Diffusion controlled ice growth with soft impingement inside biological cells during freezing

Area of Science:

• Cryobiology
• Biophysics
• Materials Science

Background:

• Intracellular ice formation (IIF) is a major challenge in cryopreservation, leading to cell damage.
• Understanding the relationship between cryoprotective agent (CPA) concentration, temperature, and IIF is crucial for optimizing cryopreservation protocols.

Purpose of the Study:

• To develop and validate an iterative method for determining IIF temperature depression relative to melting point depression for CPA concentrations >1.5M.
• To incorporate a soft impingement model into crystal growth kinetics for more accurate IIF prediction.
• To investigate the influence of CPA concentration and cooling rate on crystallized volume fraction.

Main Methods:

• An iterative method was coupled with a water transport model to simulate freezing-induced cell dehydration and intracellular ice growth.
• A geometrical model of soft impingement was integrated into Karlsson's diffusion-limited crystal growth model.
• The enhanced crystal growth model was validated against literature data for critical cooling rates required for vitrification.

Main Results:

• The developed model accurately predicts IIF temperatures across various CPA concentrations and temperatures.
• The limiting crystallized volume fraction increases with cooling progression and decreases with increasing initial CPA concentration.
• Soft impingement significantly impacts IIF predictions, particularly when the final crystallized volume fraction exceeds 0.1.

Conclusions:

• The novel iterative method provides a robust framework for predicting IIF temperatures and crystal growth kinetics.
• Accurate modeling of intracellular ice formation and growth necessitates the inclusion of soft impingement effects.
• This research contributes to the development of improved cryopreservation strategies by refining the understanding of ice nucleation and growth dynamics.