Ultra-fast preparation of multifunctional conductive hydrogels with high mechanical strength, self-healing and self-adhesive properties based on Tara Tannin-Fe3+ dynamic redox system for strain sensors applications

Flexible wearable devices are drawing a lot of interest from researchers because of their enormous potential for applications in human-computer interaction, e-skin and disease diagnosis. In particular, hydrogel-based flexible electronic devices with good bio-friendliness, excellent mechanical properties (tensile and compressive), self-adhesion, self-healing, and high electrical conductivity are the hot topics of research. Herein, we built up a dynamic redox system using Tara tannin and Fe3+ combined with the Fenton reaction to prepare a multifunctional conductive dual-network interpenetrating hydrogel (Tara-Fe3+-PAA-CSMA), which was fast prepared (1–5 min), low-cost and energy saving (reaction at room temperature). Poly(acrylic acid) (PAA) formed the first layer of the network and CSMA (chitosan modified by methacrylic acid) constructed the second layer. The obtained hydrogel has high transmittance and strong UV absorption, excellent tensile properties (900%, 0.75 MPa) and adhesion to a wide range of materials (metals, wood, skin, plastic, etc.). Meanwhile, its good self-healing ability, reliable conductivity and high sensitivity (GF = 5.33, 80% tensile strain) provided the possibility for its application as a conductive strain sensor. The hydrogel sensor can accurately capture several motion signals, such as walking, arm shaking and swallowing. What's more, it can also sharply monitor the vibration of the larynx during vocalization and distinguish different sound information according to the graph obtained. In summary, this work innovatively proposed a Tara tannin-Fe3+ based dynamic redox system that makes it possible to quickly prepare conductive hydrogels at room temperature. It is expected to advance the industrial production of wearable flexible electronic devices.