Ultrafiltration Membranes Incorporating Amphiphilic Comb Copolymer Additives Prevent Irreversible Adhesion of Bacteria

Abstract

We examined the resistance to bacterial adhesion of a novel polyacrylonitrile (PAN) ultrafiltration membrane incorporating the amphiphilic comb copolymer additive, polyacrylonitrile-graft-polyethylene oxide (PAN-g-PEO). The adhesion of bacteria (E. coli K12) and the reversibility of adhered bacteria were tested with the novel membrane, and the behavior was compared to a commercial PAN ultrafiltration membrane. Under static (no flow) bacterial adhesion tests, we observed no bacterial adhesion to the PAN/PAN-g-PEO membrane at all ionic strengths tested, even with the addition of calcium ions. In contrast significant adhesion of bacterial cells was observed on the commercial PAN membrane, with increased cell adhesion at higher ionic strengths and in the presence of calcium ions. Under crossflow filtration conditions, initial bacterial deposition rate increased with ionic strength and with addition of calcium ions for both membranes, with generally lower bacterial deposition rate with the PAN/PAN-g-PEO membrane. However, deposited bacteria were readily removed (between 97 and 100%) from the surface of the PAN/PAN-gPEO membrane upon increasing the crossflow and eliminating the permeate flow (i.e., no applied transmembrane pressure), suggesting reversible adhesion of bacteria. In contrast, bacterial adhesion on the commercial PAN membrane was irreversible, with approximately 50% removal of adhered bacteria at moderate ionic strengths (10 and 30 mM) and less than 25% removal at high ionic strength (100 mM). The resistance to bacterial adhesion of the PAN/PAN-g-PEO membrane was further analyzed via measurement of interaction forces with atomic force microscopy (AFM). No adhesion forces were detected between a carboxylated colloid probe and the PAN/PAN-g-PEO membrane, while the probe exhibited strong adhesion to the commercial PAN membrane, consistent with the bacterial adhesion tests. The exceptional resistance of the PAN/PAN-gPEO membrane to bacterial adhesion is attributable to steric repulsion imparted by the dense brush layer of polyethylene oxide (PEO) chains.