In vitro bioactivity evaluation of titanium and niobium metals with different surface morphologies.

Current orthopaedic biomaterials research mainly focuses on designing implants that could induce controlled, guided and rapid healing. In the present study, the surface morphologies of titanium (Ti) and niobium (Nb) metals were tailored to form nanoporous, nanoplate and nanofibre-like structures through adjustment of the temperature in the alkali-heat treatment. The in vitro bioactivity of these structures was then evaluated by soaking the treated samples in simulated body fluid (SBF). It was found that the morphology of the modified surface significantly influenced the apatite-inducing ability. The Ti surface with a nanofibre-like structure showed better apatite-inducing ability than the nanoporous or nanoplate surface structures. A thick dense apatite layer formed on the Ti surface with nanofibre-like structure after 1 week of soaking in SBF. It is expected that the nanofibre-like surface could achieve good apatite formation in vivo and subsequently enhance osteoblast cell adhesion and bone formation.

Hydroxyapatite/titania sol-gel coatings on titanium-zirconium alloy for biomedical applications.

A simple sol-gel method was developed for hydroxyapatite/titania (HA/TiO(2)) coatings on non-toxic titanium-zirconium (TiZr) alloy for biomedical applications. The HA/TiO(2)-coated TiZr alloy displayed excellent bioactivity when soaked in a simulated body fluid (SBF) for an appropriate period. Differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy-energy dispersive spectrometry were used to characterize the phase transformations and the surface structures and to assess the in vitro tests. The HA/TiO(2) layers were spin-coated on the surface of TiZr alloy at a speed of 3000rpm for 15s, followed by a heat treatment at 600 degrees C for 20min in an argon atmosphere sequentially. The TiO(2) layer exhibited a cracked surface and an anatase structure and the HA layer displayed a uniform dense structure. Both the TiO(2) and HA layers were 25microm thick, and the total thickness of the HA/TiO(2) coatings was 50microm. The TiZr alloy after the above HA/TiO(2) coatings displayed excellent bone-like apatite-forming ability when soaked in SBF and can be anticipated to be a promising load-bearing implant material.

Effect of thermomechanical treatment on the superelasticity of Ti-7.5Nb-4Mo-2Sn biomedical alloy.

Effects of thermomechanical treatment on the microstructure and superelasticity of Ti-7.5Nb-4Mo-2Sn biomedical alloy were investigated by using XRD measurement, optical microscope (OM), transmission electron microscope (TEM) and tensile tests. The titanium alloy samples were prepared by annealing at a temperature in the range of 600 to 1000°C after severe cold rolling; and the samples that were annealed at 800°C were further aged at 600 and 700°C. The volume fraction of α phases decreased while that of ω phases increase with increasing annealing temperature. The αâ†’ß transformation temperature of the alloy was determined to be between 700 and 800°C. The alloy that was annealed at 700°C exhibited a high level of superelasticity with relatively high first yield stress (σSIM) at room temperature because it contained a fine α phase. A certain amount of ω phases also resulted in an increase in σSIM, leading to an improvement in the superelasticity of the alloys that were annealed at 900 and 1000°C. Aging treatment led to the precipitations of α and ω phases in the alloy after annealing at 800°C; and the volume fraction of α phases decreased while that of ω phases increased with increasing aging temperature. Excellent superelasticity with high recovered strain (εrecoverable) and strain recovery rate (η) were obtained in the aged alloy due to the reinforcement of α and ω phases induced by aging treatment. The alloy annealed at 700°C for 0.5h exhibited the best superelasticity in all the thermomechanically treated alloys due to the strengthening from the subgrain refining and the precipitating of fine α phases.

Effect of process control agent on the porous structure and mechanical properties of a biomedical Ti-Sn-Nb alloy produced by powder metallurgy.

The influence of different amounts and types of process control agent (PCA), i.e., stearic acid and ethylene bis-stearamide, on the porous structure and mechanical properties of a biomedical Ti-16Sn-4Nb (wt.%) alloy was investigated. Alloy synthesis was performed on elemental metal powders using high-energy ball milling for 5h. Results indicated that varying the PCA content during ball milling led to a drastic change in morphology and particle-size distribution of the ball-milled powders. Porous titanium alloy samples sintered from the powders ball milled with the addition of various amounts of PCA also revealed different pore morphology and porosity. The Vickers hardness of the sintered titanium alloy samples exhibited a considerable increase with increasing PCA content. Moreover, the addition of larger amounts of PCA in the powder mixture resulted in a significant increase in the elastic modulus and peak stress for the sintered porous titanium alloy samples under compression. It should also be mentioned that the addition of PCA introduced contamination (mainly carbon and oxygen) into the sintered porous product.

Titanium-nickel shape memory alloy foams for bone tissue engineering.

Titanium-nickel (TiNi) shape memory alloy (SMA) foams with an open-cell porous structure were fabricated by space-holder sintering process and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The mechanical properties and shape memory properties of the TiNi foam samples were investigated using compressive test. Results indicate that the plateau stresses and elastic moduli of the foams under compression decrease with the increase of their porosities. The plateau stresses and elastic moduli are measured to be from 1.9 to 38.3 MPa and from 30 to 860 MPa for the TiNi foam samples with porosities ranged from 71% to 87%, respectively. The mechanical properties of the TiNi alloy foams can be tailored to match those of bone. The TiNi alloy foams exhibit shape memory effect (SME), and it is found that the recoverable strain due to SME decreases with the increase of foam porosity.

Processing and mechanical properties of autogenous titanium implant materials.

Pure titanium and some of its alloys are currently considered as the most attractive metallic materials for biomedical applications due to their excellent mechanical properties, corrosion resistance, and biocompatibility. It has been demonstrated that titanium and titanium alloys are well accepted by human tissues as compared to other metals such as SUS316L stainless steel and Co-Cr-Mo type alloy. In the present study, highly porous titanium foams with porosities