The ability to synthesize laser-induced graphene (LIG) on cellulosic materials such as paper opens the door to a wide range of potential applications, from consumer electronics to biomonitoring. In ...this work, strain and bending sensors fabricated by irradiation of regular filter paper with a CO2 laser are presented. A systematic study of the influence of the different process parameters on the conversion of cellulose fibers into LIG is undertaken, by analyzing the resulting morphology, structure, conductivity, and surface chemistry. The obtained material is characterized by porous electrically conductive weblike structures with sheet resistances reaching as low as 32 Ω sq–1. The functionality of both strain (gauge factor of ≈42) and bending sensors is demonstrated for different sensing configurations, emphasizing the versatility and potential of this material for low-cost, sustainable, and environmentally friendly mechanical sensing.
Fabric sensors due to favorable flexibility and comfortability have remarkable progress in wearable sensing electronics recently, but it is enormous challenge to achieve broad sensing range, high ...sensitivity, stable sensing capability and great hydrophobicity for their practical applications. Herein, a highly sensitive and superhydrophobic strain sensor based on conductive polydimethylsiloxane/Ag nanoparticles/polypyrrole/nylon strip (PDMS/AgNPs/PPy/NS) is successfully fabricated via constructing AgNPs/PPy composite conductive networks on elastic NS, and then coating a thin protective layer (PDMS). The AgNPs/PPy composite conductive networks render the PDMS/AgNPs/PPy/NS large ΔR/R0 scale, and the assembled PDMS/AgNPs/PPy/NS strain sensor presents broad sensing range (0.1%–70%), high Gauge Factor value of 1.61 × 103 (with the strain range from 60% to 70%), ultralow detection limit (0.1% strain), fast response time (70 ms) and satisfying sensing stability (5000 cycles). The protective PDMS layer not only endows PDMS/AgNPs/PPy/NS strain sensor with excellent superhydrophobicity (WCA = 156°), but also improves the stability of sensor for daily use. Owing to the high sensitivity and excellent superhydrophobicity, PDMS/AgNPs/PPy/NS strain sensor can monitor various joint motions (throat, neck, elbow, wrist, knee and finger) and even work in harsh conditions (moisture, acid, alkaline and salt environment). In addition, PDMS/AgNPs/PPy/NS with low resistance (1.09 Ω cm−1) displays an outstanding electrothermal temperature (87.4 °C at 2.0 V). These remarkable performances demonstrate great potential of PDMS/AgNPs/PPy/NS in wearable electronics such as sensors and heaters.
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Highly stretchable strain sensors based on conducting polymer hydrogel are rapidly emerging as a promising candidate toward diverse wearable skins and sensing devices for soft machines. However, due ...to the intrinsic limitations of low stretchability and large hysteresis, existing strain sensors cannot fully exploit their potential when used in wearable or robotic systems. Here, a conducting polymer hydrogel strain sensor exhibiting both ultimate strain (300%) and negligible hysteresis (<1.5%) is presented. This is achieved through a unique microphase semiseparated network design by compositing poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) nanofibers with poly(vinyl alcohol) (PVA) and facile fabrication by combining 3D printing and successive freeze‐thawing. The overall superior performances of the strain sensor including stretchability, linearity, cyclic stability, and robustness against mechanical twisting and pressing are systematically characterized. The integration and application of such strain sensor with electronic skins are further demonstrated to measure various physiological signals, identify hand gestures, enable a soft gripper for objection recognition, and remote control of an industrial robot. This work may offer both promising conducting polymer hydrogels with enhanced sensing functionalities and technical platforms toward stretchable electronic skins and intelligent robotic systems.
A conducting‐polymer hydrogel strain sensor is proposed with both high stretchability (300% strain) and ultralow hysteresis (<1.5%). The hydrogel‐based sensor harnesses a unique microphase semiseparated network to achieve enhanced sensing properties. The fabricated sensor can be applied as electronic skins to monitor physiological signals, enable a soft gripper for object recognition and remote control of an industrial robot.
