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Superhydrophobic conductive rubber band with synergistic dual conductive layer was designed and prepared for high-performance strain sensor, showing great potential for full-range monitoring of human motion and physiological signal, especially in the water environment. [Display omitted] Wearable electronic devices have received increasing interests because of their excellent flexibility, stretchability, and human friendliness. As the core components, flexible strain sensors integrated with wide working range, high sensitivity, and environment stability, especially in moisture or corrosive environments, remain a huge challenge. Herein, synergistic carbon nanotubes (CNTs)/reduced graphene oxide (rGO) dual conductive layer decorated elastic rubber band (RB) was successfully developed and treated with hydrophobic fumed silica (Hf-SiO 2) for preparing superhydrophobic strain sensor. As expected, stable entangled CNTs layer and ultrasensitive microcracked rGO layer endow the sensor with extremely low detection limit (0.1%), high sensitivity (gauge factor is 685.3 at 482% strain), wide workable strain range (0–482%), fast response/recovery (200 ms/200 ms) and favorable reliability and reproducibility over 1000 cycles. Besides, the constructed Hf-SiO 2 coating also makes the sensor exhibit excellent superhydrophobicity, self-cleaning property, and corrosion-resistance. As a proof of concept, our prepared high-performance strain sensor can realize the full-range monitoring of human motions and physiological signals even in the water environment, including pulse, vocalization, joint bending, running, and gesture recognition. Interestingly, it can also be knitted into a tactile electronic textile for spatial pressure distribution measurement. Thus, this study provides a universal technique for the preparation of high-performance strain sensors with great potential applications in the field of next-generation intelligent wearable electronics. [ABSTRACT FROM AUTHOR]

• A conductive fiber with synergistic conductive network is prepared for strain sensor. • The synergistic effect is beneficial for tunable and balanced sensing performances. • The sensor shows great potential for human motion monitoring and tactile sensing. • The fiber displays good photothermal performances even under 150% strain. With the rapid development of portable electronic products, smart wearable devices show great application potential in personalized motion monitoring, health monitoring and even in human-machine interaction. In particular, high-performance flexible fiber-shaped strain sensors are receiving more and more attention because they can be well integrated with clothes or human skin for real-time human activities monitoring. However, achieving improved sensitivity, wide detection range, diverse applications and easy operation of them remains a challenge. Here, we adopt a simple wet-spinning technique to prepare a porous fiber-shaped carbon nanotubes (CNTs)/silver nanoparticles (AgNPs)/thermoplastic polyurethane (TPU) fiber (CATF) for high-performance strain sensor, of which the synergistic conductive network of CNTs and AgNPs enables a wide detection range (∼248 %), high sensitivity (GF > 4295), fast response/recovery time (120 ms/140 ms) and excellent stability. Interestingly, strain sensing range and sensitivity of the sensor can be tuned by changing the AgNPs loading to make it suitable for different application scenarios. All the merits of the sensor make it capable for diverse human movements monitoring, pronunciation recognition, and gesture recognition. More importantly, our prepared CATF strain sensor can be easily weaved into wearable smart textiles, showing great potential for tactile sensing to realize multi-touch and pressure tracking. Finally, the CATF also displays efficient photothermal conversion capability even under different tensile strains up to 150 %, showing great potential in human body thermal management to improve the wearing comfort of wearable electronic fabric. [ABSTRACT FROM AUTHOR]

