Multilayer Binding of Proteins to Polymer Chains Grafted onto Porous Hollow-Fiber Membranes Containing Different Anion-Exchange Groups

Various anion-exchange groups were introduced into the polymer chains grafted onto a porous hollow-fiber membrane for protein recovery by radiation-induced graft polymerization and subsequent functionalization of a monomer containing an epoxy group. The graft chains extended from the pore surface toward the pore interior, resulting in the multilayer binding of proteins to the graft chains. Combinations of three anion-exchange groups, namely, amino (AM), ethylamino (EA), and diethylamino (DEA) groups, and three proteins, namely, (beta)-lactoglobulin, bovine serum albumin, and urease, were examined to evaluate the degree of multilayer binding of protein to the graft chains in the permeation mode. Multilayer binding was observed for hollowfiber membranes containing EA and DEA groups, with conversions of epoxy groups to EA or DEA groups of higher than 80%. The amount of adsorbed protein remained constant irrespective of the conversion for the hollow-fiber membrane containing an AM group. The dependence of the flux on the conversion was consistent with that of the degree of multilayer binding to the graft chains.