To quantify the effects of major surface structural factors influencing interfacial reactions induced by polymers in native blood, model surfaces of solvent-cast films of two analogous poly(ether urethanes) and three homologous polyamides (nylon 4, 6/6, and 12) were exposed ex vivo to canine blood under the well-defined hemodynamic conditions of the Stagnation Point Flow Experiment. The selected surfaces allow for incremental changes in properties and were characterized by their "Composite Surface Free ENergy Function," gamma'S, which describes the surface force field as the sum of the mean dispersion (gammaSd) and polar (gammaSp) contributions and is computed from wettability spectra obtained with ultrapure diagnostic liquids. Blood interfacial effects were measured by the shear-limited diameter of the white cell circle formed around the stagnation point, the flow parameter at which symmetric aggregation occurred, and the surface-number density of platelets, [P s], remaining adherent under fixed conditions. At identical flows, within each group of polymers, both the WBC-circle diameter and [P s] scale with gamma Sp/gamma'S, implying that 1) only the magnitude but not the interaction mechanism varies as a function of incremental structural and surface changes, 2) the primary determinant of surface-induced effects is the polar force contribution, and 3) the magnitude of gamma'S is secondary if gammaSd/gamma'S is sufficiently great.

To highlight the mechanisms of artificial surface/protein/platelet interactions, results obtained by various methods have been integrated to elucidate some of the correlations between phenomena which occur at the macromolecular level and subsequently influence those at the cellular level, such as platelet adhesion. Microcinematographic evidence obtained under the controlled conditions of the Stagnation Point Flow Experiment (SPFE) indicate that, even on glass, platelet adhesion commences only after 30-60 sees of exposure to native blood. This lag period is consistent with diffusion kinetics predicting the arrival of plasma proteins should overhwelmingly precede that of the cellular components. During the lag period, native plasma proteins collide with the artificial surface and, in most cases, adsorb with surface-induced conformational changes. The energy for altering the secondary protein structure is supplied by the heat of adsorption. The extent of adsorption and structural alterations depend upon both the type of protein and the molecular architecture of the artificial surface, viz., the number density and orientation of polar, H-bonding, etc. groups accessible to proteins. Using microparticulate glass (< μ dia.) and a microcalorimeter sensitive to ±0.00001° C in 100 ml of sample volume, serum albumin was found to adsorb, release heat, and desorb in a conformationally altered state. In contrast, γ-(7S)-globulin and fibrinogen underwent irreversible multilayer attachment releasing (1.0-1.7) χ 103 Kcal/mole of protein adsorbed directly to the glass surface. Proteins in the second, etc. sorbed layers released much smaller heats. The electrophoretic mobility of the same particles coated with varying amounts of the same proteins confirmed that the relatively greatest conformational change occurred in the protein layer directly attached to the artificial surface. On homologous Nylons exposed under identical hemodynamic conditions in the SPFE, the surface number density of platelets remaining adherent at points of identical shear was proportionate to the polar force contribution of those surfaces. These results indicate that the protein layer which settles first, is acting as a “proportional transformer” mediating the effects of artificial surfaces onto platelets.