https://www.cell.com/trends/biotechnology/pdf/S0167-7799(03)00211-7.pdf

Polymeric cryogels as promising materials of biotechnological interest.

This review deals with cryotropic gelation in polymeric systems, which takes place on moderate freezing, storing in a frozen state and subsequent thawing of solutions or colloidal dispersions containing monomeric or polymeric precursors. The polymer materials formed under these conditions are termed as cryogels. They are macroporous heterophase gels in which polycrystals of the frozen solvent act as porogens during gel formation. The current knowledge about the structure of moderately frozen solutions of low- and high-molecular-mass compounds is considered, the general regularities of the cryotropic gelation processes and their similarity to and differences from gelation at positive temperatures are discussed, the fields of application of cryotropic gelation techniques are described, and examples of using polymeric cryogel-based materials for solving applied problems are given. The bibliography includes 433 references.

https://iopscience.iop.org/article/10.1070/RC2002v071n06ABEH000720/pdf

Cryogels on the basis of natural and synthetic polymers: preparation, properties and application

In recent years, the most significant development in the field of synthetic organic chemistry has been the application of biological systems to chemical reactions. Reactions catalyzed by enzymes and enzyme systems display far greater specificities than more conventional organic reactions. Biological and/or enzymatic syntheses and transformations, that is, “microbial transformations,” have great potential. Some of these reactions have already been shown to have useful applications in the fields of synthetic organic chemistry and biotechnology. This article reviews the current status of the rapidly developing field of microbial transformation, the methodology, available technological procedures, and fields of application being described especially in relation to conventional organic synthesis methods.

Microbial and Enzymatic Processes for the Production of Biologically and Chemically Useful Compounds [New Synthetic Methods (69)]

Polymeric cryogels, the gels formed in moderately frozen gelling systems, have been empirically known for many decades, but systematic scientific research on various cryogels and the peculiarities of cryotropic gel formation only commenced at the beginning of the 1980s. This historical review briefly describes the principal stages of the studies on these very interesting gel materials. It also discusses some mechanisms of their formation, as well as summarizes published data on the main representatives of chemically crosslinked (covalent), ionically linked, and noncovalent (physical) cryogels.

A Brief History of Polymeric Cryogels

Publisher Summary This chapter introduces several techniques for biocatalyst immobilization that include inclusion, adsorption, cross-linking, or covalent grafting. One of the key parameters with regard to the feasibility of a biotechnological process is the combination of efficiency and stability of the biocatalyst used. Immobilization very often results in a greatly increased resistance to various denaturation factors: extreme pH and temperature values, high ionic strength, denaturating reagents, and proteases. Another approach to stabilization is to modify the biocatalyst microenvironment by the use of additives, such as salts, polyols, sugars, and various polymers. It has thus been possible to obtain enzyme preparations with a highly increased resistance to denaturation factors, for example, certain protease preparations used in the manufacture of detergents. The chapter discusses the possibilities of biocatalyst stabilization, on the one hand by immobilization and on the other hand by immobilization plus additives, with the help of a few significant examples. Direct comparison of the operational stability—that is, in the presence of a continuous supply of substrate—of an immobilized enzyme with that of a free enzyme is possible in the ultrafiltration reactor.

[53] Enzyme stabilization by immobilization

Lettuce thylakoids were immobilized by the action of glutaraldehyde at sub-zero temperature in presence of albumin. Particles with sponge structure and good mechanical properties were obtained. The activity yield after immobilization was found equal to 70% for the oxygen production. Photosystems I and II were both active after immobilization. The yield for the ATP production was 27%. An increase of stability of the immobilized thylakoids was observed when stored under illumination.

M. L. Champigny

Papers

Immobilization of thylakoids in porous particles and stabilization of the photochemical processes by glutaraldehyde action at subzero temperature