Correlation of In-vitro Corrosion to In-vivo Corrosion in Nitinol Stents

Friday, May 19, 2017: 10:15 AM
Sunset Ballroom 4 - 5 (Paradise Point Resort )
Dr. Stacey Sullivan , Food and Drug Administration, Silver Spring, MD
Mr. Daniel Madamba , Confluent Medical, Fremont, CA
Dr. Maureen Dreher , Food and Drug Administration, Silver Spring, MD
Dr. Shiril Sivan , Food and Drug Administration, Silver Spring, MD
Ms. Christine Trépanier , Confluent Medical, Fremont, CA
Dr. Srinidhi Nagaraja , Food and Drug Administration, Silver Spring, MD
Corrosion of nickel-containing implantable devices may result in adverse events such as loss of mechanical integrity and nickel toxicity/sensitization. Nitinol devices are of particular interest since their corrosion resistance is highly dependent on manufacturing processes. Therefore, the objective of this study was to assess whether current bench testing for corrosion accurately captures observed in-vivo corrosion and nickel leaching of Nitinol stents.

Nitinol stents were manufactured to have thermal or native oxides using one of four different surface treatments. In-vitro testing such as Auger surface characterization, nickel leach testing, and potentiodynamic polarization (ASTM F2129) were performed. In addition, these stent groups were implanted into minipigs for 6 months (IACUC #2012-022) and subsequently analyzed for corrosion using SEM and EDS. Nickel release was also assessed locally in the surrounding artery and systemically through serum and urine analyses. The following correlations were performed: (1) ASTM F2129 results with in-vivo corrosion observations (2) bench nickel leaching to in-vivo nickel measurements and (3) surface characterization to nickel release and corrosion.

ASTM F2129 testing of stent groups with limited surface processing showed breakdown potentials below 300mV with in-vivo corrosion observed in explants. These visual results were confirmed by EDS which demonstrated compositional changes (e.g. Ni/Ti ratio) in corroded regions compared to neighboring non-corroded regions and non-implanted controls. In contrast, stents with more extensive surface processing (e.g. mechanical polish) had breakdown potentials greater than 500mV and corrosion was not evident in explants. These findings provide important information on the relationship between surface processing and in-vivo corrosion resistance. 

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