Effect of Anodized TiO2-Nb2O5-ZrO2 Nanotubes with Different Nanoscale Dimensions on the Biocompatibility of a Ti35Zr28Nb Alloy

Some important factors in the design of biomaterials are surface characteristics such as surface chemistry and topography, which significantly influence the relationship between the biomaterial and host cells. Therefore, nanotubular oxide layers have received substantial attention for biomedical applications due to their potential benefits in the improvement of the biocompatibility of the substrate. In this study, a nanotubular layer of titania-niobium pentoxide-zirconia (TiO₂-Nb₂O₅-ZrO₂) was developed via anodization on a β-type Ti35Zr28Nb alloy surface with enhanced biocompatibility. Scanning electron microscopy (SEM) and surface profilometry analysis of the anodized nanotubes indicated that the inner diameter (D_i) and wall thicknesses (W_t) increased with an increase in the water content of electrolyte and the applied voltage during anodization, while the nanotube length (L_n) increased with increasing the anodization time. TiO₂-Nb₂O₅-ZrO₂ nanotubes with different D_i, W_t, and L_n showed different surface roughnesses (R_a) and surface energies (γ), which affected the biocompatibility of the base alloy. MTS assay results showed that the TiO₂-Nb₂O₅-ZrO₂ nanotubes with the largest inner diameter (D_i) of 75.9 nm exhibited the highest cell viability of 108.55% due to the high γ of the surface, which led to high adsorption of proteins on the top surface of the nanotubes. The second highest cell viability was observed on the nanotubular surface with D_i of 33.3 nm, which is believed to result from its high γ as well as the optimum spacing between nanotubes. R_a did not appear to be clearly linked to cellular response; however, there may exist a threshold value of surface energy of ∼70 mJ/m², below which the cell response is less sensitive and above which the cell viability increases with increasing γ. This indicates that the TiO₂-Nb₂O₅-ZrO₂ nanotubes provided a suitable environment for enhanced attachment and growth of osteoblast-like cells as compared to the bare Ti35Zr28Nb alloy surface.