Integration of Macro-Cross-Linker and Metal Coordination: A Super Stretchable Hydrogel with High Toughness

The development of multifunctional hydrogels with high strength and stretchability is one of the most important topics in soft-matter research owing to their potential applications in various fields. In this work, a dual physically cross-linked network was designed for the fabrication of ultrastretchable tough hydrogels. The hydrogels were prepared through in situ polymerization of acrylic acid and acrylamide in the presence of positively charged quaternary poly(ethylene imine) (Q-PEI) and micelle-forming Pluronic F127 diacrylate, thus introducing electrostatic interactions between the positively charged Q-PEI and negatively charged poly(acrylic acid-co-acrylamide). For further mechanical reinforcement, Ca²⁺ and Cu²⁺ ions were introduced into the hydrogel network to construct coordination bonds, significantly enhancing tensile strength as well as stretchability. The hydrogel prepared with Ca²⁺ ion coordination bonds was found to be stretchable to 108 times its original length and exhibited a maximum toughness of 177 MJ·m^-3, representing one of the most robust systems with both extraordinary toughness and superstretchability prepared to date. The hydrogels also exhibited excellent recovery of dimensions and reproducibility in terms of mechanical properties, providing a promising ultrastretchable soft-matter system with outstanding mechanical strength.