Surface bound heparin, fate

In this chapter we present the results of an in vitro investigation into the fate of surface bound heparin and bound inactive complex to assess the concerns with long-term use of heparin. Heparin was immobilized onto PVA using a covalent acetal coupling procedure (12) to produce a hydrogel ( 77% w/w water) in which the heparin appears to be bound through the amino acid terminus of the molecule (26). Although the detailed structure of... 

Table I. Conceivable Fates of Surface-Bound Heparin...

Careful examination of the possible fates of the bound heparin and the bound inactive complex suggests hypothetical mechanisms which, if effective, could limit the utility of heparinized materials (Table I). For example, either the surface may become saturated with a heparin complex that can no longer accelerate the inactivation of thrombin, or consumption of antithrombin, prothrombin, or other clotting factors may result, leaving the blood systematically hypocoagulable. 

Concern over the fate of the bound complex appears unnecessary, since radiolabeled thrombin or thrombin-antithrombin III complexes were readily displaced from the surfaces by defibrinated plasma containing crude antithrombin III. Therefore, the bound heparin apparently does not become saturated with inactive complex, enabling the bound heparin, if it remains active, to act catalytically to potentiate the inactivation of thrombin as it is generated. Whether the consumption rate of antithrombin III or prothrombin, on the other hand, can be controlled, or whether it would result in a systemic blood defect, remains to be examined. 

The surface of the microporous PU scaffolds can be modified to control cell fate. Similar approaches as those used for fibrous PU scaffolds can be employed." " For example, to induce endothelial cell migration into scaffolds for accelerated vascularization, heparin was bound to the scaffold surface. An aminolysis step was first used to introduce amine groups on the surface, and then the cross-finking of heparin... 

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