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A series of polyaniline (PANI) nanofibers were prepared as conductive fillers. A polyvinyl alcohol (PVA)/agarose (AG) double network hydrogel was used as a flexible substrate. A PANI/PVA/AG conductive hydrogel was prepared via in situ polymerization of polyaniline nanofibers in a PVA/AG double network hydrogel. The electrochemical performance of the PANI/PVA/AG hydrogel electrode material was linked to the fiber morphology of polyaniline. The doping of polyaniline with 0.020 mol L−1 citric acid demonstrated superior fiber morphology compared to doping with other citric acid concentrations, achieving fiber ratios of 80%. The specific capacitance of the PANI/PVA/AG hydrogel electrode materials doped with 0.020 mol L−1 citric acid was 285 mF cm−2, while the conductivity was 7.1 S m−1. The doping of polyaniline with 0.5 mol L−1 hydrochloric acid demonstrated superior fiber morphology compared to doping with other hydrochloric acid concentrations, achieving fiber ratios of 65%. The specific capacitance of PANI/PVA/AG hydrogel electrode materials doped with 0.5 mol L−1 hydrochloric acid was 249 mF cm−2, while their conductivity was 7.6 S m−1. After 500 cycles of charge–discharge, the specific capacitance retention of the material was 73%. Photosensitivity tests indicated that the hydrogel exhibited high sensitivity to shorter wavelengths of blue light (460 nm) and ultraviolet light (380 nm). The hydrogel sensor possessed high sensitivity to strain in the range of 0–120%. Gauge factors (GF) of the hydrogel strain sensor were 1.280, 2.141, 1.907, and 1.261 for strain ranges of 0–30%, 30–60%, 60–90%, and 90–120%, respectively. Cyclic strain tensile tests indicated that the relative resistance change rate (ΔR/R0) of the hydrogel sensor demonstrated a certain degree of repeatability and stability within the range of 0–100%. Thus, the hydrogel sensor is reliable and stable in the signal transmission process of detecting human movements as a flexible strain sensor. These results suggest that the PANI/PVA/AG conductive hydrogel is a multifunctional composite with good electrochemical storage performance, photosensitivity, and strain sensitivity that can be used in applications such as supercapacitors, flexible sensors and electronic wearable devices. [ABSTRACT FROM AUTHOR]

Robust adhesion is crucial for ionic hydrogels in flexible electronic pressure and strain sensors. Herein, we design a transparent and strong adhesion electronic pressure and strain sensor based on a multifunctional ionic hydrogel with double network using polyacrylamide (PAM) and gum arabic (GA). First, the effect of ionic type on the mechanical properties of hydrogels was measured. The GA/PAM–Fe3+ hydrogel with high extensibility (1835%) and toughness 1. 47 MJ / m 3 was selected as the best sensor material. Moreover, the GA/PAM–Fe3+ hydrogel has good adhesion property with various substrates, and the maximum peel strength of the hydrogel to skin could reach up to 123.9 N/m. Furthermore, the resistance of GA/PAM–Fe3+ hydrogel is sensitive to a wide strain window and the gauge factor shows stable and reliable change during deformation. Due to its compliant and excellent adhesive properties, strain sensors based on this hydrogel can be well fixed on the epidermis without adhesive tape, and can perceive large and gentle body movements. These characteristics demonstrate that GA/PAM–Fe3+ hydrogel is promising for a broad range of practical applications in wearable sensors. [ABSTRACT FROM AUTHOR]

Displacement is an important parameter for evaluating structural performance. However, the accurate measurement of global dynamic displacement remains a challenging task. To solve this problem, this paper proposes a global dynamic displacement reconstruction method for lattice tower structures, fusing limited acceleration and strain data. First, the strain-displacement mapping method for cantilever beams with variable cross-sections is presented and then extended to lattice towers. Thereafter, a modified multi-rate data fusion algorithm incorporating Kalman filtering and the proposed strain-displacement mapping methods is developed to fuse the acceleration and strain data to reconstruct the global dynamic displacement of the tower. The numerical simulation, model test and full-scale test demonstrate that the reconstructed dynamic displacements using the proposed method agree well with the reference values in both the time and frequency domains, and the parametric analysis has also been carried out, exhibiting great robustness and high reconstruction accuracy. [ABSTRACT FROM AUTHOR]

