Effect of nanotube diameters on bioactivity of a multifunctional titanium alloy

Ti–24Nb–4Zr–8Sn (abbreviated as Ti2448) is a multifunctional β type titanium alloy consisting of nontoxic alloying elements and possessing better balanced biomechanical properties of high strength and low elastic modulus. To improve its bioactivity, the anodic oxidation of Ti2448 alloy in neutral electrolyte containing small amounts of NH4F was applied to produce the nanotubes consisting of the amorphous mixed oxides of TiO2, Nb2O5, SnO2 and ZrO2. The in vitro studies of the oestoblast-like MG-63 cells were performed to evaluate the biological behavior of the nanotubes with the outer diameters of 30, 50, 70 and 90 nm in comparison with the polished pure titanium and Ti2448 alloy. The results showed that the smaller diameter of 30 nm promoted the cell adhesion, proliferation and differentiation whereas the larger diameter of 90 nm had the worst cell viability with small spreading area of cytoskeletal actin. Although the nanotubes of Ti2448 alloy consist of the amorphous mixed oxides, it exhibits similar biological behavior with that of the amorphous TiO2 of pure titanium. This suggests that the topography of the amorphous nanotube plays important role on cell response. Additionally, the studies did not detect statistical difference of the bioactivity for the polished pure titanium and Ti2448 alloy.