Pingping Wang

Channel Crack-Designed Gold@PU Sponge for Highly Elastic Piezoresistive Sensor with Excellent Detectability

It is a great challenge to fabricate piezoresistive sensors that possess high elasticity, large-area compliance, and excellent detectability to satisfy both extremely tiny and large human activity monitoring. Herein, a novel and facile strategy is reported to manufacture highly elastic channel crack-based gold@PU sponge piezoresistive material. The elastic 3D conductive network is successfully prepared by gold ion sputtering, and channel cracks are skillfully designed on the 3D sponge skeletons. Such novel structure makes these fabricated sensors are capable of monitoring both tiny and large human motions, which originate from the nanocrack joint sensing mechanism and physical contact of conductive interconnected network. Meanwhile, our sensors possess excellent elasticity, fast response time (9 ms), and ultralow detection limit (0.568 Pa), as well as good reproducibility over 1000 cycles. The desirable elasticity of channel crack-based gold@PU sensor is comparable to recently reported pressure sensors, together with advantages of reliable fabrication and large-area compliance, makes them attractive in various electronic devices, for example, biological health monitoring, sport performance monitoring, and man-machine interfaces.

Bio-based graphene/sodium alginate aerogels for strain sensors

Highly flexible strain sensors based on graphene aerogels (GAs) have been widely researched. However, most GAs are often found to be extremely weak and delicate to handle due to the π–π stacking and van der Waals interactions between adjacent graphene sheets that lead to a brittle skeleton. Thus constructing graphene structures with excellent mechanical properties, high sensitivity and effective conductive networks is still a big challenge. In this work, we fabricate a bio-based graphene/sodium alginate aerogel with high porosity (99.61%) and low density (6–7 mg cm−3) via freeze drying and chemical reduction. The resulting aerogels exhibit outstanding durability (>6000 loading–unloading cycles), excellent sensitivity to compression (gauge factor is 1.01) and bending (bending sensitivity is 0.172 rad−1). The strong hydrogen bonding interactions between graphene and SA are responsible for the synergetic enhancement of strength and elasticity. Taking advantage of the combination of the electronic conductivity and mechanical flexibility, the proposed bio-based aerogels may be a robust candidate in flexible strain sensors.

Highly stretchable fiber-shaped e-textiles for strain/pressure sensing, full-range human motions detection, health monitoring, and 2D force mapping

Textile-based electronics (e-textiles) have attracted huge attention in wearable sensors recently. Even though highly sensitive textile-based pressure sensors and highly stretchable textile-based strain sensors are widely researched and reported in recent years, it is still full of challenges to develop high stretchable textile-based sensors simultaneously and satisfy strain and pressure sensing, which is necessary for full-range detection of human motions. On the other hand, compared to traditional planar e-textiles, fiber-shaped e-textiles have plenty of advantages due to their fibrous architecture with lightweight, portable, skin compliant, and easily weave properties. In this work, a fiber-shaped textile, knitted with hierarchical polyurethane (PU) fibers, is used to fabricate a multifunctional e-textile by coating of silver nanowires (AgNWs) and styrene–butadiene–styrene. Due to the AgNWs conductive networks, the inherent stretchability of PU fibers, and the hierarchical structure, the as-prepared e-textile exhibits high conductivity, high stretchability, high sensitivity, and multi-detection of strain and pressure. What is more, the fabricated multifunctional e-textiles are also successfully weaved into electronic fabric for 2D force mapping. The simple, scalable strategy endows the multifunctional e-textiles great potentials in full-range detection and health care areas.

Liquid metal fiber composed of a tubular channel as a high-performance strain sensor

Stretchable sensors with high sensitivity, no hysteresis, high conductivity and a fiber conformation have considerable potential application in stretchable electronics, soft robotics and smart clothes—especially, for example, in implantable biomedical fiber-shaped sensors. Herein, inspired by the capability of a vessel organ for sensing temperature variation, the fabrication of a high-performance fiber sensor is reported, comprising a novel superelastic biocompatible fiber composed of a tubular channel injected with low toxicity liquid metal (LM). This study not only reports a highly promising strategy for achieving Youngs moduli matching between an inorganic conductor and a soft elastomer, but also provides a novel and facile approach to a strain sensor, learned from the vessel channel structure of higher animals. The sensing mechanism model is verified, and the sensitivity can be regulated by controlling the size of the tubular channel; hysteresis-free characteristics are also reported. The as-prepared LM fiber sensor exhibits close to no hysteresis (0.11%), a low detection limit (0.3% strain), and super-low resistance (0.344 Ω), as well as good repeatability over 3500 cycles. The LM fiber sensor presents huge potential for emerging applications in fields such as stretchable electronics, human motion monitors, and smart clothes, and especially in the development of implantable biomedical fiber-shaped sensors.

