Heparin surfaces: Impact of immobilization chemistry on hemocompatibility and protein adsorption

Immobilization of heparin to surfaces has been used for decades to reduce the thrombogenicity of blood contacting devices. This study evaluates how the mode of covalent heparin bonding affects the hemocompatibility and uptake of antithrombin on surfaces in whole blood. End-point attached (EPA) heparin, using the proprietary Carmeda Bioactive Surface (CBAS Surface), was compared with other methods of covalent heparin bonding that typically yield multiple covalent linkages (using reductive amination of periodate oxidized native heparin or EDC coupling of native heparin). All heparin surfaces were immobilized on flexible polyvinyl chloride tubing and exposed to fresh non-anticoagulated blood in an in vitro recirculating Chandler loop blood model. After exposure, biomarkers for coagulation and platelet activation were analyzed in the solution phase, and adsorbed plasma proteins were eluted from the heparin surfaces and measured for surface concentration of antithrombin and total adsorbed protein. Only the EPA-heparin surface conferred thromboresistance, as observed by the absence of clotting. Attachment and activation of platelets as well as activation of the clotting cascade was significantly lower on the EPA-heparin surface when compared with the other heparin surfaces. In addition, antithrombin constituted ∼40% of the total adsorbed plasma protein concentration on the EPA-heparin surfaces.