ozasa, Aira Matsugaki, Yoshihiro Isobe, Taro Saku, Yun Hui-suk, Takayoshi Nakano*:
Construction of human induced pluripotent stem cell-derived oriented bone matrix microstructure by using in vitro engineered anisotropic culture model,
Journal of Biomedical Materials Research: Part A, (2017), in press.
DOI: 10.1002/jbm.a.36238Abstract
Bone tissue has anisotropic microstructure based on collagen/biological apatite orientation, which plays essential roles in the mechanical and biological functions of bone. However, obtaining an appropriate anisotropic microstructure during the bone regeneration process remains a great challenging. A powerful strategy for the control of both differentiation and structural development of newly-formed bone is required in bone tissue engineering, in order to realize functional bone tissue regeneration. In this study, we developed a novel anisotropic culture model by combining human induced pluripotent stem cells (hiPSCs) and artificiallycontrolled oriented collagen scaffold. The oriented collagen scaffold allowed hiPSCs-derived osteoblast alignment and further construction of anisotropic bone matrix which mimics the bone tissue microstructure. To the best of our knowledge, this is the first report showing the construction of bone mimetic anisotropic bone matrix microstructure from hiPSCs. Moreover, we demonstrated for the first time that the hiPSCs-derived osteoblasts possess a high level of intact functionality to regulate cell alignment.Click here for this paper.
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2017.9.8
At the 161st Annual Meeting of the Japan Institute of Metals, Dr. Matsugaki received The 27th Japan Institute of Metals and Materials Young Researcher Award and our research received The 65th Japan Institute of Metals and Materials The Best Paper Award.
The 27th Japan Institute of Metals and Materials Young Researcher Award
Aira Matsugaki:
Research on the development of biomaterials for the construction of bone microstructures based on metallic materials scienceThe 65th Japan Institute of Metals and Materials The Best Paper Award
〇Aiko Sekita, Aira Matsugaki, Takayoshi Nakano:
Disruption of Collagen Matrix Alignment in Osteolytic Bone Metastasis Induced by Breast Cancer (Materials Transactions, Vol.57, No.12) -
2017.8.30
We succeeded in fabricating epsilon (hcp) single crystals of Co-Cr-Mo alloy for biomedical applications, and our paper on the plastic deformation behavior using the single crystals was published in "Scripta Materialia" as an open access journal.
W. Kaita, K. Hagihara, L.A. Rocha, T. Nakano*:
Plastic deformation mechanisms of biomedical Co–Cr–Mo alloy single crystals with hexagonal close-packed structure,
Scripta Materialia, 142C, (2018), 111-115.abstract
This is the first report of the successful fabrication of Co–Cr–Mo biomedical alloy single crystals with a hexagonal close-packed (hcp) structure and the resultant clarification of its deformation behavior. The (0001)〈11View the MathML source2¯0〉 basal and {1View the MathML source1¯00}〈11View the MathML source2¯0〉 prismatic slip systems were found to be predominately operative. The critical resolved shear stresses for the basal and prismatic slip systems at ambient temperature are ~ 204 and ~ 272 MPa, respectively, which are much higher than ~ 54 MPa for {111}〈11View the MathML source2¯〉 slip in the face-centered cubic (fcc) Co–Cr–Mo phase, quantitatively demonstrating that the hcp phase acts as an effective strengthening phase.Click here for this paper.
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2017.8.15
A paper on the discovery of "dynamic precipitation softening" in the ω-phase of βTi has been published in the journal "Scientific Reports" published by nature.
The ω-phase of βTi is not necessarily hard, and depending on the reaction with dislocations, a completely opposite phenomenon called "dynamic precipitation softening" occurs, which was discovered and named. This research was published in the journal "Scientific Report" published by nature.
However, when the direction of precipitation and the direction of dislocation motion coincide, the precipitation of the ω-phase in βTi, which is brittle but strong, is promoted and the material is simultaneously softened.
