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AbstractConductive hydrogels have promising prospects in wearable strain sensor applications. However, the complex and diverse application scenarios put forward higher requirements on the conductivity, anti-freezing, tensile, self-healing, adhesion, and moisture retention properties of the conductive hydrogel. In this study, a polymagnesium acrylate/glycerol/graphene oxide (PAMgA/GL/GO) conductive hydrogel is prepared by free radical polymerization method, with magnesium acrylate (AMgA) as the polymer monomer, glycerol (GL) as the antifreeze filler, and graphene oxide (GO) as the conductive filler. Adding GL not only enhances the antifreeze properties of the composite hydrogels but also improves the moisture retention. The addition of GO increases the conductivity and the gauge factor (GF) of the composite hydrogels. When the GO content is 0.6 wt.%, the PAMgA/GL/GO conductive hydrogel demonstrates excellent properties of antifreeze, conductivity, self-healing, adhesion, and sensitivity. These excellent properties make it suitable as a wearable strain sensor for accurately monitoring human joint movements and subtle physiological signals. [ABSTRACT FROM AUTHOR]

Chemical resistant textiles are vital for safeguarding humans against chemical hazards in various settings, such as industrial production, chemical accidents, laboratory activities, and road transportation. However, the ideal integration of chemical resistance, thermal and moisture management, and wearer condition monitoring in conventional chemically protective textiles remains challenging. Herein, the design, manufacturing, and use of stretchable hierarchical core–shell yarns (HCSYs) for integrated chemical resistance, moisture regulation, and smart sensing textiles are demonstrated. These yarns contain helically elastic spandex, wrapped silver-plated nylon, and surface-structured polytetrafluoroethylene (PTFE) yarns and are designed and manufactured based on a scalable fabrication process. In addition to their ideal chemical resistance performance, HCSYs can function as multifunctional stretchable electronics for real-time human motion monitoring and as the basic element of intelligent textiles. Furthermore, a desirable dynamic thermoregulation function is achieved by exploiting the fabric structure with stretching modulation. Our HCSYs may provide prospective opportunities for the future development of smart protective textiles with high durability, flexibility, and scalability.

Fibrous strain sensing materials with both high sensitivity and high linearity are of significant importance for wearable sensors, yet they still face great challenges. Herein, a photo‐spun reaction encapsulation strategy is proposed for the continuous fabrication of fibrous strain sensor materials (AMGF) with a core‐sheath structure. Metallogels (MOGs) formed by bacterial cellulose (BC) nanofibers and Ag nanoparticles (AgNPs), and thermoplastic elastomers (TPE) are employed as the core and sheath, respectively. The in situ ultraviolet light reduction of Ag+ ensured AgNPs to maintain the interconnections between the BC nanofibers and form electron conductive networks (0.31 S m−1). Under applied strain, the BC nanofibers experience separation, bringing AMGF a high sensitivity (gauge factor 4.36). The concentration of free ions in the MOGs uniformly varies with applied deformation, endowing AMGF with high linearity and a goodness‐of‐fit of 0.98. The sheath TPE provided AMGF sensor with stable working life (>10 000 s). Furthermore, the AMGF sensors are demonstrated to monitor complex deformations of the dummy joints in real‐time as a wearable sensor. Therefore, the fibrous hybrid conductive network fibers fabricated via the photo‐spun reaction encapsulation strategy provide a new route for addressing the challenge of achieving both high sensitivity and high linearity. [ABSTRACT FROM AUTHOR]

Real-time monitoring of human joint motion holds paramount importance in assessing joint health status, preventing and treating joint diseases, and evaluating physical flexibility and coordination. However, traditional strain sensors face limitations in meeting the substantial strain requirements associated with human joint motion. Recently, there has been considerable attention directed towards flexible strain sensors prepared using pliable substrates combined with silk and cotton fabrics. Nonetheless, these sensors exhibit insufficient linearity across the entire measurement range, thereby compromising the predictability of real joint motion based on the output signal. This paper introduced a flexible strain sensor designed to address this issue by offering an enhanced range and high linearity. Specifically, the core wire of the strain sensor was produced by coating a polybutylene terephthalate thread with conductive carbon ink integrated with carbon nanotubes, encapsulated in a thin layer of polydimethylsiloxane in an "S" configuration. The proposed strain sensor maintained excellent linearity within its strain range of 60%, along with advantages such as rapid response speed and robust durability. On-trial tests further affirmed the sensor's capability to effectively monitor the motion of human joints. [ABSTRACT FROM AUTHOR]

Flexible strain wearable sensors have attracted considerable attention due to their advantages of low cost, lightweight, high sensitivity and good flexibility. However, the strain sensors are easy to be damaged in an extreme humidity environment or by the wearer's sweat in the process of use, resulting in detection disorder or even a short circuit. Furthermore, preparation of sensors with stable properties under extreme environments is one of the most important research directions. To fill this gap, a flexible sensor was prepared by using polyurethane and carbon nanotubes, then modified by polydopamine and 1H,1H,2H,2H-perfluorodecane-mercaptan. A typical tunnel model was used to explain the working mechanism of the sensor, the sensitivity of the sensor is also explained and evaluated by the tunneling theory. The results show that the sensor has good sensitivity (the sensor has a stable sensing signal output under a strain range from 2% to 300%) and stability over 8500 cycles. At the same time, the sensor has good superhydrophobicity, the water contact angle reaches 152°, and it is still stable in a humid environment. Moreover, this sensor shows excellent performance in monitoring human joint motion (such as finger, elbow, wrist and knee) and physiological signals (such as speaking and drinking). This work provides an effective design method for the sensor which can be applied in a high humidity environment. [ABSTRACT FROM AUTHOR]

Fabrication of economical and eco-friendly flexible sensors is highly demanded in developing wearable biomedical devices. In this study, an eco-friendly strain and sweat sensor has been successfully assembled based on innovative composites consisting of carbon black (CB) and natural flour polymer, which are entirely green and biodegradable. A film-based sensing device has been developed to measure electrical resistance and strain simultaneously and continuously, owing to the highly sensitive resistance responsibility of the as-developed hybrid of CB and wheat flour (CB-dough). Furthermore, the influence of simulated sweat on the electric response of such sensor was also investigated. Repeatable relationships in resistance versus strain were revealed and obtained for varying samples with different content of simulated sweat, in which the amplitude of resistance was directly proportional to the concentration of NaCl. Accordingly, the as-developed CB-dough sensor was efficaciously used for durable surveillance of human activity and real-time feedback of sweat secretion during body motion. This work offers a simple and cost-effective way to manufacture flexible strain sensors, with a broad application prospect in wearable electronics, artificial intelligence systems, and other bio-sensors. [ABSTRACT FROM AUTHOR]

