Preparation and characterization of hydroxyapatite/titania composite coating on NiTi alloy by electrochemical deposition

NiTi alloy is used as biomaterial due to its unique properties, but the high content of Ni (about 50 at.%) in biomedical NiTi is of concern. Hydroxyapatite/titania composite coating was directly electrodeposited on the surface of NiTi alloy. The coated samples were characterized using X-ray diffraction, scanning electron microscopy, infrared spectroscopy, bonding strength test, polarization and electrochemical impedance spectroscopy (EIS). Results showed that addition of TiO2 to the electrolyte changed the morphology of hydroxyapatite from thin flake-flower-like crystals to needle-flower-like crystals, and the coating was much denser. Besides, hydroxyapatite crystal grains in the coating were preferentially arranged in the [001] direction, which was perpendicular to the surface of NiTi alloy. The addition of TiO2 improved the bonding strength between the coating and the substrate. Corrosion resistance of NiTi in the simulated body fluid at 37 °C was significantly improved by more than 50 times by electrodeposition of the hydroxyapatite/titania composite coating.