J. Gilbert, Syracuse University, Syracuse, NY
Biomedical alloys have complex, dynamic and voltage dependent surface oxides that serve as the primary surface for biological interaction. When implanted these surfaces undergo voltage-dependent changes and interact with proteins in a voltage dependent way. There are several important mechanisms by which passive oxide films may affect protein adsorption and biological interaction. One surface mechanism thought to be important is the hydrophilic character of the surface. The goal of this work is to present a simple method, based on the Wilhelmy plate method for surface tension measurement, to measure the change in surface energy with the application of a voltage. Electropolished 316L SS surfaces (2 nm RMS roughness) were subjected to controlled potentials ranging from -1V to +1V (vs Ag/AgCl) and the effects of voltage on the capillary height rise were directly measured using a glass parallel plate and digital camera. The results show that increasingly cathodic (negative) potentials significantly increased the hydrophilic character of the oxide. Potentials between 0 and +1V had little or no effect on surface tension. These results correlate with other work in our lab that shows both increased cathodic Faradaic currents and decreased fibrinogen adsorption with increasing cathodic potentials.
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