Numerical simulation of local temperature distortions during ice nucleation of cells in suspension

Knowledge of intercellular ice formation in cells embedded in an extra-cellular suspension is essential for effective design of freezing protocols. The presence of cell membrane causes super-cooling of the intra-cellular region, which nucleates at much lower temperatures than the surrounding extra-cellular space and is accompanied by the exothermic release of the latent heat. This is a dynamic process and causes thermal distortions in and around the cell where nucleation occurs. In the present study, an attempt has been made to numerically determine the magnitude of thermal distortion (ΔT) and the time (dt) it takes for this distortion to damp out to the local temperature. A two-dimensional computational model is presented in which the maximum thermal distortions (with an assumed cell diameter of 50 μm, nucleating at −5 °C while being cooled at 5 °C/min; denoted as Scenario 1) and the lowest-possible thermal distortions (with an assumed cell diameter of 5 μm, nucleating at −20 °C while being cooled at 100 °C/min; denoted as Scenario 2) are determined. Extensive computations have been performed assuming either the presence of a single, dual, or four cells in suspension. It is expected that these representative results would serve the purpose of estimating an effective sampling rate of microscale thermocouples currently being fabricated and of other biomedical devices used to measure intracellular ice formation.