Preparation and characterizations of antibacterial iodine-containing coatings on pure Ti

Iodine-containing coatings were prepared on pure Ti surfaces via electrochemical deposition to enhance their antibacterial properties. The factors influencing iodine content were analyzed using an orthogonal experiment. The electrochemically deposited samples were characterized using scanning electron microscopy with energy dispersive spectroscopy and X-ray photoelectron spectroscopy, and their antibacterial properties and cytotoxicity were evaluated. The results showed that changing the deposition time is an effective way to control the iodine content. The iodine content, coating thickness, and adhesion of the samples increased with deposition time. Iodine in the coatings mainly exists in three forms, which are I2, I3-, and pentavalent iodine. For samples with iodine-containing coatings, the antibacterial ratios against E. coli and S. aureus were greater than 90% and increased with increasing iodine content. Although the samples with iodine-containing coatings showed some inhibition of the proliferation of MC3T3-E1 cells, the cell viabilities were all higher than 80%, suggesting that iodine-containing coatings are biosafe.

Exfoliation Resistance, Microstructure, and Oxide Formation Mechanisms of the White Oxide Layer on CP Ti and Ti-Nb-Ta-Zr Alloys

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.

Design and development of metallic biomaterials with biological and mechanical biocompatibility

In the present article, the recent trends in the research and development of metallic biomaterials are discussed with focus on the results obtained by the author's group. The design of biocompatible metallic biomaterials possessing excellent biological and mechanical properties, including titanium alloys with low Young's modulus, is reviewed with focus on Young's modulus, fatigue strength, and peculiar behavior. The evaluation of biological compatibility including cell viability and living tissue compatibility using animal models and surface modifications using bioactive ceramic and blood-compatible polymers are summarized. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 944-954, 2019.

Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production

Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO₂ photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO₂, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO₂ originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.

Metastable Zr-Nb alloys for spinal fixation rods with tunable Young's modulus and low magnetic resonance susceptibility

Good ductility, low magnetic susceptibility, and tunable Young's modulus are highly desirable properties for materials usage as spinal fixation rods. In this study, the effects of niobium content on the microstructure, magnetic susceptibility, and mechanical properties of Zr-xNb (13≤x≤23wt%) alloys were investigated. For the Zr-15Nb and Zr-17Nb alloys, a remarkable increase in Young's modulus was achieved due to the occurrence of deformation-induced ω phase transformation. This was the result of the competition of two factors associated with the Nb content: an increase of the stability of β phase and a decrease of the amount of athermal ω phase with increasing Nb content. When the Nb content was 15% or 17%, the amount of deformation-induced ω phase was maximum. Moreover, the magnetic susceptibility decreased with the deformation-induced β→ω phase transformation, and the Zr-17Nb alloy with apparent kink bands exhibited a smaller amount of springback than the Zr-15Nb alloy with {332} 〈113〉 mechanical twins. Furthermore, the ions released from the Zr-xNb alloys in accelerated immersion tests were at a very low level. The combination of low initial Young's modulus, and its remarkable variation induced by deformation, low magnetic susceptibility, good ductility, and smaller springback make the Zr-17Nb alloy a potential candidate for spinal fixation rods.

STATEMENT OF SIGNIFICANCE

For the rods of spinal fixation devices, it is important but difficult to lower the springback for bending formativeness while keeping the low initial Young's modulus for biocompatibility and lower the magnetic susceptibility for postoperative examination simultaneously. In this study, Zr-17Nb alloy was successfully developed via deformation-induced ω phase transformation during loading, simultaneously meeting the abovementioned properties for spinal fixation rods.

Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants

β-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a 'single crystalline β-Ti implant' as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young's modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to <111> was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to <111> dislocations was small, in contrast to other β-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of <111> slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the "plastically almost-isotropic and elastically highly-anisotropic" nature, that is desirable for the development of 'single crystalline β-Ti implant'.

Osteoanabolic Implant Materials for Orthopedic Treatment

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.