Benefitting from the wearability, ductility and portability, flexible and stretchable strain sensors display a more extensive field of applications than traditional sensors in terms of medical diagnosis, smart home, environmental monitoring and so on. However, the critical sensing performances, such as sensitivity, sensing range, stability and detection limit of flexible strain sensors still need to be improved. Microstructural optimization has been considered as an efficient strategy for tuning the performances. In this work, a carbon nanotubes (CNTs)/carbon black (CB)/thermoplastic polyurethane (TPU) fibrous film (CCTF) is prepared through electrospinning, spraying and ultrasonic anchoring technique. Synergetic conductive layers by combining CNTs/CB and CB are constructed on both sides of CCTF. In virtue of the optimization of microstructures and the synergetic conductive network, the obtained CCTF possesses an ultrawide response range (up to 500 % strain), high sensitivity (gauge factor, GF up to 1516), short response/recovery time (80/80 ms), low detection limit (0.05 % strain), favorable sensing stability and long-term durability. CCTF with excellent strain sensing performances is assembled as a strain sensor, which accounts for full range human biological signal acquisition, including joint movements, muscle tension, and facial micro-expressions. This paper provides a certain reference significance for the preparation and fabrication of next-generation flexible strain sensors with high performances. A flexible strain sensor based on carbon nanotubes (CNTs)/carbon black (CB)/thermoplastic polyurethane (TPU) film (CCTF) is fabricated through electrospinning, spraying and ultrasonic anchoring technologies. CCTF possesses excellent sensing performance due to the optimization of the microstructure, achieving a wide sensing range (up to 500 % strain), high sensitivity (GF up to 1516), low detection limit (0.05 % strain), and short response/recovery time (80/80 ms). [Display omitted] • A fibrous strain sensor with synergetic conductive networks of CNTs/CB and CB is fabricated. • The sensor possesses both a wide sensing range (500 % strain) and high sensitivity (GF up to 1516). • Low detection limit (0.05 % strain) and short response/recovery time have also been achieved. • The sensor is demonstrated to precise full range human biological signal acquisition. [ABSTRACT FROM AUTHOR]

1a, the highly sensitive, thermal conductive and stretchable strain sensor consists of graphene nanoribbons (GNRs) as the conductive nanonetwork, TPU doped with BNNSs as the thermal conductive layer and TPU fibrous membrane as the thermal insulation layer, which has been fabricated by electrospinning, vacuum filtration, casting and stick. The favorable thermal conductivity of the strain sensor is attributed to that the BNNSs overlap with each other in the TPU-BNNSs film to form a perfect heat conduction pathway (Fig. In order to further understand the heat dissipation mechanism of the strain sensor, the interface heat conduction between the TPU-BNNS film and the air was simulated and calculated (Fig. [Extracted from the article]

[Display omitted] With the rapid development of wearable intelligent devices, low-cost wearable strain sensors with high sensitivity and low detection limit are urgently demanded. Meanwhile, sensing stability of sensor in wet or corrosive environments should also be considered in practical applications. Here, superhydrophobic microcracked conductive paper-based strain sensor was fabricated by coating conductive Ti 3 C 2 T x MXene on printing paper via dip-coating process and followed by depositing superhydrophobic candle soot layer on its surface. Owing to the ultrasensitive microcrack structure in the conductive coating layer induced by the mismatch of elastic modulus and thermal expansion coefficient between conductive coating layer and paper substrate during the drying process, the prepared paper-based strain sensor exhibited a high sensitivity (gauge factor, GF = 17.4) in the strain range of 0–0.6%, ultralow detection limit (0.1% strain) and good fatigue resistance over 1000 cycles towards bending deformation. Interestingly, it was also applicable for torsion deformation detection, showing excellent torsion angle dependent, repeatable and stable sensing performances. Meanwhile, it displayed brilliant waterproof, self-cleaning and corrosion-resistant properties due to the existence of micro/nano-structured and the low surface energy candle soot layer. As a result, the prepared paper-based strain sensor can effectively monitor a series of large-scale and small-scale human motions even under water environment, showing the great promising in practical harsh outdoor environments. Importantly, it also demonstrated good applicability for spatial strain distribution detection of skin upon body movement when assembled into electronic-skin (E-skin). This study will provide great guidance for the design of next generation wearable strain sensor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Breathable electronic skin with 3D skeleton and microcrack structures is designed. • High sensitivity and wide working range are realized for the strain sensor. • The strain sensor can accurately distinguish various human movements. • The device has photo-thermo-electric and self-powered sensing applications. With the rapid development of wearable electronic, electronic skin with excellent performance for human motion detection have been widely investigated recently. In this work, a multifunctional electronic skin with three-dimensional conductive network skeleton was prepared based on synergistic conductive filler (carboxylated multi-walled carbon nanotubes (C-MWCNT) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS)) decorated breathable thermoplastic polyurethane (TPU) electrospinning fibrous membrane. Then, microcrack structure was constructed via pre-stretching and the strain sensitivity of the resultant C-MWCNT/PEDOT:PSS/TPU (CPT) conductive fibrous membrane could be effectively adjusted by changing the microcrack density. Due to the three-dimensional conductive network skeleton, microcrack structure and the bridging effect of C-MWCNT between the adjacent crack fragments, ethylene glycol treated CPT (mass ratio of C-MWCNT and PEDOT:PSS is 9/1) (e-CPT 9/1) strain sensor exhibited high sensitivity (6008.3), wide response range (680 %), fast response/recovery time (200 ms/200 ms), low detection limit (0.5 %), excellent durability and repeatability (6000 cycles). The excellent strain sensing performances enables it to accurately monitor motion activities and physiological signals, and can also be used as a smart sensing glove to identify different letters gesture and numeric gestures. Furthermore, owing to the photothermal conversion ability and thermoelectric effect of C-MWCNT and PEDOT:PSS, the obtained e-CPT 9/1 device also displayed efficient "light-thermal-electric" conversion ability and showed the great potential as self-powered strain sensor. [ABSTRACT FROM AUTHOR]

