Abstract:Micro/nano-structured composite coating composed of titanium dioxide (TiO2) and hydroxyapatite (HA) was fabricated on TA2 pure titanium through synergistic micro-arc oxidation (MAO) and hydrothermal (HT) processing to enhance the corrosion resistance and biocompatibility of titanium substrates. The surface micromorphology of the coatings was investigated by scanning electron microscope; the roughness and hydrophilicity of the coatings were investigated by atomic force microscope and water contact angle, respectively; the corrosion resistance was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization tests in simulated human body fluids; the biocompatibility was investigated by in-vitro cell culture experiments. Results demonstrate that by doping HA into MAO electrolyte, a micrometer-sized coating loaded with nano-HA particles can be obtained, and then HT treatment can be conducted to obtain the micro/nano-structured composite coating with a HA-containing nanoflake structure. This micro/nano-structured composite coating possesses good hydrophilicity and fine corrosion resistance. The coating performance achieves optimal state when the coating is prepared with 3 g/L HA and HT-treated for 6 h. In this case, the water contact angle is as low as 24.2°, and the polarization resistance is as high as 2.467×104 Ω·cm2. In addition, the synergistic effect of nano-HA and micro/nano-structure on the coating surface greatly promotes the cell proliferation, presenting non-cytotoxic characteristic, and indicating that the coating possesses good biocompatibility.