In this study, chitin fibers (CFs) were combined with molybdenum sulfide (MoS2) to develop high-performance sensors, and chitin carbon materials were innovatively introduced into the application of gas sensing. MoS2/CFs composites were synthesized via a one-step hydrothermal method. The surface properties of the composites were greatly improved, and the fire resistance effect was remarkable compared with that of the chitin monomer. In the gas-sensitive performance test, the overall performance of the MoS2/CFs composite was more than three times better than that of the MoS2 monomer and showed excellent long-term stability, with less than 10% performance degradation in three months. Extending to the field of strain sensing, MoS2/CFs composites can realize real-time signal conversion in tensile and motion performance tests, which can help inspectors make analytical judgments in response to the analysis results. The extensive application of sensing materials in more fields is expected to be further developed. Based on the recycling of waste chitin textile materials, this paper expands the potential applications of chitin materials in the fields of gas monitoring, biomedicine, behavioral discrimination and intelligent monitoring. [ABSTRACT FROM AUTHOR]

Flexible wearable strain sensors based on hydrogels have become a research hotspot in recent years due to their advanced application in many fields. Currently, most hydrogel-based strain sensors exhibit poor mechanical properties and low sensitivity. In this work, a conductive hydrogel as a wearable strain sensor was developed based on dual crosslinked polyvinyl alcohol (PVA) networks. The PVA was the main skeleton of the hydrogel and the water-soluble amino-polysiloxane (APSi) introduced into this hydrogel was the secondary network. The APSi and PVA were locked together by phytic acid (PA), which improved the microstructure and enhanced the mechanical properties of the hydrogel. This was mainly reflected in the higher tensile strength (1.27 MPa), elongation at break (425.5%), electrical conductivity (0.975 S/m), linearity (R2 = 0.999) and tensile strain sensitivity (gauge factor (GF) of 2.29). The tensile strength (0.166–1.270 MPa) and elongation (170.2–425.5%) of the hydrogel can be regulated continuously by adjusting the amount of APSi. These silicone-enhanced PVA hydrogels have good biocompatibility and hence can be used as wearable strain sensors.

Real-time monitoring of human joint motion holds paramount importance in assessing joint health status, preventing and treating joint diseases, and evaluating physical flexibility and coordination. However, traditional strain sensors face limitations in meeting the substantial strain requirements associated with human joint motion. Recently, there has been considerable attention directed towards flexible strain sensors prepared using pliable substrates combined with silk and cotton fabrics. Nonetheless, these sensors exhibit insufficient linearity across the entire measurement range, thereby compromising the predictability of real joint motion based on the output signal. This paper introduced a flexible strain sensor designed to address this issue by offering an enhanced range and high linearity. Specifically, the core wire of the strain sensor was produced by coating a polybutylene terephthalate thread with conductive carbon ink integrated with carbon nanotubes, encapsulated in a thin layer of polydimethylsiloxane in an “S” configuration. The proposed strain sensor maintained excellent linearity within its strain range of 60%, along with advantages such as rapid response speed and robust durability. On-trial tests further affirmed the sensor’s capability to effectively monitor the motion of human joints.

Abstract Wearable strain sensors are arousing increasing research interests in recent years on account of their potentials in motion detection, personal and public healthcare, future entertainment, man–machine interaction, artificial intelligence, and so forth. Much research has focused on fiber-based sensors due to the appealing performance of fibers, including processing flexibility, wearing comfortability, outstanding lifetime and serviceability, low-cost and large-scale capacity. Herein, we review the latest advances in functionalization and device fabrication of fiber materials toward applications in fiber-based wearable strain sensors. We describe the approaches for preparing conductive fibers such as spinning, surface modification, and structural transformation. We also introduce the fabrication and sensing mechanisms of state-of-the-art sensors and analyze their merits and demerits. The applications toward motion detection, healthcare, man–machine interaction, future entertainment, and multifunctional sensing are summarized with typical examples. We finally critically analyze tough challenges and future remarks of fiber-based strain sensors, aiming to implement them in real applications.

Soft contact lenses with built-in sensors have shown great potential for real-time monitoring of intraocular pressure (IOP). This paper reports a contact lens IOP sensor based on the moiré patterns. One concentric ring grating (G1) is fabricated on a commercial contact lens, the other line grating (G2) is stored in a computer. Images of G1 are captured using a smartphone camera. Then moiré patterns are generated by superimposing the images of the two gratings in a computer. The central angle $\theta $ formed between two innermost adjacent moiré patterns is extracted as the IOP transducing signals. The performance of the sensor has been evaluated using a home-made hollow hemispherical silicone model eye. The sensitivity of the contact lens IOP sensor is ~0.15°/mmHg with high repeatability. Additionally, the sensor sensitivity is essentially independent of the initial IOP exerted on the contact lens. Furthermore, the virtual G2 provides great flexibility for the design and fabrication of the sensor, the fabrication of G1 directly on commercial contact lenses paves the way for clinic use. All these results indicate the suitability of this type of sensor for monitoring IOP. [2022-0111] [ABSTRACT FROM AUTHOR]

Wearable sensors, as the name indicates, are sensors attached directly to the body in order to monitor certain parameters by detecting human body motions. They find widespread applications in continuous monitoring of various parameters. In particular, the wearable strain sensor has been fabricated using multiwalled carbon nanotubes (MWCNTs). MWCNT were synthesized by chemical vapour deposition (CVD) and characterisation was done for morphology, optical and tensile strength studies. MWCNT were coated on different types of fabrics such as nylon, polyester, silk and cotton using the doctor blade method. Silver contacts were coated on fabric to measure the strain sensors. The strain sensors were then investigated for impedance characteristics and piezoresistive properties by applying different loads. The results showed that the nylon fabric had excellent sensitivity and strain variation compared to other fabrics, followed by polyester, silk, and cotton. [ABSTRACT FROM AUTHOR]

