Anodic Fabrication And Properties Of Interconnected Porous Layer On Titanium Biomedicalalloys

Amongst the materials available for biomedical applications,titanium-based materials have been considered as the most promising group for years. Pure titanium, for instance, has a combination of outstanding characteristics such as low density, high immunity to corrosion and excellent biocompatability, while its strength and wear resistance is relatively inferior to that of other biomaterials, like stainless-steel. The near-equiatomic nickel-titanium alloy(Ni Ti or Nitinol), compared to pure titanium, exhibits unusual mechanical properties, like high strength,shape-memory effects and superelasticity. Moreover, it has an extremely low Young’s modulus among most biomedical alloys, which is closest to that of the natural bone. However, it contains nearly 50 at% of Ni, which is proven to cause allergenic, cytotoxic and even carcinogenic reactions. This is the main concern that prevents the wide applications of Ni Ti in biomedical fields.Considering the above problems, various surface modificationshave been conducted on titanium-based alloys, by altering the surface micro-structure and chemical composition, aiming to reduce the release of toxic elements and further improve its bioactivity.In this research, surface anodic oxidation was conducted on pure titanium and Ni Ti alloys. Influences of this surface treatment on the resulted surface morphology of the oxide layer were investigated using scanning electron microscopy and atomic force microscopy, its composition analysed using X-ray differaction, X-ray photoelectron spectrum, and surface corrosion resistance evaluated by electrochemical polarization and SBF immersison tests.Results show that after anodization in F-contaning glycol-based electrolytes, a special interconnected porous layer was obtained on equiatomic Ni Ti. This special layer has a thickness of 5~10 μm and consists mainly of amouphous Ti O2, with trace oxidic or metallic Ni.Electrochemical polarization tests and SBF immersion tests show that this surface has improved corrosion resistance compared with bare Ni Ti and release of the toxic Ni is significantly supressed.Thus the above anodization treatment is effective to prepare a special interconnected porous layer with low Ni content and improved corrosion resistance, which will be a benefit for its biocompatibility. Also,the formation mechanism of the interconnected porous layer was discussed by conducting further investigation into the anodization behaviors of Nix T i 1-x alloys.