B. G. Pound, Exponent, Menlo Park, CA
Biomedical devices are finding increasing use in biliary applications. This study examined the electrochemical behavior of nitinol in two simulated bile solutions. Tests were performed on mechanically polished and electropolished nitinol wire using cyclic potentiodynamic polarization and electrochemical impedance spectroscopy. The impedance data were analyzed using equivalent circuit models to evaluate the capacitive and resistive components of the surface oxide at different potentials. The cyclic polarization results together with the impedance data were used to characterize changes in the electrochemical behavior in each bile solution and to determine whether nitinol exhibited a difference in behavior between the two bile solutions. In addition, the cyclic polarization results were compared with those obtained in phosphate-buffered saline.
Summary: The electrochemical behavior of mechanically polished (MP) and electropolished (EP) nitinol was characterized in two simulated bile solutions. The EP nitinol, unlike the MP condition, was resistant to breakdown up to 1 V in both solutions. Considerable differences were observed in the impedance components between the two surface conditions in each bile solution. The components also exhibited a marked dependence on potential. The variation in electrochemical behavior with potential was similar for the two bile solutions, suggesting that the surface oxide underwent comparable changes in each solution. Comparison of cyclic polarization results for the bile solutions with those for phosphate-buffered saline showed that electropolishing greatly increased the resistance to breakdown, irrespective of the solution.
