Mechanically strong and tough hydrogels with pH-triggered self-healing and shape memory properties based on a dual physically crosslinked network

Physically crosslinked hydrogels with a reversible nature have attracted much attention in recent decades due to their fascinating self-recovery and self-healing properties, but the low mechanical strength hinders their development for many stress-bearing applications. In this study, inspired by the multiple supramolecular interactions in nature including hydrogen bonding and ionic bonds, we proposed a simple strategy to fabricate high-performance dual physically crosslinked D-hydrogels, which is triggered by the self-complementary quadruple hydrogen bonding interactions between 2-ureido-4[1H]-pyrimidinone (UPy) dimers and Fe3+ ionic coordination bonds as the dynamic sacrificial crosslinkers, thus obviously enhancing the mechanical strength and toughness. Due to the synergistic effect of the two types of physical crosslinking interactions, the D-hydrogels exhibit outstanding mechanical properties, such as a tensile strength of 7.9 MPa, an elastic modulus of 6.9 MPa, and an elongation at break of 541%, with an optimized structure. Furthermore, these reversible dual physical crosslinks enable the D-hydrogels to efficiently dissipate energy with a high toughness (up to 29 MJ m−3) while imparting good self-recovery properties, a pH-triggered healing capability and pH-responsive shape memory to the network. This dual physically crosslinked hydrogel with excellent mechanical performance as well as good recovery and self-healing properties will hopefully be exploited as a promising candidate for various biomedical applications.