Hydrogen bonds and electrostatics drive adhesion of polar proteins to hydrophilized polymer membranes

It is commonly recognized that hydrophilic surfaces reduce protein membrane adhesion during aqueous bioprocessing due to water's strong binding through electrostatic and hydrogen bonding capability. Here, we show that when (i) a protein displaces bound water at a polymer interface, hydrogen bonding and electrostatic interactions with the polymer membrane surface drive protein adhesion, and (ii) comparing two commonly used commercial hydrophilic polymer membranes with different polar surface modification chemistries, the one with higher hydrogen bonding capability (modified polyethersulfone (mPES)) exhibited three times higher adhesion force to a hydrophilic protein (streptavidin) than the one with lower hydrogen bonding capability (modified polyvinylidene fluoride (mPVDF)). Stronger protein-membrane hydrogen bonding for mPES as corroborated by its higher electron donor surface energy component and higher hydrogen bonding propensity observed from surface energy measurements and by solvation shell spectroscopy, respectively, support our explanation of these results. Atomic force microscopy (AFM) colloid probe technique was used here to measure intermolecular forces/energy between streptavidin and two polymeric membrane surfaces. Non-contact forces at separations greater than 2 nm were modeled using the DLVO theory, while contact/adhesion forces, which include hydrogen bonding, were measured at separation ∼0.16 nm. These findings highlight the importance of protein-polymer membrane hydrogen bonding interactions in selecting polymers for membrane downstream purification and other applications.