Fabrication of Ti/TiO2(Ca)/hydroxyapatite bioceramic material by micro-arc oxidation and electrochemical deposition

Titanium with a bioceramic hydroxyapatite (HA) coating has been widely used in biomaterials owing to its excellent mechanical characteristics and high osteoconductivity. However, the interfacial strength of Ti/HA prepared by electrochemical deposition (ED) is relatively low because the physical combination is typically inadequate. In this study, to improve the interfacial strength, a micro-arc oxidation (MAO) process with calcium was introduced for preparing a connecting interlayer known as the MAO coating. Pulsed ED was employed to synthesise the HA coating on the MAO surface using an electrolyte with 6 wt% H2O2. Sample characterisations revealed that the MAO coating comprised porous TiO2 (rutile and anatase) with Ca or CaTiO3. The formation of CaTiO3 depends on the current density, reaction time, and concentration of Ca2+, in addition to voltage. The MAO coatings exhibited a higher corrosion resistance than that exhibited by Ti substrates. Furthermore, the HA coating on the MAO coating was confirmed to be plate-like Ca-deficient HA. The final sample had a Ti/TiO2(Ca)/ HA structure, and its adhesive strength was approximately double that of the Ti/HA sample. In particular, the MAO coating synthesised at a high Ca2+ concentration exhibited an improved adhesive strength (2.326 MPa). The application of the MAO coating containing Ca as a connecting interlayer is a promising strategy for improving the HA adhesion strength.