Hydrogel‐based wearable strain sensors have recently gained considerable interest due to their promising applications in real‐time health monitoring and motion detection. However, achieving integrated high‐stretchability, self‐adhesiveness, and long‐term water‐retaining property simultaneously in hydrogel systems remains a big challenge, which limits their applications in wearable electronics. Herein, a multifunctional hydrogel material designed is proposed for wearable strain sensors that can be manufactured by digital light processing (DLP) 3D printing technology. By tailoring the composition of chemically cross‐linked networks (ploy(acrylamide)/poly(acrylic acid)/poly(ethylene glycol) diacrylate), physically cross‐linked networks (ploy(acrylamide)/poly(acrylic acid)/poly(ethylene glycol) diacrylate/silk fibroin/glycerol/water) and microstructures on the surface, the 3D printed hydrogel exhibits promising superior and adjustable mechanical properties, tunable adhesion and good water‐retaining property simultaneously. In addition, through adding conductive ions, high ionic conductivity can also be achieved for stretchable sensing applications. Based on these integrated multifunctionalities, the 3D printed hydrogel is suitable for wearable strain sensors to detect various body motions. This work provides a prospect for 3D printable hydrogel systems with broad applications in wearable electronics. [ABSTRACT FROM AUTHOR]

This study presents the electrochemical reduction of graphene oxide (GO) to reduced graphene oxide (rGO) directly onto flexible interdigitated gold electrodes and its application as a strain sensor. GO reduction is achieved using cyclic voltammetry (CV). Remarkably, only a single CV cycle transformed GO into rGO to obtain low‐resistance (≈100 Ω) devices. The reduction of GO is confirmed using Raman spectroscopy and electrical measurements. rGO on flexible interdigitated gold electrodes exhibits graphene‐like characteristics when used as electrolyte‐gated field‐effect transistors. The fabricated devices display a gauge factor (GF) of ≈3.7 in the 0–794 με range. This value represents a substantial improvement, ≈60% higher than traditional metallic strain sensors, which have a GF of ≈2.1. Most importantly, the rGO strain sensor exhibits fast response (1.1 s) and recovery (0.92 s) times. The rGO sensor is mounted on a clamp with an adjustable diameter, which reveals exceptional flexibility and bendability without damage or degradation. These results highlight the potential of rGO for advancing strain‐sensing applications, offering promising opportunities for the future of this technology. [ABSTRACT FROM AUTHOR]

Soft strain sensors can accurately monitor the deformation of irregular and dynamic surfaces. However, traditional thin‐film strain sensors are generally not direction‐specific, and the sensor becomes unpredictable when stretched in different directions simultaneously. Here, a soft 1D strain sensor is reported that is only sensitive to axial deformation by rolling up a thin‐film strain sensor based on liquid metals (LM) and thermoplastic polyurethane (TPU) elastomer. The sensitivity of the 1D sensor can be regulated by rolling the 2D sensor at different angles. The 1D strain sensors have a large strain measuring range (>100%), high strain resolution (0.5%), fast responsiveness (<40 ms), and high reproducibility (over 2000 cycles), which are expected to adapt to various application scenarios with different sensitivity requirements. In addition, 1D strain sensors with different sensitivities can be braided into a three‐strand braid to provide measurements with three different sensitivities at the same time. [ABSTRACT FROM AUTHOR]

Highly sensitive strain sensors have been widely used in human motion monitoring, medical treatment, soft robots, and human–computer interaction, and the recycling of functional materials is in a huge demand for eco‐friendly and sustainable electronics. However, the manufacturing of recyclable strain sensors still remains challenging. Here, a semi‐wrapped structure based on silver nanowires and polyvinyl alcohol is proposed to realize a recyclable and stable strain sensor. It has shown excellent sensitivity, fast response, high stretchability and good environmental stability, and is successfully applied for human motion monitoring. In addition, a simple strategy is developed to effectively recycle silver nanowires in an eco‐friendly manner. The recyclable and stable strain sensor demonstrates potential applications in wearable and stretchable electronics, and the recycling strategy can be extended to other noble metal nanomaterials. [ABSTRACT FROM AUTHOR]

As the field of wearable electronics continues to expand, the integration of inorganic thermoelectric (TE) materials into fabrics has emerged as a promising development due to their excellent TE properties. However, conventional thermal methods for fabricating TE fabrics are unsuitable for wearable applications because of their high temperatures, resulting in rigid TE materials. Herein, a nonthermally fabricated silver selenide (Ag2Se) TE fabric is developed that can be effectively integrated into wearable applications. Ag2Se nanoparticles are densely formed within the fabric through a simple in situ chemical reduction process, resulting in remarkable electrical stability even after 10 000 cycles of mechanical deformation, such as stretching and compression. Notably, the fabricated Ag2Se TE fabric exhibits superior stretchability, stretching ≈1.36 times more than the thermally treated Ag2Se TE fabrics, while retaining its excellent electrical conductivity. Moreover, the TE unit exhibits 9.80 μW m−1 K−2 power factor, 134.45 S cm−1 electrical conductivity, and −26.98 μV K−1 Seebeck coefficient at 370 K. A haptic sensing glove based on the Ag2Se TE fabric as a sensor for detecting potential hazards is demonstrated. The glove effectively distinguishes between simple touch, physical pain, and high‐temperature hazards, ensuring user safety and prompt response. [ABSTRACT FROM AUTHOR]

