Hello Tasnim Waheeb

No, there is no need of gradual freezing for animal tissue. For cell lines, gradual freezing is required to maintain cell viability so that on thawing one gets the maximum number of viable cells. When temperature falls from (say) 37°C to −196°C, it damages the cells. This is due to major loss of intracellular water, resulting in a considerable increase of electrolyte concentrations in both intra and extracellular media, and the formation of ice crystals in the intracellular spaces that deform and compress the cells and even destroy the intracellular structures.

On the other hand, tissue which is mostly required for downstream analysis of DNA, RNA, protein, and morphology endpoints, may be snap frozen immediately after dissection in liquid nitrogen (vapor) or immerse in liquid nitrogen for 2 minutes or less depending on the size of the tissue specimen. You may transfer the frozen animal tissue to the liquid nitrogen (vapor) for storage purpose. However, if morphological analysis is anticipated, then the tissue specimen may be surrounded by OCT medium prior to freezing.

Best.

Hi Tasnim Waheeb

I agree with Malcolm Nobre.

* Storing Cells lines requires gradual freezing to maintain the viability whereas for the tissues are required for molecular experiments so they can be frozen directly in LN2.

Thanks,

Preserving cell lines need to keep the cells alive, so more care is needed on the media, chemicals, and the gradual decrease on temperature: https://lab.plygenind.com/how-to-cryopreserve-mammalian-cell-lines

Freezing animal tissue generally just needs to preserve some molecules in the tissue, so less care is needed.