Corrosion behaviour of electropolished implant alloys

Most medical device alloys are electropolished prior to implantation and are immediately protected by the formation of passivating metal oxides. Nevertheless, tissue and fluid present in the human body presents a very corrosive environment to metals once implanted. This is exacerbated by the effects of strain, fatigue, abrasion or wear, which may rupture the passive film exposing the underlying metal. Cyclic potentiodynamic polarization studies were conducted to compare the corrosion resistance of Nitinol and stainless steel cardiovascular stents. In an attempt to simulate their corrosion behavior under body conditions, a Phosphate Buffered Saline (PBS) solution at 37 °C was employed utilizing the ASTM F2129-01, Item 2, WK1749, Standard [1]. The results of this study indicate that both materials exhibit high corrosion resistance in the PBS solution with stainless steel exhibiting slightly better corrosion resistance. However, electropolished nitinol stents appeared to have better corrosion resistance as compared to the unpolished ones.