Protein adsorption and transport in polymer-functionalized ion-exchangers

Abstract

A wide variety of stationary phases is available for use in preparative chromatography of proteins, covering different base matrices, pore structures and modes of chromatography. There has recently been significant growth in the number of such materials in which the base matrix is derivatized to add a covalently attached or grafted polymer layer or, in some cases, a hydrogel that fills the pore space. This review summarizes the main structural and functional features of ion exchangers of this kind, which represent the largest class of such materials. Although the adsorption and transport properties may generally be used operationally and modeled phenomenologically using the same methods as are used for proteins in conventional media, there are noteworthy mechanistic differences in protein behavior in these adsorbents. A fundamental difference in protein retention is that it may be portrayed as partitioning into a three-dimensional polymer phase rather than adsorption at an extended two-dimensional surface, as applies in more conventional media. Beyond this partitioning behavior, however, the polymer-functionalized media often display rapid intraparticle transport that, while qualitatively comparable to that in conventional media, is sufficiently rapid quantitatively under certain conditions that it can lead to clear benefits in key measures of performance such as the dynamic binding capacity. Although possible mechanistic bases for the retention and transport properties are discussed, appreciable areas of uncertainty make detailed mechanistic modeling very challenging, and more detailed experimental characterization is likely to be more productive.

Characterization of lysozyme adsorption in cellulosic chromatographic materials using small-angle neutron scattering

“…About 40% of these steps are ion-exchange chromatography [6]. There is a wide variety of available chromatographic media for protein separation, ranging from conventional porous beads to polymer-derivatized materials [1,7]. These materials have evolved to accommodate the protein's macromolecular nature, which leads to requirements for the pore accessibility, surface area, and binding characteristics [8].…”

“…Better architectural understanding is especially useful in the case of stationary phases for protein chromatography. Chromatography is the dominant large-scale separation technique for proteins, such that improvements in efficiency and the development of non-chromatographic alternatives are a subject of current research [1][2][3][4]. Virtually all protein purification processes are developed around at least one chromatographic step [5], with an average of roughly three chromatographic steps per process.…”

Fabrication of high-capacity protein ion-exchangers with polymeric ion-exchange groups grafted onto micron-sized beads by atom transfer radical polymerization

“…Further evidence of protein adsorption in poly(ethylenimine) (PEI)-grafted Sepharose FF reported by Yu et al demonstrated that there was a critical ionic capacity or PEI chain density above which the protein adsorption capacity and effective diffusivity increased sharply [14]. However, the intrinsically heterogeneous architecture of these ion-exchange beads caused by the distribution of the added polymer and ligand leads to a tendency to complicate and intensify mechanistic and synthetic issues of chromatography, which must be addressed [11,15].…”

“…Protein adsorption capacity is the benchmark for binding capacity in protein chromatography [11]. The ultimate strategy for increasing binding capacity lies in improving the protein adsorption capacity of the ion-exchange beads.…”

Protein Adsorption in Tentacle-Type Anion Exchangers and the Influence of Process Related Fouling

“…This result suggests that a solid diffusion mechanism, driven by the total adsorbed concentration gradient in the particle is responsible for the rapid protein adsorption kinetics observed experimentally (Chen et al, 2002;Carta et al, 2005;Stone and Carta, 2007;Lenhoff, 2008). This trend has been seen for other polymer-grafted materials, where the small accessible pore size would generally suggest a diffusional hindrance, yet high protein adsorption is observed indicating the importance of transport in the functionalized tentacles (Stone and Carta, 2007;Perez et al, 2011;Lenhoff, 2011). As previously discussed, the diffusional hindrance due to the molecular size of the protein extends the time to achieve the equilibrium binding capacity.…”