Personalized rehabilitation training provides maximum help to stroke patients to alleviate the after-effects and restore the body to normal function. However, available monitoring devices have the disadvantages of being large, requiring professional guidance, and lacking intuitive signal display capabilities. Herein, a bio-inspired wearable high-performance strain sensor with a simple structure can simultaneous electrical signals and optical visualization in response to external stimuli. The sensor comprises a conductive layer with significant electromechanical behaviors of cellulose nanocrystals (CNC)/carbon nanotubes (CNTs)/MXene nanohybrid network, and a stretchable elastomer layer consisting of thermoplastic polyurethane and fluorescent agent. Benefiting from the designed microcracks and fluorescent material, the strain sensor exhibits ultra-high sensitivity (476800), ultra-low detection limit (0.005%), low response time (60 ms), wide working range (0–100%), and enables strain visualization for applications in visually rehabilitation training monitoring. Based on these sensing characteristics, the sensor shows great advantages in human motion and sound monitoring, with the integration of digital signals and visual images makes it show great potential in visually personalized rehabilitation training monitoring. [Display omitted] • Cellulose nanocrystals are introduced to modulate the sensitivity of the strain sensor. • CCMTPF has ultrahigh sensitivity of 476800 and ultralow detection limit of 0.005%. • CCMTPF achieves electric signals and visualization of optical images responses under strain. • CCMTPF has been demonstrated for visual rehabilitation training monitoring in real time. [ABSTRACT FROM AUTHOR]

With the rapid development of smart wearable devices, flexible and biodegradable sensors are in urgent needs. In this study, "green" electrically conductive Ag nanowire (AgNW)/cellulose nanofiber (CNF) hybrid nanopaper was fabricated to prepare flexible sensors using the facial solution blending and vacuum filtration technique. The amphiphilic property of cellulose is beneficial for the homogeneous dispersion of AgNW to construct effective electrically conductive networks. Two different types of strain sensors were designed to study their applications in strain sensing. One was the tensile strain sensor where the hybrid nanopaper was sandwiched between two thermoplastic polyurethane (TPU) films through hot compression, and special micro-crack structure was constructed through the pre-strain process to enhance the sensitivity. Interestingly, typical pre-strain dependent strain sensing behavior was observed due to different crack densities constructed under different pre-strains. As a result, it exhibited an ultralow detection limit as low as 0.2%, good reproducibility under different strains and excellent stability and durability during 500 cycles (1% strain, 0.5 mm/min). The other was the bending strain sensor where the hybrid nanopaper was adhered onto TPU film, showing stable and recoverable linearly sensing behavior towards two different bending modes (tension and compression). Importantly, the bending sensor displayed great potential for human motion and physiological signal detection. Furthermore, the hybrid nanopaper also exhibited stable and reproducible negative temperature sensing behavior when it was served as a temperature sensor. This study provides a guideline for fabricating flexible and biodegradable sensors. [ABSTRACT FROM AUTHOR]

• PTFE template with micro-cavity was prepared by micromilling. • As-prepared PTFE templates have the advantages of easy demoulding and reusability. • A facile and low-cost method to fabricate microgroove-crack-based strain sensor. • Such strain sensor exhibits high sensitivity and low detection limit. • Detect body motion underwater and sound vibration with different frequencies. Strain sensor is a crucial component of high-performance wearable electronic devices. Crack-based sensor has attracted much attention due to its high sensitivity that allow an extensive application for wearable electronic devices. However, facile, efficient and cost-effective fabricating crack-based sensors is still a challenge. Herein, a facile, highly efficient, and low-cost approach was proposed to fabricate stretchable microgroove-crack-based strain sensor whose highest sensitivity is 27818.5 and low detection limit is 0.01%. Moreover, it can be pasted on human body to detect motion both in air and underwater conditions. Furthermore, it can recognize the recorded vibration spectrum of different musical scores. This study offers a facile and efficient approach for fabricating stretchable microgroove-crack-based strain sensor, showing tremendous potential in future wearable electronic devices production. [ABSTRACT FROM AUTHOR]

