Electrochemical behaviour of oxidized NiTi shape memory alloys for biomedical applications

A new oxidation treatment (OT) for NiTi Shape Memory Alloys used in biomedical applications has been developed in a previous work to reduce Ni surface concentration and, consequently, decrease Ni ions release into the exterior medium. This OT treatment is expected to minimize adverse and toxic reactions associated to Ni ions. However, in order to assess the biocompatibility of a metallic material, its corrosion resistance has to be evaluated. In this work, the electrochemical behaviour of NiTi surfaces oxidized by the new OT treatment was compared to untreated NiTi surfaces (NT). For this purpose, tests of open-circuit potential and cyclic voltammetry were performed at 37 °C in a Hanks Balance Salt Solution. A significant increase of the corrosion (E_corr) and breakdown (E_b) potentials was observed for OT surfaces, in comparison with NT surfaces. Moreover, the qualitative potentiodynamic behaviour of OT NiTi and Ti surfaces are similar. This observation suggests that the OT treatment leads to the formation of an oxide on NiTi surface that has similar structure and electrochemical property to native Ti oxide. This new oxidation treatment is efficient to protect NiTi alloys from electrochemical degradation and, therefore, it may be an excellent candidate for biomedical applications.