HYDRAULIC PERMEABILITY OF PROTEIN LAYERS DEPOSITED DURING ULTRAFILTRATION

Although protein deposition plays an important role in determining the overall performance of ultrafiltration and microfiltration devices, there is little quantitative data on the properties of deposited protein layers formed during ultrafiltration. Experimental data were obtained for the hydraulic permeability of deposited layers of bovine serum albumin (BSA) on polyethersulfone ultrafiltration membranes (molecular weight cut-offs ranging from 30,000 to 1,000,000) and microfiltration membranes (nominal pore diameter of 0.16 μm). The protein deposit was strongly associated with the membrane, and was stable at high stirring speeds and after prolonged exposure to protein-free saline solutions. The hydraulic permeability of the protein deposit decreased with increasing filtration pressure, although the response to pressure variations was slow with a time constant of more than 100 min. This behavior was accurately described using compressible filtration theory, with the response of the layer modeled using a mechanical analog comprised of an elastic component in series with a parallel arrangement of a viscous and elastic component. The permeability of the protein deposit decreased with increasing ionic strength and was maximum at the BSA isoelectric point. These results provide insight into the intermolecular and intramolecular interactions which determine the protein layer permeability, and have important implications for the design and analysis of both ultrafiltration and microfiltration devices. © 1991.