Computational Fluid Dynamics Analysis of Cell Cooling Process

Abstract

Vitrification is the solidification of a solution without crystallization, caused by an increase of viscosity. It results from a balance between the highest realizable cooling rates and the highest concentrations of cryoprotectants (CPA) not toxic for the cells for the period of exposure. To vitrify with reduced CPA concentrations the cooling rates have to be increased. The objective of our study was to verify the thermal feasibility of a vitrification process using a computational fluid dynamics (CFD) model. The first step in our stepwise approach to our project is focused on an ultrarapid freezing process in absence of cryoprotectants. The main parameters which influence the cooldown and increased cooling rate inside the biologic material (e.g., the thermophysical parameters, the size and the shape of the specimen) have been investigated. In our test cases the living material is considered frozen by direct contact with a surface at cryogenic temperature. Both numerical values and false color images of the thermal fields are available. It is confirmed that higher cooling rates can be obtained by decreasing the thickness of the material placed on the cold surface or changing the cryogen. Variations of the other thermophysical parameters had little influence on the freezing time. From the results it appears that it is impossible to define only one cooling rate for specimen vitrification and that large quantities of biological material could be ultrarapidly frozen on wide cold surfaces with low material thickness.