Quantitative measurement and prediction of biophysical response during freezing in tissues.

Cryopreservation and cryosurgery are important biomedical applications used to selectively preserve or destroy cellular systems through freezing. Studies using cryomicroscopy techniques, which allow the visualization of the freezing process in single cells, have shown that a drop in viability correlates with the extent of two biophysical events during the freezing process: (a) intracellular ice formation and (b) cellular dehydration. These same biophysical events operate in tissue systems; however, the inability to visualize and quantify the dynamics of the freezing process in tissues has hampered direct correlation of these events with freezing-induced changes in viability. This review highlights two new techniques that use freeze substitution and differential scanning calorimetry to provide dynamic freezing data in tissue. Characteristic dimensions and parameters extracted from these new data are then used in a predictive model of biophysical freezing response in several tissues, including liver and tumor. This approach promises to help guide improved design of both cryopreservation and cryosurgical applications of tissue freezing.