Abstract: Porous and nanostructured TiO₂ coatings with different Ca, P contents were prepared on titanium by plasma electrolytic oxidation (PEO) in a Ca and P containing electrolyte at different current densities. The surface morphologies and microstructure of the coatings were observed by scanning electron microscope (SEM). Phase compositions of the coatings were characterized using X-ray diffraction (XRD). Simulated body fluid (SBF) immersion tests were conducted to evaluate the apatite forming ability and bioactivity of coatings. The results reveal that the PEO coatings mainly consist of anatase and rutile phases, their surfaces exhibit grains of about 10-100 nm in size and pores less than 10 μm in diameter. The surface grains, coating thicknesses, surface roughness and Ca, P contents of the coatings all increase with the increase of the applied current density during PEO process. The as-prepared PEO coatings with high Ca and P contents could induce apatite formation after immersed in SBF for 14 d, indicating its good bioactivity. However, PEO coatings with low Ca and P contents or heat-treated coatings are bio-inert. The Ca, P contents of the PEO coatings and its crystallization state play key roles in inducing apatite formation in SBF.

Key words: TiO₂, porous, nanostructured, bioactive, plasma electrolytic oxidation