Designing Functional Membranes with Tunable PDA/PEI Coatings for Enzyme Entrapment

Polydopamine (PDA) coatings are widely used to functionalize filtration membranes due to their ability to adhere to a broad range of surfaces and enhance biocompatibility and surface hydrophilicity. Co-adsorption of PDA with polyethylenimine (PEI) is investigated here to fabricate an enzyme-entrapped membrane, enabling the segregation of two incompatible enzymes, a protease (from B. licheniformis) and a ω-transaminase (from N. fischeri), within a nanoporous membrane using reverse filtration. PDA and PEI were coadsorbed on the membrane under varying dopamine and PEI concentrations, solution volumes, and applied pressures. Membrane permeance reduction and transaminase (TA) retention were used to evaluate the deposition effectiveness. Response surface methodology (RSM) revealed the PDA/PEI concentration to be the main driver of permeance reduction and enzyme retention, with nonlinear effects of volume and pressure and significant interactions between concentration and pressure. FTIR and AFM-IR analyses provided the chemical and spatial characterization of the coatings, showing that higher dopamine/PEI concentrations and longer residence times increased the polymer deposition and coating thickness. AFM-IR mapping at nanoscale confirmed the correlation among deposition parameters, coating distribution, and permeance reduction. This study demonstrates that membrane performance can be tuned by optimizing key deposition parameters, achieving high enzyme retention without compromising the permeance. Combining an RSM approach with micro- and nanoscale IR spectroscopy provides a robust framework for designing and characterizing enzyme-entrapped membranes, offering a reliable and quantitative approach for optimizing membrane-based biocatalysis applications.