Persistent Polarization in Polymers and Blood Compatibility

The use of persistent electrical polarization in polymers has been explored as a means of reducing surface thrombogenicity. Parallel efforts have been carried out on the characterization of surface properties related to the electret state in polymers, on the stability of the electret state in desirable prosthetic materials under simulated blood pumping conditions, and on in vitro and in vivo blood compatibility experiments. Preliminary correlations among critical surface tension, electrical polarization, and blood compatibility have been obtained. In vitro blood compatibility has been explored using both a modified Lee-White clotting test and a platelet adsorption experiment. No significant difference in clotting time was found for polarized samples; however, those with a negative charge did adsorb fewer platelets. A series of in vivo studies has been carried out using electrified right atrial flags (36) of poly-vinylidene chloride and vena cava rings (22) of FEP Teflon, Hypalon rubber, and Hypalon/2% polysulfonate. Negatively polarized samples showed improved blood compatibility in all cases. About 2/3 of the negatively charged atrial flags showed little or no thrombus and the remainder moderate thrombus whereas 2/3 of the positively charged flags showed severe thrombus. About 3/4 of the negative ring implants showed little or no thrombus. A correlation with anomalous contact angle or low charge was found in 4 of 6 cases of the rings with moderate to heavy thrombus.