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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]

• 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]

Abstract In this work, the rheological and electrical behavior of carbon black (CB) filled poly(methyl methacrylate) (PMMA) nanocomposites in the molten state as a function of CB concentration were investigated by simultaneous electrical and rheological measurements. Shear deformations applied during a stress amplitude sweep caused both changes in the linear viscoelastic behavior and electrical conductivity. The storage modulus increased with measuring time for all PMMA nanocomposites. However, the changes in the time-dependent behavior of storage modulus decreased above the percolated CB concentrations for all investigated nanocomposites, which was in good agreement with the changes in the time-dependent electrical conductivity. The different behaviors can be explained by the agglomeration of CB particles and the decrease of averaged force on a single CB particle. Highlights • Shear deformation applied during stress amplitude sweep caused both changes in the linear viscoelastic and conductivity • Time-dependent behavior of storage modulus was agreed with the conductivity at above the percolated CB content. • Different behaviors were attributed to the CB agglomeration and the decrease of averaged force on a single CB particle. [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]

The advantages of segregated conductive polymer composites are greatly hampered owing to its limited preparation technology, which seriously relies on hot compression with low efficiency. The plunger type injection molding (PTIM) is employed to fabricate segregated carbon nanotubes (CNTs)/high density polyethylene (HDPE)/ultra-high molecular weight polyethylene (UHMWPE) composites in this paper, which lowers the production cycle by 45%, compared with the conventional hot compression. The morphology and conductive properties are investigated in detail. Graceful segregated conductive network and a very low percolation threshold (0.45 vol%) of the polymer composites have both been achieved. The present processing technique with short production cycle provides a fancy idea to realize segregated conductive polymer composite in mass production. [ABSTRACT FROM AUTHOR]

Stretchable strain sensors have promising potentials in wearable electronics for human motion detection, health monitoring and so on. A reliable strain sensor with high flexibility and good stability should be designed to detect human joints motions with a large deformation. Here, a simple and facile solution mixing-casting method was adopted to fabricate a highly stretchable strain sensor based on composites mixing polydimethylsiloxane (PDMS) with hybrid carbon nanotubes (CNTs) and carbon black (CB) conductive nanofillers (CNTs-CB). Bridged and overlapped hybrid CNTs-CB nanofillers structure was achieved in the composite on the basis of the morphology observation. In monotonic stretching test, the CNTs-CB/PDMS composites strain sensors exhibited high stretchability, strain-dependent sensitivity in a wide strain sensing range ( ca. 300% strain) and an excellent linear current-voltage behavior. During stretching-releasing cycles, the strain sensors presented excellent repeatability, good stability and superior durability (2500 cycles at 200% strain). Combined with the above outstanding strain sensing performances, the fabricated stretchable strain sensors were attached onto different joints of human body to monitor the corresponding human motions, demonstrating their attractive perspective in large human motions detection. [ABSTRACT FROM AUTHOR]

In this paper, we used epoxy (EP) as a third component to tune the electromechanical performances of the conductive porous foam. A directional ice-template freezing method was utilized to fabricate a carbon nanotubes (CNTs)/EP/thermoplastic polyurethane (TPU) porous foam with a herringbone-like structure. CNTs were homogeneously distributed in the skeleton of the foam. The microstructure of the herringbone-like foam was studied in detail from both the directions perpendicular and parallel to the freezing front movement direction. An ultralow percolation threshold (0.088 vol%) of the conductive foam was achieved. The strength of the CNTs/TPU/EP foam was significantly enhanced with the increase of the CNTs and EP contents. When the foams were exposed to a compression strain from 0 to 70%, the resistance of the porous material decreased in a good linear manner. The foams showed a good differenciation capability towards different compression strain amplitude. Upon multiple cyclic compressive process, the change of the resistance tended to be stable after several compression loading-unloading cycles' measurement. After a pre-compression treatment, the resistance response also became much stable on the basis of the re-arrangement of the conductive network and the stabilized cells structure of the foam. The porous foam possesses a rapid response speed (about 160 ms). Our flexible porous foam with a good chemical resistance can be used in ethanol to sense the finger pressing, and it showed excellent sensing performances when applied to monitor human body motions. [ABSTRACT FROM AUTHOR]

Highly sensitive and flexible capacitive sensors are in great demand for wearable electronics, which can be achieved by preparing micropatterns on their dielectric layer surface. However, most micropatterns are often molded with the silicon template acquired by complex processes which are very time-consuming and costly. Here, a dielectric layer with micropatterned arrays was prepared on the thermal plastic polyurethane (TPU) film with the help of a hot-air-gun, then assembled with an ITO/PET electrode to develop a capacitive sensor with a sandwich structure. The capacitive sensor based on TPU/ITO/PET composites exhibits sensitivity of over 0.026 kPa−1, shorter response/recovery time of 99 ms, wide working range (0–13 kPa) and remarkable stability over 5000 cyclic pressing or bending. Interestingly, such sensor can monitor various physiological signals of people (e.g., voice signal, finger bending and breath). More importantly, it can distinguish different sign languages according to capacitive changes in the case of different finger gestures. The method proposed in this study will paves a new avenue for the facile preparation of micropatterned surface to improve the performance of flexible capacitive sensors. The present work represents a facile and efficient method to achieve capacitive sensor that can not only exhibit excellent sensing performances, but also it can detect a series of physiological signals and realize sign language interpretation. [Display omitted] • A cost-effective method is proposed to fabricate micropatterned surface. • Micropatterned capacitive sensor has remarkable sensing performances. • Capacitive sensor can monitor various physiological signals in the body. • Capacitive sensor can realize sign language interpretation. [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]