A compliant, self-adhesive and self-healing wearable hydrogel as epidermal strain sensor

With the ability to switch transform the mechanical stimuli of epidermal deformations to electrical signals, epidermal strain sensors can be widely applied to monitor physiological signals, detect body movements and control robots. Epidermal strain sensors are required to conform to the human body under complex motions typically from tiny epidermal deformations (<1% strain) to large body movements (10–75% strain). In this study, a compliant, self-adhesive and self-healing epidermal strain sensor was fabricated with the addition of polydopamine into polyvinyl alcohol hydrogel. Due to the compliant and self-adhesive characteristics, the as-prepared strain sensors can fix well onto the epidermis without adhesive tape, perceiving extremely gentle deformations (0.1% strain), such as pulse beats, vibration of the throat, and facial expression changes. This highly stretchable strain sensor can also monitor the large motions (up to 500% strain) of legs and fingers. Moreover, owing to the reversible boron ester bond, the hydrogel has super self-healablity (self-healed in 250 ms at ambient temperature, 25 °C), which makes our sensors more humanoid. At last, thanks to its excellent ability to detect a large range of strains, the self-healing epidermal strain sensor is effective in monitoring physiological signals and body movements.

Interface design for enhancing the wettability of liquid metal to polyacrylate for intrinsically soft electronics

Ga-Based liquid metal (Ga-LM) alloys with high conductivities and low Youngs moduli have attracted great attention, owing to their huge potential for replacing high Youngs modulus metals (gold (Au), silver (Ag), copper (Cu), etc.) and fabricating next-generation intrinsically stretchable electronics. However the simultaneous achievement of excellent stretchability and stable conductivity has been a significant challenge for preparing Ga-based LM intrinsically stretchable electronics on the grounds of the weak interfacial adhesion between Ga-LM and soft substrates. Herein, a novel adhesive interface structure between liquid eutectic gallium indium stannum (EGaInSn) and polyacrylate (PA) for simultaneously achieving high stretchability and stable conductivity is reported and their high performance as intrinsically stretchable electronics is demonstrated. The design of the interface structure follows the facile polymerization of ethyl-2-cyanoacrylate, which is triggered by water molecules sticking on the surface of gallium oxide. It was found that the interfacial polymerization not only forms an effective adhesion network but also removes the water molecules, resulting in a good bonding interface with a low resistivity of 1.3 × 10−6 Ω m and stable conductivity at tensile strains of up to 80%. The desirable intrinsically stretchable conductor is comparable to recently reported conductors, which together with the advantages of a high match for the Youngs modulus and low resistivity makes it attractive for various electronic devices.

Transparent and Waterproof Ionic Liquid-Based Fibers for Highly Durable Multifunctional Sensors and Strain-Insensitive Stretchable Conductors

Ionic liquids (ILs) are regarded as ideal components in the next generation of strain sensors because their ultralow modulus can commendably circumvent or manage the mechanical mismatch in traditional strain sensors. In addition to strain sensors, stretchable conductors with a strain-insensitive conductance are also indispensable in artificial systems for connecting and transporting electrons, similar to the function of blood vessels in the human body. In this work, two types of ILs-based conductive fibers were fabricated by developing hollow fibers with specific microscale channels, which were then filled with ILs. Typically, the ILs-based fiber with straight microchannels exhibited a high strain sensitivity and simultaneously rapid responses to strain, pressure, and temperature. The other ILs-based fiber with helical microchannels exhibited a good strain-isolate conductance under strain. Due to the high transparency of ILs along with the sealing process, the as-prepared ILs-based fibers are both highly transparent and waterproof. More importantly, owing to the low modulus of ILs and the core-shell structure, both conductive fiber prototypes demonstrated a high durability (>10 000 times) and a long-term stability (>4 months). Ultimately, the ILs-based fibrous sensors were successfully woven into gloves, flaunting the ability to detect human breathing patterns, sign language, hand gestures, and arm motions. The ILs-based strain-insensitive fibers were successfully applied in stretchable wires as well.