COVALENT IMMOBILIZATION OF HEPARIN ON POLYMETHYLACRYLATE SURFACES

Heparin, a natural anticoagulant, was immobilized via covalent bonds on the surface of polymethylacrylate (PMA) beads to create a blood-compatible surface. Two chemical routes were utilized for immobilization. In the first route, PMA was hydrolyzed to produce functional carboxyl groups on its surface and heparin was covalently linked to these surface carboxyl groups by making use of carbodiimide chemistry. This method utilizes the free amino groups on heparin: the coupling occurs in minutes. In the second route, free amino groups were fixed to surface-hydrolyzed PMA by coupling one end of a suitable alkyl diamine with a water-soluble carbodiimide. Heparin was first ionically adsorbed to this aminated surface and then attached by glutaraldehyde fixation. This process occurs within one hour. In both techniques, more crude heparin (“Stage 14”) was bound than highly purified heparin due to larger number of free amino groups in crude heparin. The extent of heparin coupling was determined with ¹⁴C-labelled heparin. In vitro blood tests indicate that these surfaces are platelet compatible and are good candidates for nonthrombogenic materials.