Using the effective thermal conductivity to evaluate the freezing process in Medaka embryos suspension

The feasibility of using thermophysical properties to evaluate extracellular freezing processes favorable for cryopreservation was demonstrated by determining the correlation between the thermal state and the viability of cells and tissue. We measured the effective thermal conductivity of Medaka embryos (Oryzias latipes) during extracellular freezing using the self-heated thermistor technique. The insulated test chamber (8x8x12 mm) had a 2.5-mm-diameter thermistor bead installed in the bottom. The effective thermal conductivity was measured at -10°C for various cooling rates (from 0.1 to 10°C/min) for embryos in 1.92 mol/kg DMSO, and measured from 6 to -20°C for a cooling rate of 1°C/min for embryos in 0 - 2.56 mol/kg DMSO. We used the hatching rate to evaluate the viability of the embryos. The effective thermal conductivity was strongly correlated with the hatching rate, increasing as the hatching rate decreased. This demonstrates that thermophysical properties of biological materials can be used as indices for evaluating the freezing process of such materials.