K. Hagihara, T. Nakano*, M. Todai:
Unusual dynamic precipitation softening induced by dislocation glide in biomedical beta-titanium alloys,
Scientific Reports, 7 (2017), srep8056.Abstract
Softening of metallic materials containing precipitates during cyclic deformation occurs through dissolution of the precipitates, because the to-and-fro motion of the dislocation causes dissolution of the precipitate particles by cutting them. Here, however, we found the completely opposite phenomenon for the first time; a “dynamic precipitation softening” phenomenon. In a Ti-35Nb-10Ta-5Zr body-centered cubic structured β-Ti alloy single crystal developed for biomedical implant, the to-and-fro motion of the dislocation “induced” the selective precipitation of the ω-phase whose c-axis is parallel to the Burgers vector of the moving dislocation, which led to the significant cyclic softening of the crystal. The formation of the ω-phase is generally believed to induce significant hardening of β-Ti alloys. However, the present results suggest that this is not always true, and control of the anisotropic features of the ω-phase via control of crystal orientation can induce unusual mechanical properties in β-Ti alloys. The unique anisotropic mechanical properties obtained by the cyclic-deformation-induced oriented ω-phase formation could be useful for the development of “single-crystalline β-Ti implant materials” with advanced mechanical performance.
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2017.8.14
Our research on Ag-containing calcium phosphate invert glass has been published in the Journal of Biomedical Materials Research: Part A as an open access journal.
S. Lee T. Nakano T. Kasuga :
Structure, dissolution behavior, cytocompatibility, and antibacterial activity of silver-containing calcium phosphate invert glasses
Journal of Biomedical Materials Research: Part A, (2017)
DOI: doi.org/10.1002/jbm.a.36173Abstract
Novel CaO-P2O5-Nb2O5-Ag2O invert glasses with substitution Ag2O for Nb2O5 were successfully prepared using a melt-quenching method. Ag2O in the glasses act as a network modifier oxide, playing the same role as Na2O, which breaks the phosphate chains. Analysis of the ultraviolet-visible absorption spectra of the glasses showed that the glass matrix contained ionic silver species and silver nanoparticles. Approximately 0.05 mM of Nb5+ ions released from the glasses, which would be expected to stimulate osteoblast differentiation. A glass containing 1 mol% Ag2O showed a linear increase in the releasing amount of Ag+ ions with increasing soaking time, whereas glasses containing 3–5 mol% Ag2O showed Ag+ ion concentrations of around 13 μM at day 3, and then maintained similar values until day 7. When the solution was replaced with fresh solution every 2 days, the Ag+ ion dissolution amounts indicated almost constantly 13 μM due to AgCl formation. There were no differences in the numbers of primary osteoblast cells on silver-free and silver-containing glasses after cultivation for 1–7 days. The silver-containing calcium phosphate invert glasses showed cytocompatibility with simultaneous antibacterial activity to Escherichia coli and Staphylococcus aureus.
Click here for this paper.
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2017.8.5
A paper on EBM in collaboration with Prof. Morita of Kyoto Institute of Technology has been published on-line in Materials Science and Engineering A.
T. Morita, C. Tsuda and T. Nakano:
Influences of scanning speed and short-time heat treatment on fundamental properties of Ti-6Al-4V alloy produced by EBM method, Materials Science and Engineering A, (2017), in press.
DOI: https://doi.org/10.1016/j.msea.2017.08.020Abstract
This study was conducted to examine the influence of the scanning speed of an electron beam on the fundamental properties of Ti-6Al-4V alloy produced by EBM (electron beam melting) method. We further investigated the effect of short-time heat treatment on those properties. By increasing the scanning speed, the desired outer shape was more closely achieved. However, molding defects became larger and the density reduced. On balance, the appropriate range of scanning speed was between 1 and 2 m/s. EBM materials had columnar microstructures elongated in the building direction. Although these characteristic microstructures were mainly composed of the stable α and β phases, the α' phase was partially generated at high scanning speed. By increasing the scanning speed, the amount of the α' phase increased and the hardness rose. The short-time heat treatment generated the fine α' and α phases in the prior β phase. This microstructural change markedly increased the hardness of EBM material.
Click here for this paper.
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2017.8.4
Our paper on the regulation of osteoblast sequencing from young mice has been published in the Journal of the Japan Institute of Metals and Materials.
Ryosuke Ozasa, Aira Matsukaki, Hitohiro Isobe, Taro Saku, Takayoshi Nakano* :
Regulation of young mouse osteoblast alignment by anisotropic collagen substrates,
Journal of the Japan Institute of Metals and Materials (2017)Click here for this paper.
