Correlation of the Surface Charge Characteristics of Polymers with Their Antithrombogenic Characteristics

A knowledge of the structure of the double layer is essential in the investigation of reactions at an inierface between two dissimilar media. This aspect is briefly presented in respect to charge separation and potential distribution in the interfacial region. The types of reactions that can occur at solid-solution interfaces (electron transfer, electrosorption, and electro-phoretic deposition) are discussed. The electrokinetic methods for determination of surface charge characteristics of insulator materials in electrodes are reviewed. Thrombosis on the blood vessel wall and on prosthetic materials is an interfacial chemical reaction. The evidence for an electrochemical mechanism of thrombosis on conducting materials is outlined. Under normal conditions, the blood vessel wall is negatively charged. Injury or atherosclerosis makes it less negatively or even positively charged. With decrease of pH, there is an increase in the surface charge density of the blood vessel wall with an isoelectric point at a pH of about 4.5. Materials treated chemically so as to introduce negatively charged groups (sulfonate, carboxylate, heparinized, anionic ioplex) tend to be antithrombogenic while positively charged surfaces (cationic Ioplex, quarternary ammonium group) are thrombogenic. A useful criterion for antithrombogenic polymer materials is that their surfaces must have a uniform negative charge.