T. Takagi, Y. Sutou, R. Kainuma, K. Ishida, M. Suzuki, K. Yamauchi, Tohoku University, Sendai, Japan
Nitinol shape memory alloys have been widely used for minimally invasive therapy, e.g., stents and guidewires, because of their excellent flexibility due to superelasticity (SE). Stents are expandable wire form, which are made of weaving thin wires or laser-cutting the thin tubes and mounted at stenosis parts to control shape of arteries in human body. Therefore, their thin materials have a risk of crash if corrosion occurs by long-term implantation. In this study, the effects of surface conditions on corrosion resistance of Nitinol were investigated. The specimens were Nitinol cold-drawn wires with a diameter of 0.38mm. Two types of surface conditions were investigated; (1) wire with a gold colored surface and(2) wire with a black colored surface, such surface being formed by oxidized stronger than the gold colored one in manufacturing process. Corrosion resistance was examined by anode polarization measurement in phosphate buffered saline (PBS) at room temperature. Surface analysis was carried out by X-ray Photoelectron Spectroscopy (XPS).
Anode polarization measurements showed that the gold Nitinol wire exhibited a much more extensive passive state than SUS316L (stainless steel in Japanese Industrial Standards: JIS) wire. However, black Nitinol wire implied pitting corrosion at electric potential of 0.38 V. Therefore, black Nitinol wire corroded in lower electric potential than SUS316L. Surface analysis, however, showed that the black Nitinol wire had a thicker oxidized layer than the gold one
Summary: In this study, the effects of surface conditions on corrosion resistance of Nitinol were investigated.
The specimens were Nitinol cold-drawn wires with a diameter of 0.38mm. Two types of surface conditions were investigated; (1) the wire with gold color surface and(2) the wire with black color surface which is more oxidized in manufacturing process. Corrosion resistance was examined by anode polarization measurement in phosphate buffered saline (PBS) at room temperature. Surface analysis was carried out by X-ray Photoelectron Spectroscopy (XPS).
Gold Nitinol wire exhibited much more extensive passive state than SUS316L wire. However, black Nitinol wire implied pitting corrosion at electric potential of 0.38 V. Therefore, black Nitinol wire corroded in lower electric potential than SUS316L. By the surface analysis, Black Nitinol wire has thick oxidized layer compared with gold one.
