Bioactivity and platelet adhesion study of a human thrombomodulin-immobilized nitinol surface

Nitinol is a newly developed biomaterial that is gaining popularity in many biomedical applications. It has been reported that nitinol would not induce an inflammatory response and repulsion by the immunization after implantation in the human body. Besides, nitinol is a kind of shape memory alloy, which can memorize shapes at different temperatures. This can improve the convenience in surgery. However, nitinol has poor blood compatibility, so that further modification was needed to improve the antithrombogenicity. Human thrombomodulin (hTM), an endothelial-cell-associated glycoprotein, can be considered as a natural potent anticoagulant by converting thrombin from a procoagulant protease to an anticoagulant. In this study, the surface of nitinol was pre-activated by utilizing silanization with amino-terminated silane. The incorporated amino groups were available for the subsequent covalent immobilization of hTM by 2,4,6-trichloro-1,3,5-triazine (TCT), the coupling reagent. The surface density of immobilized hTM was determined by the Bradford method. The bioactivity of immobilized hTM and blood compatibility of various nitinol substrates were evaluated by the protein C activation assay and platelet adhesion test. It was observed that the immobilized hTM still had the ability to enhance protein C activation, though its activity was lower than the free hTM in solution. Furthermore, the platelet adhesion test showed that only a few platelets were adhered on the hTM-immobilized nitinol substrate. Therefore, the immobilization of thrombomodulin onto nitinol substrate could improve the blood compatibility of nitinol and might have the potential of application in antithrombogenic medical applications.