Protein Transport and Fouling Behavior of Zwitterionic Ultrafiltration Membranes

Protein transport and fouling behavior of zwitterionic ultrafiltration membranes

 

High performance ultrafiltration membranes are of growing interest in areas ranging from protein purification to water treatment.  Several recent studies have shown that zwitterionic membranes containing both positive and negative charge groups can provide a very low fouling surface while retaining some of the benefits of electrically-charged membranes in terms of their high permeability and selectivity.  However, there have yet be any detailed comparisons of the performance of these zwitterionic membranes with both charged and neutral membranes under carefully controlled experimental conditions.

A series of surface modified cellulosic membranes were generated by covalent attachment of different ligands to epoxy-activated hydroxyl groups on the glucose monomers in the base cellulose membrane.  A zwitterionic surface was formed using the amino acid lysine.  Negatively-charged, positively-charged, hydrophilic, and hydrophobic surfaces were generated using the same linkage chemistry but with different ligands all having very similar chain length / size but with different end functionality.  All of the surface modified membranes had essentially the same permeability, providing an appropriate set of controls to study membrane performance and fouling.

The effective membrane surface charge density was evaluated using streaming potential measurements.  Protein fouling studies were performed using human serum IgG.  The electrostatic contributions to protein transport through these semipermeable membranes were studied using protein charge ladders, consisting of a series of protein derivatives differing only by single charge groups. The zwitterionic membranes showed the lowest amount of protein adsorption, with less than a 12% reduction in permeability over a wide range of solution pH.  The greatest amount of protein adsorption was seen with the positively- and negatively-charged membranes under conditions where the protein and membrane had opposite surface charge. Despite the very low fouling characteristics, the zwitterionic membranes showed high degrees of protein retention due to repulsive electrostatic interactions.  These results provide important insights into the behavior of these zwitterionic membranes and their potential in high performance ultrafiltration applications.