Interaction of fibrinogen with solid surfaces of varying charge and hydrophobic—hydrophilic balance I. Adsorption isotherms

Adsorption of fibrinogen to a series of polyelectrolyte complex surfaces of varying charge density (bulk ion-exchange capacity ranging from +1.21 to −1.33 meq g−1) and hydrophilicity (water content from 4.5 to 60 wt%) was studied using an iodine-labeling technique under static conditions. In the high concentration region of the isotherms (c > 0.5 mg ml−1) pseudoplateaux were observed with adsorption values in the range expected for a close-packed monomolecular layer. The surface of a material of +0.8 meq g−1 ion-exchange capacity showed a particularly high value. At low concentrations (c < 10−2mg ml−1), the data were found to fit a Freundlich-type relation with identical slopes for all surfaces. Free energies of adsorption estimated from these data were of the order of 7 kcal mole−1. These values are indicative of nonspecific relatively weak bonding perhaps of the hydrophobic interaction type. It is concluded that fixed surface charge of the order of magnitude of that used in the present work has little effect on the equilibrium (isotherm) aspects of protein adsorption.