Natural glycyrrhizic acid-tailored hydrogel with in-situ gradient reduction of AgNPs layer as high-performance, multi-functional, sustainable flexible sensors

To date, flexible sensors derived from hydrogel materials have been popularly adopted in the field of wearable electronic devices. It is urgent and prospective to create a high-performance and multi-functional hydrogel by simple and green methods to satisfy the various demands for long-term direct human contact. Herein, a sustainable physical double network hydrogel is prepared by natural glycyrrhizic acid (GL) and biocompatible polyvinyl alcohol (PVA) in water/glycerol solvent, which exhibits high mechanical properties, good biocompatible, anti-freezing and anti-drying ability. Inspired by the reducing abilities of GL, a gradient silver nanoparticles layer can be constructed in situ on the hydrogel surface without additional reducing agents. It not only affords the UV-light shielding and antibacterial effect for the hydrogel, but also effectively improves the sensing performance. The simultaneous realization of desired properties enables the hydrogel to be assembled into a sensor to detect all-dimensional human motion with high sensitivity, stability and durability. Benefiting from the renewable raw material, non-toxic reagent and facile preparation process, this work provides new insight and inspiration for the design of flexible sensors with high performance, multi-functionality and sustainability.