Graphical abstract This study reports an aligned wave-like carbon nanotubes (CNTs)/thermoplastic polyurethane (TPU) fibrous network based strain sensor with ultra-wide sensing range, low detection limit, fast response rate and excellent stability, which provides a good candidate for wearable devices and artificial intelligence (AI). Highlights • An aligned conductive fibrous mat based strain sensor with wave-like structure was fabricated. • The sensor possesses an ultrahigh stretchability of 900%, combining with an excellent stability. • An ultralow detection limit (0.5%) and a fast response time of 70 ms have both been achieved. • The sensing behaviors of the CNTs/TPU fibrous sensor agree well with the tunneling theory. • The designed wave-like structure and the joints structure caused the fine sensing performances. Abstract Recently, flexible strain sensors with large stretchability, high sensitivity and excellent stability have been widely concerned owing to their potential applications in wearable electronic devices. However, the challenge of narrow sensing range still remains for strain sensors with high performance. In this paper, we proposed a facile, cost-effective and scalable technology to manufacture the carbon nanotubes (CNTs)/thermoplastic polyurethane (TPU) fibrous strain sensor with aligned wave-like structure. Through electrospinning technique, we prepared an aligned TPU fibrous mat, then used a simple and effective assembly approach to induce CNTs to wrap TPU fibrous mat through ultrasonication. The sensing properties of CNTs/TPU mats in vertical and parallel directions were investigated, respectively. The sensing behaviors of the two sensors both agreed well with the tunneling theory. Compared with the random CNTs/TPU mats and parallel direction sample, the aligned CNTs/TPU fibrous mats in vertical direction possessed an ultra-high stretchability (900%) and excellent durability (10,000 cycles at the strain of 200%). An ultra-low detection limit (0.5%) and fast response time of 70 ms were also achieved, exhibiting a favorable sensitivity. The generation of the wave-like structure and the joints structure in the designed conductive network, which could affect the evolution of the conductive paths subsequently, led to these excellent sensing performances. The CNTs/TPU mats strain sensor was then assembled to monitor both subtle human motions, like cheek bulging and phonation; and vigorous human motions, like leg squatting and elbow bending, both showing excellent sensing performances. The present paper provides a good candidate for potential applications as artificial skins, human-activity monitoring and personal healthcare. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CB particles were wrapped on PA6 fibrous mat to pre-construct a fine conductive network. • An ultrahigh gauge factor of 9706.9 of CB/PA6/PVA composite has been achieved. • The composite shows distinguishing sensing performances towards different strain. • Excellent repeatability and durability have also been obtained. Abstract Carbon black (CB)/polyamide 6 (PA6)/poly (vinyl alcohol) (PVA) electrically conductive polymer composites were fabricated by embedding conductive CB/electrospun PA6 fibrous mat into PVA matrix. Here, the electrospun PA6 fibrous network was applied as the skeleton to pre-construct conductive channels by decorating CB particles on the surfaces of PA6 fibers; the PVA was used as matrix to protect the pre-produced conductive network. For the strain sensing performances, a very high gauge factor (GF, 9706.9) has been achieved, showing a large sensitivity. Cyclic tension tests display that the conductive fibrous composite shows distinguishing sensing behaviors towards varying tensile strain. The strain sensor also has excellent repeatability and durability during long-term stretching-releasing cycles. This work provides a facile and novel strategy to develop strain sensors combined with high sensitivity and excellent stability for human health detections. [ABSTRACT FROM AUTHOR]

Conductive polymer composites (CPCs) based strain sensors have been studied intensively recently. For a desirable strain sensor, a high sensitivity, a nice recoverability together with a good stability are required synchronously. In this study, the design of a segregated carbon black (CB) conductive network was demonstrated to be crucial for preparing polypropylene (PP)-based strain sensors with fine recoverability and stability, but a low sensitivity. The incorporation of carbon fibers (CFs) with large aspect ratio into the segregated CB/PP was utilized to build a bridged-segregated structure, leading to a synergistic conductive network. As a result, an improved sensitivity as well as a good stability was both achieved for the CF/CB/PP composite. The origin of these results was further explained on the basis of the tunneling model proposed by Simmons and the synergetic effect. This work provides a strategy for improving the performance of strain sensor with balanced sensitivity and stability by introducing a bridged-segregated structure. [ABSTRACT FROM AUTHOR]

