Proliferation and substrate effects on endothelial cell thrombogenicity. The effects of the cellular differentiation status and the adhesive-substrate on endothelial cell function in cell culture were measured with an enzyme based assay of surface thrombogenicity. A solid plastic, microporous polymeric, and fibronectin (FN) treated microporous polymeric were used as substrates for growth of endothelial cells. The microporous and FN treated synthetic substrates have been shown to aid in the induction of cellular differentiation mechanisms. Cells were studied under proliferative and nonproliferative growth conditions. The thrombogenicity of the surface created by the endothelial cell monolayers under various experimental conditions was determined using an enzyme based assay of fibrin deposition. Actively proliferating cells on the solid plastic substrate produced the most thrombogenic surface, while confluent endothelial cell monolayers grown on FN treated microporous substrate were the least thrombogenic surfaces. These data suggest that endothelial cell surface thrombogenicity is under substrate control, and also related to the cellular differentiation status. These findings are being used to design a novel approach to the small diameter synthetic vascular graft problem. 