Adhesion of hydrophilic particles (human erythrocytes) to polymer surfaces: Effect of pH and ionic strength

Abstract

The extent of adhesion of fixed human erythrocytes to several polymer substrates is investigated as a function of ionic strength and pH. At a constant pH of 6.1 there is virtually no cell adhesion at low ionic strength. Cell adhesion increases with increased ionic strength and reaches a limiting plateau value at a sodium chloride concentration of 100 m M or somewhat less. These plateaux are quite different for each polymer substrate; the extent of adhesion decreases with increasing substrate surface tension, in accordance with thermodynamic expectations. The experiments with constant ionic strength and variable pH show that at pH 6.1 and below the extent of cell adhesion is constant for each polymer substrate and extends over a substantial domain of high ionic strength and low pH. As the pH is increased, erythrocyte adhesion decreases and reaches a second plateau at pH 8 and above. These plateau levels of cell adhesion also decrease linearly with the substrate surface tension. The results suggest that at low ionic strength double-layer repulsion overpowers the van der Waals attraction more or less completely. With increasing ionic strength the double layer becomes more and more compressed, allowing a closer approach of the cells to the solid surfaces and hence an increased effect of the van der Waals attraction, leading to increasing cell adhesion. At high ionic strength, the van der Waals forces overpower the double layer repulsion completely.