In this work, a novel flexible electrically resistive-type strain sensor with special three-dimensional conductive network was developed based on reduced graphene oxide (RGO)-decorated flexible thermoplastic polyurethane (TPU) electrospun fibrous mats. Scanning electron microscopy results indicated that RGO was localized on surfaces of the TPU fibers uniformly and formed conductive paths. The interaction between electrospun TPU fibers and RGO was investigated by using Fourier transform infrared spectra and X-ray diffraction. These fibers conductive paths connected with each other and constructed an excellent three-dimensional conductive network. The special hierarchical conductive network endowed our RGO/TPU strain sensors with a desirable integration of good stretchability and high sensitivity (gage factor (GF) of 11 in strain of 10% and 79 in strain of 100% in reversible strain regime), good durability and stability (stretch/release test of 6000 cycles) and a fast response speed. The mechanism of the evolution of residual resistance and residual strain of RGO/TPU strain sensors under cyclic loading were investigated in detail. RGO/TPU strain sensors were attached on skin or clothes to monitor various human motions. The results demonstrate that our flexible strain sensors have wide application prospects in smart wearable device. [ABSTRACT FROM AUTHOR]

Nowadays, hydrogel-based sensors have drawn great attention owing to the growing demand for wearable devices. However, tailoring the property of the hydrogel sensor through a facile approach remains a great challenge. In this work, inspired by natural plants, a stretchable, adhesive and conductive hydrogel was prepared via the coordination between gallic acid (GA) and Zn2+ and chemical cross-linking. The dynamic crosslinking provided greater structural integrity for the polyvinyl alcohol / polyacrylamide (PVA/PAM) double network, endowing the hydrogel with high mechanical performance (0.25 MPa at 910% tensile strain, and 1.21 MPa at 70% compressive strain). Meanwhile, the presence of GA enabled the hydrogel with excellent repeatable adhesive performance, which greatly solved the problem of signal loss caused by poor adhesion. Moreover, the addition of ZnCl 2 enhanced the ionic conductivity and gauge factor of the hydrogel. Besides, the conductive hydrogel exhibited successively stable changes of resistance signals under different external stimuli (5–500% strains and 80–200 mm/min rates) and superior durability (over 500 cycles). The hydrogel-based wearable sensors demonstrated excellent sensing performance in detecting various human motions. The multifunctional PVA/PAM/GA-Zn2+ hydrogel has significant applications in soft robots and healthcare monitoring as the flexible strain sensor. [Display omitted] • The hydrogel was prepared via the coordination and chemical cross-linking. • The prepared hydrogel has excellent mechanical properties performance. • Plant-derived GA makes the hydrogels have good adhesion properties. • the hydrogel exhibited successively stable changes of resistance signals [ABSTRACT FROM AUTHOR]

• Waterproof conductive fiber with microcracked synergistic conductive layer was designed. • High sensitivity and wide working range were achieved for the conductive fiber strain sensor. • Tunable sensing performance was achieved for the conductive fiber strain sensor. • The sensor can precisely distinguish various human movements and physiological signals. With the rapid development of wearable smart electronic devices, flexible strain sensors with high sensitivity in a wide working range are urgently demanded. Meanwhile, good self-cleaning and anti-corrosion properties are also essential for daily use. Herein, a waterproof conductive spandex fiber strain sensor with microcracked synergistic Ag nanoparticles (AgNPs)-carbon nanotubes CNTs conductive layer was designed and fabricated via the solvent swelling, non-solvent-induced phase separation (NIPS), and low surface energy treatment process. Benefiting from the stable synergistic conductive network and the ultrasensitive microcrack structure, the sensor exhibits excellent overall strain sensing performances, including high sensitivity (gauge factor is 48,310 within 335–400% strain), wide working range (0–400%), ultralow detection limit (0.1%), fast response/recovery time (80 ms/100 ms), and long-term fatigue resistance over 10,000 cycles, making it reliably and precisely distinguish both violent human movements and subtle physiological signals. More importantly, strain sensing range and sensitivity of the sensor can also be effectively tunned through changing the AgNPs loading in the synergistic conductive network, enabling it to be applicable for different application scenarios. What's more, the waterproof surface with good self-cleaning and anti-corrosion properties also endows the sensor with great potential for real-time body motion monitoring under humid and underwater environments without being interfered. This study provides a facile one-step method for the fabrication high-performance flexible strain sensor. [ABSTRACT FROM AUTHOR]

