Tough, Healable, and Sensitive Strain Sensor Based on Multiphysically Cross-Linked Hydrogel for Ionic Skin.

Ion conductive hydrogels (ICHs) have attracted great interest in the application of ionic skin because of their superior characteristics. However, it remains a challenge for ICHs to achieve balanced properties of high strength, large fracture strain, self-healing and freezing tolerance. In this study, a strong, stretchable, self-healing and antifreezing ICH was demonstrated by rationally designing a multiphysically cross-linked network structure consisting of the hydrophobic association, metal-ion coordination and chain entanglement among poly(acrylic acid) (PAA) polymer chains. The deliberately designed Brij S 100 acrylate (Brij-100A) micelle cross-linker can effectively dissipate energy and endow hydrogels with desirable stretchability. The self-healing ability of hydrogels originates from the reversible hydrophobic association in micelles and Fe3+-COO- coordination. After the addition of NaCl, the chain-entangled physical network caused by the salting-out effect can both enhance mechanical strength and promote electron transport. With the synergy of hydrophobic association, mental-ligand coordination and chain entanglement, the PAA/Brij-100A/Fe3+/NaCl (PAA/BA/Fe3+/NaCl) hydrogels exhibited a high tensile strain of 1140%, a tensile strength of 0.93 MPa and a toughness of 3.48 MJ m-3. Besides, the PAA/BA/Fe3+/NaCl hydrogels exhibited a high conductivity of 0.43 S m-1 and good freezing resistance. The ionic skin based on the PAA/BA/Fe3+/NaCl hydrogels showed high sensitivity (GF = 5.29), wide strain range (0-950%), fast response time (220 ms) and good stability. Also, the self-healing ability of the ionic skin can significantly prolong its service time, and the antifreezing property can broaden its applicable temperature. This study offers new insight into the design of multifunctional ionic skin for wearable electronics.

Highly stable, stretchable, and versatile electrodes by coupling of NiCoS nanosheets with metallic networks for flexible electronics.

The rapid development of portable electronics has contributed to an urgent demand for versatile and flexible electrodes of wearable energy storage devices and pressure sensors. We fabricate a stretchable electrode by coupling the nickel-cobalt sulfide (NiCoS) nanosheet layer with Ag@NiCo nanowire (NW) networks. NiCoS wrinkled nanostructure, highly conductive networks, and intense interactions between substrate/networks and active materials/networks endow the electrodes with excellent energy storage capacity, superior electrochemical/mechanical stability, and good conductivity. A high-performance asymmetric supercapacitor is developed using the composite electrode. It operates in a wide potential window of 1.4 V and achieves a maximum energy density of 40.0 W h kg-1 at a power density of 1.1 kW kg-1; it also exhibits excellent mechanical flexibility and good waterproof performance. Moreover, a sandwiched capacitive pressure sensor constructed using the same electrodes has a wide sensing range (up to 260 kPa), low detection limit (∼47 mN), fast response (∼66 ms), and excellent mechanical stability (10 000 cycles). This study demonstrates that the appropriate design of the functional electrode facilitates the construction of various high-performance devices, denoting the versatility of our electrodes in the development of wearable electronics.

Large-Scale, Cuttable, Full Tissue-Based Capacitive Pressure Sensor for the Detection of Human Physiological Signals and Pressure Distribution.

The increasing demand for flexible and wearable electronics has promoted the rapid development of the pressure sensors capable of monitoring diverse human movements and physiological signals. However, more and more research requires the pressure sensor to possess high sensing performance and desires the fabrication to exhibit the characteristics of low cost, large-scale production, high reproduction, even disposability. Here, we propose a full tissue-based capacitive pressure sensor with a sandwiched structure consisting of two MXene-coated tissue electrodes and a blank tissue dielectric layer. The tight contact and adequate adsorption of the MXene sheets with the cellulose fibers endow the electrode with uniform conductivity and high stability over a large area. In addition, the flexible sensor could be conveniently cut into any shape and size to meet the diverse application requirements. Thereby, the pressure sensor exhibits a sensitivity of 0.051 kPa-1 (<7 kPa), a wide detection range of 0.02-160 kPa, a fast response (∼100 ms), and good repeatability. The flexible device has been demonstrated to monitor a variety of human activities and physical stimuli. The assembled sensor array can accurately and reliably detect the pressure distribution.

Natural bamboo leaves as dielectric layers for flexible capacitive pressure sensors with adjustable sensitivity and a broad detection range.

Developing a high-performance capacitive sensor for diverse application scenarios has posed requirements for the sensor to have high sensitivity, broad detection range, and cost-effectiveness. In this experiment, a flexible pressure sensor with a high sensitivity of 2.08 kPa-1 at pressure lower than 1 kPa, as well as a wide working range of 0-600 kPa and remarkable stability (for at least 4000 cycles), was designed. In the device structure, silver nanowires (Ag NWs)/MXene-composite-coated polydimethylsiloxane (PDMS) and natural bamboo leaves at different growth stages were used as the electrode and the micro-structured dielectric layers, respectively. The rough surface of the composite conductive materials and the hierarchical microstructure of the bamboo leaves ensured a high sensitivity and broad pressure range of the sandwich-structured sensor, and the different sizes of the microstructures yielded adjustable sensitivity of the sensor. Furthermore, the outstanding performance of the proposed device made it possible to detect the actual object load, human physical stimuli, and proximity distance, demonstrating applications of flexible and wearable devices in various fields, such as weight/force tapping, breath/wrist pulse/speech, joint bending, and approach distance.

Correction: Natural bamboo leaves as dielectric layers for flexible capacitive pressure sensors with adjustable sensitivity and a broad detection range.

[This corrects the article DOI: 10.1039/D1RA03207K.].