Sol-gel derived Ag-containing TiO2 films on surface roughened biomedical NiTi alloy

Ag-containing TiO₂ films (Ag/Ti=3.3, 9.1 at%) were sol-gel coated on NiTi alloy that had been surface roughened by the NaOH-HCl treatment for antibacterial application. Thermal analyses of the dried gels reveal that the addition of 9.1 at% Ag lowers the anatase-rutile transformation temperature from 618 to 586 °C. Morphological observation shows that surface roughening and silver addition improve structural integrity of the TiO₂ films. X-ray diffraction reveals that the addition of Ag does not obviously change crystallinity of the anatase films. X-ray photoelectron spectroscopy results indicate metallic nature of Ag in the film and complete coverage of the films on the roughened alloy substrate. Microindentation test exhibits that the Ag-TiO₂ film on the roughened substrate has higher cohesive strength than that on the polished substrate. The potentiodynamic polarization test in a Ca-free Hank's balanced salt solution demonstrates good protection of the TiO₂ and Ag-TiO₂ films for the alloy substrate. Ultraviolet light illumination for 3 h can increase surface hydrophilicity of the coated NiTi samples by reducing contact angles from >65° to