ABSTRACT
Cryogel, enzyme, immobilization, macroporous structure, wide-porous structure
11.1 Introduction ..................................................................................................308 11.2 Protein Immobilization by Covalent Attachment to Cryogel Matrix ...........309 11.3 Protein Immobilization via Entrapment Technique ..................................... 315 11.4 Protein Immobilization by Ionic Binding ..................................................... 320 11.5 Protein Immobilization by Affine Binding .................................................. 320
11.5.1 Protein Immobilization via Antigen-Antibody Binding ................... 321 11.5.2 Protein Immobilization via Lectin Affinity Binding........................ 322 11.5.3 Protein Immobilization via Metal Ion Chelating Binding ................ 322
11.6 Protein Immobilization by Combined Methods ........................................... 325 11.7 Conclusion .................................................................................................... 325 List of Abbreviations .............................................................................................. 326 References .............................................................................................................. 326
Enzymatic and protein-based products for biomedicine and biotechnology are becoming increasingly widespread. However, due to the natural characteristics of macromolecules used in these products, additional treatment or specific production conditions are required in order to enhance their stability during storage and everyday use. Immobilization of proteins/enzymes on/in various carriers has been successfully applied for these purposes (Sheldon and van Pelt, 2013); in addition to the fact that immobilization enhances the durability of catalytic and functional properties, it adds the possibility of reusing stabilized forms of enzymes/proteins in various biotechnological processes, which improves their economic attractiveness. A variety of techniques employing various carriers is used to immobilize enzymes/proteins; among these, cryogel-type polymeric matrices are particularly notable. Processes of cryotropic gelation of polymeric systems occur in the nondeep freezing, storage in the frozen state and thawing of the solutions or colloidal dispersions containing monomeric or polymeric precursors potentially capable of producing gels. Polymeric materials formed under these conditions are termed cryogels and they possess some specific features as compared to conventional gels formed at temperatures higher than the crystallization point of the solvent (Lozinsky, 2008). Thawing of the frozen sample produces a cryogel containing cavities filled with the liquid that formed in the sites of melted crystals. Thus, polycrystals of the frozen solvent act as a porogen during cryogel formation. Depending on the properties and initial concentration of the precursors and conditions of cryogenic processing, it is possible to produce macroporous matrices with the pores from tenth fractions of micrometers to ~10 μm in the cross-section and wide-porous (spongy) systems with pores of tens and hundreds of micrometers. Therefore, there are two main types of cryogel carriers with wideporous and macroporous structure, respectively.
