Preparation of Multi-Modal Membranes for Protein Chromatography

While traditional ion-exchange membrane adsorbers, modified by atom transfer radical polymerization (ATRP), have been successful at weak ionic strengths, their performance declines significantly at higher ionic strengths. Membranes functionalized with “multi-modal” ligands (i.e., ligands capable of multiple types of protein-ligand interactions) could exhibit a larger operating range than traditional ion-exchange membranes. Membranes were prepared by using the monomer, glycidyl methacrylate (GMA), and grafting the polymer from the regenerated cellulose substrate via ATRP. The resulting nanolayer was further functionalized by adding 4-mercaptobenzoic acid (4-MBA), capable of multi-modal interaction, to the epoxide portions of the poly(glycidyl methacrylate) (PGMA) polymer. After each functionalization, attenuated total reflectance Fourier transform infrared (ATR-FTIR) analyses were performed. These IR spectra demonstrated successful polymer growth and addition of the multi-modal ligand. Direct-flow water flux measurements were taken for modified and unmodified membranes. Flux for all polymerization times were similar, suggesting that a thin film (i.e., < 10 nm) of PGMA had been grafted. Static protein binding capacity for PGMA + 4-MBA membranes was shown to be approximately 20 mg/mL, compared to a binding capacity of 1 mg/mL from an unmodified membrane. Membranes modified by only PGMA, however, showed binding capacities equivalent to that of unmodified membranes; therefore, protein binding was determined to occur primarily on the ligand.