Long-term storage in liquid nitrogen: Should I keep frozen cells in the liquid phase or in the vapor phase?

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Cells can be stored in liquid nitrogen (LN2) for years without loss of cell viability. The storage temperature must be kept permanently below -130°C to prevent ice crystal formation inside the cells. It is recommended to store cryopreserved cells in the vapor phase of LN2. This method of storage reduces the risk of liquid nitrogen entering cryotubes which can result in the explosion of the tubes upon thawing. In addition, it has been described that contaminating organisms can be transferred from one cryotube to the other when the tubes are stored in the liquid phase of LN2 (1). Storage in the vapor phase reduces the risk of spreading existing contaminations, but it requires careful monitoring of the LN2 level in order to avoid the tank running empty. Cryostorage containers that are equipped with temperature and level indicator and/or are fitted with alarms support safe long-term storage of cell lines.

(1) Tedder RS et al. (1995) Hepatitis B transmission from contaminated cryopreservation tank. The Lancet. 346(8968): 137-40.

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