Chemical stability of the titania layer formed synthetically on NiTi shape memory alloy as a barrier to prevent nickel ion release

To improve the biocompatibility of NiTi shape memory alloy (SMA), a titanium oxide layer was fabricated on the surface of NiTi SMA using an established H₂O₂-oxidation and hot water aging technique. The chemical stability of the titania surface layer in simulated body fluids was investigated via potentiostatiodynamic polarization tests. After the chemical stability tests, the surface morphology of samples was examined using a scanning electron microscope (SEM). Compared to the untreated NiTi SMA samples, higher corrosion potential (E_corr) and breakdown potential (E_b) and lower breakdown current were observed for NiTi SMA samples with the synthetic titanium oxide surface layer. The results suggest that NiTi SMA samples covered by the titania layer had better chemical stability. This oxide layer could act as a physical barrier to prevent Ni ion release from NiTi SMA implants.