Synthesis and Structure–Property Relationships of Cryogels

Polymeric gels belong to the most important class of functional polymers in modern biotechnology. They are useful materials for drug delivery systems, artificial organs, separation operations in biotechnology, processing of agricultural products, on–off switches, sensors, and actuators. Despite this fact and considerable research in this field, the design and control of gel-based devices still present some problems due to the their poor mechanical performance and slow rate of response to external stimuli. Cryogelation techniques discovered more than 30 years ago overcome these limitations by producing macroporous gels with high toughness and superfast responsivity. This chapter discusses how and why the properties of gels significantly alter upon transition from homogeneous gelation to a cryogelation regime. The formation and structure–property relationships of cryogels starting from monovinyl–divinyl monomers, as well as from linear polymer chains, are reviewed using examples from the recent literature. Some novel cryogels with a wide range of tunable properties and their applications are also presented in detail. These include DNA cryogels for the removal of carcinogens from aqueous environments, silk fibroin cryogels as mechanically strong scaffolds for bone tissue engineering applications, poly(acrylic acid) cryogels as self-oscillation systems, and rubber cryogels as reusable oil sorbent for the removal of oil spill from seawater.