Characteristic and biocompatibility of the TiO2-based coatings containing amorphous calcium phosphate before and after heat treatment

TiO₂-based coating containing amorphous calcium phosphate (CaP) was prepared on titanium alloy by microarc oxidation (MAO). The increase in the EDTA-2Na concentration was unfavorable for the crystallization of TiO₂. After heat treatment, the amorphous CaP was crystallized. The thickness of the MAO coatings did not change when heat-treated at 400, 600 and 700 °C; while it increased slightly after heat treatment at 800 °C due to the crystallization of amorphous CaP and growth of TiO₂. No apparent discontinuity between the coatings and substrates was observed at various heat-treatment temperatures, indicating the MAO coatings with good interfacial bonding to the substrate. The heat treatment did not alter the chemical composition of the MAO coating and the chemical states of Ti, Ca and P elements. However, it increased the roughness (Ra) of the MAO coating and improved the wetting ability of the MAO coating. In this work, preliminary investigation of the MG63 cell proliferation on the surface of the MAO and heat-treated MAO coatings was conducted. The MAO coating surface with about Ra = 220 nm may be suitable for the MG63 cell adhesion and proliferation. The increased roughness of the heat-treated MAO coatings may result in a decrease in the ability for cell adhesion and proliferation.