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

The feasibility of using thermophysical properties to evaluate extracellula r freezing processes favorable for cryopreservation was demonstrated by det ermining the correlation between the thermal state and the viability of cel ls and tissue. We measured the effective thermal conductivity of Medaka emb ryos (Oryzias latipes) during extracellular freezing using the self-heated thermistor technique((1)). The insulated test chamber (8 x 8 x 12 mm) had a 2.5-mm-diameter thermistor bead installed in the bottom. The effective the rmal conductivity was measured at -10 degrees C for various cooling rates ( from 0.1 to 10 degrees C/min) for embryos in 1.92 mol/kg DMSO, and measured rom 6 to -20 degrees C for a cooling rate of 1 degrees C/min for embryos i n 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 de monstrates that thermophysical properties of biological materials can be us ed as indices for evaluating the freezing process of such materials.