Electrochemical and Cell Culture Testing of Nitinol Stents Under Fretting and Flow Conditions

Nitinol stents are common cardiovascular devices for implantation due to their shape memory and superelastic properties as well as their excellent biocompatibility.  In this study, the open circuit potential of overlapping Nitinol stents was monitored during fretting and under flow conditions.  Testing was performed in a phosphate buffered saline solution (PBS) at a pH of 7.4.  Additional tests were performed with a PBS solution with a pH of 5.5, which would simulate a wound scenario.  Four different cells were set up for each of the two solutions for 14 Days, 30 Days, 60 Days and 90 Day durations.  After testing the samples were examined via SEM/EDS to provide information on the morphology of the stent surfaces.  Cyclic polarization was then performed on one of the stents to quantify the general and localized corrosion behavior.  Nickel ion measurements were obtained from the solutions during fretting/flow testing.  In addition, cell culture testing was performed with endothelial cells after exposure on one of the overlapping stents to see if the fretting/flow condition affected the biocompatibility of the stent.