Plasma protein interactions at biological interfaces

The adsorption of plasma proteins, especially fibrinogen at the endoendothelial interface and to the surfaces of the blood cellular elements in contact with blood is relevant to both hemostasis and thrombogenesis. The intact endothelium is the most thrombo-resistant surface known and the exact nature of this structure holds the answer to developing adequate biocompatibility for implants and prosthetic devices. Under physiological conditions the endoendothelial surface, blood cellular elements and plasma proteins all possess net negative charges which will play a role in their interactions. The density and charge sign of ionizable surface groups will determine the local value of pH at that surface. Distributions of surface charge are possible which could lead to local pH values which vary from one region to another by several units of pH. Erythrocytes and platelets possess adsorbed fibrinogen and the endothelial surface is likely also to attract fibrinogen. The presence of one or more layers of fibrinogen on the endothelial lining is, therefore, a well founded physicochemical expectation. Aggregation of the blood cellular elements is mediated by calcium ions, fibrinogen and other agents depending upon the cell type. The presence of fibrinogen is essential for platelet aggregation induced by adenosine diphosphate and for the observed changes in platelet surface charge. There is evidence that in general electrostatic interactions are important in the contact relationships between the blood cellular elements and other surfaces either natural or foreign.