Biomedical titanium alloys with Young's moduli close to that of cortical bone

Biomedical titanium alloys with Young’s moduli close to that of cortical bone, i.e., low Young’s modulus titanium alloys, are receiving extensive attentions because of their potential in preventing stress shielding, which usually leads to bone resorption and poor bone remodeling, when implants made of their alloys are used. They are generally β-type titanium alloys composed of non-toxic and allergy-free elements such as Ti–29Nb–13Ta–4.6Zr referred to as TNTZ, which is highly expected to be used as a biomaterial for implants replacing failed hard tissue. Furthermore, to satisfy the demands from both patients and surgeons, i.e., a low Young’s modulus of the whole implant and a high Young’s modulus of the deformed part of implant, titanium alloys with changeable Young’s modulus, which are also β-type titanium alloys, for instance Ti–12Cr, have been developed. In this review article, by focusing on TNTZ and Ti–12Cr, the biological and mechanical properties of the titanium alloys with low Young’s modulus and changeable Young’s modulus are described. In addition, the titanium alloys with shape memory and superelastic properties were briefly addressed. Surface modifications for tailoring the biological and anti-wear/corrosion performances of the alloys have also been briefly introduced.

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

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.

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

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, and proliferation.

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

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, εeq 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 εeq, and the HPT-processed alloy (CCMHPT) for εeq=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 εeq<45 become better-defined grain boundaries with high-angle of misorientation after HPT processing for εeq=45. Kernel average misorientation (KAM) maps from EBSD indicate that KAM inside grains increases with εeq for εeq<45, and then decreases for εeq=45. The volume fraction of the ε (hcp) phase in the CCMHPT samples slightly increases at εeq=9, and decreases at εeq=45. In addition, the strength of the CCMHPT samples increases at εeq=9, and then decrease at εeq=45. The decrease in the strength is attributed to the decrease in the volume fraction of ε phase, annihilation of dislocations, and decrease in strain in the CCMHPT sample processed at εeq=45 by HPT.

Microstructures, mechanical properties and cytotoxicity of low cost beta Ti-Mn alloys for biomedical applications

The microstructures, mechanical properties and biocompatibility of low cost β-type Ti-(6-18)Mn alloys were investigated after solution treatment. Ti-9 Mn exhibits the best combination of tensile strength and elongation among the fabricated alloys, and its performance is comparable to or superior to those of Ti-6Al-4V ELI (Ti-64 ELI) in terms of every parameter evaluated. A hardness of 338 HV, a Young's modulus of 94 GPa, a 0.2% proof stress of 1023 MPa, an ultimate tensile strength of 1048 MPa and elongation of 19% were obtained for Ti-9 Mn. Furthermore, the cell viability and metallic ion release ratios are comparable to those of commercially pure titanium, making this alloy promising for biomedical applications. The Young's modulus is also lower than that of Ti-64 ELI (110 GPa), which can possibly reduce the stress shielding effect in implanted patients.

STATEMENT OF SIGNIFICANCE

This study evaluates mechanical and biological performance of low cost solution treated β-type Ti-(6, 9, 13 and 18 mass%)Mn alloys. It includes alloys containing a Mn content range higher than most previously published works (which is around or lower than 8 mass%). Furthermore, the effects of the ω phase and the β phase stability of the alloys over some mechanical properties and microstructures are discussed. Ion release behavior under simulated body fluids and cell viability are also evaluated. For the case of the Ti-9 Mn, a mechanical and biological performance that is comparable to or superior than that of the widely used Ti-6Al-4V ELI and commercially pure Ti was observed.

β-Type titanium alloys for spinal fixation surgery with high Young's modulus variability and good mechanical properties

Along with a high strength, ductility, and work hardening rate, a variable Young's modulus is crucial for materials used as implant rods in spinal fixation surgery. The potential in this context of Ti-(9,8,7)Cr-0.2O (mass%) alloys is reported herein. The microstructural and mechanical properties of the alloys were systematically examined as a function of their chromium content, and the ion release of the optimized alloy was investigated to assess its suitability as an implant material. In terms of the deformation-induced ω-phase transformation required for a variable Young's modulus, the balance between β-phase stability and athermal ω-phase content is most favorable in the Ti-9Cr-0.2O alloy. In addition, this composition affords a high tensile strength (>1000MPa), elongation at break (∼20%), and work hardening rate to solution-treated (ST) samples. These excellent properties are attributed to the combined effects of deformation-induced ω-phase transformation, deformation twinning, and dislocation gliding. Furthermore, the ST Ti-9Cr-0.2O alloy proves resistant to metal ion release in simulated body fluid. This combination of a good biocompatibility, variable Young's modulus and a high strength, ductility, and work hardening rate is ideal for spinal fixation applications.

