Factor Xa inactivation by a heparinized hydrogel.

Incubating Factor Xa and plasma in the presence of "beads" of a heparinized hydrogel (heparin-PVA) resulted in a loss of Factor Xa activity as measured by clotting time or chromogenic substrate assays. This loss in activity was attributed to the activity of the heparin immobilized to the polyvinyl alcohol (PVA) hydrogel. The immobilized heparin retained an apparent activity approximately 1% that of a similar mass of heparin in solution. The loss in apparent activity was in part attributed to diffusion effects which limited the accessibility of the enzyme and inhibitor to the heparin immobilized in the interior of the gel "beads". The chromogenic substrate activity of adsorbed Factor Xa was also measured and was found to decrease after exposure to antithrombin III to similar extents regardless of the sequence of exposure. This suggests that Factor Xa and antithrombin III have similar affinities for this immobilized heparin, unlike the situation for thrombin (Thromb-Res., 20, 543-554, 1980).