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 hydrophil icity by graft polymerization of 2-hydroxyethyl methacrylate and a model pr otein (hen egg-white lysozyme, Lz) suggest that altering either the chemist ry of the polymer surface or the solution conditions should lead to a minim ization of protein adhesion and hence fouling for a specific protein/polyme r combination. Using the surface forces apparatus, normalized adhesion forc es were measured below, at and above the pi of Lz, and compared with corres ponding permeation flux ratios from ultrafiltration experiments. Simple exp onential correlations were obtained relating the normalized adhesion forces to several different permeation flux ratios. Also, the amount of protein a dsorbed onto the membrane from solution during filtration was linearly rela ted to the adhesion force through the choice of solution pH. The correlatio ns imply that protein-polymer adhesive interactions are important during ul trafiltration. The results obtained for both a hydrophilic and a hydrophobi c surface were compared. The hydrophilic surface exhibited lower contact an gles, reduced adhesion forces, reduced adsorbed amount, and most importantl y, reduced protein fouling. Long range attraction between adsorbed protein and hydrophobic polysulfone films was absent with the hydrophilic films. Th e 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.