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Conductive hydrogels usually suffer from weak mechanical properties and are easily destroyed, resulting in limited applications in flexible electronics. Concurrently, adding conductive additives to the hydrogel solution increases the probability of agglomeration and uneven dispersion issues. In this study, the biocompatible natural polymer chitosan was used as the network substrate. The rigid network employed was the Cit3−ion crosslinked chitosan (CS) network, and the MBA chemically crosslinked polyacrylamide (PAM) network was used as the flexible network. Tannic acid-reduced graphene oxide (TA-rGO), which has excellent conductivity and dispersibility, is used as a conductive filler. Thus, a CS/TA-rGO/PAM double network conductive hydrogel with excellent performance, high toughness, high conductivity, and superior sensing sensitivity was prepared. The prepared CS/TA-rGO/PAM double network conductive hydrogels have strong tensile properties (strain and toughness as high as 2009 % and 1045 kJ/cm3), excellent sensing sensitivity (GF value was 4.01), a wider strain detection range, high cycling stability and durability, good biocompatibility, and antimicrobial properties. The hydrogel can be assembled into flexible wearable devices that can not only dynamically detect human movements, such as joint bending, facial expression changes, swallowing, and saying, but also recognize handwriting and enable human-computer interaction. [ABSTRACT FROM AUTHOR]

Recently, wearable services that are flexible and based on conductive hydrogels have rapidly evolved and found numerous applications. These conductive hydrogels must possess remarkable mechanical strength, electrical conductivity, and sensing stability, while also being able to withstand low temperatures. However, creating hydrogels that meet all these requirements can be a lengthy and complicated process. Herein, we quickly (10 s) generated a double network conductive hydrogels (PHTF@DNH) using the double autocatalytic system consisting of TA (Tannic acid) and Fe3+. Due to the hydrogen bonding interactions between polyacrylamide (PAM), chitosan quaternary ammonium salt (HACC), TA, cross-linking of N, N′-methylene-bis-acrylamide (MBA), and ionic conduction of sodium citrate (Na 3 Cit), the hydrogel exhibit excellent tensile property (stress of 177.40 kPa, elongation at break of 788%), compressive performance (compressive strength of 1.1 MPa at 80% deformation), desirable toughness (702.60 kJ/m3), and exceptional cyclic compression and swelling properties. The hydrogel-based sensors show exceptional electrical conductivity (59.02 mS/cm), sensitivity (GF value of 1.13 at 100–550% strain), broad detection range and good signal stability. Even at −30 °C, the hydrogels still maintained stable. Eventually, it is harmless to human skin. We believe that the PHTF@DNH offer a new approach to the manufacture of sensitive wearable electronic devices. [Display omitted] • Double network conductive hydrogels (PHTF@DNH) were prepared under double autocatalytic conditions. • The hydrogel showed exceptional electrical conductivityand sensitivity. • The hydrogel exhibited excellent mechanical and swelling properties. • At a very low temperature (−30 °C), the hydrogel could maintain stable. [ABSTRACT FROM AUTHOR]

In recent years, hydrogels have attracted extensive attention due to their unique properties. More and more studies have added new functions to hydrogels through modification, but the modified hydrogels only show unique properties in a specific aspect, which limits the application of hydrogels. Therefore, how to endow hydrogels with two or more functions at the same time has become a research hotspot. In this study, polyacrylamide and chitosan quaternary ammonium salt were used as the matrix of the hydrogel. The surface of magnetic ferric oxide nanoparticles (Fe 3 O 4 NPs) was modified by tannic acid (TA). TA and Fe 3 O 4 NPs were connected by coordination bonds to improve the surface properties of Fe 3 O 4 NPs. Then aniline molecules were coated on the surface of Fe 3 O 4 -TA NPs by the electrostatic attraction through in-situ chemical polymerization under the action of sulfuric acid doping to obtain composite Fe 3 O 4 NPs with electromagnetic dual functions. The electromagnetic bifunctional hydrogel was prepared by introducing the composite Fe 3 O 4 NPs into the hydrogel through physical doping. The results showed that the hydrogel had excellent mechanical properties (the tensile strength was 113.3 kPa, the elongation was 1070%). Due to the existence of polyaniline, the hydrogel showed outstanding electrical properties (the conductivity was up to 24.3 mS/cm and the gauge factor was up to 9.43). In addition, Fe 3 O 4 NPs gave the hydrogel good magnetism, and the hydrogel underwent a certain deformation in the switching magnetic field, which further expanded the application field of the hydrogel. Synthesis process and structure of electromagnetic bifunctional hydrogel. [Display omitted] • Tannic acid used as coupling agent to connect Fe 3 O 4 with polyaniline. • Fe 3 O 4 composite particles act as physical cross-linking points in the hydrogel. • Hydrogels have electromagnetic dual functions and high sensing sensitivity. [ABSTRACT FROM AUTHOR]