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

Abstract

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 3h can increase surface hydrophilicity of the coated NiTi samples by reducing contact angles from >65° to <20°.