Immobilized heparin: spacer arm effects on biological interactions.

Heparin immobilized to polymer surfaces via different length diaminoalkane spacer arms was evaluated for anticoagulant activity and for platelet interactions. The anticoagulant activity of the immobilized heparin, as determined by APTT assays, was found to increase with increasing spacer arm length. Variations in spacer arm length produced no affect on platelet retention or PF 4 release for heparin immobilized materials. To investigate immobilized heparin-adsorbed plasma protein interactions, XPS analysis of heparinized surfaces, before and after plasma contact, was conducted. Immobilized heparin was not able to penetrate adsorbed plasma protein layers with any spacer arm length evaluated, indicating that immobilized heparin does not directly interact with platelets.