Cryoprotective Ice-Philic Black Phosphorus Nanosheets for Augmented Thawing of Frozen Cells

Controlling ice formation is critical in fields such as atmospheric science and biological cryopreservation. However, thermal heterogeneity during freezing and thawing in cryopreservation causes uneven ice crystallization and melting, leading to mechanical and thermal stress-induced damage. This study introduces biocompatible and biodegradable black phosphorus (BP)-polyethylene glycol-amine nanosheets (NS) to address this issue. BP NS primarily localize at ice grain boundaries, while amine groups of NH₂-PEG-NH₂ form hydrogen bonds with H₂O molecules, penetrating ice crystals. In situ cross-sectional observations confirmed that BP-PEG-NH₂ NS promotes uniform melting and facilitates ice cracks and boundaries. Heat transfer analysis using a bidirectional heating system revealed that the internal heat energy varies based on BP dispersion within the ice crystals. When applied to the cryopreservation of human tongue squamous cell carcinoma cells, BP-PEG-NH₂ NSs significantly improved post-thaw viability. It presents a promising strategy for designing thawing materials after cryopreservation of cells, tissues, and organs.