Preparing Of TiO₂Nanotubes Array On Ti-Based Shape Memory Alloys And Cellular Compatibility

Biomedical Ti-22Nb-6Zr shape memory alloy exhibits unique shape memory effect andsuperelasticity, nontoxicity, good biocompatibility and biomechanical compatibility, hence itbecomes an excellent implant biomaterial with comprehensive application prospects. In orderto further increase its bioactivity, the fabrication of a stable and bioactive oxide layer on itssurface is one of the research interests in biomedical metal materials. In this study, highlyordered TiO₂nanotubes layer with high specific surface area were prepared on Ti-22Nb-6Zralloy by anodizing. The morphology and microstructure were characterized using XRD, SEMand TEM. The effect of anodizing and heat treatment parameters on the morphology andmicrostructure was investigated systematically. Finally, the cellular compatibility on variousTiO₂nanotubes was assessed by culturing cell. The main results were given as follows:The TiO₂nanotube layer can be successfully prepared on Ti-22Nb-6Zr alloy byanodizing. The diameter of TiO₂nanotube increases with improving anodizing voltage, and itdepends on the established balance time between corrosion rate and oxidation rate. Thelongest nanotube of about8μm can be obtained at60V. The single-diameter and highlyordered TiO₂nanotubes can form on Ti-22Nb-6Zr alloy, which is resulted from the splitting ofthe larger nanotubes and the combining from the smaller nanotubes under high voltage andextending oxidation time.Moreover, the as-anodized TiO₂nanotube layer presents amorphous structure, and can becrystallized through annealing. It has been found that the half amorphous and halfsingle-crystal anatase TiO₂nanotubes can be obtained by annealing at450℃for2hours. Thecrystallization of TiO₂nanotubes begins on the nanotubes layer/substrate interface, and thesingle-crystal growth is along the direction of the TiO₂nanotubes length by layer-by-layergrowth and oriented attachment. Furthermore, the crystal growth orientation is the normaldirection of （011） face of anatase TiO₂nanotube. Meanwhile, various defects were formedduring the process of crystallization, such as step, edge dislocation, screw dislocation andmixed dislocation. Additionally, the crystallinity of TiO₂nanotube layer is increases withannealing time, at last the whole single-crystal anatase TiO₂nanotube can be expected to beobtained. The results showed that the single-crystal anatase TiO₂nanotuber layer is morebeneficial to cell attachment and proliferation on it, hence, it exhibit better cell compatibilitythan amorphous TiO₂nanotubes layer.Finally, the TiNb₂O₇and Ti₂Nb₁₀O₂₉oxides can be observed in the TiO₂nanotube withincreasing the annealing temperature, which due to Nb precipitation from solid solution TiO₂ nanotube. However, the anatase TiO₂nanotube starts to transform to rutile structure as thetemperature rises up to850℃, which is due to the limitation of the Ti-O-Nb bond, oxygenvacancy and thickness of nanotubular wall. Whereafter, the nanotubular structure began to becollapsed due to the formation of rutile structure and Ti₂Nb₁₀O₂₉oxide with higher density,the tubular structure was completely destroyed at950℃.