Recent Trends in Cryogelation Phenomenon & Factors Affecting Cryotropic Gelation

Polymeric gels represent one of the most important classes of functional biomaterials for biomedical applications. A variety of methods had been devised to fabricate polymeric gels with an aim to incorporate suitable porosity, appropriate mechanical strength, and functionality for specific biological applications. It is challenging to simultaneously incorporate these three properties via many such methods like thermally induced phase separation, salt leaching, three-dimensional printing, etc., owing to reasons such as the complexity of the procedure, involvement of toxic/harsh chemicals, or formation of toxic intermediates during synthesis and high-cost of the procedure. Cryogels, obtained by cryogelation of polymeric/monomeric precursors usually in an aqueous solvent at sub-zero temperatures, offer an easy and cost-effective way of incorporating macro/micro porosity, mechanical strength, and chemical cues simultaneously into polymeric gels for biomedical applications. Therefore, this review aims to provide comprehensive and updated information on the recent trends in the phenomenon of cryogelation and factors affecting cryotropic gelation. The three major stages of cryogelation, i.e., freezing, incubation/polymerization, and thawing are described in depth along with various kinds of crosslinking mechanisms such as covalently, physically, or ionically crosslinked cryogels. Further, the parameters affecting cryogelation, i.e., ice nucleation and temperature regime, the effect of solutes, the effect of solvent, precursor composition, etc. are also discussed in detail. All this information is expected to greatly assist in understanding the mechanism and factors affecting cryogelation, which in turn can be used for future modifications to yield advanced cryogels for biomedical applications.