JOURNAL OF COLLOID AND INTERFACE SCIENCE 176, 95–100 (1995) Hydrodynamic Evaluation of Three-Dimensional Adsorption of Protein to a Polymer Chain Grafted onto a Porous Substrate SATOSHI TSUNEDA,* HIROKI KAGAWA,* KYOICHI SAITO,* ,1 AND TAK ANOBU SUGO² * Department of Chemical Engineering, Faculty of Engineering, University of Tokyo, Hongo, Tokyo 113, Japan; and ² Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, Takasaki, Gunma 370-12, Japan Received December 12, 1994; accepted May 2, 1995 vinyl monomer onto the hydrophilic polymer matrix; this A porous hollow-fiber membrane was modified with dieth- ion exchanger showed higher binding capacities for proteins ylamino (DEA) and ethanolamino (EA) groups by radiation-in- than conventional ion-exchange beads. He demonstrated that duced graft polymerization and subsequent chemical modifica- the ion-exchange-group-containing polymer chain grafted tions. Adsorption behavior of bovine serum albumin (BSA) was onto the bead can hold the protein in multilayers in a tenta- investigated by permeating a BSA buffer solution through the cle-like manner. membrane. A polymerchain grafted onto the pore surface of the Multilayer binding of the protein in the graft chain has membrane held BSA in multilayers, i.e., three-dimensionally in a been discussed solely on the basis of its relative binding tentacle-like manner. The membrane with a DEA group density capacity to theoretical monolayer adsorption. Other ap- of 2.5 mol / kg had a binding capacity for BSA of 443 g / kg, equiva- lent to 11 times the monolayer adsorption. Permeation of a buffer proaches to this phenomenon should be explored to elucidate solution containing 0.5 M NaCl as an eluent caused the graft chain the tentacle-like binding structure. Radiation-induced graft to shrink, resulting in restricted diffusion of BSA departing from polymerization can append an ion-exchange-group-con- the graft chain toward the pore interiorwhile realizing a quantita- taining polymer chain uniformly onto the pore surface of a tive elution. Hydrodynamic analysis of the change in permeation porous membrane (12, 13). pressure accompanying BSA binding to the graft chain showed In this study, in order to obtain an idea of multilayer that the BSA molecules layered in the graft chains form a closely adsorption of the proteins in the polymer chain grafted onto packed structure.  1995 Academic Press, Inc. the pore surface of the porous membrane, we investigated Key Words: porous membrane; graft chain; protein adsorption; ( i ) the protein transport into the graft chains during tentacle- three-dimensional adsorption; hydrodynamic evaluation. like adsorption and subsequent elution by determining the breakthrough and elution curves in a permeation mode and (ii) the pore volume change accompanying the tentacle- INTRODUCTION like adsorption by measuring permeation pressure across the membrane at a constant permeation rate. Protein adsorption on a solid surface is of great interest in various fields of science and technology (1–3). Chroma- tography based on adsorption phenomena is an important EXPERIMENTAL technique for the separation of biomolecules. In particular, ion-exchange chromatography has been used extensively for Materials purification of proteins (4–6). Ion-exchange beads used for biochromatography require both a porous structure to allow A porous membrane of hollow-fiber form was used as a proteins to diffuse into the pore interior and a hydrophilic trunk polymer for grafting. The inner and outer diameters surface to retard nonselective adsorption to the pore surface of the hollow fiber were 1.95 and 3.01 mm, respectively. (7). The protein binding capacity of the ion-exchange bead The porous hollow-fiber membrane, which was made of has been considered to depend on the surface area of the polyethylene, had a three-dimensional pore network with a bead (8–10). Recently, however, Muller (11) has prepared nominal 0.34-mm pore diameter and 71% porosity. Tech- a novel ion-exchange bead, a tentacle-type ion exchanger, nical-grade glycidyl methacrylate (GMA, CH 2 ICCH 3- by chemical grafting of an ion-exchange-group-containing COOCH 2 CHOCH 2 ) was purchased from Tokyo Kasei Co., Japan, and used without further purification. Diethylamine (NH(CH 2 CH 3 ) 2 ) and ethanolamine ( NH 2 CH 2 CH 2 OH ) were 1 To whom correspondence should be addressed at Department of Spe- purchased from Wako Pure Chemical Industry Co., Japan. cialty Materials, Faculty of Engineering, Chiba University, Inage, Chiba 263, Japan. Bovine serum albumin ( No. A-7030, initial fractionation by 95 0021-9797/95 $12.00 Copyright  1995 by Academic Press, Inc. All rights of reproduction in any form reserved.