Gold nanoparticles-deranged double network for Janus adhesive-tough hydrogel as strain sensor

Adhesive, tough, and conductive hydrogels have broad application prospects in wearable and flexible sensors. The construction of adhesive-tough hydrogels still remains a challenge. Here, for the first time, we develop Janus adhesive-tough hydrogel by a medium-guided (filter paper absorbing HAuCl4) diffusion method, followed in-situ generation of gold nanoparticles (AuNPs) in gelatin-polyacrylamide (GA) double network hydrogel. The as-generated AuNPs in the adhesive surface restrict the formation of triple helixes of gelatin, thus enhancing the adhesion to various materials such as steel, polytetrafluoroethylene (PTFE), ceramic, wood, stone, rubber, copper, glass, and skin. The tough side maintains double network structure, resulting in high toughness with good recovery ability. The thickness of the adhesive surface can be regulated by adjusting the diffusion time and the concentration of HAuCl4. By adding lithium chloride (LiCl), the hydrogel can be applied as strain sensor to monitor human motion such as finger, cervical vertebrae, wrist, and elbow. These findings may contribute to the design of Janus adhesive-tough hydrogels and provide a model for strain sensors.