STATEMENT OF SIGNIFICANCE

Extensive efforts have been devoted over the past decades to developing β-type titanium alloys with low Young's moduli for biomedical applications. In spinal fixation surgery however, along with excellent mechanical properties, the spinal-support materials should possess high Young's modulus for showing small springback during surgery to facilitate manipulation but low Young's modulus close to bone once implanted to avoid stress shielding. None of currently used metallic biomaterials can satisfy these abovementioned requirements. In the present study, we have developed a novel alloy, Ti-9Cr-0.2O. Remarkably variable Young's modulus and excellent mechanical properties can be achieved in this alloy via phase transformations and complex deformation mechanisms, which makes the Ti-9Cr-0.2O preferred material for spinal fixation surgery.

Mechanical properties and cytocompatibility of oxygen-modified β-type Ti-Cr alloys for spinal fixation devices

In this study, various amounts of oxygen were added to Ti-10Cr (mass%) alloys. It is expected that a large changeable Young's modulus, caused by a deformation-induced ω-phase transformation, can be achieved in Ti-10Cr-O alloys by the appropriate oxygen addition. This "changeable Young's modulus" property can satisfy the otherwise conflicting requirements for use in spinal implant rods: high and low moduli are preferred by surgeons and patients, respectively. The influence of oxygen on the microstructures and mechanical properties of the alloys was examined, as well as the bending springback and cytocompatibility of the optimized alloy. Among the Ti-10Cr-O alloys, Ti-10Cr-0.2O (mass%) alloy shows the largest changeable Young's modulus following cold rolling for a constant reduction ratio. This is the result of two competing factors: increased apparent β-lattice stability and decreased amounts of athermal ω phase, both of which are caused by oxygen addition. The most favorable balance of these factors for the deformation-induced ω-phase transformation occurred at an oxygen concentration of 0.2mass%. Ti-10Cr-0.2O alloy not only exhibits high tensile strength and acceptable elongation, but also possesses a good combination of high bending strength, acceptable bending springback and great cytocompatibility. Therefore, Ti-10Cr-0.2O alloy is a potential material for use in spinal fixture devices.

Contribution of β' and β precipitates to hardening in as-solutionized Ag-20Pd-12Au-14.5Cu alloys for dental prosthesis applications

Dental Ag-20Pd-12Au-14.5Cu alloys exhibit a unique hardening behavior, which the mechanical strengths enhance significantly which enhances the mechanical strength significantly after high-temperature (1123K) solution treatment without aging treatment. The mechanism of the unique hardening is not clear. The contribution of two precipitates (β' and β phases) to the unique hardening behavior in the as-solutionized Ag-20Pd-12Au-14.5Cu alloys was investigated. In addition, the chemical composition of the β' phase was investigated. The fine β' phase densely precipitates in a matrix. The β' phase (semi-coherent precipitate), which causes lattice strain, contributes greatly to the unique hardening behavior. On the other hand, the coarse β phase sparsely precipitates in the matrix. The contribution of the β phase (incoherent precipitate), which does not cause lattice strain, is small. The chemical composition of the β' phase was determined. This study reveals that the fine β' phase precipitated by high-temperature solution treatment leads to the unique hardening behavior in dental Ag-20Pd-12Au-14.5Cu alloys in the viewpoints of the lattice strain contrast and interface coherency. It is expected to make the heat treatment process more practical for hardening. The determined chemical composition of β' phase would be helpful to study an unknown formation process of β' phase.

Precipitation of β' phase and hardening in dental-casting Ag-20Pd-12Au-14.5Cu alloys subjected to aging treatments

The age-hardening behavior of the dental-casting Ag-20Pd-12Au-14.5Cu alloy subjected to aging treatment at around 673K is well known, and this hardening has been widely employed in various applications. To date, the age-hardening of this alloy has been explained to attribute to the precipitation of a β phase, which is a B2-type ordered CuPd phase or PdCuxZn1-x phase. In this study, results obtained from microstructural observations using a transmission electron microscopy and a scanning transmission electron microscopy revealed that a fine L10-type ordered β' phase precipitated in the matrix and a coarse-structure region (consisting of Ag- and Cu-rich regions) appeared after aging treatment at 673K and contributed to increase in hardness. The microstructure of the coarse β phase, which existed before aging treatment, did not change by aging treatment. Thus, it is concluded that the fine β' phase precipitated by aging treatment contributed more to increase in hardness than the coarse-structure region and coarse β phase.

