Due to their outstanding flexibility and high sensitivity, stretchable ionic conductive hydrogel-based sensors are considered one of the best candidates for the real-time monitoring of human body motion as a wearable health-care detection electronic device. In the detection of body motion, the ionic conductive hydrogel is sensitive to its deformation. However, the current reported hydrogels struggle to recover their initial shape after numerous repeated stretching cycles owing to fatigue, leading to their response insensitivity and service life degradation. In this work, a super-stretchable and recoverable ionic conductive hydrogel (double network polymer hydrogel (SA–Zn): ZnSO₄/sodium alginate/poly acrylic-acrylamide) was designed as a stretchable sensor for human body motion detection. The SA–Zn hydrogel exhibited outstanding stretchability (up to 4000% tensile strain) and excellent shape self-recovery ability (20 min recovery time). After self-recovery for 50 cycles, the hydrogel still retained good flexibility, stable self-recovery ability and high conductivity. More importantly, the assembled wireless wearable stretchable sensor (SA–Zn-W) could transform human body motion into a visual electrical signal when combined with a Wi-Fi transmitter, revealing its excellent sensitivity, fast response, effective identification and stable electromechanical repeatability. The superior performance of the SA–Zn-W offers a promising solution for effectively and remotely detecting human body motion.

As an important part of artificial intelligence, electronic skin has received more and more attention recently. However, two serious issues, slow self-healing and lack of direction recognition, have limited the burgeoning of electronic skin largely. Herein, for the first time we report a dual network flexible hydrogel, which was synthesized via cross-linking polyvinyl alcohol (PVA) and polyethylenimine (PEI) with 4-formylbenzoboric acid (Bn) to form a polymer network and then incorporating MXene into the polymer network. Due to the synergy of multiple reversible dynamic covalent bonds and supramolecular interactions, the PVA/Bn/PEI/MXene (PBPM) hydrogel exhibits direction-aware and ultrafast self-healing abilities (self-healing time ∼0.06 s) as well as rapid response performance (signal response time ∼0.12 s). Furthermore, an electronic skin strain sensor assembled by using the PBPM hydrogel can not only efficiently detect the movements in different parts of the prosthetic person body but also specifically identify the directions of the movements including head-down/up and wrist-down/up. The flexible PBPM hydrogel in this work has shown great potential in the applications of artificial skin, soft robots, health monitoring and human-machine exchange interfaces.

With the rapid development of flexible wearable electronic devices and the growing energy demands of modern society, flexible energy storage equipment is attracting increasing attention. Recently, flexible Zn-ion hybrid supercapacitors (ZHSs), as a new type of flexible energy storage device, have been reported. However, the limited energy density of the currently reported flexible ZHSs should be further improved to realize their large-scale applications. Herein, we designed a novel redox bromide-ion additive hydrogel electrolyte (SA–Zn–Br) for flexible Zn-ion hybrid supercapacitors (BH-ZHSs) via the introduction of extra faradaic contributions (3Br⁻/Br₃ ⁻) into the hydrogel electrolyte to improve their energy density. Additionally, the assembled flexible BH-ZHS displays a maximum energy density of 605 W h kg⁻¹ at a power density of 1848 W kg⁻¹ at an amazing voltage of 2.6 V, which is better than that of most reported flexible ZHSs. After a 5000 cycle charge/discharge cycling test, capacity retention of 87.7% is retained. Interestingly, the strong interactions between the charged groups and Zn²⁺ ion in the SA–Zn–Br hydrogel electrolyte can harmonize Zn²⁺ migration with uniform nucleation on a Zn foil surface, leading to layered zinc deposition. Additionally, the SA–Zn–Br hydrogel electrolyte can also serve as an inhibitor of water/oxygen, resulting in the mitigation of corrosion and highly reversible zinc stripping/depositing. The strategy described in this study should provide a new insight for exploring flexible ZHSs with boosted energy density and controllable zinc deposition.