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The pursuit of stretchable ionic conductive hydrogels for skin‐inspired sensors is highly attractive but challenging due to the difficulty in fabricating an ionic conductive hydrogel with combined characteristics of high stretchability, notch insensitivity, self‐healability, and unique reprocessability. Herein, a dual‐dynamic‐network ionic conductive hydrogel (DICH) with both hydrophobic association network and metal coordination network is one‐pot synthesized. Benefiting from the formation of the highly dynamic double networks, the resultant DICH exhibited large stretchability (>2800%) and excellent fracture toughness (4820 kJ m−3). The DICH also demonstrated autonomous healability, notch insensitivity, and unique remoldability because of the formation of the active reversible interactions including hydrophobic association and metal coordination. Due to the integration of high stretchability and favorable ionic conductivity of the DICH containing substantial amounts of electrolytic ions, stretchable ionic strain sensors could be assembled, displaying high sensitivity (gauge factor of 2.6), fast response time (180 ms), and wide response range (0.5%–600% strain). The ionic sensors could also maintain excellent strain‐sensing abilities even after being cut/self‐healed or reprocessed. Wearable DICH resistive‐type strain sensors could be assembled, demonstrating high performance in detecting and distinguishing both large and subtle motions of a human body. [ABSTRACT FROM AUTHOR]

Regenerated silk fibroin (RSF) hydrogels have been extensively studied in the fields of biomedicine and wearable devices in recent years due to their outstanding biocompatibility. However, the pure RSF hydrogels usually exhibited frangibility and low ductility, limiting their application in many aspects severely. Herein, we demonstrate a tough RSF/poly (N , N -dimethylallylamine) hydrogel with semi-interpenetrating network, which possesses good mechanical properties with high stretchability (ε b = 900%), tensile strength (σ b = 101.7 kPa), toughness (W f = 516.7 kJ/m3) and tearing fracture energy (T = 407.3 J/m2). Besides, the gels show low residual strain in the cyclic tests and rapid self-recovery (80% toughness recovery within 5 min with the maximum strain of 400%). Moreover, the gels also show high ionic conductivity due to the incorporation of the NaCl and the hydrogel can act as an ideal candidate for strain sensor with high sensitivity (GF = 1.84), admirable linearity, and good durability (1000 cycles with the strain of 100%). When used as a wearable strain sensor for monitoring human movements, it also can detect small and large deformations with high sensitivity. It is expected that this work can provide a new strategy for the fabrication of smart RSF-based hydrogels and expand their application in multiple scenarios. [ABSTRACT FROM AUTHOR]

Since hydrogels are conductive, easily engineered, and sufficiently flexible to imitate the mechanical properties of human skin, they are seen as potential options for wearable strain sensors. However, it is still a great challenge to prepare a hydrogel through simple and straightforward methods that integrate excellent stretchability, ionic conductivity, toughness, self-adhesion, and self-healing. Herein, an acrylamide/3-acrylamide phenylboronic acid cross-linked network is modified to produce a semi-interpenetrating cross-linked hydrogel in just one easy step by adding starch. The prepared hydrogel contains dynamic boronic ester bonds and hydrogen bonds, which endow the exceptional stretchability (5769–13,976 %, 20–50 wt%), ideal transmittance (>90 %), self-adhesiveness (0.636 ± 0.060 kPa, 30 wt%), and self-healing properties. Notably, the self-healing process is completed instantly, achieving a healing strength of up to 81.21 %. Additionally, the aforementioned hydrogel exhibits a broad working strain range (≈ 500 %) and high sensitivity (gauge factor = 1.99) as a strain sensor, allowing it to record and track human actions precisely. This work provides a novel approach to synthesizing hydrogels with optimal overall mechanical characteristics, with the potential to facilitate the development of wearable strain sensing system based on hydrogels for real-world applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, chitin fibers (CFs) were combined with molybdenum sulfide (MoS2) to develop high-performance sensors, and chitin carbon materials were innovatively introduced into the application of gas sensing. MoS2/CFs composites were synthesized via a one-step hydrothermal method. The surface properties of the composites were greatly improved, and the fire resistance effect was remarkable compared with that of the chitin monomer. In the gas-sensitive performance test, the overall performance of the MoS2/CFs composite was more than three times better than that of the MoS2 monomer and showed excellent long-term stability, with less than 10% performance degradation in three months. Extending to the field of strain sensing, MoS2/CFs composites can realize real-time signal conversion in tensile and motion performance tests, which can help inspectors make analytical judgments in response to the analysis results. The extensive application of sensing materials in more fields is expected to be further developed. Based on the recycling of waste chitin textile materials, this paper expands the potential applications of chitin materials in the fields of gas monitoring, biomedicine, behavioral discrimination and intelligent monitoring.

• This review covers the recent advances and challenges of polymer–graphene nanocomposites (PGNs) as materials for wearable strain sensors, to monitor various human motions and physiological signals. • The classification of PGNs based on the types of graphene and the strain sensing mechanisms, and discussions regarding the fabrication methods of PGN-based strain sensors have been introduced. • It showcases the functional PGN-based strain sensors using various polymers and their applications in different fields, and identifies the future directions of PGN-based wearable strain sensors for accurate and reliable physiological signal monitoring. Wearable strain sensors are emerging as promising devices for monitoring human motions and physiological signals in various fields, such as healthcare, robotics, and sports. Among various materials, polymer–graphene nanocomposites (PGNs) have attracted considerable attention due to their excellent mechanical, electrical, and thermal properties, as well as their facile fabrication methods. This review summarised the recent progress and challenges of PGN-based wearable strain sensors for physiological signal monitoring. First, the classification of PGNs based on the structural derivatives of graphene (such as graphene sheets, graphene oxide, reduced graphene oxide, and graphene quantum dots) and the strain sensing mechanisms (such as resistive and capacitive) were introduced. Then, we discussed the fabrication approaches of PGN-based strain sensors, including solution processing, melt blending, in-situ polymerization, spinning, printing, and coating. Afterward, this article highlighted the functional PGN-based strain sensors using various polymers and their applications in monitoring subtle and significant physiological signals. Finally, this work identified the underlying challenges and future perspectives of PGN-based wearable strain sensors for accurate and reliable physiological signal monitoring. This review provides a comprehensive overview of the current state-of-the-art of PGN-based wearable strain sensors and inspires further research in this field. [ABSTRACT FROM AUTHOR]

Highlights: General principles for fiber functionalization and strain sensor fabrication are briefly reviewed. Future application potentials of wearable strain sensors are summarized and evaluated. Challenges and perspectives of fiber-based wearable strain sensors are critically discussed.Wearable strain sensors are arousing increasing research interests in recent years on account of their potentials in motion detection, personal and public healthcare, future entertainment, man–machine interaction, artificial intelligence, and so forth. Much research has focused on fiber-based sensors due to the appealing performance of fibers, including processing flexibility, wearing comfortability, outstanding lifetime and serviceability, low-cost and large-scale capacity. Herein, we review the latest advances in functionalization and device fabrication of fiber materials toward applications in fiber-based wearable strain sensors. We describe the approaches for preparing conductive fibers such as spinning, surface modification, and structural transformation. We also introduce the fabrication and sensing mechanisms of state-of-the-art sensors and analyze their merits and demerits. The applications toward motion detection, healthcare, man–machine interaction, future entertainment, and multifunctional sensing are summarized with typical examples. We finally critically analyze tough challenges and future remarks of fiber-based strain sensors, aiming to implement them in real applications. [ABSTRACT FROM AUTHOR]

