Increased corrosion resistance of stent materials by converting current surface film of polycrystalline oxide into amorphous oxide

Current efforts of new stent technology have been aimed largely at the impr ovement of intravascular stent biocompatibility. Among the chemical charact eristics of metallic stents, surface oxide corrosion properties are paramou nt. Using our unique technique, the currently marketed 316 L stainless stee l and nitinol stent wires covered with polycrystalline oxide were chemicall y etched and then passivated to form amorphous oxide. Excellent metallic-st ent corrosion resistance with an amorphous oxide surface was demonstrated i n our previous in vitro study. For in vivo validation, we compared the corr osion behavior of different oxide surfaces on various forms of test wires i n the abdominal aorta of mongrel dogs using open-circuit potential and cycl ic anodic polarization measurements. After conduction, the retrieved test w ires were observed under scanning electron microscope. No passivity breakdo wn was found for wires covered with amorphous oxide, while wires with polyc rystalline oxide showed breakdown at potentials between +0.2 to +0.6 V. It has been proven that severe pitting or crevice corrosion occurred on the su rface of polycrystalline oxide, while the surface of amorphous oxide was fr ee of degradations in our experiment. We have demonstrated that this amorph ous oxide coating on metallic material provides better corrosion resistance , not only in vitro but also in vivo, and it is superior not only in streng th safety but also in medical device biocompatibility. (C) 2000 John Wiley & Sons, Inc.