Optimization of pressure-flow limits, strength, intraparticle transport and dynamic capacity by hydrogel solids content and bead size in cellulose immunosorbents

The design of existing beaded adsorbent materials for column-mode protein purification has emphasized the impact of diffusional transport phenomena upon adsorbent capacity. A design model is presented here that optimizes molecular accessibility of proteins relative to the mechanical stability at low operating pressures by manipulation of size and solids content for uncross-linked cellulose beads. Cellulose beads of several different sizes ranging from about 250 to 1000 μm diameter and having different solids contents were evaluated. Solids content of greater than about 9% cellulose greatly reduced the permeability of large proteins such as thyroglobulin and β-amylase into the beaded matrix at bead contacting times of about 5 and 50 s. Furthermore, the amount of permeation at 3% solids content by thyroglobulin at bead contacting times of about 5 s was about tenfold larger than predicted by diffusion models using the binary diffusivity in a purely aqueous continuum. The utility of a low solids content, large bead cellulose support was shown with immobilized IgG (M_r 155 kDa) capturing recombinant human Protein C (M_r 62 kDa). A 1000 μm diameter beaded cellulose immunosorbent having 3% solids content gave equivalent capacity to a 140 μm diameter beaded, cross-linked agarose support containing 4% solids. In contrast to the smaller diameter, cross-linked beaded agarose, the low solids content beaded cellulose benefitted from greater physical stability due to more optimal pressure-flow characteristics imparted by large bead size.