Structure and in vitro bioactivity of titania-based films by micro-arc oxidation

Titania-based films on titanium were formed by micro-arc oxidation in electrolytic solutions containing sodium carbonate, sodium phosphate, acetate monohydrate and β-glycerophosphate disodium salt pentahydrate using a pulse power supply. The morphology, elemental composition and phase components of the films were investigated as a function of the electrolytes composition and the applied voltage (in the range of 200-500 V). In vitro bioactivity of the films was evaluated in a most commonly used simulated body fluid as proposed by Kokubo et al. The results showed that the films were porous with 1-8 μm pores and nano-crystallized, without apparent interface to the titanium substrates. The phase components of the films could be anatase, rutile, CaTiO₃, β-Ca₂P₂O₇ and α-Ca₃(PO₄)₂, strongly depending on the electrolytes composition and the applied voltage. The pore size and the content of Ca and P tended to increase with the applied voltage. Among the prepared titania-based films, only the film containing CaTiO₃, β-Ca₂P₂ O₇ and α-Ca₃(PO₄)₂ could induce an apatite layer on its surface, exhibiting bioactivity. The bioactive response of the micro-arc oxidized films to the structural factors and the apatite-induced mechanism were discussed.