Taking the strain: An emulsion gel with high stretchability and conductivity was fabricated and could be used as a strain sensor to detect human motion over a broad operating temperature. First, an ...emulsion that was ultra‐stable at high and low temperatures was prepared by introducing glycerol into a W/W emulsion. Then, the continuous phase was polymerized to produce a macroporous emulsion gel. Finally, an emulsion‐gel‐based strain sensor with good flexibility, conductivity, self‐healing, and adhesion properties was fabricated to detect the full range of human body movement. The sensor exhibited remarkable sensing sensitivity, rapid responsiveness, and reliability. For more information, see the Full Paper by J. Hao et al. (DOI: 10.1002/chem.202101472).
Textile-based electronics have attracted much attention as they can perfectly combine the functionality of wearable devices with the soft and comfortable properties of flexible textile fibers. In ...this work, we report a dynamically stretchable high-performance supercapacitor for powering an integrated sensor in an all-in-one textile system to detect various biosignals. The supercapacitor fabricated with MWCNT/MoO3 nanocomposite electrodes and nonaqueous gel electrolyte, along the course direction of the fabric, exhibits stable and high electrochemical performance under dynamic and static deformation, including stretching in real time, regardless of the strain rate. The strain sensor created along the wale direction of the fabric shows a high sensitivity of 46.3 under an applied strain up to 60%, a fast response time of 50 ms, and high stability over 10 000 cycles of stretching/releasing. Finally, the supercapacitor and strain sensor are integrated into an all-in-one textile system via liquid-metal interconnections, and the sensor is powered by the stored energy in the supercapacitor. This system sewed into cloth successfully detects strain due to joint movement and the wrist pulse. This work demonstrates the high feasibility of utilizing the fabricated stretchable all-in-one textile system for real-time health monitoring in everyday wearable devices.
Tough, self-adhesive and conductive hydrogels have recently attracted considerable interest due to their promising applications in electronic skins, wearable devices and flexible sensors. In this ...work, we designed a mussel-inspired nanocomposite hydrogel derived from water-soluble tannic acid/polyaniline coated cellulose nanocrystals (TA/PANI@CNCs) and various functional acrylic monomers. The incorporated TA/PANI@CNCs not only endowed the nanocomposite hydrogels with enhanced electrical conductive network and mechanical performance, but also played an important role in repeatable and durable adhesiveness to human skin without additional fixation. By taking the advantage of double networks based on various supramolecular interactions and dynamic borate ester bonds, the hydrogels exhibited a dramatic breaking strain of 974%, fracture stress of 759 kPa and rapid self-healing ability at room temperature without external stimuli. In addition, the as-prepared nanocomposite hydrogels had great strain sensitivity and excellent electrical conductivity, which can be employed as flexible strain sensors for tracking human body motion with a broad range of strain or directly assembled on other materials surfaces as electrical circuits. Compared with previous conductive hydrogels, this work will provide a novel pathway to fabricate nanocomposite hydrogels with self-healing, self-adhesive, strain sensitive and robust mechanical properties for potential applications in wearable strain sensors, flexible electrical interconnection and human motion monitoring.
Stretchable strain sensors play a pivotal role in wearable devices, soft robotics, and Internet‐of‐Things, yet these viable applications, which require subtle strain detection under various strain, ...are often limited by low sensitivity. This inadequate sensitivity stems from the Poisson effect in conventional strain sensors, where stretched elastomer substrates expand in the longitudinal direction but compress transversely. In stretchable strain sensors, expansion separates the active materials and contributes to the sensitivity, while Poisson compression squeezes active materials together, and thus intrinsically limits the sensitivity. Alternatively, auxetic mechanical metamaterials undergo 2D expansion in both directions, due to their negative structural Poisson's ratio. Herein, it is demonstrated that such auxetic metamaterials can be incorporated into stretchable strain sensors to significantly enhance the sensitivity. Compared to conventional sensors, the sensitivity is greatly elevated with a 24‐fold improvement. This sensitivity enhancement is due to the synergistic effect of reduced structural Poisson's ratio and strain concentration. Furthermore, microcracks are elongated as an underlying mechanism, verified by both experiments and numerical simulations. This strategy of employing auxetic metamaterials can be further applied to other stretchable strain sensors with different constituent materials. Moreover, it paves the way for utilizing mechanical metamaterials into a broader library of stretchable electronics.
