Skin-Inspired Packaging of Injectable Hydrogel Sensors Enabled by Photopolymerizable and Swellable Hydrogels toward Sustainable Electronics

Flexible hydrogel-based sensors have attracted considerable interest for their potential applications in human motion detection, physiological monitoring, and electronic skin. However, the durability of hydrogel sensors is seriously hindered due to inevitable water evaporation and the lack of reusability. Herein, inspired by the skin's delamination structures that perform sensing and barrier functions, packaged hydrogel strain sensors (PHSSs) were fabricated by employing injectable conductive hydrogel wires as strain sensing elements and another photopolymerizable hydrogel film as an external packaging layer. Thanks to the packaging strategy, multiple properties of the high sensitivity (GF = 1.63 at a strain range of 0–100%), linear sensing property (R2 > 0.99), good transparency (∼85% transmittance), and conformal adhesion (0.24–1.53 kPa) were integrated into one PHSS, which was further demonstrated to possess the capability of detecting human motions and electrophysiological signals precisely. More importantly, the enhanced lifespan (2.5 times) was achieved as a result of water evaporation inhibition by packaging, while the swelling property of the external hydrogel film endowed the PHSS with good reusability (reused for three cycles). This study provides a new strategy for fabricating sustainable hydrogel-based electronics.