Hydrogel-based flexible electronic devices are essential in future healthcare and biomedical applications, such as human motion monitoring, advanced diagnostics, physiotherapy, etc. As a satisfactory flexible electronic material, the hydrogel should be conductive, ductile, self-healing, and adhesive. Herein, we demonstrated a unique design of mechanically resilient and conductive hydrogel with double network structure. The Ca2+ crosslinked alginate as the first dense network and the ionic pair crosslinked polyzwitterion as the second loose network. With the synthetic effect of these two networks, this hydrogel showed excellent mechanical properties, such as superior stretchability (1,375%) and high toughness (0.57 MJ/m3). At the same time, the abundant ionic groups of the polyzwitterion network endowed our hydrogel with excellent conductivity (0.25 S/m). Moreover, due to the dynamic property of these two networks, our hydrogel also performed good self-healing performance. Besides, our experimental results indicated that this hydrogel also had high optical transmittance (92.2%) and adhesive characteristics. Based on these outstanding properties, we further explored the utilization of this hydrogel as a flexible wearable strain sensor. The data strongly proved its enduring accuracy and sensitivity to detect human motions, including large joint flexion (such as finger, elbow, and knee), foot planter pressure measurement, and local muscle movement (such as eyebrow and mouth). Therefore, we believed that this hydrogel had great potential applications in wearable health monitoring, intelligent robot, human-machine interface, and other related fields.

Conductive hydrogels as wearable devices meet the basic demands of mechanical flexibility and smart sensing. However, achieving anti-freeze property in conductive hydrogels is still challengeable. Here, a novel anti-freezing system based on ice structuring proteins and CaCl 2 was introduced to enable a conductive hydrogel with low-temperature adaptability. Both formation of ice nuclei and ice growth of the hydrogel at sub-zero temperature could be inhibited. Supported by the anti-freeze system, the hydrogel revealed good flexibility (890% at −20 °C), recovery and conductivity (0.50 S/m at −20 °C) at both room temperature and sub-zero temperature. The low-temperature adaptability enabled the hydrogel to be used as strain and temperature sensors at both room temperature and sub-zero temperature. The anti-freeze system in this work is expected to open up a new avenue to promote the conductive hydrogel with low-temperature adaptability. [ABSTRACT FROM AUTHOR]

Conductive hydrogels are widely used as sensors in wearable devices. However, hydrogels cannot endure harsh low-temperature environments. Herein, a new regulatory system based on natural ice-structuring proteins (ISPs) and cellulose nanofibers (CNFs) is introduced into hydrogel network consisting of chemically crosslinked network of copolymerized acrylamide and 2-acrylamide-2-methylpropanesulfonic acid, and physically crosslinked polyvinyl alcohol chains, affording an anti-freezing hydrogel with high conductivity (2.63 S/m). These hydrogels show excellent adhesion behavior to various matrices (including aluminum, glass, pigskin, and plastic). Their mechanical properties are significantly improved with the increase in CNF content (tensile strength of 106.4 kPa, elastic modulus of 133.8 kPa). In addition, ISPs inhibit the growth of ice. This endows the hydrogels with anti-freezing property and allows them to maintain satisfactory mechanical properties, conductivity and sensing properties below zero degrees. Moreover, this hydrogel shows high sensitivity to tensile and compressive deformation (GF = 5.07 at 600–800 % strain). Therefore, it can be utilized to develop strain-type pressure sensors that can be attached directly to human skin for detecting various body motions accurately, reliably, and stably. This study proposes a simple strategy to improve the anti-freezing property of hydrogels, which provides new insights for developing flexible hydrogel electronic devices for application in winter sports. [ABSTRACT FROM AUTHOR]

The extraction of keratin from discarded feathers for the preparation of poly (vinyl alcohol) (PVA) ionic conductive hydrogels with enhanced mechanical properties shows promise for applications in green flexible electronics. Here, we first extracted feather keratin (FK) from duck feather fibers using the lactic acid/ l -cysteine deep eutectic solvents. Subsequently, the composite ionic conductive hydrogel composed of FK, PVA, and CaCl 2 was constructed by a one-pot freeze-thawing strategy. The introduction of FK resulted in a denser structure of the fabricated hydrogel, which significantly enhanced its mechanical properties, including high elongation at break of 639.3%, high breaking strength of 270 kPa, and durable fatigue resistance. Impressively, the hydrogel-based wearable strain sensor demonstrated high strain sensing sensitivity (GF = 1.26), wide strain detection range (5%–200%), fast response, and stable reliability, enabling it to accurately monitor and distinguish the difference in electrical signals generated by large and tiny human motions. This work provides a reliable method for the green extraction of FK and the design of high-performance PVA hydrogel-based flexible electrical devices. [Display omitted] • FK was extracted from feathers using a novel deep eutectic solvent. • PVA based ionic conductive hydrogels were constructed by a one-pot freeze-thawing strategy. • FK enhanced mechanical properties and ionic conductivity of hydrogels. • The hydrogel demonstrated superior strain sensing performance. • The hydrogel sensors are suitable for human motion monitoring. [ABSTRACT FROM AUTHOR]

Real‐time, continuous acquirement of human pulse signal in daily activity has important clinical significance for cardiovascular disease diagnosis and healthcare system. Here, a wearable strain sensor is developed based on reduced graphene oxide (rGO) fabrics/foam tape/rGO fabrics structure to realize this goal. The wearable device is designed and fabricated with two‐layered rGO fabrics: the lower rGO fabrics that can directly attach to the skin surface acquire the superposition signal of the human daily activity and pulse, while the upper rGO fabrics can only acquire human daily activity signal because the foam substrate between the two rGO fabrics components can preclude the response of the upper rGO film to the weak pulse beat. Through comparing two signal modules, the human daily activity signal of the superposition signal can be marked and further eliminated by band‐pass filter method and the pulse signal in daily activity can be obtained. This wearable sensor displays capability to monitor human pulse signal during various daily activities, including index finger bending, middle finger bending, wrist flexion and extension, fist clenching and continuous finger flexion with different rates, thus providing a promising solution to monitor human pulse in daily activity. [ABSTRACT FROM AUTHOR]

