Composite biocoating of hydroxyapatite/Al2O3 on titanium formed by Al anodization and electrodeposition

A new composite biocoating of hydroxyapatite/Al2O3 on titanium, in which hydroxyapatite served as the outer layer and porous Al2O3 as the intermediate layer, was fabricated by a multi-step process consisting of physical vapor deposition (PVD), anodization, electrodeposition, and hydrothermal treatment. The obtained composite biocoatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). Characterization results indicated that micrometric plate-like Ca-deficient hydroxyapatite (CDHA) crystals formed the outer layer of the composite biocoating during electrodeposition and then were converted into nanosized needle-like Ca-rich hydroxyapatite (CRHA) ones by hydrothermal treatment in alkaline ammonia medium. The CRHA outer layer in the hydrothermally-formed composite biocoating showed good ability for the induction of apatite in simulated body fluid (SBF). A possible mechanism was proposed for the formation of CRHA.