Assessment of mechanical and corrosion properties of plasma oxidized medical grade NiTi wire

Abstract

Nitinol is an excellent biomaterial amongst smart materials, which have shape and form memory effects and superelasticity, and is mainly used as orthodontic wire and coronary stent. One of the associated drawbacks, however, is nickel release into bloodstream, which can achieve critical levels. In this work, F2063 Nitinol wire was plasma-oxidized in order to obtain a TiO2 protective layer ranging from 50 to 80 nm, which helps blocking nickel release and enhances corrosion properties, thus avoiding or decreasing foreign body reactions. Two power sources (DC and RF) were evaluated and the resulting surfaces from plasma treated samples were characterized. According to the obtained results, tensile tests showed a slight improvement in superlastic elongation and in vitro corrosion resistance in specimens treated by plasma. The findings also suggest that RF power source is best suited to achieve a desired nano-scale layer in NiTi alloys. In this new light, plasma-assisted treatments can be performed in memory-shape alloys, aiming the obtention of a well adhered, corrosion improving and mechanical properties enhancing coating.