– Cryopreservation is a method of preserving biological material by reducing the temperature to very low levels, usually below -130 °C, using liquefied gases such as nitrogen or carbon dioxide.

– Cryopreservation can prevent ice crystal formation and dehydration that can damage the cells and tissues during the freezing process.

The viability of cells and tissues after cryopreservation depends on several factors, such as:

• The type and concentration of cryoprotective agents (CPAs) used to protect the cells and tissues from freezing damage. CPAs are substances that lower the freezing point of water and reduce the amount of ice formed inside and outside the cells. CPAs can be classified into permeating (e.g., glycerol, dimethyl sulfoxide, ethylene glycol) and non-permeating (e.g., sugars, proteins, polymers) agents.

• The cooling and warming rates applied to the cells and tissues during cryopreservation. The optimal cooling and warming rates depend on the size and complexity of the biological material, as well as the type and concentration of CPAs used. Generally, slow cooling (e.g., 1-10 °C/min) and rapid warming (e.g., 100-1000 °C/min) are preferred for most cells and tissues.

• The storage temperature and duration of the cells and tissues in the frozen state. The lower the storage temperature, the longer the cells and tissues can be preserved without significant loss of viability. However, storage temperatures below -150 °C may require special equipment and facilities, such as liquid nitrogen tanks or vapor-phase freezers.

• The thawing and recovery procedures applied to the cells and tissues after cryopreservation. The thawing process should be done quickly and uniformly to avoid ice recrystallization and thermal stress that can damage the cells and tissues. The recovery process should include the removal of CPAs, the restoration of physiological conditions, and the assessment of cell viability and function.

– When cryopreservation is done correctly, it can preserve the original quality and integrity of the biological material for long periods of time or indefinitely. It can also inhibit bacterial growth and prevent spoilage or contamination.

However, cryopreservation is not a perfect process, and some degree of cell injury or death is inevitable.

– Therefore, it is important to optimize the cryopreservation protocol for each specific cell or tissue type, and to evaluate the post-thaw viability and functionality of the preserved material before using it for any downstream application.

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