Multi-bond network hydrogels with robust mechanical and self-healable properties

Multi-bond network (MBN) which contains a single network with hierarchical cross-links is a suggested way to fabricate robust hydrogels.In order to reveal the roles of different cross-links with hierarchical bond energy in the MBN,here we fabricate poly(acrylic acid) physical hydrogels with dual bond network composed of ionic cross-links between carboxylFe3+ interactions and hydrogen bonds,and compare these dually cross-linked hydrogels with singly and ternarily cross-linked hydrogels.Simple models are employed to predict the tensile property,and the results confirm that the multi-bond network with hierarchical distribution in the bond energy of cross-links endows hydrogel with effective energy-dissipating mechanism.Moreover,the dually cross-linked MBN gels exhibit excellent mechanical properties (tensile strength up to 500 kPa,elongation at break ～ 2400％) and complete self-healing after being kept at 50 ℃ for 48 h.The factors on promoting self-healing are deeply explored and the dynamic multi-bonds are regarded to trigger the self-healing along with the mutual diffusion of long polymer chains and ferric ions.