Hybrid Oxidation of Titanium Substrates for Biomedical Applications

Issues related to the improvement in bioactivity of titanium materials used in implantology for the regeneration and replacement of bone tissue are of great application importance due to the elimination of undesirable interactions between tissues with physiological fluids during the operation of implants. Therefore titanium oxidation for biomedical applications is still a challenge in obtaining both good mechanical and physicochemical properties of thin oxide layers as well as the required good adhesion to titanium substrates and of course bioactivity. Interesting techniques for TiO₂ layers formation are electrochemical methods (anodizing), electric discharge treatments, plasma methods (PVD) and diffusive methods (Fluidized Bed FB). Each method aims to create a thin homogenous oxide layer characterized by thermal stability and re-passivation in the presence of body fluid environment. However, an important aspect here is also phase composition of thin oxide layers, essential in the processes of osseointegration. Accordingly research carried out by the Author aims to produce such a titanium substrate, where surface zone is Ti_α(O) solid solution formed with Fluidized Bed diffusion process (883K, 913K for 6h / 8h) and the outer layer is TiO₂ oxide produced by PVD magnetron sputtering. Effects of such hybrid oxidation on titanium physiochemical properties were investigated with TEM / EFTEM, SIMS, RS and Nanoindentation tests. Results showed that hybrid oxidation made it possible to generate favourable synergetic effect between Fluidized Bed and PVD oxide layers and to reduce the stresses at their interface. In turn, variable share of TiO₂ oxide phases (rutile + anatase mixture) obtained at the titanium surface allowed for the significant enhancement of hydroxyapatite growth which was confirmed by 7 / 14 days Kokubo tests. Hybrid processes also influenced the decrease in the surface roughness parameters, important for implant materials. Intensive formation of hydroxyapatite compounds shows the potential of applying hybrid oxidation for the improvement of titanium surface bioactivity and confirms the method is novel outlook in TiO₂ oxide layers properties modification for biomedical applications.