Intermolecular forces between a protein and a hydrophilic modified polysulfone film with relevance to filtration

Correlations between intermolecular forces and ultrafiltration measurements for a thin polysulfone film and membranes modified for increased hydrophilicity by graft polymerization of 2-hydroxyethyl methacrylate and a model protein (hen egg-white lysozyme, Lz) suggest that altering either the chemistry of the polymer surface or the solution conditions should lead to a minimization of protein adhesion and hence fouling for a specific protein/polymer combination. Using the surface forces apparatus, normalized adhesion forces were measured below, at and above the pi of Lz, and compared with corresponding permeation flux ratios from ultrafiltration experiments. Simple exponential correlations were obtained relating the normalized adhesion forces to several different permeation flux ratios. Also, the amount of protein adsorbed onto the membrane from solution during filtration was linearly related to the adhesion force through the choice of solution pH. The correlations imply that protein-polymer adhesive interactions are important during ultrafiltration. The results obtained for both a hydrophilic and a hydrophobic surface were compared. The hydrophilic surface exhibited lower contact angles, reduced adhesion forces, reduced adsorbed amount, and most importantly, reduced protein fouling. Long range attraction between adsorbed protein and hydrophobic polysulfone films was absent with the hydrophilic films. The results provide a fundamental molecular basis to the widely reported and observed phenomenon that hydrophilic membranes are known to foul less than hydrophobic ones during membrane filtration of protein solutions.