The design and synthesis of conductive hydrogels with antifreezing, long-term stable, highly sensitive, self-healing, and reusable is a critical procedure to enable applications in flexible electronics, medical monitoring, soft robotics, etc. Herein, a novel zwitterionic composite hydrogel possessing antifreezing, fast self-healing performance, water retention, and adhesion was synthesized via a simple one-pot method. LiCl, as an electrolyte and antifreeze, was promoted to dissociate under the electrostatic interaction with zwitterions, resulting in the composite hydrogels with high electrical conductivity (7.95 S/m) and excellent antifreeze ability (−45.3 °C). Meanwhile, the composite hydrogels could maintain 97% of the initial water content after exposed to air (25 °C, 55% RH) for 1 week due to the presence of salt ions. Moreover, the active groups of zwitterions could form conformal adhesion between the composite hydrogels and skin, which was particularly crucial for the stable signal output of the sensor. The dynamic borate ester bonds, active group of zwitterions, and the hydrogen bond between different components could achieve rapid self-healing (2 h, self-healing efficiency to 97%) without any external intervention. Notably, the developed PBAS-Li (poly­(vinyl alcohol) Borax/acrylamide/zwitterionic-LiCl) hydrogel not only succeeded in sensitively detecting human motions but also could precisely captured handwritings signals and subtle pulse waves on the neck and wrist. The above findings demonstrated the great potential of PBAS-Li hydrogels in the field of flexible electronic devices.

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into elastic materials such as polyurethane. [7] Although these nanofillers provided excellent electrical conductivity to the elastomer, the phase separation between the nanoparticles and the elastomer material could lead to the shedding of the nanofillers during use. [8,9] Also, the introduction of these nanofillers tends to reduce the transparency of the material. Since most of the substrate materials for these strain sensors were polyurethanebased materials, [10] resulting in the preparation of sensors that are stiffer relative to the human skin. [11,12] Hydrogels and ionic liquid gels had great potential for the preparation of flexible conductive sensors. [3,13] Xia et al. prepared a conductive wearable sensor using a dual physical cross-linked double network hydrogel composed of polyacrylamide as the first network and Ca 2+ cross-linked alginate as the second network. [14] This dualnetwork structure imparts high strength, toughness, stretchability, and excellent selfrecovery properties to the hydrogel. Jiang et al. prepared a flexible and transparent (94.3%) ionic gel as a skin sensor by mixing ionic liquid (IL) and thermoplastic polyurethane. This flexible conductive sensor can operate at −40 °C to 100 °C. [15] Jin et al. successfully prepared a strong and tough self-adhesive hydrogel by introducing chitosan and 2-acrylamide-2-methylpropanesulfonic acid into a polyacrylamide network using a one-pot method. [16] This hydrogel had good adhesion properties and the prepared sensor can be directly adhered to the surface of human skin. In summary, all of these efforts had their outstanding merits, but in many aspects, there were also shortcomings. In the previous work, we learned that most conventional intrinsically conducting polymers are based on hydrogels and ionic liquid gels. [17][18][19] Hydrogels are generally difficult to use properly in harsh environments, and both low and high temperatures can destroy the original properties of hydrogels. Although ionic liquids were resistant to harsh environments, they were generally expensive and somewhat toxic. Usually, in order to ensure a close fit of the sensor to the skin, we expect the prepared gel to be self-adhesive, which not only improves the sensitivity of the sensing but also does not require any tape assistance. [20][21][22]

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