Cryopreservation is the process of preserving biological material at ultralow temperatures, typically below −80°C and often at −196°C in liquid nitrogen, to halt all metabolic and biochemical processes and enable long-term storage. The technique is indispensable in cell biology, reproductive medicine, tissue banking, and biopharmaceutical manufacturing. Successful cryopreservation requires the prevention of lethal intracellular ice formation, minimization of osmotic stress, and maintenance of cellular integrity upon thawing.
Principles of Cryopreservation
The central challenge of cryopreservation is the phase transition of water to ice. During freezing, the formation of extracellular ice increases the solute concentration in the unfrozen fraction, creating a hypertonic environment that draws water out of cells. If cooling is too rapid, water cannot exit the cell sufficiently, leading to intracellular ice formation, which is mechanically lethal. If cooling is too slow, cells are exposed to prolonged hypertonic stress and potentially toxic cryoprotectant concentrations. The optimal cooling rate balances these competing risks and is cell-type specific, typically ranging from 0.5 to 5°C per minute for mammalian cells.
Applications
Cryopreservation is essential in reproductive medicine (sperm, oocytes, embryos), stem cell research (iPSCs, MSCs, HSCs), cell therapy manufacturing (CAR-T cells), tissue banking (cartilage, bone, skin), and biopharmaceutical production (CHO cells, hybridomas). It enables the establishment of master and working cell banks, facilitates global shipping of biological materials, and preserves genetic diversity in endangered species.
