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When is the best time for cell cryopreservation?
During in vitro growth, cells are usually divided into three stages: latent period, exponential growth period, and plateau period. The incubation period usually occurs when cells have just been passaged, at which point they begin to attach to the matrix and extend the skeleton. Metabolic activity is focused on the expression of adhesion proteins and skeleton proteins, and the cell count hardly increases during this period. Subsequently, the cells begin an exponential growth phase, with vigorous nucleic acid transcription and translation, frequent DNA unwinding and pairing, rapid intracellular material transfer, and a rapid increase in cell numbers. If frozen during this period, it is actually forcibly freezing the cells at a certain moment of metabolism, which will inevitably cause mechanical damage to the untwisted DNA, RNA and proteins involved in transcription and translation, and increase the risk of errors in individual processes. As the number of cells increases, the confluence of cells in the culture container reaches over 90%. Most cells stop high-speed metabolism and proliferation due to "contact inhibition", and intracellular activity tends to flatten out. So, we suggest freezing cells at the beginning of the plateau phase, which can obtain sufficient cells without causing excessive mechanical damage to the cells.