Highly improved Nitinol biomaterial devices by magnetoelectropolishing (MEP)

In recent years, the use of Nitinol as a metallic biomaterial being compound of nickel and titanium, has been steadily growing, particularly in medical and dental devices markets. However, further application of Nitinol has been slowed down due to leaching nickel and unavoidable inclusions appearing on the surface during manufacture of this intermetallic compound. Electropolishing of Nitinol biomaterial samples as-received (AR) was carried out under different conditions: (a) on the plateau level (EP), (b) above the plateau (EP+), and (c) in the magnetic field (MEP). This work is to present magnetoelectropolishing (MEP) as an electrochemical processing method able to significantly improve the Nitinol biomaterial properties. Following our previous SEM/EDS studies, and corrosion resistance improvement of Nitinol, in this work XPS and XRD study methods were used. First of all, as indicated by XPS study results concerning biocompatibility, it was proved that MEP leaves Nitinol surface enriched in oxygen and with nickel reduced to zero. Thus the titanium oxides, generally TiO2, are formed on Nitinol surface. It appears that by introducing a magnetic field into the electrolysis system, another effect relying on a considerable increase of Nitinol mechanical properties is obtained. The experiments carried out on surgical needles show an unusual multiple growth in resistance to bending until fracture. Further increase in fatigue resistance is usually limited by different size of inclusions which happen to appear on the Nitinol part surface. Moreover, in this work also a simple method is proposed to reject the Nitinol parts, with the inclusions detected on the biomaterial surface, before their application.