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 carboxyl-Fe3+ 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 similar to 2400%) and complete self-healing after being kept at 50 A degrees C 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.