Annealing Temperature Effect on Tribocorrosion and Biocompatibility Properties of TiO₂ Nanotubes

TiO₂ nanotubes array gives entirely new types of interactions between titanium surfaces and cells due to the surface area increase and topography that resemble native bone tissue, and has been extensively studied as a promising technique to surface modification of implants. It is also well established that the annealing of anodized titanium surfaces significantly affects the properties of TiO₂ nanotubes, as well as the interaction with cells. Usually, titanium implants are subjected to micromovements under loading conditions in an aggressive biological environment, which causes tribocorrosion. The resulting debris from a tribocorrosive process could lead to infectious problems and eventually implant loss. This work aimed to evaluate the influence of the annealing treatment on the microstructure and mechanical properties of a TiO₂ nanotube layer produced on titanium, and consequently, on the tribocorrosive resistance, and the biological response to human dermal fibroblasts (HDF). Commercially pure titanium (grade 4) samples were anodized through the potentiostatic method using an aqueous electrolyte containing Ca and P and, after anodizing, submitted to annealing at different temperatures. The modified surfaces were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), X-ray diffraction (DRX), tribocorrosion tests, and bioactivity using HDF. Our results show that the annealing affects significantly the mechanical and tribological properties of the nanotubes layer. We also observed an increase in phosphorous amount with annealing temperature, which, along with the increase in the rutile crystalline phase amount, increases cells’ adhesion and proliferation.