Intermolecular forces between proteins and polymer films with relevance to filtration

In order to understand the effects of protein fouling during ultrafiltration of biological fluids, we have investigated the molecular interactions between a thin polysulfone film and hen egg lysozyme with the surface forces apparatus (SFA). The normalized forces between the adsorbed protein layers and polymer films were measured below, at and above the pI of lysozyme, and compared with four different permeation fluxes obtained from ultrafiltration experiments. The intermolecular forces between two protein layers were also measured at the different pH values. Adsorption kinetics of lysozyme onto mica were also obtained. Buffer and lysozyme solutions at similar pH values and concentrations were filtered with 6 kD polysulfone membranes to obtain flux decline and hence fouling measurements. Hydrophobic membranes, such as polysulfone, exhibit extremely long-range attractive interactions (on the order of 1500−2000 A) with proteins such as lysozyme. Even in the presence of electrostatic repulsion at pH values ab...