Fig. 2. Vitrification agents for cryopreservation.

To achieve vitrification, a sample must be cooled to obtain a glassy, amorphous state without heterogeneous (via foreign particles) or homogeneous (through random ordering of water molecules) ice nucleation. a | Schematic phase diagram of an aqueous sample with different concentrations of a cryoprotectant, adapted with permission from ref.⁴³. T_m and the solid line denote the equilibrium melting temperature, T_h and the dashed line denote the temperature of homogeneous ice nucleation, and T_g and the dashed/dotted line denote the glass transition temperature of the sample. For dilute samples (<40% cryoprotectant), vitrification is difficult to achieve due to the likelihood of nucleation occurring. b | Structures of small molecules that have been investigated for toxicity neutralization: dimethyl sulfoxide (DMSO), urea and formamide³⁴. c | Macromolecular compounds such as poly(vinyl alcohol)-co-poly(vinyl acetate) (PVA-co-PVAc) copolymers and carboxylated ε-poly-L-lysine (COOH-εPLL) have been used to limit devitrification of samples during warming⁴³. Panel a adapted with permission from ref.¹⁹³, Elsevier.