![]() ![]() Hydrogen bonds are promising dynamic bonds to impart fascinating properties, such as self-healing 21, 22, 23, toughness 24, 25, and shape memory 26. These reversible crosslinked sacrificial bonds or microstructures synergically dissipated energy, which endows hydrogels with high stretchability and toughness. Hybrid hydrogel systems by introducing crystallites 16 and microspheres 17, micelles 18, nanocomposite 19, 20 into the hydrogels have also been reported. Attempts to introduce other chemical structures or physical crosslinks as sacrificial bonds have been made, such as ionic bonds 12, 13, triblock copolymers 14 and polyampholytes 15. The toughness and elasticity of DN hydrogel originate from the mechanism of disruption of sacrificial bonds, which dissipated energy 11. However, permanent chemical fracture in DN hydrogels led to poor fatigue resistance. DN hydrogels show robust mechanical strength and toughness. The soft network absorbs the energy and prevents the formation of macroscopic crack. The internal fracture of covalent bonds in the brittle network, which dissipates significant energy 10. 9 reported a double network hydrogel (DN hydrogel) by introducing a soft hydrogel network with slippery chains into a rigid hydrogel network. Intensive efforts have been devoted to developing tough and elastic hydrogels. Since the hydrogels undergo dynamic actions in these applications, such as stretching, compression and torsion, they should have appropriate mechanical strength, flexibility and stretchability under deformation. Stretchable hydrogels are promising materials for diverse applications, such as biomaterials 1, force sensors 2, 3, supercapacitors 4, actuators 5, optical fibers 6, stretchable conductors 7 and soft electronics 8. ![]()
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