Ultra-strong mechanical property and force-driven malleability of water-poor hydrogels.

Hydrogels are known as soft and wet materials. Development of metal-like hydrogels with super strong and malleable properties is highly desirable as it allows for broader application and reprocessability. Here we report a dual nanocomposite hydrogel with peculiar mechanical properties in water-poor region. The gel with water content of 35% exhibits excellent recovery and fatigue resistance with elongation at break exceeding 800%, while the gel with 15 wt% of water content shows an ultra-high compressive strength and modulus of more than 1 GPa. The dual nanocomposite structure and bound water endowed the gel with high strength. Besides, the gel modulus can be easily switched by temperature change in a reversible way due to hybrid crosslinking network of the hydrogel in which physical network breaks and reforms rapidly while chemical network remains the gel state. So the gel shows a force-driven softening behavior and can be molded into different shapes due to reversible thermo-induced modulus decline. The softening behavior is also beneficial for the self-healing of the gel. The peculiar mechanical properties make the hydrogel a potential candidate for a new generation of advanced engineering materials.