Bioactivity of Plasma-Sprayed TiO₂ Coating in Simulated Body Fluid by Hydrofluoric Acid Treatment

TiO2 coatings on titanium alloy substrates were prepared by atmospheric plasma spraying using commercial nano-powders. Then, as-sprayed coatings were treated using 10% hydrofluoric acid (HF) at room temperature for 30 seconds. As-sprayed and HF-treated titania coatings were soaked in simulated body fluid to investigate the formation of apatite on their surface. Field-emission scanning electron microscopy was used to observe the surface morphologies, and the phase composition of the as-sprayed coating and apatite were analyzed by X-ray diffraction and energy-dispersive X-ray spectrometry. As-sprayed titania coating is composed of rutile, anatase, and a small quantity of Ti3O5. It exhibited excellent adhesion between the TiO2 coatings and titanium alloy substrates, and the bonding strength was about 38 MPa. After in vitro experiment, a new substance containing calcium and phosphate was formed on the surface of HF-treated TiO2 coatings after being soaked in SBF, while the new substance was not formed on the surface of as-sprayed TiO2 coatings. The results indicated that the bioactivity can be induced to the surface of plasma sprayed TiO2 coatings by hydrofluoric acid treatment.