Effect of zirconia nanotube coating on the hydrophilicity and mechanochemical behavior of zirconium for biomedical applications

Zirconium has attracted considerable attention in the biomedical field owing to its biocompatibility and desirable tribological and mechanical properties. In this study, we anodized pure zirconium in an ammonium fluoride and ethylene glycol electrolyte, which produced a coating of ZrO₂ nanotubes (NTs). The ZrO₂ coated samples were annealed at different temperatures, and the morphology and structure of the coated substrates were studied using XPS, SEM, TEM, EDS, and SAED. The micro/nanomechanical properties and corrosion resistance of the samples were evaluated. Wear tests performed on bare and coated substrates revealed that the coated samples annealed at 400 °C had a significantly lower average coefficient of friction than the other substrates. The corrosion test was performed on different substrates, and the results showed that the corrosion resistance of the coated sample annealed at 400 °C was considerably higher than that of the other substrates. According to the nanoindentation tests, the elastic modulus of the Zr sample decreased from 74.3 to 31.7 GPa after anodization and the creation of ZrO₂ NTs. Biocompatibility tests revealed that cell attachment to the surface of the ZrO₂ NTs decreased due to the presence of F⁻; however, the cell viability increased after the ZrO₂ NT-coated samples were annealed at 200 and 400 °C.