What are the changes in viability against time in stem cells population?

There is no evidence at this time that the cryopreserved cells at -196 ° C (liquid nitrogen) lose the set in-vitro viability or biological activity.

Therefore, at this time, no "expiration date" cannot be defined in cord blood frozen in liquid nitrogen conditions.

A study published by Broxmeyer showed that after 20 years of cryopreservation of cord blood stem cells, they retain all their biological functions.

Broxmeyer HE et al, 2003. High efficiency recovery of functional haematopoietic progenitorand stem cells from human cord blood cryopreserved for 15 years. PNAS USA, 100(2): 645-50.
CD34+ AND VIABILITY MEASUREMENTS IN STORED UMBILICAL CORD BLOOD GRAFTS Vasiliki E. Kalodimou, et all, Transfusion abstracts Sept. 2008,
Koliakos G, Alamdari D, Tsagias N, Kouzi-Koliakos K, Michaloudi E, Karagiannis V. A novel high-yield volume-reduction method for the cryopreservation of UC blood units. Cytotherapy. 2007, 9(7):654-9.