Heparin-poly(ethylene glycol)-poly(vinyl alcohol) hydrogel: preparation and assessment of thrombogenicity

Heparin was immobilized on to poly(vinyl alcohol) hydrogel (PVA) through the free isocyanate end-group on a poly(ethylene glycol) (PEG2000) which had been previously covalently linked to the hydrogel via a urethane moiety. The intention was to reduce the platelet reactivity of the PVA while also suppressing fibrin formation. Elemental nitrogen analysis revealed that the total amount of bound heparin was 19 +/- 7 mumol/g of dried gel. An increase in the in vitro whole blood clotting time of PVA was observed. This was attributed to bound heparin, as the elution rate of heparin from the gel (23 pmol/m2 min) was too low to produce a significant bulk concentration to interfere with fibrin formation. Ex vivo assessment using a chronic canine A-V shunt showed that the bound heparin hydrogel had no effect on the drop in the number of platelets induced by PVA hydrogel, but increased the fractional rate of platelet destruction from approximately 0.35/d to an average value of 0.42/d.