Enhancement of hydroxyapatite formation on anodic TiO2 nanotubular arrays via precalcification

Hydroxyapatite (HA) depositions on metallic biomedical implants have been widely applied to generate bioactive surfaces in simulated biological environments. Meanwhile, highly ordered TiO₂ nanotubular arrays obtained via anodization have attracted increasing interest for biomedical applications. However, capability to grow HA coating on TiO₂ nanotubular arrays at room temperature remains problematic. In this study, we applied a precalcification treatment on anodic TiO₂ nanotubular arrays to examine the formation of HA coating in simulated biological fluid. The as-formed TiO₂ nanotubular arrays on titanium were immersed in boiling saturated Ca(OH)₂ solutions for up to 40 min. The specimens readily grew HA once immersed in the simulated biological fluid (SBF) after 4 days immersion. The carbonated HA coating was formed with more than 5 μm thickness after 12 days of immersion while only a few calcium phosphate particles were observed on annealing TiO₂ nanotubular arrays immersed in the same solution for the same duration. This treatment dramatically improved efficiency for promoting HA formation on anodic TiO₂ nanotubular arrays without high temperature treatment.