• A kind of mussel-inspired l -DMA–PCL hydrogel was prepared by UV curing technology. • The l -DMA–PCL hydrogel exhibites reversible adhesion to various substrates. • The l -DMA–PCL hydrogel displays tunable mechanical properties. • The hydrogel-based wearable strain sensor shows high conductivity (0.0550 S/cm). Flexible and wearable hydrogel strain sensors have attracted significant attention for human activity monitoring and electronic skins. However, it remains a great challenge to develop an integrated hydrogel strain sensor showing intrinsic adhesive performances, tunable mechanical and high strain-sensitive properties. Marine mussels show a superior capacity to adhere to various substrates (including organic and inorganic), while polycaprolactone (PCL) can be easily modified into crosslinkers with different degrees of functionality (bi-, tri-, and quadri-functional groups) to control the crosslinking density. Therefore, the developed mussel-inspired 3,4-dihydroxyphenyl- l -alanine acrylamide–polycaprolactone (l -DMA–PCL) hydrogels could address these issues and serve as the potential wearable strain sensors for biomaterials and healthcare monitoring. l -DMA monomers were successfully crosslinked by functionalized PCL (bi-, tri-, and quadri-functional) using UV light (wavelength ~ 365 nm) to prepare the l -DMA–PCL hydrogel. Adhesive behaviors, tunable mechanical properties and strain sensing performances of the l -DMA–PCL hydrogels were systematically studied. The l -DMA–PCL hydrogel exhibited reversible adhesion to various material substrates (including steel, aluminum, ceramics, poly(ethylene terephthalate) (PET), wood, rubber, even for polypropylene (PP) and polytetrafluoroethylene (PTFE)) as well as skin. Moreover, the mechanical properties (stress: 50.2–72.4 KPa, strain: 700–1140%, Young's modulus: 8.6–14.8 KPa, and toughness: 16.4–53.6 KJ/m3) of the hydrogels could be readily tuned by the modulation of functionality degree (bi-, tri-, and quadri-functional) of PCL. Intriguingly, the hydrogel-based wearable strain sensor showing high conductivity (0.0550 S/cm) and sensitive responses to both large (e.g., joint bending) and subtle human motions (e.g., frowning and speaking). Based on these achievements, this work provides new insights into the development of hydrogel with adhesiveness, controllable mechanical performance and high strain sensitivity as a flexible and wearable hydrogel strain sensors. [ABSTRACT FROM AUTHOR]

Abstract Wearable strain sensors based on flexible conductive polymer composites (FCPCs) have attracted great attention due to their applications in the fields of human–machine interaction, disease diagnostics, human motion detection, and soft robotic skin. In recent decades, FCPC‐based strain sensors with high stretchability and sensitivity, short response time, and excellent stability have been developed, which are expected to be more versatile and intelligent. Smart strain sensors are required to provide wearable comfort, such as breathability, self‐cooling ability, and so forth. To adapt to the harsh environment, wearable strain sensors should also be highly adaptive to protect the skin and the sensor itself. In addition, portable power supply system, multisite sensing capability, and multifunctionality are crucial for the next generation of FCPC‐based strain sensor.

Wearable strain sensors based on flexible conductive polymer composites (FCPCs) have attracted great attention due to their applications in the fields of human–machine interaction, disease diagnostics, human motion detection, and soft robotic skin. In recent decades, FCPC‐based strain sensors with high stretchability and sensitivity, short response time, and excellent stability have been developed, which are expected to be more versatile and intelligent. Smart strain sensors are required to provide wearable comfort, such as breathability, self‐cooling ability, and so forth. To adapt to the harsh environment, wearable strain sensors should also be highly adaptive to protect the skin and the sensor itself. In addition, portable power supply system, multisite sensing capability, and multifunctionality are crucial for the next generation of FCPC‐based strain sensor. [ABSTRACT FROM AUTHOR]

In this study, we fabricated a wearable strain sensor to monitor human respiration by lock-stitching stretchable conductive yarn onto a textile substrate. We developed the strain sensor by using conductive yarn consisting of silver-plated and unplated nylon yarns twisted around a lycra fiber with a lock wrinkle structure that could stretch after sewing. The slopes of the strain-stress curves of three fabricated strain sensors with a 10% strain load increased to 121 kPa, 189 kPa, and 241.5 kPa, and the relative change in resistance ($\Delta \text{R}/\text{R}_{\sf 0}$) of the strain sensor increased from 67% to 116% and from 8% to 109% by respectively applying more tension and fewer locks to the conductive yarn. In addition, as we strained the strain sensor to more than 4,000 cycles, the relative change in resistance decreased by only 6% from its initial value. A respiration measurement test was conducted with the developed sensor to monitor four different respiration patterns: slow (10 bpm), fast (30 bpm), deep, and shallow respiration, and the results were compared to those of reference respiration monitoring devices. Consequently, the proposed stretchable conductive yarn-based strain sensor worked as well as commercial respiration sensors, and its feasibility was demonstrated for use in respiration monitoring for daily living. [ABSTRACT FROM AUTHOR]

Sodium alginate (SA), as the eco-friendly and human-safe biomass material not only can achieve effective dispersion of graphene nanoplatelets (GnPs), but also improve the interaction between GnPs and cellulose macromolecules. Based on this, a flexible and wearable GnPs/cellulose strain sensor with a special 2 × 2 double rib knitted fabric structure (KFGS) was prepared by a simple dip-coating method that could be used on a large scale. The KFGS exhibited dual sensing performance with high sensitivity (25.32 kPa−1 at 3 kPa pressure, gauge factor 32.62 at 25% tensile strain), stretchability (ε > 25%) and dynamic stability (signal drift < 6% after 300 cycles). Its potential application prospects were also predicted by the monitoring of human movement and physical parameters through a wireless Bluetooth connection. [ABSTRACT FROM AUTHOR]

