Electrolytic deposition of fluorine-doped hydroxyapatite/ZrO2 films on titanium for biomedical applications

A novel method of electrolytic fluorine-doped hydroxyapatite/ZrO2 double-layer coating was conducted on medical titanium in ZrO(NO3)2 aqueous solution and subsequently in the mixed solution of Ca(NO3)2, NH4H2PO4 and NaF. The microstructure, phase composition, bond strength, dissolution rate and corrosion resistance of the films were studied. Results revealed that the additions of F− reduced the crystallite and increased the crystallinity of hydroxyapatite, structure of apatite was changed from micro-petal-like crystals to nano-needle-like crystals, which aligned vertically to the substrate. The approximately 10 μm thick layers was much denser and uniform. Addition of ZrO2 buffer layer could improve the bond strength between the fluorine-doped hydroxyapatite layer and the substrate. The bond strength of the double-layer coating was found to be significantly higher than that of pure hydroxyapatite coating even after soaking in normal saline for two weeks. In physiological solution, the double-layer coating showed lower dissolution rate and stronger corrosion resistance than pure hydroxyapatite coating.