Guar Gum-based multifunctional hydrogels with high sensitivity and negligible hysteresis for wearable electronics

As a classic flexible material, hydrogel shows great potential in wearable electronics. However, it remains a challenge to prepare hydrogels that simultaneously have robust toughness, strong mechanical properties, high conductivity, fit to human skin, and strain sensitivity. In this work, oxidized guar gum (OGG) and acrylamide (AM) were used to create a novel hydrogel that is highly strain-sensitive. The hydrogel reveals a skin-like elastic modulus (∼ 29 kPa), high toughness (732.3 kJ·m−3), high breaking elongation (1060%), high adhesion, high self-healing efficiency (96%), and negligible lag (η = 3.9%, energy loss coefficient). Meanwhile, it has good biocompatibility and outstanding antimicrobial qualities. In addition, the introduction of iron ions may increase the conductivity (1.1 S·m−1) while maintaining high transparency, and the gel-based sensor exhibits high sensitivity (GF=11.82). The highly sensitive sensors exhibit very fast response time (55–60 ms) and adequate stability (2000 cycles). Interestingly, hydrogel sensors can monitor a variety of human movements, including large-scale joint bending and tiny facial expressions, gesture recognition and handwriting. In addition, it has been successfully used to transmit encrypted information, human-machine interaction and wireless sensing.