ULTRAFILTRATION MEMBRANE SURFACES WITH GRAFTED POLYMER TENTACLES - PREPARATION, CHARACTERIZATION AND APPLICATION FOR COVALENT PROTEIN-BINDING

Ultrafiltration (UF) membranes from polysulfone (PSf) were functionali zed by heterogeneous photo-initiated graft copolymerization of acrylic acid (AA). With radiation susceptible PSf, only proper selection of t he UV energy (lambda > 350 nm; for selective excitation of the photoin itiator) yielded membranes with preserved UF barrier layer. Possibilit ies for adjusting structure and morphology of the graft polymer (g-PAA ) layer by variation of functionalization parameters such as AA concen tration and UV irradiation time were investigated. Very long grafted c hains (M-W > 10(5) g mol(-1)) at varied grafting density (GD = 0.01 .. . 1.2 nmol cm(-2), relative to the outer surface area) were obtained. Partial penetration of the UF barrier layer by g-PAA was verified. Cov alent immobilization of bovine serum albumin (BSA), gamma-globulin (ga mma-Gl) and alkaline phosphatase (APh) was achieved by coupling with a water soluble carbodiimide. Bound BSA and gamma-Gl amounts were up to Gamma = 10 mu g cm(-2), for membranes accessible only from the outer surface thus not using the entire pore volume. Locally addressed coval ent protein immobilization after photo-patterning the PSf surface coul d be visualized with a fluorescent FITC-BSA conjugate. A strong salt e ffect onto immobilized APh activity (increase with NaCl concentration) was observed, indicating internal transport/accessibility limitations in the g-PAA layer, Correlations between PAA structure (M-w, GD) and accessibility (from BSA or gamma-Gl binding and APh activity) could be established. The 'tentacle' g-PAA functionalized PSf UF membranes hav ing preserved UF barrier and, e.g., with surface-bound receptors will find application in cell cultures under diffusion or perfusion conditi ons. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.