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The study investigates the effect of Hydroxyapatite (HA) coating thickness on the inflammation and osseointegration properties of Ti–29Nb–13Ta-4.6Zr (TNTZ) implants for orthopedic implant applications. TNTZ screws were used as based samples, and the HA coating was deposited using an Electrophoretic Deposition (EPD) method to achieve various coating thickness. The thin (50–70 μm), medium (70–90 μm), and thick (90–110 μm) coating thicknesses were obtained by applying different voltage and time exposure during the EPD process, while the uncoated screw was used as the control sample. The screws were implanted into the right tibia of male Rattus norvegicus Wistar rats, and the animals were kept in cages and provide with ad libitum food for two weeks. After termination of the test animals, blood samples were collected to measure levels of Tumor Necrosis Factor-α (TNF-α) using an ELISA method, and a removal torque test was performed on the implanted screws. Additionally, tibial bone tissue around the implant area was collected for histopathology analysis. The result of the study indicate that HA coating thickness has an effect on TNF-α concentration, removal torque value, and new bone growth. The optimal thickness of the HA layer was found to be in the medium range (70–90 μm), resulting in low inflammation levels, relatively high osseointegration rates, and optimal new bone tissue growth. These finding are expected to be applicable in future orthopedic implant applications.

In this study, the influence of the high-pressure torsion (HPT) processing parameters and solution treatment (ST) on the corrosion and tribocorrosion behavior of CoCrMo (CCM) alloys was investigated for possible usage in biomedical applications. The corrosion behavior of the CCM alloys was investigated by using potentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS) tests. Tribocorrosion tests were carried out in a reciprocating ball-on-plate tribometer at 1 Hz, 1 N load, and 3 mm stroke length for 2 h. All electrochemical measurements were performed using a potentiostat in standard phosphate-buffered saline (PBS) solution at body temperature (37 ± 2 °C). The samples were characterized by using a scanning electron microscope (SEM), transmission electron microscope (TEM), optical microscope (OM), and X-ray diffraction (XRD). The deepness and width of wear tracks were examined by using a profilometer. The results showed that HPT and ST processes did not affect significantly the corrosion resistance of samples. However, the ST-treated samples had a higher material loss during sliding in standard phosphate-buffered saline (PBS) at body temperature as compared to HPT-treated samples.

In order to know precisely the corrosion behavior of a new developed β type titanium alloy Ti-29Nb-13Ta-4.6Zr (TNTZ) and ordinary titanium alloy Ti-6Al4V (for comparison) in oral cavity environment, corrosion rate of these alloys in an artificial saliva solution was then investigated. Corrosion measurement was conducted in 600 ml solution of Fusayama-Meyer artificial saliva containing of 0,4 g NaCl, 0.4 g KCl, 0.795 g CaCl2.2H2O, 0.69 g NaH2PO4, and 1 g urea using a potentiostat model (VERSA studio-200) controlled by a personal computer. The solution was maintained at pH 5.2 and 37oC to imitate oral cavity condition. After corrosion test, specimen surfaces were observed by SEM, EDX and XPS. The result show that the averaged corrosion rate of TNTZ and Ti-6Al-4V is 4.5×10-9 mmy-1 and 6.4×10-8 mmy-1 , respectively. This indicates that the corrosion resistance of TNTZ is relatively high, and it is better than that of Ti6Al-4V. This is due to the formation of a multiple layer of Ti, Nb and Zr oxides in the surface of TNTZ. However, formation of micro-pitting corrosion is more intense in TNTZ due mainly to the alloying elements segregation and the presence of high impurities. It is recommended that, therefore, an intense homogenizing process is neccessary to apply in TNTZ for homogenizing the elemental distribution and, subsequently, for minimizing pitting corrosion attack. Having low pitting corrosion attack is an important thing for dental application in order to reduce stress concentration and crack initiation, and then to avoid mechanical failure during application.

We found that specific biomedical Ti and its alloys, such as CP Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O, form a bright white oxide layer after a particular oxidation heat treatment. In this paper, the interfacial microstructure of the oxide layer on Ti–29Nb–13Ta–4.6Zr and the exfoliation resistance of commercially pure (CP) Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O were investigated. The alloys investigated were oxidized at 1273 or 1323 K for 0.3–3.6 ks in an air furnace. The exfoliation stress of the oxide layer was high in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, and the maximum exfoliation stress was as high as 70 MPa, which is almost the same as the stress exhibited by epoxy adhesives, whereas the exfoliation stress of the oxide layer on CP Ti was less than 7 MPa, regardless of duration time. The nanoindentation hardness and frictional coefficients of the oxide layer on Ti–29Nb–13Ta–4.6Zr suggested that the oxide layer was hard and robust enough for artificial tooth coating. The cross-sectional transmission electron microscopic observations of the microstructure of oxidized Ti–29Nb–13Ta–4.6Zr revealed that a continuous oxide layer formed on the surface of the alloys. The Au marker method revealed that both in- and out-diffusion occur during oxidation in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, whereas only out-diffusion governs oxidation in CP Ti. The obtained results indicate that the high exfoliation resistance of the oxide layer on Ti–29Nb–13Ta–4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O are attributed to their dense microstructures composing of fine particles, and a composition-graded interfacial microstructure. On the basis of the results of our microstructural observations, the oxide formation mechanism of the Ti–Nb–Ta–Zr alloy is discussed.

