Covalent bonding of heparin to a vinyl copolymer for biomedical applications.

In order to prepare polymer surfaces of vinyl type, provided with long-term haemocompatibility, a commercial ethylene-vinyl alcohol copolymer (EVAL) was covalently heparinized, employing two different bifunctional reagents (adipoil chloride and hexamethylene diisocyanate). The amount and activity of the heparin bonded to the polymer films were evaluated as a function of the concentration of the heparin solutions employed. Also, the influence exerted by the presence of various hydrophilic 'spacing arms' of different molecular weights, either neutral or provided with electrical charge, was investigated. By in vitro measurements of activated partial thromboplastin time it was seen that all the heparinized samples possessed a high degree of haemocompatibility. For the sake of comparison, heparin was also bonded ionically to EVAL functionalized by introduction of quaternary ammonium groups bonded covalently (by adipoil chloride) to the hydroxyl groups of the polymer. It was seen that the covalent immobilization system provides the polymer surfaces with a superior haemocompatibility.