Antifouling and pH-Responsive Ultrafiltration Membrane of PAA-co-NH₂/PEOX-co-NH₂ Multilayer for Protein Purification

Membrane fouling has been a persistent challenge in the protein ultrafiltration process. Stepwise interfacial complexation demonstrates an effective strategy to improve anti-fouling property. The poly(acrylic acid)/poly(2-ethyl-2-oxazoline) (PAA/PEOX) multilayer exhibits excellent anti-fouling property, yet only applied in acid environment (pH < 5). Herein, the amine-crosslinked (PAA-co-NH₂/PEOX-co-NH₂)_n membranes are fabricated, which show broadened pH stability (pH 2∼12) upon FT-IR characterization. In addition, the static BSA adsorption and dynamic cyclic filtration results confirm the superior anti-fouling property of the (PAA-co-NH₂/PEOX-co-NH₂)_n membranes, displaying 30%-57% decline in static BSA adsorption and 54%-76% decrease in total fouling ratio compared to PVDF. It contributes to their enhanced hydrophilicity (53°), smoother surface (22.3 nm), and increased negative surface charge (-22.5 mV) compared to PVDF (89°, 33.8 nm, and -11.4 mV). Benefiting from the chain conformation transformation of PAA-co-NH₂, membranes possess remarkable pH-triggered cleaning ability, leading to a ∼100% recovery in water flux. Moreover, the membranes exhibit superior water flux (227 L·m^-2·h^-1) and BSA retention (97%) compared to PVDF (retention, 63%). This work provides a facile and effective strategy to develop polymer complex-based coatings with pH-response and anti-fouling property to improve protein separation performance for ultrafiltration membranes.