What is the principle of cell cryopreservation and resuscitation? Its principle and mechanism are discussed.

A: The principle of cell cryopreservation and resuscitation is slow freezing and quick melting. Cryopreservation of cells is a method of long-term preservation of cells at ultra-low temperature. At the ultra-low temperature of-196℃, cells are dormant, so they can be preserved for a long time. In the frozen state, cells are often damaged by the increase of electrolyte concentration and the formation of ice crystals in solution. Therefore, frozen cells must be suspended in specific protective agents which are non-toxic, low molecular weight, high solubility and can quickly penetrate into living cells, such as glycerol, dimethyl sulfoxide, polyvinylpyrrolidone, ethylene glycol and glucose, among which the first two are the most commonly used. The cooling rate during freezing has a great influence on the formation of ice crystals. If the freezing speed is too fast, the water in the cell will not seep out of the cell when it is frozen outside the cell, so that ice crystals will form inside the cell and damage the cell. If the temperature drops too slowly, the extracellular solution will freeze for too long, resulting in a large amount of water oozing out of the cells and cell contraction and death. The suitable cooling rate is that after the temperature drops from 1℃ to -70℃ per minute, it is put into a liquid nitrogen tank to quickly cool down to-196℃, which can withstand long-term storage.

Cell resuscitation is to restore cell suspension from frozen state to normal temperature at a certain rate of rewarming. At the temperature below -70℃, the biochemical reaction in cells is extremely slow and even stops. When it returns to normal temperature, the morphological structure of the cell remains normal and the biochemical reaction can be restored. In the process of cell resuscitation, if the rewarming rate is improper, it may also cause intracellular freezing and cell loss. In the process of resuscitation, the temperature generally rises at a relatively fast speed, and returns to normal temperature within 65438±0 ~ 2min, so that the cells can quickly pass through the most easily damaged -5 ~ 0℃, and large ice crystals will not re-form inside and outside the cells, nor will they be exposed to a solution with high solute concentration for a long time, so that the damage of ice crystals and solutes to the cells is minimized, and the normal structure and function can be maintained after resuscitation. Therefore, the principle of cell cryopreservation and resuscitation is slow freezing and quick melting.