Thin-Film Evaporation Heat Transfer of Liquid Nitrogen and Its Application in Cell Vitrification

Cell vitrification has been an important method of cell cryopreservation. The faster the cooling rate is, the higher the cell survival rate is. However, in conventional cell vitrification methods, film boiling forms a vapor-blanket on the surface, which hinders further improvement of the cooling rate. To eliminate the problem, this article attempted to replace film boiling with thin-film evaporation (TFE) of liquid nitrogen. The experimental system was developed to investigate the TFE heat transfer characteristics of liquid nitrogen. Then, prostate cancer cells were cryopreserved by TFE vitrification method, open pulled straw vitrification method, and equilibrium freezing method. The results showed that the vitrification method of TFE obtained a higher cooling rate and better cell survival rate than the two other cell cryopreservation methods. Thus, the feasibility of this method was preliminarily proved viable when applied to the cell vitrification process. In addition, both the cooling rate and the cell survival rate are affected by the concentration of the cryoprotectant in the cell suspension. The cooling rate decreases as the concentration of the cryoprotectant increases, but the cell survival rate increases first and decrease afterward with an increase in the cryoprotectant concentration, in which an optimum value exists. This study demonstrates the practicality of the new ultrafast cell vitrification method.