Activity toward thrombin-antithrombin of heparin immobilized on two hydrogels.

Commercially obtained (Diosynth) heparin was covalently bonded to poly (vinyl alcohol) (PVA) hydrogels and to polyethylene oxide (PEO) hydrogels activated by tresyl chloride. We found that as tresyl chloride activation of PVA increased, the specific activity of the bound heparin toward thrombin and antithrombin decreased by nearly a factor of 10 and that commercial heparin bound to PEO had nearly ten-fold greater activity than when bound to PVA at comparable concentrations. These findings suggest that the long 'leash' provided by PEO hydrogels may give the heparin more access to the thrombin-antithrombin pair than the tight bond to PVA, and that crowding of heparin units on a surface limits access of the thrombin-antithrombin pair.