Flexible and wearable strain sensors based on conductive polymer composites (CPCs) for human motion detection have been highlighted recently. Herein, two flexible conductive composites were fabricated by mixing matrix polydimethylsiloxane (PDMS) with zero-dimensional conductive filler carbon black (CB) and one-dimensional carbon nanotubes (CNTs), respectively. A low percolation threshold of CB/PDMS (0.48 vol%) was achieved, while this value was higher than that of CNTs/PDMS (0.13 vol%). In strain-dependent response tests, compared with CNTs/PDMS with a gauge factor ( GF ) of 4.36 (a strain of 10%), CB/PDMS composites showed a higher sensitivity with a larger GF of 15.75 (a strain of 10%). A good reproducibility was obtained in stretching-releasing process for the two composites. In long-term cyclic test, CB/PDMS showed more stable sensing behaviors, while a slight drifting and fluctuation was observed for CNTs/PDMS. Generally, two composites both possessed satisfactory durability. Mathematical models were proposed to explain the mechanism of the distinct strain sensing behaviors. A smart glove was assembled to monitor the finger motion to evaluate the application of the two composites as flexible strain sensors. [ABSTRACT FROM AUTHOR]

Stretchable strain sensors with integrated attributes of flexibility and robustness are urgently required owing to their promising applications in healthcare monitoring and environment detection. Herein, we achieved a highly stretchable thermoplastic polyurethane (TPU) mat (PUM) through electrospinning, then decorated with polyaniline (PANI) nanoparticles bridged by reduced graphene oxide (rGO) nanosheets by in-situ polymerization and ultrasonication. The rGO/PANI/TPU mat (GPTM) was then assembled as the strain sensor (GPTSS), showing a wide sensing range of 0.1%–300% strain, high gauge factor (GF) of 3000.2, favorable sensing stability, short response time (90 ms) and excellent long-term durability after 10000 stretching/releasing cycles, which endows the strain sensor with high discernibility for detecting intricate human motions. The GPTSS shows the capacity to precisely monitor ammonia gas (as low as 5 ppm), which can be used to detect harmful gases. The integrated capabilities of strain sensing and environmental monitoring promote the progress of high-performance electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

Flexible and wearable strain sensors with multi-functionalities have aroused tremendous attention for various applications in disease diagnostics, environment detection and healthcare monitoring, etc. However, limited electromechanical performance and complicated fabrication process of strain sensors restrict their extensive applications in full-range stimuli monitoring. Herein, we fabricated flexible and wearable strain sensors, consisting of a robust fiber with helical structure and two polyaniline (PANI) layers bridged by reduced graphene oxide (rGO) layer through in-situ polymerization and ultrasonication. The flexible and wearable sensor possesses wide healthcare monitoring range (0.1%–200% strain), high sensibility especially for subtle deformation, excellent response stability, fast response/recovery time (100 ms/100 ms) and favorable durability. Meanwhile, our conductive PANI-rGO-PANI fiber (CPGPF) is assembled as a wearable sensor with the capability of precisely monitoring human body motions, temperature fluctuation and poisonous gas, indicating a promising multifunctional application in human-machine interaction and environment monitoring. [ABSTRACT FROM AUTHOR]

Smart and wearable strain sensors have sparked enormous research interests in various applications of flexible electronic devices. For this topic, it remains a huge challenge to acquire wide sensing range, high sensitivity, superior durability and fast response synergistically. Herein, we present an ultra-sensitive and durable strain sensor with sandwich structure to address the issues, which is mainly composed of the composite of carbon black (CB)/aligned thermoplastic polyurethane (TPU) fibrous mat and the Ecoflex. The CB/TPU/Ecoflex strain sensor (CTESS) is prepared via decorating CB nanoparticles onto the aligned electrospun TPU fibrous mats by ultrasonication, then encapsulated with Ecoflex to develop a sandwich structure. This structure provides effective protection for the conductive CB/TPU fibrous network, endowing the strain sensor with excellent sensing performances, including low detection limit (0.5% strain), wide response range (up to 225% strain), ultrahigh sensitivity (maximum gauge factor of 3186.4 at strain of 225%), fast response time (70 ms) and favorable repeatability even after 5000 stretching/releasing cycles. CTESS also shows an excellent anti-interference capability to external humidity and temperature. The CTESS is then assembled as artificial electronic skins to monitor various human motions, exhibiting great application prospects in next-generation wearable electronics. Image 1 [ABSTRACT FROM AUTHOR]

