GROSS DAMAGE ACCUMULATION IN FROZEN RABBIT LIVER DUE TO MECHANICAL-STRESS AT CRYOGENIC TEMPERATURES

The second phase of a pilot study dealing with the mechanical response of frozen biological tissues to external compressive load is presente d. This stage deals with histological observations of the damage accom panying mechanically induced permanent deformation in frozen rabbit li ver. No significant gross histological damage was observed in the live r samples due to either processing the tissue in the frozen state, due to slow cooling of the liver tissues down to -20 degrees C, or due to rapid cooling of the samples down to -196 degrees C. No histological changes were observed in tissue samples that were loaded within the el astic regime, that is, below the yield strength of the material. There fore, it is concluded that histological changes due to mechanical stre sses are associated with plastic (permanent) deformations. Histologica l observations indicate that Linear cracks which appear to have no pre ferred orientation develop due to mechanical stress beyond the yield s trength of the frozen tissue. These cracks accumulate until final fail ure of the frozen tissue, when the tissue sample collapses to rubble. Based an histological observations and concepts from solid mechanics, an interaction between crack formation and irregularities in the froze n medium is suggested. Significant sources for such irregularities. in an homogeneous tissue such as the liver, are blood vessels and bile d ucts, These irregularities may either initiate crack formation or, on the other hand, may also arrest propagating cracks. (C) 1997 Academic Press.