SURFACE MODIFICATION OF POLYMERS TO PERMIT ENDOTHELIAL-CELL GROWTH

The interaction between endothelial cells (EC) and polymers has become relevant to medicine as a result of attempts to improve the biocompatibility of vascular prostheses. In man, endothelialization is minimal, so that vascular surgeons have attempted to pre-seed vascular grafts with autologous EC. The poor results of EC seeding of commonly used materials for vascular rafts, such as expanded polytetrafluoroethylene (ePTFE) or woven polyester (Dacron) has led to attempts to modify the surface of these and other polymers. Three principal modification techniques have been employed: 1. adsorption of bioactive molecules from applied solutions. Examples are fibronectin, collagen types I and IV and fibrin-containing mixtures. 2. Formation of reactive groups. This includes carbon coating, plasma discharge and hydrolytic etching. We describe new experiments, using radiation induced grafting (RIG) techniques, with which polymers such as polyamide, polyethylene and ePTFE were surface modified to form electroneutral or positively or negatively charged groups. Scanning electron microscopy (SEM) following in vitro seeding of these modified polymers with both bovine and adult human EC showed that such techniques can be successfully applied to make an unreceptive polymer surface able to promote EC adhesion, spreading and growth. The numerous permutations available for RIG offer a promising method to improve vascular graft surfaces for EC seeding. Such modification techniques are readily applicable to industry. 3. Covalent coupling of bioactive molecules. Techniques have been developed to allow proteins or oligopeptides to be covalently coupled via bifunctional spacer molecules on to polymer surfaces.