THE THROMBORESISTANCE OF A HEPARIN-POLYVINYL ALCOHOL HYDROGEL

Heparin immobilized onto polyvinyl alcohol (PVA) by action of glutaraldehyde has been shown to be biologically active in a novel parallel flow arteriovenous shunt in dogs. The heparin-PVA hydrogel originally devised by Merrill and his collaborators was applied as a coating to chromic acid etched polyethylene tubing. A pair of Y-connectors was used to divert <2% of the flow in the AV shunt through the heparinized tube, which remained patent for longer than two hours while a control tube without heparin was occluded within 30 minutes at a main shunt flow rate of similar to 150 mL/min. This enhanced patency was achieved without significant release from the surface, consistent with earlier experiments attributing the thromboresistance of the heparin-PVA hydrogel to the formation of a surface bound inactive thrombin-antithrombin Ill complex. Radiolabelled thrombin adsorbed onto beads made from the gel was readily displaced by arvinized plasma, indicating that the inactive complex was not itself permanently bound to the surface. These results demonstrate the utility of Merrill's hydrogel for preparing materials with potential long term thromboresistance and for testing the validity of the hypothesized limitations to the long term use of immobilized heparin.