Adsorption and Separation of Native and Pegylated Proteins on Anion Exchange Resins with Varying Degrees of Polymer Grafting

Ion exchange resins containing charged polymer grafts have been shown to enhance protein binding capacity and mass transfer rates as a result of the dynamic nature of the polymer structure. Most of the previous work in this area has, however, been devoted to cation exchange resins. In this work, we have examined the adsorptive and chromatographic properties of native and PEGylated proteins on a range of anion exchange (AEX) resins that are based on the same macroporous backbone matrix, but that contain different amounts of grafted polymers. BSA, PEGylated BSA, and thyroglubulin are used as model proteins covering a broad range of molecular sizes and strength of interaction with the charged ligands on the resin. Adsorption isotherms and batch uptake kinetics were determined for each protein in order to quantify the macroscopic behavior, while confocal laser scanning microscopy (CLSM) was used to elucidate intraparticle transport for single and multicomponent adsorption. The results show that the performance of these resins depends on a balance of size-exclusion and electrostatic interactions. Polymer grafting increases the binding capacity and leads to an enhancement of adsorption rates for the smaller proteins. On the other hand, as molecular size increases a point is reached where size-exclusion becomes dominant resulting in poorer performance. An optimum grafted polymer content seems to exist that optimizes the balance of these two properties.