Showing papers by "Masaaki Nakai published in 2016"

Fabrication of low-cost beta-type Ti-Mn alloys for biomedical applications by metal injection molding process and their mechanical properties

Abstract: Titanium and its alloys are suitable for biomedical applications owing to their good mechanical properties and biocompatibility. Beta-type Ti–Mn alloys (8–17 mass% Mn) were fabricated by metal injection molding (MIM) as a potential low cost material for use in biomedical applications. The microstructures and mechanical properties of the alloys were evaluated. For up to 13 mass% Mn, the tensile strength (1162–938 MPa) and hardness (308–294 HV) of the MIM fabricated alloys are comparable to those of Ti–Mn alloys fabricated by cold crucible levitation melting. Ti–9Mn exhibits the best balance of ultimate tensile strength (1046 MPa) and elongation (4.7%) among the tested alloys, and has a Young’s modulus of 89 GPa. The observed low elongation of the alloys is attributed to the combined effects of high oxygen content, with the presence of interconnected pores and titanium carbides, the formation of which is due to carbon pickup during the debinding process. The elongation and tensile strength of the alloys decrease with increasing Mn content. The Ti–Mn alloys show good compressive properties, with Ti–17Mn showing a compressive 0.2% proof stress of 1034 MPa, and a compressive strain of 50%.

Osteoanabolic Implant Materials for Orthopedic Treatment

Abstract: Osteoporosis is becoming more prevalent due to the aging demographics of many populations. Osteoporotic bone is more prone to fracture than normal bone, and current orthopedic implant materials are not ideal for the osteoporotic cases. A newly developed strontium phosphate (SrPO4 ) coating is reported herein, and applied to Ti-29Nb-13Ta-4.6Zr (wt%), TNTZ, an implant material with a comparative Young's modulus to that of natural bone. The SrPO4 coating is anticipated to modulate the activity of osteoblast (OB) and osteoclast (OC) cells, in order to promote bone formation. TNTZ, a material with excellent biocompatibility and high bioinertness is pretreated in a concentrated alkaline solution under hydrothermal conditions, followed by a hydrothermal coating growth process to achieve complete SrPO4 surface coverage with high bonding strength. Owing to the release of Sr ions from the SrPO4 coating and its unique surface topography, OB cells demonstrate increased proliferation and differentiation, while the cellular responses of OC are suppressed, compared to the control case, i.e., bare TNTZ. This TNTZ implant with a near physiologic Young's modulus and a functional SrPO4 coating provides a new direction in the design and manufacture of implantable devices used in the management of orthopedic conditions in osteoporotic individuals.

Using Cavitation Peening to Improve the Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting

Abstract: Although Electron Beam Melting (EBM) is an innovative technology, the fatigue properties of materials manufactured by EBM may be lower than those of casted and wrought materials due to defects and surface roughness. In order to enhance the fatigue life of components or structures manufactured by EBM, a mechanical surface treatment technology, e.g., peening, would be effective because peening introduces high compressive residual stress at the surface which can extend the fatigue life considerably. In the present study, specimens were manufactured by EBM using titanium alloy Ti-6Al-4V powder. Two types of specimens were prepared: as-built and as-machined specimens. Specimens of each type were treated by cavitation peening or shot peening. The fatigue lives of the specimens were evaluated by a plate bending fatigue tester. The residual stress and surface roughness were also evaluated. The results obtained showed that the fatigue strength of as-built specimens can be improved by 21% by cavitation peening or shot peening, and the fatigue life under particular applied stresses can also be extended by 178% by cavitation peening.

Developing biomedical nano-grained β-type titanium alloys using high pressure torsion for improved cell adherence

Abstract: Proper surface characteristics for a titanium implant are crucial for the formation of different cellular protrusions known as filopodia and lamellipodia, both of which have a significant impact on cell attachment, spreading, migration, and proliferation. Microstructural features such as grain boundaries and defects of implant surface can modulate the cellular components and structure at the leading edge of cells. Here, a nano-grained Ti–29Nb–13Ta–4.6Zr (NG TNTZ) substrate was produced by high-pressure torsion (HPT) for improved biofunctionality. Cellular response of human osteoblast cells on nano-grained TNTZ substrates is evaluated and compared with the cellular response of those on coarse-grained TNTZ. High wettability, which depends on high internal energy due to the nano-sized grains that are full of boundaries, interfaces, and high dislocation density, influenced the hOBs cells on NG TNTZ to form highly developed cellular protrusions. Large number of filopodia protrusions resulted in excellent cell attachment as consistent with high level of vinculin and superior cell proliferation. This study demonstrates the advantages of nanocrystalline surface modification using HPT for processing metallic biomaterials that are proper for orthopedic implants.

