Preferential Vitrification of Water in Small Alginate Microcapsules Significantly Augments Cell Cryopreservation by Vitrification

A major challenge to the eventual success of the emerging cell-based medical technologies such as tissue engineering, regenerative medicine and cell transplantation is the limited availability of the desired cell sources [1]. This challenge can be alleviated by cell microencapsulation to avoid undesired immune response (i.e., immunoisolation) so that non-autologous cells can be used to treat human diseases, and by cell cryopreservation to establish banks of important living cells for wide distribution to end users so that they are readily available when needed in the future [2,3]. Although cell microencapsulation has been investigated since 1960s with promising outcomes, cryopreservation of microencapsulated cells has not been well studied. The major challenges are associated with the cell toxicity of the high concentration (> 4–6 M) of cryoprotectants used for vitrification and the loss of microcapsule integrity due to ice formation during slow freezing [4]. Therefore, it is of great interest to achieve vitrification at a low, nontoxic cryoprotectant concentration for the cryopreservation of microencapsulated cells.