As a large number of strain sensors are put into practical use, their stability should be considered, especially in harsh environments containing water or microorganisms, which could affect strain sensing. Herein, a novel strategy to overcome liquid interference is proposed. The strain sensor is constructed with a sandwich architecture through layer‐by‐layer (LBL) spray‐coating of a 3‐(aminopropyl)triethoxysilane (APTES) bonding layer and multi‐walled carbon nanotubes/graphene (MWCNT/G) conductive layers on an elastomeric polydimethysiloxane (PDMS) substrate, and is further decorated with silver (Ag) nanoparticles and the (heptadecafluoro‐1,1,2,2‐tetradecyl) trimethoxysilane (FAS, F in short) to obtain a F/Ag/MWCNG/G‐PDMS (FAMG) strain sensor. The superhydrophobicity and underwater oleophobicity of the outer cover layer causes this FAMG strain sensor surface to exhibit stable strain sensing resistant to liquid interference upon stretching in the Cassie−Baxter wetting state, and resistance to bacterial adhesion (Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)). The sensor attains ultrasensitivity (with a maximum gauge factor of 1989 in the condition of liquid interference), broad strain range (0.1–170%), fast response time (150 ms), and stable response after 1000 stretching–releasing cycles. The ultrasensitivity is provided by propagation of cracks in MWCNT/G conductive layers and terminal fracture of the intermediate separating layers (APTES/MWCNT/G). The microbridge effect of MWCNTs and slippage of APTES/MWCNT/G provide a large strain range. The FAMG strain sensor is successfully used to monitor a series of human activities and an electronic bird under artificial rain and bacterial droplets, indicating the potential use of this sensor in complex environments. [ABSTRACT FROM AUTHOR]

Conductive hydrogels usually suffer from weak mechanical properties and are easily destroyed, resulting in limited applications in flexible electronics. Concurrently, adding conductive additives to the hydrogel solution increases the probability of agglomeration and uneven dispersion issues. In this study, the biocompatible natural polymer chitosan was used as the network substrate. The rigid network employed was the Cit3−ion crosslinked chitosan (CS) network, and the MBA chemically crosslinked polyacrylamide (PAM) network was used as the flexible network. Tannic acid-reduced graphene oxide (TA-rGO), which has excellent conductivity and dispersibility, is used as a conductive filler. Thus, a CS/TA-rGO/PAM double network conductive hydrogel with excellent performance, high toughness, high conductivity, and superior sensing sensitivity was prepared. The prepared CS/TA-rGO/PAM double network conductive hydrogels have strong tensile properties (strain and toughness as high as 2009 % and 1045 kJ/cm3), excellent sensing sensitivity (GF value was 4.01), a wider strain detection range, high cycling stability and durability, good biocompatibility, and antimicrobial properties. The hydrogel can be assembled into flexible wearable devices that can not only dynamically detect human movements, such as joint bending, facial expression changes, swallowing, and saying, but also recognize handwriting and enable human-computer interaction. [ABSTRACT FROM AUTHOR]

This paper is dedicated to the fast-developing area of flexible sensors for various applications, including resistive, capacitive, optical, and other wearable strain sensors. These devices open opportunities in different fields and can serve personalized applications in healthcare care, human body motion detection in the sport of rehabilitation, soft robotics, precision and automated agriculture, and many other areas. Except for their implementation in practical cases, these sensors have a significant scientific interest in various aspects of research. A specific interest in sensor research that raises a high level of interest is the development of new sensitive materials with particular properties. Another important issue is mosaicking in various combinations of sensitive materials in the sensor design and creating arrays of sensors with corresponding signal data acquisition. Enhancement of sensors by using nanomaterials, microcracks in sensing films as an additional array for sensing improvement, and alternation of the tunneling resistance application for resistive-type sensors opens the door to many existing and new sensor implementation cases. The idea of circular economy promotes the reuse of discarded sensors and their parts and efficiently consumes materials. The same ideas demand us to reduce the consumption of nanocomposites, noble metals, and other expensive or dangerous materials for the environment. Another way to comply with environmental requirements is to use natural materials from plants. This review was built using the publication analysis and counting the keywords found according to the area of interest. The analysis focuses on stretchable strain sensors of various designs and their integrity with mounting media. Applications of stretch sensors are also not left behind and take a significant space within review. The last part of this paper contains an analysis of sensor disposal, recycling, and reuse. The study ends with a discussion and conclusions. [Display omitted] [ABSTRACT FROM AUTHOR]

Addressing the critical requirement for real-time monitoring of tumor progression in cancer care, this study introduces an innovative wearable platform. This platform employs a thermoplastic polyurethane (TPU) film embedded with hafnium oxide nanoparticles (HfO 2 NPs) to facilitate dynamic tracking of tumor growth and regression in real time. Significantly, the synthesized HfO 2 NPs exhibit promising characteristics as effective sonosensitizers, holding the potential to efficiently eliminate cancer cells through ultrasound irradiation. The TPU-HfO 2 film, acting as a dielectric elastomer (DE) strain sensor, undergoes proportional deformation in response to changes in the tumor volume, thereby influencing its electrical impedance. This distinctive behavior empowers the DE strain sensor to continuously and accurately monitor alterations in tumor volume, determining the optimal timing for initiating HfO 2 NP treatment, optimizing dosages, and assessing treatment effectiveness. Seamless integration with a wireless system allows instant transmission of detected electrical impedances to a smartphone for real-time data processing and visualization, enabling immediate patient monitoring and timely intervention by remote medical staff. By combining the dynamic tumor monitoring capabilities of the TPU-HfO 2 film with the sonosensitizer potential of HfO 2 NPs, this approach propels cancer care into the realm of telemedicine, representing a significant advancement in patient treatment.

Graphical abstract Highlights • Skin-inspired hydrogels exhibit excellent adhesiveness, toughness and conductivity. • Hydrogels exhibit high strain sensitivity and stability as strain sensors. • Hydrogel sensors can detect large-range human motions and physiological signals. • Hydrogels can form safe interfaces with the biological tissues. Abstract With increasing interest and demand for wearable sensor devices, fabricating a flexible hydrogel sensor combining high toughness and adhesiveness is necessary but remains challenging. In this work, inspired by the delamination structure of skin, an ultra-stretchable wearable hydrogel strain sensor with double layers is successfully prepared via in-situ polymerization of nucleobase-driven adhesive hydrogels on the surface of conductive tough hydrogels crosslinked by hydrophobic association. The hydrogel exhibits ultra-stretchability, high mechanical strength, and robust adhesion to various solid materials as well as skin. Furthermore, the hydrogel also exhibits high strain sensitivity and stability as a flexible and wearable strain sensor to detect large-range human motions and tiny physiological signals. Notably, the adhesive layer not only ensures a robust adhesion between the sensors and skin, but also protects skin from current harm when the hydrogels contact with skin directly, because of effectively blocking the current from the conductive tough layer. It is envisioned that the skin-inspired strategy would provide novel inspiration for the development of hydrogel strain sensors. [ABSTRACT FROM AUTHOR]

