Structure, cell response and biomimetic apatite induction of gradient TiO₂-based/nano-scale hydrophilic amorphous titanium oxide containing Ca composite coatings before and after crystallization

Chemical treatment was used to modify the surface of microarc oxidized (MAO) coating containing Ca and P. And the chemically treated MAO (C-MAO) coating was further heat-treated at 400-800 °C. The average roughness of the MAO and C-MAO coatings is about 250 nm; further heat treatment improved the roughness of the C-MAO coating. The chemical and heat treatment enhanced the wetting ability of the MAO coating. During SBF immersion, amorphous Ca- and P-containing precipitate (Ca-P) appeared firstly, eventually transforming to crystalline apatites. At the same time, the apatite firstly formed at the concave region on the surface, and then spreads on the whole surface. The induced biomimetic apatite possessed a porous structure on two-scales of micron and nanometer levels. In the interlayer and outlayer of the C-MAO coating, the elements of Ca, P and Ti showed a gradient distribution. In the apatite layer, Ti disappeared basically, and the concentrations of Ca and P did not change obviously. In this work, continuous MG63 cell layer was observed on the surface of the C-MAO coating, which can provide good environment for the cell proliferation.