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Tough hydrogel adhesives that can bond strongly to wet surfaces have shown great potential in various applications. However, it still remains a challenge to develop the adhered hydrogels integrated with strong wet adhesion, high transparency, exceptional mechanical properties, and fast self-recovery. Herein, tough nanocomposite hydrogels demonstrating high tensile strength, high transparency, and fast self-recovery are reported. The strong wet adhesion between two tough hydrogel films can be realized by introducing chemical bridging across the hydrogel-hydrogel interface, while the interfacial adhesion energy and shearing adhesion strength are up to 2216 J m -2 and 385 N m -1 , respectively. The strong adhesion and superior toughness of our hydrogels enable their reassembly capability to produce stretchable sealed balloons that can endure high air pressure without leakage. Most interestingly, the combination of excellent sealability and high transparency also allows our hydrogel balloons to turn into hydraulically driven fast tunable focus convex lenses, which is first reported here for hydrogel lenses. The hydrogel adhesives may open up the door to develop soft sealed containers and intelligent optical devices.

Water evaporation as a source of energy to trigger moisture-responsive soft materials is an emerging field in a variety of energy-harvesting devices, which has attracted widespread attention. Here, we design and fabricate bioinspired nacrelike composite film actuators consisting of graphene oxide and sodium alginate, which demonstrate an obvious shrinkage in volume when their state transfers from wet to dry and the contractile stress is up to 42.3 MPa. Based on these features, the film actuators can show rapid and continuous movements under the water gradient. The flipping frequency of the actuators can reach up to 76 rounds min -1 , which is much faster than those in previous reports. The film can flap back and forth quickly on water vapor even after loading a cargo that is 9 times its own weight. Moreover, high mobility with multimodal motion including blooming, stretching, folding, and twisting can also be achieved by modulating the shapes of films. Thus, film actuators may hold great potential in many fields, such as microrobots, artificial muscles, and sensors on grounds of their rapid response speed and adjustable motion models.

Flexible conductors are emerging soft materials for diverse electrical applications. However, it still remains a great challenge to fabricate high-performance soft conductors that are highly conductive, largely stretchable, and rapid room-temperature self-healable. Here, we design and fabricate flexible conductive bilayer composite films composed of healable elastomeric substrates and wrinkled graphenes. The elastomeric substrates, obtained by a facile bulk copolymerization of N-isopropylacrylamide and 2-methoxyethyl acrylate, show fast room-temperature self-healing efficiency of up to 96%, imparted by the reversible hydrogen bonds. Importantly, the substrates also display strong interfacial adhesion crucial to the formation of stable bilayer composite films based on a prestrain route. The synergy between self-healing of the substrates and wrinkled structures of graphene is endowed to the composite films for mechanical and electrical healing. By adjusting the prestrain ratio of the substrates, the composite films could display the tunable stretchability, conductivity, and self-healing. The optimal bilayer composite film exhibits a high conductivity of 126 S cm -1 , a large stretchability of 300%, and rapid room-temperature self-healing. Moreover, it is demonstrated that the composite films are strain-sensitive and can be used as strain sensors to monitor stretching deformation and human motion. These prominent demonstrations suggest a great potential of the bilayer composite films in next-generation wearable electronics.

Materials combining high porosity, mechanical durability, and multifunctionality have drawn significant research interest because of their potential in engineering applications. Herein, the porous air-dried nanocomposite aerogels containing reduced graphene oxide (RGO) and chitosan (CS) are fabricated by self-assembling an aqueous dispersion of graphene oxide and chitosan with the addition of hydroiodic acid (HI) followed by recasting the hybrid hydrogel with an ice-template method. The strong cross-linked composite aerogels obtained have reversible compressibility, exceptional elasticity, and high electrical conductivity, which are derived from the restacking inhibition and steric hindrance of the polymer chains. What's more, the successive soaking-drying experiments indicate that the as-prepared graphene-based aerogels exhibit excellent environmental stability and reuseability. The regenerated electrical conductivity remains almost the same and more than 90% of its maximum compressive stress at a strain of up to 92% is retained after five cycles. This makes them ideal candidates for potential applications in areas of supercapacitors and energy storage.