Tough and Fatigue-Resistant Hydrogels with Triple Interpenetrating Networks

Biomimetic hydrogels with triple networks have been developed via in situ polymerization and addition of graphene oxide (GO) nanosheets, which achieve improved toughness and superior fatigue resistance, simultaneously. Compared with pristine calcium alginate/polyacrylamide double network (DN) hydrogels, the integration of a calcium-induced graphene oxide network enhances the crosslinking degree of triple network (TN) hydrogels with improved compressive strength by 172% and toughness by 174%. In addition, cyclic compressive loading-unloading curves depict excellent fatigue resistance because of reversible calcium alginate and calcium-induced GO networks, whereas high strength and toughness of traditional DN gels derive from the first sacrificial network, which leads to inferior fatigue resistance. Toughness of these TN gels was still kept at 110 kJ m^-3 at the fifth cycle which is equal to that of articular cartilages. The swelling property of these DN and TN hdyrogels is also systematically explored, which exhibits that GO can reduce the swelling to maintain the mechanical properties of TN gels. The internal fracture mechanisms of these TN hydrogels are studied via swelling tests of precompressed and as-prepared gels. These synergistic effects of the reversible ions crosslinking polymer network and nanofillers open a new platform to design supertough and fatigue-resistant hydrogels. In addition, these TN hydrogels are talented replacements for load-bearing parts, like cartilage due to its high toughness and superior fatigue resistance.