Cryoprotective\nIce-Philic Black Phosphorus Nanosheets\nfor Augmented Thawing of Frozen Cells

Controlling ice formation is critical in fields such\nas atmospheric\nscience and biological cryopreservation. However, thermal heterogeneity\nduring freezing and thawing in cryopreservation causes uneven ice\ncrystallization and melting, leading to mechanical and thermal stress-induced\ndamage. This study introduces biocompatible and biodegradable black\nphosphorus (BP)-polyethylene glycol-amine nanosheets (NS) to address\nthis issue. BP NS primarily localize at ice grain boundaries, while\namine groups of NH<sub>2</sub>-PEG-NH<sub>2</sub> form hydrogen bonds\nwith H<sub>2</sub>O molecules, penetrating ice crystals. In situ cross-sectional\nobservations confirmed that BP-PEG-NH<sub>2</sub> NS promotes uniform\nmelting and facilitates ice cracks and boundaries. Heat transfer analysis\nusing a bidirectional heating system revealed that the internal heat\nenergy varies based on BP dispersion within the ice crystals. When\napplied to the cryopreservation of human tongue squamous cell carcinoma\ncells, BP-PEG-NH<sub>2</sub> NSs significantly improved post-thaw\nviability. It presents a promising strategy for designing thawing\nmaterials after cryopreservation of cells, tissues, and organs.