Conductive hydrogels, characterized by their unique features of flexibility, biocompatibility, electrical conductivity, and responsiveness to environmental stimuli, have emerged as promising materials for sensitive strain sensors. In this study, a facile strategy to prepare highly conductive hydrogels is reported. Through rational structural and synthetic design, silver nanowires (AgNWs) are incorporated into poly(N‐acryloyl glycinamide) (PNAGA) hydrogels, achieving high electrical conductivity (up to 0.88 S m−1), significantly enhanced mechanical properties, and elevated deformative sensitivity. Furthermore, surface modification with polyhexafluoropropylene oxide (PHFPO) has substantially improved the water retention capacity and dressing comfort of this hydrogel material. Based on the above merits, these hydrogels are employed to fabricate highly sensitive wearable strain sensors which can detect and interpret subtle hand and finger movements and enable precise control of machine interfaces. The AgNWs/PNAGA based strain sensors can effectively sense finger motion, enabling the control of robotic fingers to replicate the human hand's gestures. In addition, the high deformative sensitivity and elevated water retention performance of the hydrogels makes them suitable for flow sensing. These conceptual applications demonstrate the potential of this conductive hydrogel in high‐performance strain sensors in the future. [ABSTRACT FROM AUTHOR]

This study explores a novel approach to obtaining 3D printed strain sensors, focusing on how changing the printing conditions can produce a different piezoresistive response. Acrylonitrile butadiene styrene (ABS) filled with different weight concentrations of carbon nanotubes (CNTs) was printed in the form of dog bones via fused filament fabrication (FFF) using two different raster angles (0–90°). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) in TUNA mode (TUNA-AFM) were used to study the morphological features and the electrical properties of the 3D printed samples. Tensile tests revealed that sensitivity, measured by the gauge factor (G.F.), decreased with increasing filler content for both raster angles. Notably, the 90° orientation consistently showed higher sensitivity than the 0° orientation for the same filler concentration. Creep and fatigue tests identified permanent damage through residual electrical resistance values. Additionally, a cross-shaped sensor was designed to measure two-dimensional deformations simultaneously, which is applicable in the robotic field. This sensor can monitor small and large deformations in perpendicular directions by tracking electrical resistance variations in its arms, significantly expanding its measuring range. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) semiconductor components have excellent physical attributes, such as excellent mechanical ductility, high mobility, low dielectric constant, and tunable bandgap, which have attracted much attention to the fields of flexible devices, optoelectronic conversion, and microelectronic devices. Additionally, one-dimensional (1D) semiconductor materials with unique physical attributes, such as high surface area and mechanical potency, show great potential in many applications. However, isolated 1D and 2D materials often do not meet the demand for multifunctionality. Therefore, more functionality is achieved by reconstructing new composite structures from 1D and 2D materials, and according to the current study, it has been demonstrated that hybrid dimensional integration yields a significant enhancement in performance and functionality, which is widely promising in the field of constructing novel electronic and optoelectronic nanodevices. In this review, we first briefly introduce the preparation methods of 1D materials, 2D materials, and 1D/2D heterostructures, as well as their advantages and limitations. The applications of 1D/2D heterostructures in photodetectors, gas sensors, pressure and strain sensors, as well as photoelectrical synapses and biosensors are then discussed, along with the opportunities and challenges of their current applications. Finally, the outlook of the emerging field of 1D/2D heterojunction structures is given. [ABSTRACT FROM AUTHOR]

The molten‐salt synthesis and electrochemical capacitive behaviors of porous carbon are reported using anthracite as the precursor. Upon synthesis, the binary KCl/K2CO3 molten salt not only exfoliates bulky anthracite to carbon nanosheets but also creates rich micro‐ and mesopores in the structure. The resulting porous carbon shows a large surface area of 1399.7 m2 g−1 and a total pore volume of 1.50 cm3 g−1. In 6.0 mol L−1 KOH aqueous electrolyte, it delivers a high specific capacitance of 245.6 F g−1 at a current density of 0.5 A g−1. Flexible micro‐supercapacitors with this porous carbon are assembled following an interdigitated design. The micro‐supercapacitor affords an area capacitance of 18.0 mF cm−2 and an energy density of 1.58 µWh cm−2 at a power density of 20 µW cm−2, and sustains 89.6% of the capacitance after 2000 cycles. Furthermore, the strain sensor fabricated by replacing the current‐collecting fluid at both ends of the electrode provides consistent and stable signal output, regardless of the degree of bending and the number of cycles. This study demonstrates the great potential of anthracite‐based porous carbon in flexible energy and electronic microdevices. [ABSTRACT FROM AUTHOR]

