Immobilization of human thrombomodulin onto biomaterials. Comparison of immobilization methods and evaluation of antithrombogenicity.

Human thrombomodulin (hTM), which is a newly described endothelial cell associated protein that functions as a potent natural anticoagulant by converting thrombin from a procoagulant protease to an anticoagulant, was immobilized on to various substrates by two immobilization methods. As the substrates of immobilization, poly(acrylic acid) surface grafted poly(ethylene) (PAAc-g-PE) film, poly(vinylamine) surface grafted poly(ethylene) film, and PAAc surface grafted nylon were used. For immobilization, simultaneous preactivation methods were used. The effect of the immobilization reaction on hTM activities, the comparison of the activities of immobilized hTM with those of free hTM, and the effect of the thrombin incorporation on antithrombogenic activity were studied. The hTM immobilized onto PAAc-g-PE by preactivation showed the highest antithrombogenic activity. The thrombin incorporation affected protein C activation activity but not the fibrinogen clotting time. hTM immobilized nylon showed greater antithrombogenicity in vitro.