Elastic Nanoparticle-Reinforced, Conductive Structural Color Hydrogel With Super Stretchability, Self-Adhesion, Self-Healing as Electrical/Optical Dual-Responsive Visual Electronic Skins.

Developing smart hydrogel with excellent physicochemical properties and multiple signal output capability for interactively electronic skin still remains challenging. Here, conductive structural color hydrogels with desirable physicochemical properties (including high stretchability and robustness, self-adhesion and self-healing) were developed to provide synchronous electronic and visual color signals for e-skins. Highly charged elastic nanoparticles were elaborately used as building units for structural color and the hydrogel were prepared by the self-assembly of the nanoparticle to form a non-close-packed array in a mixture comprised of acrylamide, silkworm silk fiber proteins (SF), reduced graphene oxide (rGO) and then photopolymerization. Benefiting from the improved interfacial compatibility between flexible hydrogel network and elastic nanoparticle, covalent cross-linking network structure and synergistic multiple non-covalent bonding interactions, the hydrogel exhibits extraordinary mechanical properties, excellent self-adhesion to diverse substrates and self-healing at room temperature. In addition, the hydrogel exhibited sensitive resistance changes and synchronous structural color changes under strain. As a proof-to-concept, the hydrogel displayed superior capability for the color-response and the electrical signal response of various human motions, the spatial distribution of external mechanical stimuli as well as identification of different external stimuli, indicating promising applications in the fields of interactive visual electronic skin, wearable devices, and human-machine interfaces.