The rise of the metaverse concept has brought about widespread attention in wearable gesture recognition devices. Data gloves based on flexible strain sensors have been favoured by researchers owing to their low cost, light weight, direct and continuous monitoring of finger movements. In this review, we first compare the advantages and disadvantages of four different approaches based on the vision sensors, myoelectric sensors, inertial and magnetic sensors, and flexible strain sensors in designing data gloves, and demonstrate the superiority of the flexible strain sensor-based data glove used for metaverse applications. Next, some latest commercial data gloves are exampled and the function modules of the data gloves are presented based on the flexible strain sensors. Meanwhile, the potential applications of gesture recognition in the metaverse are summarized in diversified fields. Finally, the existing problems and development prospects of the current data gloves based on flexible strain sensors are concluded. We are optimistic that novel flexible strain sensor-based data gloves will make transformational impact to realize accurate, low-latency, and immersive gesture interaction in the metaverse. [ABSTRACT FROM AUTHOR]

Four-point bending tests have been widely applied for investigating flexural behavior of different materials. However, there are no guidelines or standards relating to four-point bending tests for pipes. A steel pipe with a diameter of 154 mm and 3.4-mm wall thickness was instrumented with distributed fiber-optic strain sensors and tested in four-point bending. The measured strains at the crown, springlines, and invert deviated from results calculated using beam theory. This strain deviation is investigated using numerical analyses, and it is found that local deformations along the length of the pipe due to concentrated loads at load and support locations contributed to the deviation. Parametric studies are conducted using different geometries of wood support blocks, specimen lengths, and pipe thicknesses to investigate their impact on the strain distribution with the pipe. Recommendations for reducing the strain deviation at the midspan of the specimen are given for four-point bending tests carried out on the steel pipes. [ABSTRACT FROM AUTHOR]

[Display omitted] Electrically conductive fiberfibre/fabric composites (ECFCs) are competitive candidates for use in wearable electronics. Therefore, it is essential to develop mechanically robust ECFC strain sensors with sensing performance. In this study, MXene assembly and hot-pressing were combined to prepare strong yet breathable ECFCs for strain and temperature sensing. Hydrogen bonding between MXene and polyurethane (PU) and ultrasonication-induced interfacial sintering were responsible for MXene nanosheets assembly on the PU nanofibers. MXene decoration made PU nanofibers electrically conductive, resulting in a conductive network. Hot-pressing improved interface adhesion among the conductive nanofibers. Thus, the mechanical properties of the nanofiber composites, including tensile strength, toughness and fracture energy, were enhanced. The nanofiber composites exhibited surface stability and durability. When the nanofiber composites were used as strain sensors, they showed breathability with a linear resistance response ranging from 1 % to 100 % and cycling stability. In addition, they produced stable sensing signals over 1000 cycles when a notch was present. They could also monitor temperature variations with a negative temperature coefficient (−0.146 %/°C). This study provides an interfacial regulation method for the preparation of multi-functional nanofiber composites with potential applications in flexible and wearable electronics. [ABSTRACT FROM AUTHOR]

Flexible sensors are garnering substantial interests for various promising applications, including medical electronics, environmental monitoring, and wearable devices. Developing a flexible sensor with high compliance, high sensitivity, and high reliability through the construction of a novel composite conductive hydrogel based on the synergistic enhancement effect of conductive polymers and metal ions is a remarkable achievement. Herein, an electronic/ionic‐conductive double network hydrogel (polypyrrole (PPy)/carboxymethyl cellulose (CMC)‐Al3+/polyvinyl alcohol (PVA)) with soft compliance, highly conductivity, and stability is presented. Moreover, owing to the synergistic reinforcement effect of the relatively immobilized "islands" of PPy particles and large amounts of movable "bridges" of aluminum ions (Al3+) within the double network hydrogel, the as‐optimized PPy/CMC‐Al3+/PVA composite gels exhibit excellent conductivity (σ = 3.47 ± 0.25 S m−1) and mechanical properties (E = 18.53 ± 0.67 kPa). Furthermore, it has been developed as strain sensors with relatively high linear sensitivity (gauge factor = 2.58) within a broad linearity range (0–400%). It can also be served as a monitoring devices for subtle physiological signals emanating from various parts of the human body. The robust sensor has great potential to be developed as wearable electronic devices and applied in healthcare monitoring fields. [ABSTRACT FROM AUTHOR]