Simulated Body Fluid (SBF) has served as a useful standard to check the bioactivity of implant materials for years. However, it is not perfectly able to imitate human serum; sometimes disparities between the SBF test and animal test were confirmed. Therefore, to ensure the reliability of the results of the SBF test obtained from our previous study, an animal study was performed to check osteoconductivity of surface modified implant materials. Three types of solution processes, hydrothermal (H), electrochemical (E), and hydrothermal-electrochemical (HE), were performed on the Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) to improve its bioactivity, and their bioactivities were measured in vivo using bone-implant contacts (BICs). BICs of the HE- and H-treated samples were significantly higher than that of the control. Metal ion diffusion towards the bone was also evaluated to examine the adverse effect of metal ions. No metal ion diffusion was observed, indicating the safety of our solution processed implant materials.

Currently, β-type Ti-Nb-Ta-Zr alloys are gaining attention owing to their feasibility for use as biomedical materials. However, the deformation behaviors of these alloys have not yet been clarified. In this study, the Nb content of the Ti-30Nb-10Ta-5Zr (TNTZ) alloy was altered between 1.0 and 3.0 mass% from 30 mass%, and the corresponding changes in the superelasticity and shape-memory characteristics were investigated by tensile loading-unloading tests, X-ray diffraction (XRD) analysis, and microstructural analysis using a transmission electron microscopy (TEM). When the Nb content is less than approximately 29 mass%, the loading-unloading stress-strain curves show two-step gradients and are similar to those of common shape-memory alloys such as Ti-Ni alloys; these gradients result from stress-induced martensitic transformation and its reversion. When the Nb content is approximately 30 mass%, the tensile loading-unloading curves show a nonlinear gradient corresponding to superelastic behavior, which can not be explained by XRD and TEM microstructural analyses on stress-induced martensitic transformation and its reversion in the present state. When the Nb content is approximately 31 mass%, the tensile loading-unloading curves show a single gradient. The elastic deformation is mainly caused by the elastic strain in the lattice. Changes in the chemical content of Nb in TNTZ within a very narrow range are found to alter the superelastic behavior of this alloy.

Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy has excellent mechanical properties and bone conductivity. For dental application, TNTZ surfaces were converted to white oxidized layer by a simple heat treatment in air to achieve the formation of aesthetic surfaces. The oxidized layer formed by the heat treatment at 1000°C for 0.5 or 1 hr was whiter and joined to TNTZ substrate more strongly than that formed by the treatment at 900°C. The layer consisted of TiO2 (rutile), TiNb2O7, and TiTa2O7 and possessed ~30 μm in thickness for the sample heat-treated at 1000°C and ~10 μm for that heat-treated at 900°C. The surface average roughness and the wettability increased after the heat treatment. The spreading and proliferation level of mouse osteoblast-like cell (MC3T3-E1 cell) on the heat-treated sample were almost the same as those on as-prepared one. The cell spreading on TNTZ was better than those on pure titanium (CP Ti) regardless of the heat treatment for the samples. There was no deterioration in the in vitro cell compatibility of TNTZ after the oxidized layer coating by the heat treatment.

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.

Nb, Ta and Zr are the favorable non-toxic alloying elements for titanium alloys for biomedical applications. Low rigidity titanium alloys composed of non-toxic elements are getting much attention. The advantage of low rigidity titanium alloy for the healing of bone fracture and the remodeling of bone is successfully proved by fracture model made in tibia of rabbit. Ni-free super elastic and shape memory titanium alloys for biomedical applications are energetically developed. Titanium alloys for not only implants, but also dental products like crowns, dentures, etc. are also getting much attention in dentistry. Development of investment materials suitable for titanium alloys with high melting point is desired in dental precision castings. Bioactive surface modifications of titanium alloys for biomedical applications are very important for achieving further developed biocompatibility. Low cost titanium alloys for healthcare goods, like general wheel chairs, etc. has been recently proposed.

This paper proposes the concept and fabrication process of titanium alloy rods for spinal fixation. A part of rod for fixing the lower side of the lumbar vertebra is strengthened, while the other part for fixing the upper side has low stiffness. The results obtained by finite element analysis reveal that a rod with partially lowered Young's modulus has higher flexibility and fixity compared with a rod possessing high Young's modulus throughout. Using Ti-29Nb-13Ta-4.6Zr alloys with oxygen contents of 0.2 and 0.4% as the model alloys, rods with partially different Young's moduli were fabricated by aging treatment at 723 K, followed by partial heating up to above the β-transus temperature and quenching by high-frequency induction heating (IH-treatment). A single β-phase, which has low Young's modulus, is obtained by IH-treatment and has lower strength. With regard to the as-aged parts, the precipitated condition of the a-phase can be changed by varying the aging time. The obtained Young's modulus and strength reflect this change. Near the boundary between the as-aged and IH-treated parts, the hardness is gradually changed, and it is possible to gradually soften the material from the as-aged part to the IH-treated part. [ABSTRACT FROM AUTHOR]