Deformation-induced ω phase in modified Ti-29Nb-13Ta-4.6Zr alloy by Cr addition

For spinal-fixation applications, implants should have a high Young's modulus to reduce springback during operations, though a low Young's modulus is required to prevent stress shielding for patients after surgeries. In the present study, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) with a low Young's modulus was modified by adding Cr to obtain a higher deformation-induced Young's modulus in order to satisfy these contradictory requirements. Two newly designed alloys, TNTZ-8Ti-2Cr and TNTZ-16Ti-4Cr, possess more stable β phases than TNTZ. These alloys consist of single β phases and exhibit relatively low Young's moduli of <65GPa after solution treatment. However, after cold rolling, they exhibit higher Young's moduli owing to a deformation-induced ω-phase transformation. These modified TNTZ alloys show significantly less springback than the original TNTZ alloy based on tensile and bending loading-unloading tests. Thus, the Cr-added TNTZ alloys are beneficial for spinal-fixation applications.

Experimental application of pulsed laser-induced water jet for endoscopic submucosal dissection: mechanical investigation and preliminary experiment in swine

BACKGROUND AND AIM

A current drawback of endoscopic submucosal dissection (ESD) for early-stage gastrointestinal tumors is the lack of instruments that can safely assist with this procedure. We have developed a pulsed jet device that can be incorporated into a gastrointestinal endoscope. Here, we investigated the mechanical profile of the pulsed jet device and demonstrated the usefulness of this instrument in esophageal ESD in swine.

METHODS

The device comprises a 5-Fr catheter, a 14-mm long stainless steel tube for generating the pulsed water jet, a nozzle and an optical quartz fiber. The pulsed water jet was generated at pulse rates of 3 Hz by irradiating the physiological saline (4°C) within the stainless steel tube with an holmium-doped yttrium-aluminum-garnet (Ho:YAG) laser at 1.1 J/pulse. Mechanical characteristics were evaluated using a force meter. The device was used only for the part of submucosal dissection in the swine ESD model. Tissues removed using the pulsed jet device and a conventional electrocautery device, and the esophagus, were histologically examined to assess thermal damage.

RESULTS

The peak impact force was observed at a stand-off distance of 40 mm (1.1 J/pulse). ESD using the pulsed jet device was successful, as the tissue specimens showed precise dissection of the submucosal layer. The extent of thermal injury was significantly lower in the dissected bed using the pulsed jet device.

CONCLUSION

The results showed that the present endoscopic pulsed jet system is a useful alternative for a safe ESD with minimum tissue injury.

Biocompatibility of Ti-alloys for long-term implantation

The design of new low-cost Ti-alloys with high biocompatibility for implant applications, using ubiquitous alloying elements in order to establish the strategic method for suppressing utilization of rare metals, is a challenge. To meet the demands of longer human life and implantation in younger patients, the development of novel metallic alloys for biomedical applications is aiming at providing structural materials with excellent chemical, mechanical and biological biocompatibility. It is, therefore, likely that the next generation of structural materials for replacing hard human tissue would be of those Ti-alloys that do not contain any of the cytotoxic elements, elements suspected of causing neurological disorders or elements that have allergic effect. Among the other mechanical properties, the low Young's modulus alloys have been given a special attention recently, in order to avoid the occurrence of stress shielding after implantation. Therefore, many Ti-alloys were developed consisting of biocompatible elements such as Ti, Zr, Nb, Mo, and Ta, and showed excellent mechanical properties including low Young's modulus. However, a recent attention was directed towards the development of low cost-alloys that have a minimum amount of the high melting point and high cost rare-earth elements such as Ta, Nb, Mo, and W. This comes with substituting these metals with the common low cost, low melting point and biocompatible metals such as Fe, Mn, Sn, and Si, while keeping excellent mechanical properties without deterioration. Therefore, the investigation of mechanical and biological biocompatibility of those low-cost Ti-alloys is highly recommended now lead towards commercial alloys with excellent biocompatibility for long-term implantation.

Optimization of Cr content of metastable β-type Ti-Cr alloys with changeable Young's modulus for spinal fixation applications

Metallic implant rods used in spinal fixtures should have a Young's modulus that is sufficiently low to prevent stress shielding for the patient and sufficiently high to suppress springback for the surgeon. Therefore, we propose a new concept: novel biomedical titanium alloys with a changeable Young's modulus via deformation-induced ω phase transformation. In this study, the Cr content in the range of 10-14 mass% was optimized to produce deformation-induced ω phase transformation, resulting in a large increase in the Young's modulus of binary Ti-Cr alloys. The springback and cytotoxicity of the optimized alloys were also examined. Ti-(10-12)Cr alloys exhibit an increase in Young's modulus owing to deformation-induced ω phase transformation. In this case, such deformation-induced ω phase transformation occurs along with {332}(β) mechanical twinning, resulting in the maintenance of acceptable ductility with relatively high strength. Among the examined alloys, the lowest Young's modulus and largest increase in Young's modulus are obtained from the Ti-12Cr alloy. This alloy exhibits smaller springback than and comparable cytocompatibility to the biomedical Ti alloy Ti-29Nb-13Ta-4.6Zr.

