Abstract
A new method detecting the effective thermal diffusivity to assess the ice formation in the biological tissues during the cryopreservation process was proposed. Human fibroblasts cultured in collagen sponge with the cell densities of 10^6 and 10^7 cells/cm^3 were used as the mock biological tissue (φ20x1 mm). The experimental apparatus was equipped with a cylindrical chamber (φ24x4 mm), cooling device, and a programmable temperature-controller. From 4 to -196℃, the specimen was cooled with 35wt% propylene glycol (cryoprotectant) at different cooling rates of 30 to 1700℃/min. The temperature of the specimen was increased stepwise from -190 to -185℃, the effective thermal diffusivity was determined by the Laplace transform method. The specimen was thawed; the post-thaw viability was evaluated with the trypan blue exclusion assay. As a result, with increasing the cooling rate at both cell densities, the effective thermal diffusivity decreased, and the post-thaw viability increased. Our results demonstrate that the effective thermal diffusivity could be the index to assess the cryopreservation during the process.
