Biomembrane surfaces as models for polymer design: the potential for haemocompatibility.

A major restriction in the application of polymeric biomaterials is the propensity of their surfaces to support thrombosis. Theoretical approaches to the design of thromboresistant polymers have been inadequate because of the complexity of surface thrombosis. We have developed a new, practical approach to this problem--the design of polymers which mimic the thromboresistant surfaces of blood cell membranes. Haemostatic processes are mediated by reactions which occur at membrane-plasma interfaces. The extra-cellular surfaces of the plasma membranes of red blood cells and quiescent platelets are thromboresistant; in contrast, their cytoplasmic surfaces are thrombogenic. The simplest common feature among the blood-compatible cellular and model membranes is the high content of the electrically neutral phospholipids which contain the phosphorylcholine head group. We have developed model systems of biological membranes which utilize polymerizable phosphatidylcholines and which mimic nonreactive cell surfaces. Polymeri phospholipids represent a new class of hybrid biomaterials with characteristics both of biomembranes (polar surfaces, nonthrombogenic, low antigenic potential and low permeability) and of synthetic polymers (chemical and physical stability).