In cryopreservation protocols maximum survivability is achieved when cooling occurs slowly enough to avoid Intracellular ice formation (IIF) yet fast enough to avoid solute effects injury (1). IIF plays a significant role in cell damage during cryopreservation. IIF has been extensively studied using cryomicroscopy. This technique is a useful tool to understand the dynamic processes during cooling, i.e. volume change of cells and IIF occurrence associated with temperature. However it has some limitations in being applied to biological systems. The central assumption in cryomicroscopy is that the projected two-dimensional area of the cell can be extrapolated to a spherical three-dimensional volume. While reasonable for spherical cell systems, this assumption is inappropriate for obtaining quantitative volumetric information in nonspherical cell systems. Differential scanning calorimetry (DSC), however, can be applied to nonspherical cell systems. Thus, DSC exotherms during freezing needed to be compared with cryomicroscopy observations in simple spherical cell systems. Several studies related to IIF using DSC havebeen reported (2)–(5). Most of them, however, discussed only IIF peaks and/or Extracellular ice formation (EIF). In order to predict the optimum cooling rate from DSC results, it is important to quantify not only IIF and EIF but also water transport (WT) during cooling at various cooling rates.
Intracellular ice formation in yeast cells vs. cooling rate: Predictions from modeling vs. experimental observations by differential scanning calorimetry