A novel approach, i.e. manipulating the size of incorporated polymer matrix particles, was proposed to tune the positive temperature coefficient (PTC) characteristics of carbon nanotubes (CNTs)/polypropylene (PP) composites with a segregated microstructure. For the conductive properties of CNTs/PP composites, the percolation threshold decreased from 1.32 vol% to 0.44 vol% when the matrix particle size enlarged from 20 to 1200 µm, showing an inverse correlation effect. The controllable PTC characteristics in resistivity are attributed to the microstructure development of conductive pathways and the heat-induced volume expansion of polymer matrix particles. An extremely high PTC material has also been achieved through this method. The present work provides an effective route to acquire a tunable temperature-resistivity sensor. [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]

A carbon black (CB)/polypropylene (PP)/ultrahigh-molecular-weight polyethylene (UHMWPE) composite with a segregated structure was fabricated by using binary polymer granules as matrices. In preparation, an ethanol-assisted dispersion method was employed to disperse CB particles on the surface of the two polymer granules. The segregated conductive network was then constructed by hot compaction based on the volume exclusion effect of the polymer matrices. The conductive composite shows an ultralow percolation threshold of 0.34 vol.%. In temperature-resistivity test, a double positive temperature coefficient (PTC) effect was observed. In addition, the negative temperature coefficient (NTC) effect was eliminated significantly. These interesting temperature-resistivity behaviors were ascribed to the introduction of the binary polymer matrices and the mobility limitation of CB particles located at the PP/UHMWPE interface. These characteristics were probed by in situ morphology observation in heating process. The present paper provides a novel route for preparing conductive composites with an ultralow percolation threshold, a wider PTC region, and a zero NTC effect. [ABSTRACT FROM AUTHOR]

Abstract: Under the assistance of carbon fibers (CFs) with a large aspect ratio, an evident reduction in the percolation threshold of a segregated carbon black (CB)/polypropylene (PP) conductive polymer composite (CPC) has been achieved. The origin of the ultra-low percolation threshold 0.94vol% is ascribed to the design of a shish–calabash-like conductive network, where the CFs function as bridges between the segregated CB particles and CB particles act as calabashs contributing to the conductive framework. This interesting microstructure causes a synergistic effect on the conductive properties. A model is proposed to evaluate the percolation behavior of the unique CF/CB/PP composite. [Copyright &y& Elsevier]

The strain-sensing behaviors of carbon black (CB)/polypropylene (PP) and carbon nanotubes (CNTs)/PP conductive composites prepared by the vacuum-assisted hot compression were studied and compared. When ten extension-retraction cycles were applied, it was found for CB/PP, the value of the maximum responsivity (Δ R/ R, Δ R-the instantaneous variation of the resistance during the test, R-the original resistance) decreased gradually with increasing the cycle number, but it began to rise from the seventh cycle. The value of the min Δ R/ R increased during the whole test. While for CNTs/PP, both the values of the max and min Δ R/ R decreased rapidly. It is suggested that the different behaviors mainly depend on the distinction in the dimension of the conductive fillers and the preparation technique. [ABSTRACT FROM AUTHOR]

Abstract: Electrically conductive carbon black (CB)/polyamide 6 (PA6)/high density polyethylene (HDPE) composite with a low percolation threshold was fabricated by embedding conductive CB/PA6 membrane into the HDPE matrix. The CB/PA6 membrane was prepared by localizing CB particles on the surfaces of the electrospun PA6 fibrous membrane by a dip-coating method. Percolation threshold of this CB/PA6/HDPE composite was only ca. 4.3vol%, showing a considerable reduction compared to that of the common CB/HDPE (8.5vol%). Through the present method, a conductive polymer composite with enhanced processability and lowered cost has been achieved with extremely low loading of PA6 (1.5vol%). [Copyright &y& Elsevier]

Resistivity variations of carbon black (CB)/polypropylene (PP) and carbon nanotubes (CNTs)/PP conductive polymer composites subjected to different tensile speeds were studied with the same maximum strain 3%. With increasing tensile speed, the responsivity (ΔR/R0, R0is the original resistance, ΔR is instantaneous change in resistance) shows an obvious increase for both CPCs, although the increase degree is different. CB/PP has a higher responsivity than that of CNTs/PP during the tension and unloading process. It is proposed that the difference depends mainly on the distinction in the microstructure of conductive fillers and the interaction between the fillers and the matrix. [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]

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]

Stretchable, flexible, and strain‐sensitive hydrogels have gained tremendous attention due to their potential application in health monitoring devices and artificial intelligence. Nevertheless, it is still a huge challenge to develop an integrated strain sensor with excellent mechanical properties, broad sensing range, high transparency, biocompatibility, and self‐recovery. Herein, a simple paradigm of stretchable strain sensor based on multifunctional hydrogels is prepared by constructing synergistic effects among polyacrylamide (PAM), biocompatible macromolecule sodium alginate (SA), and Ca ion in covalently and ionically crosslinked networks. Under large deformation, the dynamic SA‐Ca2+ bonds effectively dissipate energy, serving as sacrificial bonds, while the PAM chains bridge the crack and stabilize the network, endowing hydrogels with outstanding mechanical performances, for instance, high stretchability and compressibility, as well as excellent self‐recovery performance. The hydrogel is assembled to be a transparent and wearable strain sensor, which has good sensitivity and very wide sensing range (0–1700%), and can precisely detect dynamic strains, including both low and high strains (20–800% strain). It also exhibits fast response time (800 ms) and long‐time stability (200 cycles). The sensor can monitor and distinguish complicated human motions, opening up a new route for broad potential applications of eco‐friendly flexible strain‐sensing devices. [ABSTRACT FROM AUTHOR]