Protein Binding to Amphoteric Polymer Brushes Grafted onto a Porous Hollow‐Fiber Membrane

Three kinds of ampholites, i.e., 3‐aminopropionic acid (NH2C2H4COOH), (2‐aminoethyl)phosphonic acid (NH2C2H4PO3H2), and 2‐aminoethane‐1‐sulfonic acid (NH2C2H4SO3H), were introduced into an epoxy group‐containing polymer brush grafted onto a porous hollow‐fiber membrane with a porosity of 70% and pore size of 0.36 μm. The amphoteric group density of the hollow‐fiber ranged from 0.50 to 0.72 mmol/g. Three kinds of proteins, i.e., lactoferrin (Lf), cytochrome c (Cyt c), and lysozyme (Ly), were captured by the amphoteric polymer brush during the permeation of the protein solution across the ampholite‐immobilized porous hollow‐fiber membrane. Multilayer binding of the protein to the amphoteric polymer brush, with a degree of multilayer binding of 3.3, 8.6, and 15 for Lf, Cyt c, and Ly, respectively, with the (2‐aminoethyl)phosphonic acid‐immobilized porous hollow‐fiber membrane, was demonstrated with a negligible diffusional mass‐transfer resistance of the protein to the ampholite immobilized. The 2‐aminoethane‐1‐sulfonic acid‐immobilized porous hollow‐fiber membrane exhibited the lowest initial flux of the protein solution, 0.41 m/h at a transmembrane pressure of 0.1 MPa and 298 K, and the highest equilibrium binding capacity of the protein, e.g., 130 mg/g for lysozyme. Extension and shrinkage of the amphoteric polymer brushes were observed during the binding and elution of the proteins.