Affinity Membranes

K. Haupt, Lund University, Lund, Sweden

S. M. A. Bueno, Universidade Estadual de

Campinas, Brazil

Copyright © 2000 Academic Press

The rapid development in biotechnology and the large potential of biomolecules for applications in medicine, food industry and other areas, result in an increasing demand for efficient and reliable tools for the purification of proteins, peptides, nucleic acids and other biological substances. This situation is being additionally enforced by the increasing number of recombinant gene products that have arrived on the market or that are currently being investigated, such as insulin, erythropoietin and interferons. The recovery of fragile biomolecules from their host environments requires their particular characteristics to be taken into account for the development of any extraction or separation process. On the other hand, there is a demand for techniques that can easily be scaled up from laboratory to industrial production level.

In this context, the use of affinity methods has the advantage that coarse and fine purification steps are united through the introduction of a specific recognition phenomenon into the separation process. The most widely used method for preparative affinity separation of biomolecules is liquid chromato-graphy on beaded resins (soft gels). Despite the commercial availability of many affinity ligands immobilized on to gel beads for use in column chromatography, there are some drawbacks in a large scale application of these supports. Flow rates and thus performance are limited by the compressibility of the resins and pore diffusion. Because of these intrinsic limitations, other chromatographic techniques, such as perfusion chromatography, or different separation techniques, such as affinity precipitation and affinity phase partitioning, have been suggested as possible alternatives. Another technique that is gaining increasing importance is membrane-based separation. Adsorptive membrane chromatography was introduced as a purification method in the mid 1980s. Microporous membranes have been successfully coupled with biological or biomimetic ligands, yielding affinity membrane chromatography supports. Several of them, with for example protein A and G, dye or metal chelate ligands, are commercially available. Affinity membrane chromatography is in fact a hybrid technique combining affinity gel chromatography and membrane filtration, with the advantages of the two technologies.

The purpose of the present review is to discuss relevant aspects and developments that are important for the design of an affinity membrane chromatography process, including the choice of the membrane material, coupling chemistry, affinity ligands, membrane configurations, operation modes and scale-up. In a wider sense, membrane-based affinity fractionation also comprises affinity filtration methods where the target molecule binds to an affinity ligand coupled to nanoparticles, which can then be separated by filtration through a membrane. However, this application will not be discussed here in detail.

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