Supported by the National Natural Science Foundation of China (Grant Nos. T2125009, 12102388, 92048302, 12321002), Professor Li Tiefeng and Researcher Yang Xuxu from the team of Academician Yang Wei at Zhejiang University, in collaboration with Professor Luo Zisheng and Associate Researcher Li Dong, have made significant progress in the research of hydrogels that can withstand extreme temperatures. To address the challenge of hydrogels undergoing phase transitions and losing their inherent properties under environmental changes, the team proposed a universal “hydro-locking” strategy through molecular-level mechanical design. This strategy enables the fabrication of hydrogels that maintain flexibility and functionality within a temperature range of -115°C to 143°C. The findings were published in Science on February 28, 2025, under the title “Hydro-locking in Hydrogel for Extreme Temperature Tolerance” (https://doi.org/10.1126/science.adq2711).

Hydrogels are soft polymer networks filled with water molecules. Temperature fluctuations can cause the free water molecules within the polymer network to evaporate or freeze, altering the mechanical properties of the hydrogel and making it lose its stretchability and become prone to fracture. Traditional functional modifications and solvent replacements fail to effectively immobilize water molecules within the polymer network, leaving the temperature limits of hydrogels constrained by the phase transition temperature of the solution used.

To address these issues, the research team proposed a “hydro-locking” strategy. This involves creating bridges between water molecules and the polymer network, effectively anchoring the water molecules within the network and inhibiting water phase transitions, thereby stabilizing the hydrogel. The “hydro-locking” strategy can be achieved through the interaction of sulfuric acid with double-network hydrogels: On one hand, the strong interactions between sulfuric acid and water, and between sulfuric acid and the polymer, generate sulfuric acid hydrates that anchor water molecules within the polymer network, effectively suppressing water phase transitions at extreme temperatures; On the other hand, the introduction of a sacrificial network that reacts with sulfuric acid to form a carbon layer in situ on the hydrogel’s main chain protects the backbone and ensures the stability of the polymer network under extreme conditions. The resulting hydrogel maintains high fracture toughness at extreme temperatures, with an elongation rate of 3 times at -100°C and over 4 times at 140°C. The team further implemented this strategy in single-network gels and other solvent systems, demonstrating its universality. This research revealsthe impact of water molecules within hydrogels on their mechanical properties and functionality. By designing materials at the microscopic mechanical level, the team has expanded the applicable temperature limits of traditional hydrogels, providing a new paradigm for the design of soft polymer materials adaptable to extreme temperature environments.

Figure: “Hydro-Locking” Hydrogel Design and Its Mechanical Properties. (a) Schematic of the Microstructure of “Hydro-Locking” Hydrogel. (b) High Elasticity of Hydrogel in Extreme Temperature Environments. (c) DSC Test Demonstrating Stability from -115°C to 143°C. (d) Mechanical Stability of “Hydro-Locking” Hydrogel at Extreme Temperatures.