Silica-based strong anion exchange media for protein purification

The main objective of our research was to develop silica-based, polymer-functionalized ion exchange materials for single-use bioprocess applications, with the ultimate goal of achieving maximal binding capacity for target proteins. Herein we report the utilization of Grace® wide pore silica gel and bonding the silica with cationic polymers. The strong anion exchange materials have been prepared by a two-step process involving initial bonding with two trimethoxysilanes and subsequent aqueous solution radical polymerization with quaternary ammonium ion containing monomers and an azo initiator. Using the binding capacities for bovine serum albumin (BSA), a model protein for the evaluation of the new materials, we optimized the processes with regard to the median pore size of the silica gel, as well as polymer composition and ratios, which were determined by reagent ratios and reaction conditions. The products were also characterized by both chemical and physical methods. It has been found that higher binding capacities are associated with lower ligand density and higher molecular weight for the attached polymers, with over 20% higher in both static and dynamic binding capacity values with the same amount of attached polymers. The advantages of a large pore size distribution and optimal median pore size for the base silica are discussed. Optimal pore size range of 500-1500 Å and distribution of Span 90 for over 1.0 give the highest BSA binding capacities. Silica-based strong anion exchange materials showed excellent flow characteristics when packed into a column and were superior to commercial agarose-based strong anion exchange material with respect to dynamic binding capacity, elution of proteins, and baseline separation of a mixture of three model proteins.