General Strategy To Fabricate Strong and Tough Low-Molecular-Weight Gelator-Based Supramolecular Hydrogels with Double Network Structure

Low-molecular-weight gelator (LMWG)-based supramolecular hydrogels, self-assembled by small molecules via noncovalent interactions, have recently attracted great attention due to their unique structure-property relationship and potential applications spanning from functional materials to biomedical devices. Unfortunately, many LMWG-based supramolecular hydrogels are mechanically weak and can not even be handled by conventional tensile and tearing tests. Here, we propose several design principles to fabricate new LMWG-based hydrogels with a true double-network structure (G4 center dot K+/PDMAAm DN gels), consisting of the supramolecular self-assembly of guanosine, B(OH)(3) and KOH as the first, physical G4 center dot K+ network and the covalently cross-linked poly(N,N'-dimethyacrylamide) (PDMAAm) as the second, chemical network. Different from those LMWG-based supramolecular hydrogels, G4 center dot K+/PDMAAm DN gels exhibit high tensile properties (elastic modulus = 0.307 MPa, tensile stress = 0.273 MPa, tensile strain = 17.62 mm/mm, and work of extension = 3.23 MJ/m(3)) and high toughness (tearing energies = 1640 J/m(2)). Meanwhile, the dynamic, noncovalent bonds in the G4 center dot K+ network can reorganize and reform after being broken, resulting in rapid self-recovery property and excellent fatigue resistance. The stiffness/toughness of G4 center dot K+/PDMAAm DN gels can be recovered by 65%/58% with 1 min resting at room temperature, and the recovery rates are further improved with the increase of temperatures and resting times. Interestingly, G4 center dot K+/PDMAAm DN gels also exhibit UV-triggered luminescence due to the unique G4-quartet structure in the G4 center dot K+ supramolecular first network. A new toughening mechanism is proposed to interpret the high strength and toughness of G4 center dot K+/PDMAAm DN gels. We believe that our design principles, along with new G4 center dot K+/PDMAAm DN gel system, will provide a new viewpoint for realizing the tough and strong LMWG-based gels.