High-performance hydrogel electrolytes with eminent toughness, high conductivity and anti-freezing properties have extensive applications in wearable devices or implantable sensors. However, it is still difficult to integrate excellent mechanical properties and high conductivity into one hydrogel sample simultaneously. This work introduced NaCl into a poly(vinyl alcohol)/poly(acrylic amide) (PVA/PAM) double network hydrogel to prepare PVA/PAM/NaCl supramolecular hydrogel electrolytes via a one-pot method. NaCl introduces physical entanglement into the PVA/PAM/NaCl hydrogel electrolytes and provides a dense and wrinkled three dimensional (3D) network nanostructure. The PVA/PAM/NaCl hydrogel electrolytes not only showed excellent mechanical properties (tensile strength up to 477 kPa, elongation at break to 1072% and a fracture energy of 2.484 MJ m⁻³), but also had high conductivity (up to 6.23 S m⁻¹). A strain sensor based on the PVA/PAM/NaCl hydrogel electrolytes exhibited very high sensitivity (gauge factor = 24.901) with the ability of precise and reliable detection of human motions. Hydrogels also showed excellent anti-freezing properties and maintained excellent mechanical properties and conductivity at −20 °C. Introducing a physically cross-linking network through the effects of a metal salt could promote the performance of the hydrogels. This work provides a new insight into the design of multifunctional materials with applications on electronic skin, wearable devices and biosensors.

The rapid development of human–machine interface technologies is dependent on flexible and wearable soft devices such as sensors and energy storage systems. One of the key factors for these devices is the hydrogel electrolyte. In this work, firstly we constructed an anti-freezing, self-healing, adhesive and tough conductive double network ionic organohydrogel by simultaneously introducing NaCl and glycerol (Gly) into poly(vinyl alcohol)/poly(acrylic amide-acrylic acid) (PVA/PAMAA). Then, based on this organohydrogel, a strain sensor and a flexible all-solid-state supercapacitor were assembled separately and their properties were measured. The fabricated strain sensor showed a highly sensitive response (gauge factor = 8.303) in a broad strain range (from 500 to 1000%), enabling the accurate and reliable detection of various mechanical deformations. Meanwhile, the flexible all-solid-state supercapacitor demonstrated a specific capacitance of 75.75 mF cm⁻², high cycling stability (90.2% retention rate after 5000 cycles) and excellent mechanical stability. Lastly, a self-powered integrated system composed of the strain sensor and flexible all-solid-state supercapacitor was fabricated. The sensor can be driven by the supercapacitor and operate stably in a wide strain range sensing test with low power consumption. More importantly, the self-powered integrated system could be directly attached to the human body to detect human motions, showing its great potential application in wearable devices. This work would enlarge the research and application of high-performance ionic hydrogel electrolytes.

The conductive hydrogel has shown extensive applications in multifunctional sensors. However, the intrinsic characteristics of conductive hydrogels, such as lacking anti-freezing, mechanical strength, and being easily dehydrated have hindered their application in wearable devices. Herein, reduced graphene oxide (rGO) and graphene oxide (GO) nanosheets were incorporated into a porous cross-linking poly(vinyl alcohol) (PVA) hydrogel network within dimethyl sulfoxide (DMSO)/H₂O binary solvent. A honeycomb-like dense micro-network and uniform dispersion conductive tough fillers endow high toughness (3.1 MPa @ 600% strain) and conductivity to the organohydrogel. With the intense interaction between water and DMSO, the organohydrogel exhibits reliable mechanical and electronic performance in a wide range of temperatures (−30 to 60 °C) and possesses excellent ambient stability. The organohydrogel had excellent sensitivity and linear repeatable response ability in both mechanical and thermal stimulation. With the integrated unique features, the sensitive organohydrogel was developed for a multifunctional sensor. As a strain/pressure sensor, it exhibited a sensitive response to the applied tensile or compressed strain with repeatability and durability. As a temperature sensor, it presented excellent linear and reliable thermal response with a high sensing accuracy. This work provides a new paradigm for designing a wearable multifunctional sensor or E-skin, which is used to detect the motion or temperature of the human in the future.

Natural biological tissues such as ligaments, due to their anisotropic across scale structure, have high water content, while still maintaining high strength and flexibility. Hydrogels are ideal artificial materials like human ligaments. However, conventional gel materials fail to exhibit high strength or fatigue resistance at high water content in human tissues. To address this challenge, we propose a simple integrated strategy to prepare an anisotropic hierarchical hydrogel architecture for artificial ligaments by combining freeze-casting assisted compression annealing and salting-out treatments. The hybrid polyvinyl alcohol hydrogels are of water content up to 79.5 wt%. Enhanced by the added carbon nanotubes, the hydrogels exhibit high strength of 4.5 MPa and a fatigue threshold of 1467 J m⁻², as well as excellent stress sensitivity. The outstanding durability of the artificial ligament provides an all-around solution for biomedical applications.

Conductive elastomers with both softness and conductivity are widely used in the field of flexible electronics.