Potential therapeutic applications of proteins have greatly increased the rate of productionof various proteins and enzymes.  Remarkably, sales of therapeutic proteins are projected to reach $90 billion in 2010.  Accompanying the increased protein production in basic research and the pharmaceutical industry is a need for rapid purification. Affinity-based separations are often at the heart of this procedure.

Despite the great success of affinity-based protein isolation, the rate of separations of large macromolecules with affinity columns is low, as slow diffusion of large biomacromolecules to binding sites requires long purification times.  The use of membranes as substrates for affinity purification has the potential to overcome this limitation because the protein solutions being treated must flow through the membrane pores. 

Membranes lack, however, the high surface area that is found in most beads, so their binding capacities are low.  We are overcoming this challenge by growing polymer brushes in membranes to facilitate binding of multilayers of proteins within large pores as shown in the figure on the right.  Polymer brushes are assemblies of polymer chains, as illustrated above, and because these materials are swollen, they are capable of creating membranes that bind as much as 150 mg of protein/cm³.  This capacity is 3-fold higher than that of commercial membranes and may lead to new, rapid methods for protein purification.  For more details and an example, click here.  This work is supported by the National Institutes of Health (GM080511) and was recently described in Biomacromolecules, 2010, 11, 1019–1026.

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