Electrochemical surface treatment of a β-titanium alloy to realize an antibacterial property and bioactivity

Abstract: In this study, micro-arc oxidation (MAO) was performed on a β-type titanium alloy, namely, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), to improve not only its antibacterial property but also bioactivity in body fluids. The surface oxide layer formed on TNTZ by MAO treatment in a mixture of calcium glycerophosphate, calcium acetate, and silver nitrate was characterized using surface analyses. The resulting porous oxide layer was mainly composed of titanium oxide, and it also contained calcium, phosphorus, and a small amount of silver, all of which were incorporated from the electrolyte during the treatment. The MAO-treated TNTZ showed a strong inhibition effect on anaerobic Gram-negative bacteria when the electrolyte contained more than 0.5 mM silver ions. The formation of calcium phosphate on the surface of the specimens after immersion in Hanks’ solution was evaluated to determine the bioactivity of TNTZ with sufficient antibacterial property. As a result, thick calcium phosphate layers formed on the TNTZ specimen that underwent MAO treatment, whereas no precipitate was observed on TNTZ without treatment. Thus, the MAO treatment of titanium-based alloys is confirmed to be effective in realizing both antibacterial and bioactive properties.

Microstructural evolution and mechanical properties of biomedical Co-Cr-Mo alloy subjected to high-pressure torsion.

Abstract: The effects of severe plastic deformation through high-pressure torsion (HPT) on the microstructure and tensile properties of a biomedical Co-Cr-Mo (CCM) alloy were investigated. The microstructure was examined as a function of torsional rotation number, N and equivalent strain, eeq in the HPT processing. Electron backscatter diffraction analysis (EBSD) shows that a strain-induced martensitic transformation occurs by the HPT processing. Grain diameter decreases with increasing eeq, and the HPT-processed alloy (CCMHPT) for eeq=45 exhibits an average grain diameter of 47nm, compared to 70μm for the CCM alloy before HPT processing. Blurred and wavy grain boundaries with low-angle of misorientation in the CCMHPT sample for eeq<45 become better-defined grain boundaries with high-angle of misorientation after HPT processing for eeq=45. Kernel average misorientation (KAM) maps from EBSD indicate that KAM inside grains increases with eeq for eeq<45, and then decreases for eeq=45. The volume fraction of the e (hcp) phase in the CCMHPT samples slightly increases at eeq=9, and decreases at eeq=45. In addition, the strength of the CCMHPT samples increases at eeq=9, and then decrease at eeq=45. The decrease in the strength is attributed to the decrease in the volume fraction of e phase, annihilation of dislocations, and decrease in strain in the CCMHPT sample processed at eeq=45 by HPT.

Adhesive strength of bioactive oxide layers fabricated on TNTZ alloy by three different alkali-solution treatments.

Abstract: Bioactive oxide layers were fabricated on Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) by three different alkali solution treatments: hydrothermal (H), electrochemical (E), and hydrothermal-electrochemical (HE). The adhesive strength of the oxide layer to the TNTZ substrate was measured to determine whether this process achieves sufficient adhesive strength for implant materials. Samples subjected to the HE process, in which a current of 15mA/cm(2) was applied at 90°C for 1h (HE90-1h), exhibited a comparatively higher adhesive strength of approximately 18MPa while still maintaining a sufficiently high bioactivity. Based on these results, an oxide layer fabricated on TNTZ by HE90-1h is considered appropriate for practical biomaterial application, though thicker oxide layers with many cracks can lead to a reduced adhesive strength.

Optimization of Microstructure and Mechanical Properties of Co–Cr–Mo Alloys by High-Pressure Torsion and Subsequent Short Annealing

Abstract: 1Department of Materials Science, Tohoku University, Sendai 980–8579, Japan 2Institute for Materials Research, Tohoku University, Sendai 980–8577, Japan 3Joining and Welding Research Institute, Osaka University, Ibaraki 567–0047, Japan 4Graduate School of Engineering, Osaka University, Suita 565–0871, Japan 5Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819–0395, Japan 6WPI, International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 819–0395, Japan 7Department of Materials Processing, Tohoku University, Sendai 980–8579, Japan

Effect of Solute Oxygen on Compressive Fatigue Strength of Spinal Fixation Rods Made of Ti–29Nb–13Ta–4.6Zr Alloys

Abstract: In spinal xation devices, the activity of the patient can cause fretting of the metal-to-metal contacts between the rod and plug, which may result in failures. In this study, compressive fatigue tests were conducted with rods made of Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) with oxygen contents of 0.06 mass% (06O) and 0.89 mass% (89O) and Ti–6Al–4V extra low interstitial alloy (Ti64) as comparison in both air and saline solution. The fatigue strength increases in the order of 06O < 89O < Ti64 in both air and saline solution. These results indicate that solid-solution strengthening by oxygen improves the fretting fatigue resistance of the TNTZ rod. [doi:10.2320/matertrans.MI201504]

