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The levitation (“hovering”) of a liquid droplet on the surface of the coolant such as liquid nitrogen (LN2) is a useful model for studying the Leidenfrost effecr (LFE), that is formation of a vapor film of boiling coolant around the surface of a relative,ly hotter sample, at cryogenic temperatures. Several models of the cryogenic droplet levitation (CDL) have been proposed but no experimental verifications had been proposed for this model in earlier papers. Utkan Demirci’s group has recently developed fast ice-free cooling (vitrification) of microdroplets formed by an ink-jet printer. The group proposed a combination of a theoretical model of film boiling on a hot sphere with the zone theory of non-isothermal kinetic ice propagation within an initially liquid levitating droplet, and they gave theoretical predictions and experimental evaluations of the CDL (Leidenfrost) time tLF of droplets hovering on the surface of LN2 [6]. Here, we report our own experiment results of verification of the data and predictions reported in [6] and describe a thermodynamical model that for elucidating the fate of the levitating droplets. This model adequately explains our experimental results on measuring tLF but almost predicts somewhat 4-fold departure from the numbers claimed by Demirci’s group. We also discuss possible flaws of the model and, especially, experimental claims presented in [6].

Kinetic (very rapid) vitrification (KVF) is a very promising approach in cryopreservation (CP) of biological materials as it is simple, avoids lethal intracellular ice formation (IIF) and minimizes damaging dehydration effects of extracellular crystallization. Moreover, achieving the ultra-high rates, which would prevent IIF during cooling and devitrification during resuscitation, and achieve KVF for practically any type of cells with one protocol of cooling and re-warming would be the “Holy Grail” of cell cryobiology [3]. However such hyperrapid rates currently require very small sample size which, however, is insufficient for many applications such as stem cells, blood or sperm. As the result, even smallest droplets of 0.25 microliters cannot be vitrified sufficiently fast to avoid the use of potentially toxic external vitrification agents such as DMSO or EG due to the Leidenfrost effect (LFE). In this presentation, we describe an entirely new system for hyperfast cooling of one-two order of magnitude larger samples that we call “KrioBlastTM”, which completely eliminates LFE. We have successfully vitrified up to 4,000 microliters of 15% glycerol solutions, which theoretically corresponds to the critical cooling rate of hundreds of thousands °C/min. We believe that such a system can revolutionize the future cryobiological paradigm.

Human pluripotent stem cells (hPSCs) and their progeny such as hPSC-derived cardiomyocytes and neural cells hold great potential as a source for cell therapy and regenerative medicine, as well can be effectively used for high high content screening (HCS) of drug candidates and for toxicity tests. Cryopreservation (CP), storage, and shipment of the cells are key elements for eventual clinical, pharmaceutical and environmental applications, which will require large numbers of quality controlled and ready for use cells. Traditionally, the cells are frozen in suspensions of either fully dissociated cells) or loosely associated clusters such as clumps of hPSCs, clusters of beaters”of cardiomyocytes, (“or neurospheres of neural precursors. Beside logistical inconvenience for some applications such as HCS, additional manipulation with the cells (detachment, dissociation and centrifugation) can introduce substantial stress to the cells prior to freezing and after thawing, which per se may tremendously decrease the cell cryosurvival and functionality. Here, we are presenting ComfortFreezer™, a novel bench-top device specifically designed for cryopreservation in multi-well plates for cell-based high content screening (HCS), which combines a liquid-nitrogen (LN2) free programmable freezer This cryogenic equipemnt can bring serious advantage for HCS in drug screening, environmental toxicity evaluation, and other variety of HCS-based applications.

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