Nylon-Based Affinity Membranes: Impacts of Surface Modification on Protein Adsorption

Nylon microfiltration membranes were activated with bisoxirane and formaldehyde at terminal amino groups and amide groups of the nylon polymer, respectively. Dextrans were covalently immobilized on these activated membranes to yield dextran-coated membrane matrices. Both procedures led to a significant reduction of hemoglobin adsorption; however, bisoxirane activation required additional cross-linking of dextran and a second dextran layer to yield comparable quality of dextran-coated membranes than formaldehyde activation. Formaldehyde activation was easiest and cheapest and resulted in membranes with highest dextran density and relatively lowest nonspecific hemoglobin adsorption. Dextrans of &Mmacr;w >/= 40,000 were required for bisoxirane-activated membranes, whereas dextrans of &Mmacr;w = 6000 were sufficient for formaldehyde-activated membranes. Both activation methods resulted in stable coatings at low and high pH; however, formaldehyde-activated membranes were unstable under strongly acidic conditions at pH < 3. Dextran coils were found responsible for the reduction of the hydraulic permeability but also for the high ligand densities obtained after immobilization of Cibacron Blue F3G-A (360 nmol/cm2) and iminodiacetic acid (400 nmol/cm2). The thermodynamics of protein adsorption on dye ligand affinity (DLA) membranes corresponded with chromatographic sorbents and dye ligand conjugates, with the dextran coating demonstrating similar structure than dextrans in solution. Protein adsorption took place in the extended coil structure of dextrans with binding capacities up to 730 µg/cm2 lysozyme on DLA membranes and 470 µg/cm2 concanavalin A on metal chelate affinity membranes. Copyright 1997 Academic Press.