Self-healing and tough hydrogels with physically cross-linked triple networks based on Agar/PVA/Graphene.

The aim of this work was to prepare polyvinyl alcohol (PVA)/Agar/Graphene nanocomposite hydrogels through a one-pot and green solution mixing method using water as solvent. Herein a novel strategy for designing stiff, tough and self-healing triple network (TN) hydrogels was proposed. The prepared TN hydrogels composed of strong Agar polysaccharide as the first network, tough PVA biopolymer gel as the second network, and graphene nanoplatelets as the third network. Interestingly, similar to natural biomaterials, all of the networks of the nanocomposite hydrogel were physically cross-linked via dynamic hydrogen bonding associations, i.e. Agar helix bundles, PVA crystallites and polymer chain physisorption on graphene. Therefore, the prepared hydrogels demonstrated simultaneous high strength, toughness, and autonomous self-healing within a short time of 10min, which is rare in the literature. The developed hydrogels can be a promising material in many biomedical applications, such as scaffolds, cartilages, tendons and muscles.

Bioinspired fully physically cross-linked double network hydrogels with a robust, tough and self-healing structure.

The conventional covalently cross-linked double network (DN) hydrogels with high stiffness often show low toughness and self-healing property due to the irreversible bond breakages in their networks. Therefore, scarcity of hydrogels that possess simultaneous features of stiffness, toughness, and autonomous self-healing properties at the same time remains a great challenge and seriously limits their biomedical applications. While, many natural materials acquire these features from their dynamic sacrificial bonds. Inspired by biomaterials, herein we propose a novel strategy to design stiff, tough and self-healing DN gels by substitution of both covalently cross-linked networks with strong, dynamic hydrogen bond cross-linked networks. The prepared fully physically cross-linked DN gels composed of strong agar biopolymer gel as the first network and tough polyvinyl alcohol (PVA) biopolymer gel as the second network. The DN gels demonstrated multiple-energy dissipating mechanisms with a high modulus up to 2200kPa, toughness up to 2111kJm-3, and ability to self-heal quickly and autonomously with regaining 67% of original strength only after 10min. The developed DN gels will open a new avenue to hydrogel research and holds high potential for diverse biomedical applications, such as scaffold, cartilage, tendon and muscle.