Auxetic mechanical metamaterials are employed to significantly enhance the sensitivity of stretchable strain sensors, by regulating the transverse Poisson effect due to auxetic expansion. High sensitivity with almost 24‐fold improvement is achieved, together with high maximum stretchability and cyclic durability. Additionally, the underlying mechanism, elongated microcracks, is proven by both experiments and numerical simulations.
Thin and flexible photonic sensor foils are proposed, fabricated, and tested as a promising alternative for monitoring composite structures. Sensor foils are implemented using two different optical ...polymers and as such optimized for multi‐axial sensing and embedding within composite materials, respectively. It is first shown that those sensor foils allow multi‐axial strain sensing by multiplexing a multitude of Bragg grating sensors in a rosette configuration. Secondly, those sensors can be realized in very thin foils (down to 50 µm) making them suitable for embedding in composite materials during their production. This is proven by visually inspecting and by testing the functionality of the embedded sensors. Finally, owing to their low Young's modulus and flexibility, polymer sensor foils can be bent to small curvature radii and withstand large elongations. Herein, the sensors are bent down to a radius of 11 mm, and elongated by 1.4% without losing functionality.
Thin and flexible photonic sensor foils allow multi‐axial strain sensing of composites by multiplexing a multitude of Bragg grating sensors. Those foils can be made very thin (down to 50 μm) making them suitable for embedding. Owing to their low Young's modulus and flexibility, polymer sensor foils can be bent to small curvature radii and withstand large elongations.
It is desired to create skin strain sensors composed of multifunctional conductive hydrogels with excellent toughness and adhesion properties to sustain cyclic loadings during use and facilitate the ...electrical signal transmission. Herein, we prepared transparent, compliant, and adhesive zwitterionic nanocomposite hydrogels with excellent mechanical properties. The incorporated zwitterionic polymers can form interchain dipole–dipole associations to offer additional physical cross-linking of the network. The hydrogels show a high fracture elongation up to 2000%, a fracture strength up to 0.27 MPa, and a fracture toughness up to 2.45 MJ/m3. Moreover, the reversible physical interaction imparts the hydrogels with rapid self-healing ability without any stimuli. The hydrogels are adhesive to many surfaces including polyelectrolyte hydrogels, skin, glasses, silicone rubbers, and nitrile rubbers. The presence of abundant zwitterionic groups facilitates ionic conductivity in the hydrogels. The combination of these properties enables the hydrogels to act as strain sensors with high sensitivity (gauge factor = 1.8). The strategy to design the tough, adhesive, self-healable, and conductive hydrogels as skin strain sensors by the zwitterionic nanocomposite hydrogels is promising for practical applications.
Flexible skin-mimicking electronics are highly desired for development of smart human–machine interfaces and wearable human-health monitors. Human skins are able to simultaneously detect different ...information, such as touch, friction, temperature, and humidity. However, due to the mutual interferences of sensors with different functions, it is still a big challenge to fabricate multifunctional electronic skins (E-skins). Herein, a combo temperature–pressure E-skin is reported through assembling a temperature sensor and a strain sensor in both of which flexible and transparent silk-nanofiber-derived carbon fiber membranes (SilkCFM) are used as the active material. The temperature sensor presents high temperature sensitivity of 0.81% per centigrade. The strain sensor shows an extremely high sensitivity with a gauge factor of ∼8350 at 50% strain, enabling the detection of subtle pressure stimuli that induce local strain. Importantly, the structure of the SilkCFM in each sensor is designed to be passive to other stimuli, enabling the integrated E-skin to precisely detect temperature and pressure at the same time. It is demonstrated that the E-skin can detect and distinguish exhaling, finger pressing, and spatial distribution of temperature and pressure, which cannot be realized using single mode sensors. The remarkable performance of the silk-based combo temperature–pressure sensor, together with its green and large-scalable fabrication process, promising its applications in human–machine interfaces and soft electronics.
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