(114d) Side-by-Side Comparison of Protein Adsorption and Transport In Macroporous Cation Exchangers with and without Polymeric Surface Extenders

This work compares the physical properties and protein adsorption characteristics of two polymeric cation exchangers: UNOsphere S, which has an open macroporous architecture, and Nuvia S, which is based on a similar backbone matrix but which contains polymeric surface extenders. Both materials were obtained from Bio-Rad Laboratories (Hercules, CA) and a purified mAb was used as a model adsorbate. The characteristic pore sizes, determined by inverse size exclusion chromatography (iSEC) with dextran probes, were about 130 nm for UNOsphere S, and only about 12 nm for Nuvia S, indicating that the polymeric extenders occupy a substantial portion of the base matrix pores. Somewhat greater exclusion limits were, however, found for Nuvia S in 1M NaCl, suggesting that the polymeric extenders are not rigid but collapse partially at high ionic strength. mAb pulse response experiments under these non-binding conditions showed near complete exclusion on Nuvia S, consistent with the dextran behavior. Very large mAb equilibrium binding capacities were obtained, however, at low ionic strength (20 mM), approaching 330 mg mAb/ml of particle for Nuvia S compared to about 100 mg/ml for UNOsphere S. Much higher adsorption rates were also found for Nuvia S and the rate was nearly independent of protein concentration in solution, suggesting that the polymeric extenders enhance both adsorption capacity and diffusional mass transfer. Confocal laser scanning microscopy (CLSM) showed very sharp intraparticle protein concentration profiles for UNOsphere S, perfectly consistent with a pore diffusion mechanism, but diffuse concentration profiles for Nuvia S, consistent with a solid diffusion mechanism. Further studies are conducted with a PEGylated protein where introduction of the PEG chain alters molecular size and interactions with the chromatographic surface and polymeric surface extenders.