A New Paradigm for Low Fouling Synthetic Membranes: Balancing Electrostatics
Hongwei Liu, Arpan Nayak, and Georges Belfort. Howard P. Isermann Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, 110 8th st, Troy, NY 12180-3590
Most attempts to date to develop protein-resistant membranes or surfaces have focused on choosing hydrophilic monomers such as polyethylene glycol as protective coatings or as the trunk polymer. Using a completely different approach, we have sought charged and neutral surfaces that exhibit protein resistance. To accomplish this goal using our simple, inexpensive and patented UV-assisted photo-polymerization grafting process to modify poly(ether sulfone) (PES) ultrafiltration membranes, we have synthesized or purchased five charged vinyl monomers [3-methacryloylaminopropyltrimethyl ammonium chloride (MAPM), 3-sulfopropyl methacrylate potassium salt (SPMA), 2-methacryloyloxyethyl dimethyl 3-sulfopropyl ammonium hydroxide (sulfobetaine), 2-methacryloyloxyethyl dimethyl 2-carboxymethyl ammonium (carboxybetaine), and 2-methacryloyloxyethyl phosphorylcholine (phosphobetaine)]. These grafted membranes were then challenged with 1 g/l protein (bovine serum albumin, BSA) in phosphate buffer solution (PBS) at pH 7.2 using a dead-end stirred filtration cell. All the modified charged PES membranes exhibited lower protein fouling compared with the unmodified PES control membranes. Positively charged monomer (MAPM) membranes exhibited similar low protein fouling to that of negatively charged monomer (SPMA) membranes. This occurred even though the protein was negatively charged at pH 7.2. For the monomers containing both positive and negative charge, phosphobetaine exhibited the lowest protein fouling. After protein filtration, 90% of the membrane's initial PBS resistance was recovered without cleaning or back-flushing.