A surface energetic criterion of blood compatibility of foreign surfaces

Abstract

Based on the twin considerations of minimizing the thermodynamic driving force for the adsorption of blood components as well as maintaining a mechanically stable blood-biomaterial interface, a surface energetic criterion of biocompatibility of foreign surfaces is suggested. While the former requirement calls for a very low (preferably zero) blood-biomaterial interfacial tension, γ sl, the latter condition demands a sufficiently high value of γ sl. In order to reconcile these two requirements, a blood-biomaterial interfacial tension of the order of 1 to 3 dyn/cm is considered satisfactory. This range of values is selected on the basis of the fact that the cellular elements of blood, which are highly compatible with blood and whose interface with blood plasma is also mechanically stable, maintain an interfacial tension with blood plasma generally in the above mentioned range. Using a simplified model which accounts only for the nonspecific interactions (i.e., dispersion and polar) between blood and biomaterial, it is shown that the above criterion can be satisfied when the polar and dispersion surface free energy components of a biomaterial are separately sufficiently near to their respective surface-free energy counterparts of blood. As a result of this condition, even solids which differ appreciably in their total surface free energies can remain equally compatible with blood. It is also noted that, as a result of this condition, nonpolar surfaces are not expected to remain in long-term compatibility with blood. Second, the ability of many solid surfaces to undergo structural alterations in the aqueous environment (in comparison to the air environment) is discussed in relation to its implications for the surface energetic properties of biomaterials in the blood environment. Based on this consideration and the suggested surface energetic criterion, the performance of some prominent biomaterials is examined. Finally, the possibility of improving the surface energetic properties of polymeric biomaterials (by ultraviolet irradiation of their surfaces) and thereby enhancing their blood compatibilities, is discussed.