Heat and mass transport in freezing injury: Linking thermal history, biophysical response and tissue viability

Low temperature is currently used extensively in clinical and biomedical applications to both preserve and destroy mammalian cells and tissues. Although cryobiology is of demonstrated importance in the medical and biomedical setting, its use has not been optimized in most applications. Much fundamental research into the mechanism of cell and tissue injury during and after freezing and thawing (or cryoinjury) is still necessary to realize the full potential of low temperature technology in its current and future applications. Engineers can contribute to the field of cryobiology through continuing to develop and expand upon the mathematical models for thermal and biophysical processes in biosystems, and through a systematic approach to further investigation of the link between thermal and biophysical events in cells and tissues and mechanisms of cryoinjury. In this study, engineering principles of thermodynamics, heat and mass transfer, optimization and experimental methods are applied to specific problems in cryopreservation and cryosurgery, to address the following three goals: (1) o investigate the cell-level biophysical behavior of two biomedically-relevant tissue systems (normal rat liver cells and tissue in the presence and absence of cryoprotectant and Dunning AT-1 rat prostate tumor) in an effort to extend application of biophysical models to these systems; (2) o determine the functional relationship between thermal history during a freeze/thaw process and resulting cellular injury in the AT-1 tumor tissue model, including a parametric study on AT-1 cell survival over the four thermal parameters which characterize a freeze/thaw cycle (cooling rate, end temperature, hold time and thawing rate); (3) o improve thermal models of freezing in bulk biological systems by determining how thermophysical property assumptions affect predictions and proposing a new way of incorporating cell-level biophysical behavior into freezing predictions.;The results of each specific study are discussed in terms of implications for the intended biomedical application in each case, and contributions towards accomplishment of the three goals outlined above.