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2017.8.4
A paper on the correlation between bone matrix anisotropy and the vascular network in bone has been published in Materials Transactions as an open access journal.
A. Sekita A. Matsugaki T. Nakano :
Structural Crosstalk between Crystallographic Anisotropy in Bone Tissue and Vascular Network Analyzed with a Novel Visualization Method,
Materials Transactions, Vol.58 [2] (2017) , pp.266-270abstract
Bone tissue has a highly anisotropic microstructure derived from the crystallographic orientation of apatite and the related collagen matrix alignment. Bone is also a highly vascularized tissue; intraosseous vascularization and bone formation are intimately coupled. Meanwhile, the structural relations between intraosseous vascular networks and bone microstructure are as yet unknown, partially due to technical difculties in visualizing precise intraosseous vasculatures. The aim of this study is to develop a visualization method suitable for the structural analysis of intraosseous vascular networks and to reveal the relations between bone microstructure and the arrangement patterns of intraosseous vasculatures. Three-dimensional vascular networks were successfully visualized, and region-dependent arrangement patterns of blood vessels were claried using ‑uorescent dye-conjugated lectin. Interestingly, the anisotropic structural correlation between bone matrix and the vascular system in a region-specic manner was claried. The obtained results indicate the molecular interactions between the vascular system and bone tissue as a novel contributor for realization of anisotropic bone matrix construct.
Click here for this paper.
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2017.8.1
An article on the development of ultra-high temperature resistant materials is published in the column section of Tsukuba Science News.
Click here for this PDF.
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2017.7.29
Dr. Todai delivered a lecture at the Chu-Shikoku Branch Meeting of the Japan Institute of Light Metals, and received the Research and Development Encouragement Award.
July 29 (Sat) The Japan Institute of Light Metals, Chu-Shikoku Section Lecture Meeting
Mitsuyo Todai, Takao Hori, Takeshi Nagase, Koji Hagiwara, Takayoshi Nakano:
Beta-Ti Alloying and Crystal Orientation Control by Laser Additive Manufacturing -
2017.7.20
A paper showing that both bone matrix orientation and mechanical function are reduced in c-src KO mice has been published in Bone.
T. Ishimoto, B. Sato, J. -W. Lee, T. Nakano*:
Co-deteriorations of anisotropic extracellular matrix arrangement and intrinsic mechanical property in c-src deficient osteopetrotic mouse femur,
Bone, 103C (2017), pp.216-223
DOI : //doi.org/10.1016/j.bone.2017.06.023abstract
Osteopetrotic bone shows dissociation between bone mineral density (BMD) and bone strength. In this study, volumetric BMD; preferential orientation of the extracellular matrix (ECM), which is composed of collagen fibers and apatite crystals as bone material quality; and mechanical properties of the src−/− osteopetrotic and normal mouse femoral cortical bone were analyzed and compared with each other at a bone tissue level. The degree of preferential orientation of ECM along the femoral long axis was significantly decreased in the src−/− mice femur, suggesting deteriorated bone quality. Young's modulus, as a tissue-level mechanical property analyzed by nano-indentation technique along the long bone direction, also was decreased in the src−/− mice cortical femur, in spite of the similar volumetric cortical BMD. To the best of our knowledge, this is the first report to demonstrate the synchronous deterioration of Young's modulus and anisotropic ECM organization in the src−/− osteopetrotic mouse bone. These results indicate that the deterioration of the preferential ECM orientation is one major cause of the impaired mechanical property in the src−/− mouse bone.
Click here for this paper.
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2017.7.3
Our paper on unstable β-alloy single crystals has been published online with open access in International Journal of Plasticity.