Osteoanabolic Implants: Osteoanabolic Implant Materials for Orthopedic Treatment (Adv. Healthcare Mater. 14/2016)

Abstract: On page 1740, Xiao-Bo Chen and co-workers report an orthopedic implant material specifically designed for osteoporotic bone fractures. A newl strontium phosphate coating applied to a bone-mimicking low elastic titanium alloy with a comparative Young's modulus to that of natural bone results in upregulating the growth of osteoblasts and downregulating that of osteoclasts. Such a promising osteoanabolic effect reveals a suitability in particular for patients who suffer from low quality bone organism and slow fracture recovery.

Preparation and Characterization of Chitosan/Hydroxyapatite Sol-Gel Coating on Ti-6Al-4V

Abstract: SERAP (GUNGOR) KOC, BURAK DIKICI, MEHMET TOPUZ, HAKAN YILMAZER, ISMAIL OZDEMIR, MITSUO NIINOMI, MASAAKI NAKAI Yuzuncu Yil University, Mechanical Engineering Department, Van, 65080, Turkey, serapgungor@yyu.edu.tr Yildiz Technical University, Metallurgical and Materials Engineering, Istanbul 34210, Turkey Katip Celebi University, Department of Mechanical Engineering, Izmir 35620, Turkey Meijo University, Graduate School of Engineering, Nagoya 468‐8502, Japan Kindai University, Department of Mechanical Engineering, Osaka 577‐8502, Japan

Beta-Type Titanium Alloys for use as Rods in Spinal Fixation Devices

Abstract: Ti-12Cr has been developed for use in various biomedical applications, in particular; it is expected to be used for the rods of the spinal fixation devices. When Ti-12Cr is deformed, its Young’s modulus increases because of deformation-induced ω phase transformation. If a spinal rod made of Ti-12Cr is bent during operation, only the Young’s modulus of the bent region will increase; this phenomenon decreases the springback of the rod so that the bent shape is maintained. The compression fatigue strength of Ti-12Cr obtained from compression fatigue tests performed according to ASTM F1717 can be significantly improved by cavitation peening. Details of the development of this Ti-Cr alloy for use as spinal rods are discussed.

Evaluation of antibacterial activity of copper by hydrogen sulfide-producing salmonella

Abstract: A novel method for detecting antimicrobial activity using an innate property of the Salmonella bacteria, namely, the ability of Salmonella to produce hydrogen sulfide (H2S) was developed in this study. The effectiveness of the method was evaluated by comparing the antibacterial activity of copper to that of aluminum. Salmonella was inoculated over the entire surface of deoxycholate hydrogen sulfide lactose (DHL) agar plates that included Ammonium ferric citrate (C6H8FeN). Approximately 25 mL of cupric chloride (CuCl2, 1 weight ratio) solution or aluminum chloride (AlCl3, 1 weight ratio) solution was added to the center of the medium. The surface of the medium was covered with plastic PET (polyethylene terephthalate) material to induce an anaerobic state. Salmonella was cultured under anaerobic conditions at 310 K (37°C) for 86.4 ks (24 h). The antibacterial activity of copper was determined by observing the medium surface color change due to iron sulfide (FeS) formation, which was caused by the production of H2S by Salmonella; blackness indicated presence of newly formed FeS. A quantitative evaluation of copper's antimicrobial activity was performed using a gradient of CuCl2 concentrations; results were compared with those of the present standard method, KirbyBauer disk diffusion method on the Mueller Hinton medium. Finally, in order to evaluate the antibacterial activity of metals, Salmonella was inoculated on DHL agar plates. Subsequently, Japanese coins (1 yen, 5 yen, 10 yen, 50 yen, 100 yen and 500 yen coins) were placed on the agar and cultured at 310 K for 86 ks. Salmonella cultured in the presence of AlCl3 produces black color, while no blackening is observed with CuCl2, suggesting that copper possesses an antibacterial property against Salmonella. CuCl2 suppresses H2S production by Salmonella, as Cu2+ forms a transparent circle or ellipse (new halo) around the point at which CuCl2 had has been plated. The size of the new halo increases in direct proportion to the concentration of CuCl2. The halo is no longer visible at 0.034 mg of CuCl2 in our method, while the halo disappears with 4.34 mg of CuCl2 in the KirbyBauer method. Therefore, the present method is 129 times more sensitive than the standard method, suggesting increased usefulness and effectiveness in testing antibacterial activity. No FeSdependent black circle is formed under any of the coins, with the exception of the 1yen coin, which contains aluminum and no copper. Therefore, the coppercontaining coins have an antibacterial effect. [doi:10.2320/jinstmet.J2015049]