Towards ready-to-use 3-D scaffolds for regenerative medicine: Adhesion-based cryopreservation of human mesenchymal stem cells attached and spread within alginate-gelatin cryogel scaffolds

Cultivation and proliferation of stem cells in three-dimensional (3-D) scaffolds is a promising strategy for regenerative medicine. Mesenchymal stem cells with their potential to differentiate in various cell types, cryopreserved adhesion-based in fabricated scaffolds of biocompatible materials can serve as ready-to-use transplantation units for tissue repair, where pores allow a direct contact of graft cells and recipient tissue without further preparation. A successful cryopreservation of adherent cells depends on attachment and spreading processes that start directly after cell seeding. Here, we analyzed different cultivation times (0.5, 2, 24 h) prior to adhesion-based cryopreservation of human mesenchymal stem cells within alginate-gelatin cryogel scaffolds and its influence on cell viability, recovery and functionality at recovery times (0, 24, 48 h) in comparison to non-frozen control. Analysis with confocal laser scanning microscopy and scanning electron microscopy indicated that 2 h cultivation time enhanced cryopreservation success: cell number, visual cell contacts, membrane integrity, motility, as well as spreading were comparable to control. In contrast, cell number by short cultivation time (0.5 h) reduced dramatically after thawing and expanded cultivation time (24 h) decreased cell viability. Our results provide necessary information to enhance the production and to store ready-to-use transplantation units for application in bone, cartilage or skin regenerative therapy.