Antifreezing hydrogels: from mechanisms and strategies to applications

Antifreezing hydrogels have emerged as an innovative solution for maintaining functional performance and mechanical integrity in subzero environments, offering a robust alternative to traditional water-free antifreezing materials that often fail under wet and cold conditions. These water-rich hydrogels leverage their porous, crosslinked, polymeric networks, which serve as the structural basis for implementing two parallel strategies: the incorporation of antifreezing additives (peptides/proteins, salts, ionic liquids, and organics) and the meticulous engineering of polymer systems and network structures for manipulating the water-ice phase equilibrium to significantly enhance antifreezing properties. This review synthesizes recent findings to provide a fundamental overview of the important advancements in antifreezing hydrogels, focusing on their designs, mechanisms, performances, and functional applications. Various types of antifreezing hydrogels have been developed, utilizing strategies like the incorporation of antifreeze agents, use of strongly water-bound polymers, and design of highly crosslinked networks to illustrate different antifreezing mechanisms: freezing point depression, ice recrystallization inhibition, and network freezing inhibition. This review also explores the diverse functions of antifreezing hydrogels in biomedical devices, soft robotics, flexible electronics, food industry, and environmental engineering. Finally, this review concludes with future directions, emphasizing the potential of integrating machine learning and advanced molecular simulations into materials design. This strategic vision is aimed at promoting continuous innovation and progress in the rapidly evolving field of antifreezing hydrogels.