To explore the effect of copper content in a copper-doped hydroxyapatite coating (CuHAp) on its antibacterial activity and biocompatibility, a layer of CuHAp was deposited on the surface of pure Ti using an electrochemical deposition method. An orthogonal experiment was used to determine the Cu content in the coating by varying the concentration of Cu2+ in the electrolyte. The antibacterial properties and biocompatibility of the CuHAp coatings were also evaluated. The antibacterial effect increased with increasing Cu content in the sample. When the content of Cu in the coating was 1.57%, the deposited CuHAp coating exhibited excellent biocompatibility, and the number of living cells after culturing was significantly higher than that for the HAp coating. When the content of Cu increased to 6.85%, the coating exhibited cytotoxicity. Thus, the CuHAp sample with a Cu content of 1.57% exhibited good antibacterial and biocompatibility, and thus could be a suitable material for use in biomedical applications. [ABSTRACT FROM AUTHOR]

Cu-doped amorphous calcium phosphate (ACP) coatings were fabricated on the surface of pure titanium (Ti) by electrochemical deposition at initial electrolyte temperatures of 35, 45, and 55°C. The antibacterial activities of the coatings were then evaluated by the plate counting method using Escherichia coli as the indicator. The Cu concentrations on the surfaces of samples are increased from 6.90 to 15.05 mass% as initial electrolyte temperature is increased from 35 to 55°C. The Cu-doped ACP coatings show that they can fully inhibit the growth of E. coli. [ABSTRACT FROM AUTHOR]

Titanium alloys have applications in air frames for commercial aircraft, and jet engine components such as fans and compressor disks, which function at low temperatures (up to 673 K). Near ß-type Ti-5Al-2Sn-2Zr-4C-4Mo (Ti-17) exhibits greater strength, crack propagation resistance, and creep resistance at intermediate temperatures compared to the (a + ß)-type Ti-6Al-4V. It is important to estimate the fatigue life of engine components made of Ti-17. This requires problem quantitative relationship between the fatigue properties and microstructural factors of Ti-17. Therefore, the fatigue properties including tensile properties and microstructures of Ti-17 samples fabricated by hot-forging at various temperatures, followed by high- and low-temperature solution treatment (ST), and same aging treatment were investigated to define a quantitative relationship between the fatigue properties and the microstructures. The microstructures of all forged Ti-17 samples exhibit elongated prior ß-grains composed of two microstructural feature regions: acicular a and fine equiaxed a-phase regions. The volume fraction of the acicular a region decreases with increasing ST temperature. The Vickers hardness, 0.2% proof stress and tensile strength increases with increasing ST temperature. However, the elongation and reduction of area exhibit a reverse trend. The Ti-17 samples forged at 1173 K followed by solution treatment at 1073 K and aging treatment exhibits the highest fatigue limit of around 975 MPa. The fatigue strength of the forged Ti-17 samples is strongly related to the microstructural factor such as the volume fraction of the equiaxed a-phase region, which is one of the crack initiation sites in the forged Ti-17 samples subjected to low temperature ST and aging, and the strength difference between the acicular a-phase and the fine (a + ß)-phase, which leads to the crack initiation in the forged Ti-17 sample subjected to high temperature ST and aging. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors discuss various topics within the issue, including additive manufacturing (AM), the microstructural evolution of titanium and its alloys, and their biomedical applications.

Ti-29Nb-13Ta-4.6Zr (TNTZ) is one of the Ti alloys used for orthodontic wire. However, there is a problem that the metallic color of TNTZ may spoil the appearance of a row of teeth. In previous studies, white oxide coating on disk-shaped TNTZ samples was obtained by heat treatment or atmospheric-pressure plasma (APP) treatment. In this study, the fabrication process of white orthodontic wire by applying APP treatment is proposed. As a result, TNTZ wire which has a white oxide layer with comparable brightness to the surface of Japanese teeth has been successfully fabricated. [ABSTRACT FROM AUTHOR]

In this study, the relationships among oxidation condition, color tone, and the cross-sectional microstructure of the oxide layer on commercially pure (CP) Ti and Ti–36Nb–2Ta–3Zr–0.3O were investigated. “White metals” are ideal metallic materials having a white color with sufficient strength and ductility like a metal. Such materials have long been sought for in dentistry. We have found that the specific biomedical Ti alloys, such as CP Ti, Ti–36Nb–2Ta–3Zr–0.3O, and Ti–29Nb–13Ta–4.6Zr, form a bright yellowish-white oxide layer after a particular oxidation heat treatment. The brightness L* and yellowness +b* of the oxide layer on CP Ti and Ti–36Nb–2Ta–3Zr–0.3O increased with heating time and temperature. Microstructural observations indicated that the oxide layer on Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O was dense and firm, whereas a piecrust-like layer was formed on CP Ti. The results obtained in this study suggest that oxide layer coating on Ti–36Nb–2Ta–3Zr–0.3O is an excellent technique for dental applications. [ABSTRACT FROM AUTHOR]