Stretchable conductive fibers have attracted significant attention due to their ability to be directly woven into or stitched onto fabrics, making them ideal for use in the design of integrated wearable strain sensors. Here, we report on a highly stretchable multi-walled carbon nanotube (MWCNT)/Thermoplastic Polyurethane (TPU) fiber produced via a wet spinning process. The effects of MWCNT content and alignment on the structural, mechanical, electrical and strain-sensing properties of the composite fibers were investigated. The highest conductivity (6.77 S cm−1), tensile strength (28 MPa) and maximum elongation at break (565%) were obtained by controlling the MWCNT content. Gauge factor (GF) values were also affected by the content and MWCNT alignment in the composite fibers, as these parameters determine the change in the effective contact area and number of conductive paths available during stretching. The well-aligned MWCNT/TPU fiber showed a high GF value of 5200. Wearable strain sensors capable of obtaining real-time mechanical feedback for various human motion detections with different GFs and working strain ranges could be realized by controlling the MWCNT concentrations in the TPU matrix. Image 1 [ABSTRACT FROM AUTHOR]

In recent years, flexible sensors for data gloves have been developed that aim to achieve excellent wearability, but they are associated with difficulties due to the complicated manufacturing and embedding into the glove. This study proposes a knitted glove integrated with strain sensors for pattern recognition of hand postures. The proposed sensing glove is fabricated at all once by a knitting technique without sewing and bonding, which is composed of strain sensors knitted with conductive yarn and a glove body with non-conductive yarn. To verify the performance of the developed glove, electrical resistance variations were measured according to the flexed angle and speed. These data showed different values depending on the speed or angle of movements. We carried out experiments on hand postures pattern recognition for the practicability verification of the knitted sensing glove. For this purpose, 10 able-bodied subjects participated in the recognition experiments on 10 target hand postures. The average classification accuracy of 10 subjects reached 94.17% when their own data were used. The accuracy of up to 97.1% was achieved in the case of grasp posture among 10 target postures. When all mixed data from 10 subjects were utilized for pattern recognition, the average classification expressed by the confusion matrix arrived at 89.5%. Therefore, the comprehensive experimental results demonstrated the effectiveness of the knitted sensing gloves. In addition, it is expected to reduce the cost through a simple manufacturing process of the knitted sensing glove.

Creating strain and pressure sensors based on hydrogels with excellent mechanical and conducting properties is a major problem for scientists in the fields of artificial intelligence, soft robotics, tissue engineering, human motion detection, electronic skin, etc. Therefore, in this study graphene oxide (GO) incorporated hydrophobically associated hydrogels with acrylamide (Amm) and butyl acrylate (BA) polymer segments with excellent mechanical properties, fracture strain of 1630%, and stress 551 kPa, showing good anti-fatigue resistance with five continuous cycles at 500% strain were developed. The hydrogel showed excellent strain response with conductivity of 0.246 S/m and can sense small strains of 1% to large strains of 700% with GF = 29.52 at 850% strain) and response time of 110 msec. The designed hydrogel can detect different human motions like wrest bending, elbow motion, finger at one angle as well as at different angles, puffing, and chewing different things. The hydrogel can also act as a pressure sensor and shows a clear response towards constant and uniform pressure. The prepared hydrogel behaved as an electronic pen and connected the electronic surface with human skin. [Display omitted] • Ion-electron based conductive hydrogels for wearable strain sensor. • Sensor demonstrates great cycling stability, large stretchability, quick response times, and a high gauge factor. • The designed hydrogel exhibits outstanding qualities of mechanical toughness and strain 1630%. • Hydrogels were capable of detecting both small and large human movements. • The designed hydrogel successfully behave as an electronic pen. [ABSTRACT FROM AUTHOR]

Abstract: Conductive fabrics have achieved significant attention in the field of wearable electronics. Herein, a novel and simple method was developed to fabricate nickel-coated cotton fabrics. Triazine groups were bonded onto the cotton fabrics through treating by cyanuric chloride solution to absorb silver ions and to form a catalytical layer on the fabrics, which could successfully initiate the subsequent electroless deposition (ELD) of nickel (Ni). The cyanuric chloride concentration and ELD time were optimized. Compared to conventional methods, superior conductivity as well as good adhesion was obtained because of the stable affinity of triazine groups to metals. The surface conductivity of the as-prepared Ni-coated fabrics was as high as 21.82 S cm−1. The strain sensing properties of the Ni-coated fabrics were studied, demonstrating high sensitivity and rapid response. These attractive properties of the Ni-coated cotton fabrics suggest that the proposed method is expected to be used in the fabrication of wearable strain sensors.Graphical Abstract: [ABSTRACT FROM AUTHOR]

• A conductive cotton yarn was prepared using low-temperature sintering of silver. • The conductive yarn was characterized with high conductivity and flexibility. • The resultant conductive yarn could be used for motion detecting and electric heating. Flexible wearable textiles have attracted increasing attention, due to their potential applications in human motion detection, electric heating and humidity monitoring. However, the rigidity of metal materials contradicts the flexibility of textiles, and the complex preparation process and unfriendly environment hinder the development of metal materials as conductive materials of smart textiles. This study proposed a simple and environmentally friendly solution for smart textile preparation. Drawing on the bionic design principle of long-horned beetle's exocuticle, the conductive layer on the surface of cotton yarn (CY) was formed by sintering the silver paste under low temperature of 200 ˚C. Silver Paste (SP) mainly composed with silver particles, terpineol (TE) and ethyl cellulose (EC). The resultant conductive yarn was characterized with high flexibility and high conductivity (4.08 × 103 S/cm). The conductivity of the yarn increases under tensile force, while decreases under non-tensile bending action. The strain sensor prepared by the yarn has a wide working range and high sensitivity, with distinguish performances of signal output according to the motion of different human body parts. The sensing behavior was also highlighted with the capability of micro-vibration strain of the human body, such as response to the pulse and throat. Furthermore, the conductive property of sintered silver paste cotton yarn (SSP-CY) has the capability of electric heating. The electric heating device based on SSP-CY can realize wired and radio heating, which resulted a maximum temperature of about 41 ℃. Therefore, the novel conductive cotton yarn has great potential in the application of high-sensitive wearable electronic devices. [ABSTRACT FROM AUTHOR]

