Transient, printable and recyclable gelatin hydrogels with enhanced mechanical sensing and electromagnetic shielding performance by incorporation of reduced graphene oxide

Transient and recyclable elastic materials have gained tremendous attention in the development of next-generation electronics. However, the fabrication of robust and printable electronic materials at mild conditions with biopolymer-based materials remains challenging. As a common and benign natural polymer, gelatin has easy availability, water solubility, good flexibility, and full biodegradability, yet its electromechanical performance is poor. Herein, a transient and recyclable gelatin hydrogel with remarkable mechanical resilience, conductivity and printability is constructed by a mild two-step reduction of the incorporated graphene oxide (GO) in ascorbic acid and sodium citrate solutions. The integration of reduced graphene oxide (rGO) in the gelatin hydrogel not only provides abundant multiple non-covalent interactions to dissipate the mechanical energy but also endows the hydrogel with desirable electrical conductivity, with the fracture stress and conductivity improved by 53 and 33 times, respectively. Under the synergistic merits, the hydrogel can be assembled as a compliant electromagnetic shielding layer with a shielding effectiveness of 29.4 dB, as well as resistive and capacitive sensors with high sensitivity (0.84 kPa−1), large gauge factor (8.2) and excellent stability (>20000 cycles under 60 kPa). As a proof-of-concept, the hydrogel was directly injected onto skin and assembled into a fully degradable self-powered sensing system for Morse code demonstration, and the hydrogel is permeable, photothermally healable, and washable. This work is a step towards the low-cost, ambient and scalable fabrication of green, reliable and versatile flexible electronics.