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Since hydrogels are conductive, easily engineered, and sufficiently flexible to imitate the mechanical properties of human skin, they are seen as potential options for wearable strain sensors. However, it is still a great challenge to prepare a hydrogel through simple and straightforward methods that integrate excellent stretchability, ionic conductivity, toughness, self-adhesion, and self-healing. Herein, an acrylamide/3-acrylamide phenylboronic acid cross-linked network is modified to produce a semi-interpenetrating cross-linked hydrogel in just one easy step by adding starch. The prepared hydrogel contains dynamic boronic ester bonds and hydrogen bonds, which endow the exceptional stretchability (5769-13,976 %, 20-50 wt%), ideal transmittance (>90 %), self-adhesiveness (0.636 ± 0.060 kPa, 30 wt%), and self-healing properties. Notably, the self-healing process is completed instantly, achieving a healing strength of up to 81.21 %. Additionally, the aforementioned hydrogel exhibits a broad working strain range (≈ 500 %) and high sensitivity (gauge factor = 1.99) as a strain sensor, allowing it to record and track human actions precisely. This work provides a novel approach to synthesizing hydrogels with optimal overall mechanical characteristics, with the potential to facilitate the development of wearable strain sensing system based on hydrogels for real-world applications., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Yanyan Li reports financial support was provided by Youth Science Foundation of Shanxi Province (202203021222012). Jian Zhang reports financial support was provided by Natural Science Foundation of Shanxi Province (20210302123458). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Huge electronic wastes motivated the flourishing of biodegradable electrically conductive cellulosic paper-based functional materials as flexible wearable devices. However, the relatively low sensitivity and unstable output in combination with poor wet strength under high moisture circumstances impeded the practical application. Herein, a superhydrophobic cellulosic paper with ultrahigh sensitivity was proposed by innovatively employing ionic sodium carboxymethyl cellulose (CMC) as bridge to reinforce the interfacial interaction between carbon black (CB) and multilayer graphene (MG) and SiO 2 nanoparticles as superhydrophobic layer. The resultant paper-based (PB) sensor displayed excellent strain sensing behaviors, wide working range (-1.0 %-1.0 %), ultrahigh sensitivity (gauge factor, GF = 70.2), and satisfied durability (>10,000 cycles). Moreover, the superhydrophobic surface offered well waterproof and self-cleaning properties, even stable running data without encapsulation under extremely high moisture conditions. Impressively, when the fabricated PB sensor was applied for electronic-skin (E-skin), the signal capture of spatial strain of E-skin upon bodily motion was breezily achieved. Thus, our work not only provides a new pathway for reinforcing the interfacial interaction of electrically conductive carbonaceous materials, but also promises a category of unprecedentedly superhydrophobic cellulosic paper-based strain sensors with ultra-sensitivity in human-machine interfaces field., Competing Interests: Declaration of competing interest There are no conflicts to declare., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Owning to the viscoelastic properties, good biocompatibility and high strain sensitivity, choline chloride-based deep eutectic solvent (DES) hydrogels have been considered to be promising wearable strain sensors for human motion. However, traditional hydrogels are far away from the wearable strain sensor applications caused by their unsatisfied conductivity and weak mechanical properties. Herein, the strategy for functional ionic inorganic/organic interpenetrating (IPN) hydrogels preparation by cyclic freezing/thawing method was successfully developed. Polyvinyl alcohol (PVA) was proposed to dissolve in choline chlorede-based DES as hydrogel matrix for the first time. Encouragingly, the obtained DES/PVA/CNCs/g-C 3 N 4 hydrogel (choline chloride with glucose) exhibits excellent mechanical properties, included excellent tensile strength (≈ 2.55 MPa), high elongation (≈1200 %) and satisfactory tensile modulus (≈3.65 MPa). Interestingly, the thermal diffusivity (the maximum value was 0.675 W/mK) and conductivity (the maximum value was 0.18 mm 2 /s) of the DES-hydrogels were successfully achieved through adding graphitic-like nitride nanosheet (g-C 3 N 4 ) and sustainable cellulose nanocrystalline (CNCs). These enhancements were attributed to the synergistic interactions of powerful hydrogen bonding among DES, CNCs, g-C 3 N 4 and PVA chains. More importantly, the as-prepared hydrogels have the potential as a human motion sensor to accurately in-situ detect human activities on the fingers, wrists, elbows and knee joints. Those hydrogel-type strain sensors with flexibility, excellent mechanical properties, self-recovery, good heat transfer, and electrical conductivity have broad application prospects in the fields of intelligent robot, bionic prostheses, and human care areas., (Copyright © 2020 Elsevier Ltd. All rights reserved.)