Effect of Ti-OH groups on microstructure and bioactivity of TiO2 coating prepared by micro-arc oxidation

► TiO2 bioactivity coating was fabricated by a two-step micro-arc oxidation (MAO). ► The Ti-OH groups took a key role in the apatite formation inducing and promoting in this study. ► The previous introduction of Ca and P could increase the opportunity to form hydroxyapatite. ► The combination of MAO treatment and heated alkaline MAO treatment showed beneficial effects on the biocompatibility of Ti implant. ► TiO2 coating with Ti-OH groups showed superior bioactivity.