Beta type Ti-Mo alloys with changeable Young's modulus for spinal fixation applications

To develop a novel biomedical titanium alloy with a changeable Young's modulus via deformation-induced ω phase transformation for the spinal rods in spinal fixation devices, a series of metastable β type binary Ti-(15-18)Mo alloys were prepared. In this study, the microstructures, Young's moduli and tensile properties of the alloys were systemically examined to investigate the effects of deformation-induced ω phase transformation on their mechanical properties. The springback of the optimal alloy was also examined. Ti-(15-18)Mo alloys subjected to solution treatment comprise a β phase and a small amount of athermal ω phase, and they have low Young's moduli. All the alloys investigated in this study show an increase in the Young's modulus owing to deformation-induced ω phase transformation during cold rolling. The deformation-induced ω phase transformation is accompanied with {332}(β) mechanical twinning. This resulted in the maintenance of acceptable ductility with relatively high strength. Among the examined alloys, the Ti-17Mo alloy shows the lowest Young's modulus and the largest increase in the Young's modulus. This alloy exhibits small springback and could be easily bent to the required shape during operation. Thus, Ti-17Mo alloy is considered to be a potential candidate for the spinal rods in spinal fixation devices.

Microstructures and mechanical properties of metastable Ti-30Zr-(Cr, Mo) alloys with changeable Young's modulus for spinal fixation applications

In order to develop a novel alloy with a changeable Young's modulus for spinal fixation applications, we investigated the microstructures, Young's moduli, and tensile properties of metastable Ti-30Zr-(Cr, Mo) alloys subjected to solution treatment (ST) and cold rolling (CR). All the alloys comprise a β phase and small athermal ω phase, and they exhibit low Young's moduli after ST. During CR, deformation-induced phase transformation occurs in all the alloys. The change in Young's modulus after CR is highly dependent on the type of deformation-induced phase. The increase in Young's modulus after CR is attributed to the deformation-induced ω phase on {3 3 2} mechanical twinning. Ti-30Zr-3Cr-3Mo (3Cr3Mo), which exhibits excellent tensile properties and a changeable Young's modulus, shows a smaller springback than Ti-29Nb-13Ta-4.6Zr, a β-type titanium alloy expected to be useful in spinal fixation applications. Thus, 3Cr3Mo is a potential candidate for spinal fixation applications.

Mechanical and biodegradable properties of porous titanium filled with poly-L-lactic acid by modified in situ polymerization technique

Porous titanium (pTi) can possess a low Young's modulus equal to that of human bone, depending on its porosity. However, the mechanical strength of pTi deteriorates greatly with increasing porosity. On the other hand, certain medical polymers exhibit biofunctionalities, which are not possessed intrinsically by metallic materials. Therefore, a biodegradable medical polymer, poly-L-lactic acid (PLLA), was used to fill in the pTi pores using a modified in-situ polymerization technique. The mechanical and biodegradable properties of pTi filled with PLLA (pTi/PLLA) as fabricated by this technique and the effects of the PLLA filling were evaluated in this study. The pTi pores are almost completely filled with PLLA by the developed process (i.e., technique). The tensile strength and tensile Young's modulus of pTi barely changes with the PLLA filling. However, the PLLA filling improves the compressive 0.2% proof stress of pTi having any porosity and increases the compressive Young's modulus of pTi having relatively high porosity. This difference between the tensile and compressive properties of pTi/PLLA is considered to be caused by the differing resistances of PLLA in the pores to tensile and compressive deformations. The PLLA filled into the pTi pores degrades during immersion in Hanks' solution at 310 K. The weight loss due to PLLA degradation increases with increasing immersion time. However, the rate of weight loss of pTi/PLLA during immersion decreases with increasing immersion time. Hydroxyapatite formation is observed on the surface of pTi/PLLA after immersion for ≥8 weeks. The decrease in the weight-loss rate may be caused by weight gain due to hydroxyapatite formation and/or the decrease in contact area with Hanks' solution caused by its formation on the surface of pTi/PLLA.

