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Monday, May 17, 2010 - 3:30 PM

The Effect of Material Removal On the Corrosion Resistance and Biocompatibility of Nitinol Laser-Cut and Wire-Form Products

J. Fino Decker, C. Trepanier, L. Vien, A. Pelton, Nitinol Devices & Components, Fremont, CA

Laser cutting and wire forming are two of the most commonly used processes in the manufacture of Nitinol medical devices. Because these two fabrication methods subject the part to very different external conditions, it is prudent to understand how post-process surface treatment methods may need to be adjusted to achieve optimal in vivo corrosion resistance and biocompatibility. This study explores how varying the amount of material removed during the final surface treatment steps affects the corrosion resistance of Z-type stents that have either been laser-cut from tube or shape set from wire. The parts were subjected to a typical heat treatment process necessary to achieve an Austenite finish temperature of 28°C, and were subsequently post-processed with one of two different surface treatments, an electrochemical passivation or a chemical passivation. The total weight loss during post-processing was recorded and the process adjusted to create groups with low, medium, and high amounts of weight loss. Corrosion testing was conducted per ASTM F2129 on all of the samples to determine how the amount of weight loss affects the corrosion resistance of the devices. Visual and scanning electron microscopy were used to correlate surface features with corrosion sites. Also, because nickel has been known to cause adverse reactions in vivo, the best and worst corrosion performers from each group were subjected to a 7- day nickel ion release study to determine biocompatibility.  As such, this study links surface processing, corrosion with a link to in vivo biocompatibility.

Summary: This study explores how varying the amount of material removed during the final surface treatment steps affects the corrosion resistance of Z-type stents that have either been laser-cut from tube or shape set from wire. The parts were subjected to a typical heat treatment process necessary to achieve an Austenite finish temperature of 28°C, and were subsequently post-processed with one of two different surface treatments, an electrochemical passivation or a chemical passivation. The total weight loss during post-processing was recorded and the process adjusted to create groups with low, medium, and high amounts of weight loss. Corrosion testing was conducted per ASTM F2129 on all of the samples to determine how the amount of weight loss affects the corrosion resistance of the devices. Visual and scanning electron microscopy were used to correlate surface features with corrosion sites. Also, because nickel has been known to cause adverse reactions in vivo, the best and worst corrosion performers from each group were subjected to a 7- day nickel ion release study to determine biocompatibility.