Abstract
Ice formation in living cells is a lethal event during freezing and its characterization is important to the development of optimal protocols for not only cryopreservation but also cryotherapy applications. Although the model for probability of ice formation (PIF) in cells developed by Toner et al. has been widely used to predict nucleation-limited intracellular ice formation (IIF), our data of freezing Hela cells suggest that this model could give misleading prediction of PIF when the maximum PIF in cells during freezing is less than 1 (PIF ranges from 0 to 1). We introduce a new model to overcome this problem by incorporating a critical cell volume to modify the Toner's original model. We further reveal that this critical cell volume is dependent on the mechanisms of ice nucleation in cells during freezing, i.e., surface-catalyzed nucleation (SCN) and volume-catalyzed nucleation (VCN). Taken together, the improved PIF model may be valuable for better understanding of the mechanisms of ice nucleation in cells during freezing and more accurate prediction of PIF for cryopreservation and cryotherapy applications.
Highlights
Cryopreservation and cryotherapy are the two typical biomedical applications of cryogenics
Freezing injury emerged in this process is generally believed to be related to these two fates of intracellular water: dehydration or solution effect [13] and intracellular ice formation (IIF) [14,15]
We present a modified probability of ice formation (PIF) model in this study by incorporating a new parameter, the critical cell volume (Vf), into the Toner’s model
Summary
Cryopreservation and cryotherapy are the two typical biomedical applications of cryogenics. A good understanding of the response of tumor cells to freezing is of importance and significance for optimizing the freezing protocols to improve the treatment outcome of cryotherapy. Ice forms in the extracellular water first. Water either osmoses out of the cells through their plasma membrane (and cells dehydrate) or undergoes phase change to form ice in the cells. Freezing injury emerged in this process is generally believed to be related to these two fates of intracellular water: dehydration or solution effect [13] and intracellular ice formation (IIF) [14,15]. It is important to understand IIF during freezing to either minimize it (for cryopreservation) or maximize it (for cryotherapy)
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