The preparation of a satisfactory strain sensor integrated with ultrahigh sensitivity, large application range and superior stability is still a huge challenge. Herein, a highly stretchable carbon black/thermoplastic polyurethane fibrous strain sensor with porous and core-sheath structure is successfully prepared via an efficient coaxial wet-spun approach. The fiber possesses a porous monolith structure owing to countercurrent diffusion of the solvent and coagulation. An ultrahigh sensitivity (maximum gauge factor of 28,084), fast response time (200 ms), favorable durability (>11,000 cycles) and large strain range (>200%) are achieved simultaneously. Intriguingly, the values of ln (R/R 0) of the fiber show a good linearity versus tensile strain, which can be used to predict changes of sensitivity in application. The tunneling theory is employed to analyze the response behaviors. The fibrous strain sensor is then utilized for detecting various human movements and tactile sensing, proving its tremendous potential as wearable electronics. Image 1 [ABSTRACT FROM AUTHOR]

• A flexible CB/TPU foam with a pinnate-veined aligned porous structure was prepared. • The foam can both serve as a flexible strain sensor and an adsorption material. • The foam sensor has excellent sensing discernibility and high sensitivity. • The sensor exhibits superior response stability in a wide sensing range. In this paper, flexible conductive carbon black (CB)/thermoplastic polyurethane (TPU) foam (CTF) with an intriguing pinnate-veined aligned porous structure was fabricated via a unidirectional freeze-drying process. The density, porosity and average pore size of the composite foam are 0.13 g cm−3, 83.7% and 24.9 μm, respectively. CB particles are uniformly dispersed in the skeleton of the as-prepared foam, resulting in a low percolation threshold of 0.48 vol%. The CTF is capable of distinguishing different compressive strain by change of the relative resistance. Its responsive behaviors towards compressive strain present an excellent linear characteristic with a high gauge factor (GF) up to 1.55. In the piezoresistive tests, the CTF shows a fast response/relaxation time (150/150 ms), fascinating recoverability, excellent response stability within a wide workable detection range up to 80% strain (corresponding pressure of 584.4 kPa) and a superior durability (>10000 cycles), which is mainly related to the pinnate-veined aligned porous structure along the orientation direction. The CTF was then assembled as a wearable sensor to monitor various human motions such as arm bending, squatting, tiptoeing, etc., showing good detection performances. The sensor can also deal with water pollution through oil/water separation, suggesting its multifunctionality and promising prospects in complicated situations. [ABSTRACT FROM AUTHOR]

Various sensors have been developed to monitor the changes in physical quantities to meet the growing demand for wearable electronics. While it is still a huge challenge to design a multifunctional flexible sensor with both high strain responsivity and good breathability. In this work, through electrospinning, ultrasonication and in-situ polymerization of dopamine, we prepared a multifunctional strain sensor. We decorated polydopamine (PDA) onto the surface of reduced graphene oxide (RGO)/thermoplastic polyurethane (TPU) fibers. Here, PDA containing hydrophilic groups (-OH, –NH 2) was used to improve the hydrophilic breathability of the membrane and prevent the RGO falling off from TPU fibrous mat. The PDA/RGO/TPU (PRT) fibrous strain sensor exhibits excellent comprehensive performance of excellent stretchability, good durability (stretching/releasing test of 9000 cycles under 50% strain), high sensitivity (gauge factor (GF) 23.2 within 60% strain, 185 towards 60%–100% strain), and fast response time (100 m s). Specially, owing to the introduction of PDA, the water vapor volatilization rate of our PRT strain sensor (38%) is almost the same as the blank control group (39%), indicating that our fibrous sensor has excellent breathability. In order to monitor various movements of human body parts (finger, wrist, elbow, and leg bending), our sensors were attached to volunteers' joints to monitor resistance changes in real time. In addition, our PRT fibrous mat also has excellent sensitive performances towards organic gases and humidity, showing its multifunctional ability for detecting various environment stimuli. Image 1 [ABSTRACT FROM AUTHOR]