K. Hagihara, T. Nakano*:
Experimental clarification of the cyclic deformation mechanisms of β-type Ti–Nb–Ta–Zr-alloy single crystals developed for the single-crystalline implant,
International Journal of Plasticity, (2017)
DOI : doi.org/10.1016/j.ijplas.2017.06.006.Abstract
Quaternary Ti-Nb-Ta-Zr (TNTZ) type β-Ti alloys with a body-centered cubic (bcc) structure have been of great interest as new implant biomaterials for bone replacement. Recently, we have proposed a “single crystalline β-Ti implant” as a novel hard-tissue replacement to suppress the stress shielding to bone after healing. To develop this, the fatigue properties and its controlling mechanisms of the TNTZ single crystals must be clarified. In this study, we focused on three alloys: Ti-25Nb-10Ta-5Zr(25Nb), Ti-29Nb-13Ta-4.6Zr(29Nb), and Ti-35Nb-10Ta-5Zr(35Nb) (mass%), and the cyclic deformation behaviors were examined using their single crystals. The shapes of the hysteresis loops were significantly different for these alloys, which was ascribed to the operation of different deformation modes: stress-induced α”-martensite ( α”-SIM), {332}<113> twinning, and {101}<111> slip in the 25Nb, 29Nb, and 35Nb alloys, respectively. The hysteresis loops during cyclic deformation exhibited very irregular shapes for 25Nb and 29Nb, accompanied by a flow-stress asymmetry in tension and compression. This was caused by the polarized feature on the formation of them in tension and compression. In addition, the apparent yield stress in a hysteresis loop greatly decreased after the second cycle, owing to the reversible motion of the interfaces of the SIM and {332} twins by altering the direction of the applied stress. Although the cyclic deformation behavior was controlled by a similar mechanism in them, 29Nb was found to exhibit a much shorter fatigue life than 25Nb. This is because of the difference in the decreasing tendency of the reversibility for the SIM and {332} twins as cyclic deformation proceeded. The obtained results demonstrate that the controls of their asymmetric features and the reversible motion are the important factors to develop these alloys as a practical “single crystalline β-Ti implant”.
Click here for this paper.
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2017.7.3
Our paper on unstable β-alloy single crystals has been published online with open access in International Journal of Plasticity.
K. Hagihara, T. Nakano*:
Experimental clarification of the cyclic deformation mechanisms of β-type Ti–Nb–Ta–Zr-alloy single crystals developed for the single-crystalline implant,
International Journal of Plasticity, (2017)
DOI : doi.org/10.1016/j.ijplas.2017.06.006.Abstract
Quaternary Ti-Nb-Ta-Zr (TNTZ) type β-Ti alloys with a body-centered cubic (bcc) structure have been of great interest as new implant biomaterials for bone replacement. Recently, we have proposed a “single crystalline β-Ti implant” as a novel hard-tissue replacement to suppress the stress shielding to bone after healing. To develop this, the fatigue properties and its controlling mechanisms of the TNTZ single crystals must be clarified. In this study, we focused on three alloys: Ti-25Nb-10Ta-5Zr(25Nb), Ti-29Nb-13Ta-4.6Zr(29Nb), and Ti-35Nb-10Ta-5Zr(35Nb) (mass%), and the cyclic deformation behaviors were examined using their single crystals. The shapes of the hysteresis loops were significantly different for these alloys, which was ascribed to the operation of different deformation modes: stress-induced α”-martensite ( α”-SIM), {332}<113> twinning, and {101}<111> slip in the 25Nb, 29Nb, and 35Nb alloys, respectively. The hysteresis loops during cyclic deformation exhibited very irregular shapes for 25Nb and 29Nb, accompanied by a flow-stress asymmetry in tension and compression. This was caused by the polarized feature on the formation of them in tension and compression. In addition, the apparent yield stress in a hysteresis loop greatly decreased after the second cycle, owing to the reversible motion of the interfaces of the SIM and {332} twins by altering the direction of the applied stress. Although the cyclic deformation behavior was controlled by a similar mechanism in them, 29Nb was found to exhibit a much shorter fatigue life than 25Nb. This is because of the difference in the decreasing tendency of the reversibility for the SIM and {332} twins as cyclic deformation proceeded. The obtained results demonstrate that the controls of their asymmetric features and the reversible motion are the important factors to develop these alloys as a practical “single crystalline β-Ti implant”.
Click here for this paper.
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2017.7.3
A commentary on recent achievements in metal AM (3D printer) was published by the Japan Society of Powder and Powder Metallurgy.
Takayoshi Nakano, Takuya Ishimoto, Koji Hagiwara :
Adding Anisotropy by Controlling Shape and Microstructure Using Powder Additive Manufacturing Method,
J. Jpn. Soc. Powder Metallurgy, Vol.64 [6] (2017) pp.259-264.Click here for this article.