Bone bonding bioactivity of Ti metal and Ti-Zr-Nb-Ta alloys with Ca ions incorporated on their surfaces by simple chemical and heat treatments

Ti15Zr4Nb4Ta and Ti29Nb13Ta4.6Zr, which do not contain the potentially cytotoxic elements V and Al, represent a new generation of alloys with improved corrosion resistance, mechanical properties, and cytocompatibility. Recently it has become possible for the apatite forming ability of these alloys to be ascertained by treatment with alkali, CaCl2, heat, and water (ACaHW). In order to confirm the actual in vivo bioactivity of commercially pure titanium (cp-Ti) and these alloys after subjecting them to ACaHW treatment at different temperatures, the bone bonding strength of implants made from these materials was evaluated. The failure load between implant and bone was measured for treated and untreated plates at 4, 8, 16, and 26 weeks after implantation in rabbit tibia. The untreated implants showed almost no bonding, whereas all treated implants showed successful bonding by 4 weeks, and the failure load subsequently increased with time. This suggests that a simple and economical ACaHW treatment could successfully be used to impart bone bonding bioactivity to Ti metal and Ti-Zr-Nb-Ta alloys in vivo. In particular, implants heat treated at 700 °C exhibited significantly greater bone bonding strength, as well as augmented in vitro apatite formation, in comparison with those treated at 600 °C. Thus, with this improved bioactive treatment process these advantageous Ti-Zr-Nb-Ta alloys can serve as useful candidates for orthopedic devices.

Development of biomedical porous titanium filled with medical polymer by in-situ polymerization of monomer solution infiltrated into pores

Porous metallic materials can have a low Young's modulus, which is approximately equal to that of human bone, by controlling the porosity. On the other hand, certain medical polymers exhibit biofunctionalities that are not intrinsically present in metallic materials. Therefore, a composite consisting of these materials is expected to possess both these advantages for biomedical applications. However, in the case of using porous metallic materials, the deterioration of mechanical properties should of concern because a stress concentration may be induced near the pores. In this study, for the fabrication of the abovementioned composite, a versatile process for filling a medical polymer into a porous metallic material has been developed using porous pure titanium (pTi) and polymethylmethacrylate (PMMA). Then, the tensile strength and Young's modulus of pTi filled with PMMA (pTi/PMMA) fabricated using this process are systematically investigated. The tensile strength of pTi can be improved by the PMMA filling. Particularly, the improvement in the tensile strength of pTi pretreated using a silane coupling agent before PMMA filling is greater than that of the non-pretreated pTi because the stress concentration near the pores may be reduced by the improvement in the interfacial adhesiveness between the titanium particles and the PMMA. In contrast, the effect of the PMMA filling on the Young's modulus of pTi is smaller than that on the tensile strength because the Young's modulus of PMMA is considerably lower than that of pTi. Further, tensile strengths and Young's moduli comparable to the tensile strength and Young's modulus of the human bone are successfully obtained in the case of some pTi/PMMA samples.

Metallic biomaterials

Ti alloys composed of nontoxic and allergy-free elements and Ni-free stainless steels and Co-Cr alloys are currently being developed. Ni-free Ti alloys exhibiting superelastic behavior, or the shape memory effect, are also being developed. beta-type Ti alloy with a low elastic modulus has proved to be effective for inhibiting bone absorption and enhancing bone remodeling. Simple bioactive surface modifications such as alkali-treatment processes and the calcium phosphate glass-ceramic dip-coating method are applicable to newly developed beta-type Ti alloys such as lowmodulus Ti-29Nb-13Ta-4.6Zr. Blood-compatible polymers such as poly(ethylene glycol) have been successfully fixed on the surface of Ti via chemical bonding by an electrodeposition method. Ti alloys for dental applications have also been recently developed.

Experiment study on fracture fixation with low rigidity titanium alloy: plate fixation of tibia fracture model in rabbit

In order to investigate bone tissue reaction to the low rigidity titanium alloy of TNTZ in bone plate fixation, animal experiment with rabbit was performed with X-ray follow-up and histological observation. Experimental fractures were made in rabbit tibiae, and fixed by different bone plates of SUS316L, Ti-6Al-4V and TNTZ. Although there was no significant difference in fracture healing, bone atrophy was observed in cortical bone especially under the bone plate, which was different in time course among three materials. The bone atrophy under the bone plate was confirmed as porous or poor bone tissue in histological observation. In addition, the diameter of the tibia bone was increased in TNTZ as the result of bone remodeling with a new cortical bone. It is confirmed that the elastic modulus of the bone plate will naturally influence bone tissue reaction to the bone plate fixation according to the Wolff's law of functional restoration.