Cryoprotectants: the essential antifreezes to protect life in the frozen state

In the fifty years since the establishment of the cryoprotective effect of glycerol, cell banking by cryopreservation has become routine in many areas of biotechnology and medicine. Cryoprotectant addition has become a rather mundane step within the overall protocol. However, for future advances in cryobiology and to meet new challenges in the clinical use of cryopreserved cells or tissues, it will be essential to have an understanding of the development and current status of the biological and chemical knowledge on cryoprotectants (CPA). This review was undertaken to outline the history of CPA use, the important properties of CPA in relation to freezing damage, and what can be learnt from natural freezing-tolerant organisms. The conflicting effects of protection and toxicity resulting from use of CPA are discussed, and the role of CPA in enhancing glassy states in the emerging field of vitrification are also set out.