Enhanced Control over Ice Nucleation Stochasticity Using a Carbohydrate Polymer Cryoprotectant.

Metastable supercooling has emerged as a transformative technique for ice-free biopreservation, but issues of stability inherent to the stochastic nature of ice formation have thus far limited its translation out of the laboratory. In this work, we explore the influence of the bio-based carbohydrate polymer FucoPol on aqueous supercooling using an isochoric nucleation detection technique. We show that FucoPol, a high-molecular-weight, fucose-rich polysaccharide, which has previously been shown to reduce average ice crystal sizes after nucleation, also induces a concentration-dependent stabilization of metastable supercooled water, as evidenced by both a significant reduction in nucleation stochasticity (i.e., the spread in temperatures over which the system will nucleate upon cooling) and a corresponding increase in the predicted induction time of nucleation. FucoPol is found to confine the stochasticity of ice nucleation to a narrow, well-defined band of temperatures roughly one-third as wide as that of pure water under identical conditions. Importantly, this substantial reduction in stochasticity is accompanied by only a minimal (<1 °C) change in the average nucleation temperature, suggesting that this effect is distinct from colligative freezing point depression. Reducing and characterizing the stochasticity of aqueous supercooling is essential to the engineering design of practical biopreservation protocols, and the results reported herein suggest that high-viscosity polymer systems may provide a powerful and largely unexplored lever by which to manipulate metastable-equilibrium phase change kinetics at subzero temperatures.