Dramatic performance improvement of weak anion-exchange membranes for chromatographic bioseparations

This contribution describes a two-step surface modification method to prepare high-capacity anion-exchange membranes for chromatographic bioseparations. In the first step, commercially available regenerated cellulose membranes were functionalized with initiator. In the second step, initiator-functionalized membranes were modified by surface-initiated atom transfer radical polymerization of 2-dimethylaminoethyl methacrylate (DMAEMA). Initiator grafting density and molecular weight of poly(DMAEMA) chains were varied independently to yield surface-modified, macroporous, weak anion-exchange membranes with exceptionally high protein binding capacities (dynamic capacities up to 130 mg/mL for bovine serum albumin) at high linear flow velocities (>350 cm/h) and low transmembrane pressure drop (<3 bar). Initiator grafting density was increased by increasing the concentration of initiator precursor in solution during the membrane initiator-functionalization reaction. Average molecular weight of poly(DMAEMA) chains was increased by increasing polymerization time at constant initiator grafting density. Dynamic protein binding capacities were found to be independent of the linear flow velocity. Dynamic capacities decreased in regular fashion with increasing ionic strength in the loading buffer, but maintained relatively high values (>35 mg/mL) even at 100 mM ionic strength. Separation performance of the newly designed membranes was evaluated by fractionating a mixture of bovine serum albumin and hemoglobin. The purities of recovered proteins were high (>97%), and the recoveries also were high (>98%).