THERMAL-EXPANSION MEASUREMENTS OF FROZEN BIOLOGICAL TISSUES AT CRYOGENIC TEMPERATURES

Thermal expansion data are essential for analyses of cryodestruction a ssociated with thermal stresses during cryopreservation protocols as w ell as during cryosurgery. The present study tests a commonly used hyp othesis that the thermal expansion of frozen tissues is similar to tha t of pure water ice crystals. This study further provides insight into the potential effect of the presence of cryoprotectants on thermal ex pansion. A new apparatus for thermal strain measurements of frozen bio logical tissues within a cryogenic temperature range is presented. Res ults are presented for fresh tissue samples taken from beef muscle, ch icken muscle, rabbit muscle, rabbit bone, and pig liver. Pilot studies of the effect of cryoprotectants on thermal expansion are further pre sented for rabbit muscle immersed in dimethyl sulphoxide (2 mols/l) an d glycerol (2 mols/l), and for pig liver perfused with dimethyl sulpho xide (2 mols/l). Thermal expansion of frozen soft biological tissues w as found to be similar to that of water ice crystals in the absence of cryoprotectant. Thermal expansion of the rabbit bone was found to be about one half of that of frozen soft tissues. A significant reduction in the thermal expansion at higher temperatures was observed in the p resence of cryoprotectants. A rapid change of thermal strain near -100 degrees C was also observed which is likely to be associated with the glass transition process of the cryoprotectant solutions.