PromoCell cells are frozen down in the gas phase of liquid nitrogen (computer-controlled freezing machine) and then stored in the liquid phase of LN2.
The cryopreservation in LN2 is an acknowledged method for long-term storage of primary cells and stem cells. When stored in liquid nitrogen, the cells can be maintained for a period of > 10 years without affecting viability.
For example, Kumar et al. showed that adipose-derived stem cells stored in LN2 for about 12 years still retained their regenerative potential, stem cell property, viability as well as differentiation ability.