Huge electronic wastes motivated the flourishing of biodegradable electrically conductive cellulosic paper-based functional materials as flexible wearable devices. However, the relatively low sensitivity and unstable output in combination with poor wet strength under high moisture circumstances impeded the practical application. Herein, a superhydrophobic cellulosic paper with ultrahigh sensitivity was proposed by innovatively employing ionic sodium carboxymethyl cellulose (CMC) as bridge to reinforce the interfacial interaction between carbon black (CB) and multilayer graphene (MG) and SiO 2 nanoparticles as superhydrophobic layer. The resultant paper-based (PB) sensor displayed excellent strain sensing behaviors, wide working range (−1.0 %–1.0 %), ultrahigh sensitivity (gauge factor, GF = 70.2), and satisfied durability (>10,000 cycles). Moreover, the superhydrophobic surface offered well waterproof and self-cleaning properties, even stable running data without encapsulation under extremely high moisture conditions. Impressively, when the fabricated PB sensor was applied for electronic-skin (E-skin), the signal capture of spatial strain of E-skin upon bodily motion was breezily achieved. Thus, our work not only provides a new pathway for reinforcing the interfacial interaction of electrically conductive carbonaceous materials, but also promises a category of unprecedentedly superhydrophobic cellulosic paper-based strain sensors with ultra-sensitivity in human-machine interfaces field. [Display omitted] [ABSTRACT FROM AUTHOR]

To avoid conductive failure due to the cracks of the metal thin film under external loads for the wearable strain sensor, a stretchable metal/polymer composite film embedded with silver nanowires (AgNWs) was examined as a potential candidate. The combination of Ag film and AgNWs enabled the fabrication of a conductive film that was applied as a high sensitivity strain sensor, with gauge factors of 7.1 under the applied strain of 0−10% and 21.1 under the applied strain of 10−30%. Furthermore, the strain sensor was demonstrated to be highly reversible and remained stable after 1000 bending cycles. These results indicated that the AgNWs could act as elastic conductive bridges across cracks in the metal film to maintain high conductivity under tensile and bending loads. As such, the strain sensor engineered herein was successfully applied in the real-time detection and monitoring of large motions of joints and subtle motions of the mouth.

[Display omitted] • A silicone-enhanced polyvinyl alcohol (PVA) hydrogel sensor with three-dimensional (3D) microporous structure is designed. • Modest amino-polysiloxanes (APSi) can increase tensile strength and elongation of the PVA hydrogel by 765.06% and 250.0%, respectively. • The calculation results verify the existence of ionic interaction and hydrogen bond between APSi and phytic acid (PA). • The strain sensor could detect the joint activity with high sensitivity and good stability. Flexible wearable strain sensors based on hydrogels have become a research hotspot in recent years due to their advanced application in many fields. Currently, most hydrogel-based strain sensors exhibit poor mechanical properties and low sensitivity. In this work, a conductive hydrogel as a wearable strain sensor was developed based on dual crosslinked polyvinyl alcohol (PVA) networks. The PVA was the main skeleton of the hydrogel and the water-soluble amino-polysiloxane (APSi) introduced into this hydrogel was the secondary network. The APSi and PVA were locked together by phytic acid (PA), which improved the microstructure and enhanced the mechanical properties of the hydrogel. This was mainly reflected in the higher tensile strength (1.27 MPa), elongation at break (425.5%), electrical conductivity (0.975 S/m), linearity (R2 = 0.999) and tensile strain sensitivity (gauge factor (GF) of 2.29). The tensile strength (0.166–1.270 MPa) and elongation (170.2–425.5%) of the hydrogel can be regulated continuously by adjusting the amount of APSi. These silicone-enhanced PVA hydrogels have good biocompatibility and hence can be used as wearable strain sensors. [ABSTRACT FROM AUTHOR]

• A novel eutecto-/hydro-gel (EHG) is proposed for flexible wearable strain sensing. • Dynamic balance between hydration and dehydration endows EHG with super stability. • EHG shows excellent ionic conductivity, mechanical strength and transparency. • EHG containing photonic crystals (EHG-PC) enables visual and electronic sensing. • Dual-mode visual and electronic sensing work independently and complementarily. In recent years, hydrogels (HGs) have been extensively utilized as potential substrates for flexible wearable strain sensors, due to their excellent biocompatibility, stretchability and ease to incorporate various ionic /electronic conductive materials. However, water evaporation (i.e., dehydration) and low temperature intolerance severely restrain their sensing performance and lifetime. Eutectogels (EGs) as new emerging substrates, exhibit impressive low temperature tolerance and sound ionic conductivity, but they are prone to absorb water (i.e., hydration) in air and thus instable in morphology and ionic conductivity. Herein, we propose a novel concept of eutecto-/hydro-gel (EHG) with super stability, high ionic conductivity and transparency. As a proof-of-concept, we demonstrate the fabrication and strain sensing performance of a new EHG containing N -acryloyl glycinamide (NAGA), choline chloride (ChCl), glycerol (Gly) and water. EHG can maintain the dynamic balance between hydration and dehydration, and thus show much better long-term sensing performance. More importantly, we further show that flexible wearable visual and electronic strain sensor can be constructed by integrating photonic crystals into EHG. Due to the remarkable difference in sensing principles, the two sensing modes in this strain sensor can not only work properly without mutual interference, but also supplement each other to improve the sensing accuracy. The EHG material system and the fabrication strategy for dual-mode flexible wearable strain sensor provide a new solution for the development of high-performance flexible wearable devices. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) polyurethane (PU) sponges featuring high mechanical elasticity, compressibility, and durability have emerged as an ideal substrate for building wearable strain sensors. However, the 3D porous structures easily soak up rain, water vapor, sweat, etc., and the constructed sensor's long-term conductivity may be eroded by droplets and experience irreversible damage, rendering the preparation of a wearable flexible sponge sensor with environmental adaptation challenging. Here, by reducing the Ag particles in the carbon nanotube (CNT) suspension, forming a conductive filler Ag-CNTs, and combining with poly (vinylidene fluoride) (PVDF) solution, surface modification with polydimethylsiloxane (PDMS) solution, the PDMS/Ag-CNT-PVDF/PU sponge sensor with 3D conductive network and superhydrophobic structure was fabricated. The results revealed that this modified sponge had a wide strain detection range of 0–80 %, superior conductive sensitivity up to 4.24 kPa−1 in 0–20 kPa, and a fast and stable response time (170 ms) with great reproducibility over 1200 compression-resilience cycles. Furthermore, good superhydrophobicity endows the sensor with remarkable resistance to mechanical wear and chemical corrosion, which can be effectively used to detect human motion in high air humidity environment. This PDMS/Ag-CNTs-PVDF/PU sponge sensor is expected to be used as a practical, flexible wearable sensor and demonstrates potential application prospects in complex environments. [Display omitted] • The superhydrophobic conductive Ag-CNTs sponge was fabricated by simple dipping method. • The as-obtained sponge showed excellent self-cleaning, acid and alkali corrosion resistance, and wear resistance. • The sponge is conductively sensitive and could adapt to high air humidity environments to achieve external stimuli perception. [ABSTRACT FROM AUTHOR]