In recent years, the research and development of various flexible wearable devices have rapidly advanced due to the continuous introduction of flexible electronic product. These devices have found applications in health monitoring, cardiovascularcare, internal and external workload, and more.Flexible sensors, being a vital component of flexible devices, determine the functionalities and performance capabilities of the devices. Metal nanomaterials, especially silver nanowires, are widely used in flexible sensors in past research due to their great advantages in flexibility and sensitivity. In this work, Silver nanowires with aspect ratios of 600, 1000, and 1400 were synthesized by adjusting the synergy of Br‐ and Cl‐, along with other process parameters, leading to an improved production efficiency of silver nanowires.The stability of the conductive network is enhanced when the aspect ratio of silver nanowires is 1000 and 1400.The sensor demonstrated high sensitivity at high strain, along with an extended strain range.Moreover, it was observed that increasing the aspect ratio of silver nanowires led to a more stable conductive network, thus enhancing the sensor's stability with over 10000 stretching cycles. under the appropriate deposition density, silver nanowires with aspect ratio of 600 have high sensitivity to low strain, and silver nanowires with aspect ratio of 1400 have high sensitivity to high strain, up to 247.3. Introducing microstructures on the surface of PDMS resulted in an increased maximum sensitivity of the sensor with decreasing microstructure size, reaching a maximum sensitivity of 322.2. [ABSTRACT FROM AUTHOR]

Developing emerging technologies in Internet of Things and artificial intelligence requires high-speed, low-power, high-sensitivity, and switchable-functionality strain sensors capable of sensing subtle mechanical stimuli in complex ambience. Resonant tunneling diodes (RTDs) are the good candidate for such sensing applications due to the ultrafast transport process, lower tunneling current, and negative differential resistance. However, notably enhancing sensing sensitivity remains one of the greatest challenges for RTD-related strain sensors. Here, we use piezotronic effect to improve sensing performance of strain sensors in double-barrier ZnO nanowire RTDs. This strain sensor not only possesses an ultrahigh gauge factor (GF) 390 GPa−1, two orders of magnitude higher than these reported RTD-based strain sensors, but also can switch the sensitivity with a GF ratio of 160 by adjusting bias voltage in a small range of 0.2 V. By employing Landauer–Büttiker quantum transport theory, we uncover two primary factors governing piezotronic modulation of resonant tunneling transport, i.e., the strain-mediated polarization field for manipulation of quantized subband levels, and the interfacial polarization charges for adjustment of space charge region. These two mechanisms enable strain to induce the negative differential resistance, amplify the peak-valley current ratio, and diminish the resonant bias voltage. These performances can be engineered by the regulation of bias voltage, temperature, and device architectures. Moreover, a strain sensor capable of electrically switching sensing performance within sensitive and insensitive regimes is proposed. This study not only offers a deep insight into piezotronic modulation of resonant tunneling physics, but also advances the RTD towards highly sensitive and multifunctional sensor applications. [ABSTRACT FROM AUTHOR]

Conductive hydrogels have potential applications in the field of wearable devices as carrier materials for flexible strain sensors. In this work, antifreeze filler glycerol (GL) and conductive filler graphene oxide (GO) were introduced into sodium polyacrylate (PAAS) chemical cross-linking network hydrogels, and the PAAS/GO/GL antifreeze conductive hydrogels were prepared by one-pot method. The structures and properties of the hydrogels were characterized and tested. The results showed that the addition of GO improved the mechanical properties and conductivity of the hydrogel. When the addition of GO was 0.6 wt%, the tensile strength of PAAS/GO/GL hydrogel reached the maximum of 0.215 MPa, the corresponding elongation at break reached 1180%, and the conductivity reached 1.056 S·m−1 at room temperature. The addition of GL resulted in good freezing resistance and moisture retention of the hydrogel, with a conductivity of 0.846 S·m−1 even after freezing at −20 °C. The PAAS/GO/GL hydrogel showed good sensing performance. When the tensile deformation reached 600%, the gauge factor (GF) reached 10.82. In addition, PAAS/GO/GL hydrogel also has good self-healing and adhesion, which has potential application value in flexible wearable sensors. [ABSTRACT FROM AUTHOR]

3D printing technology has driven the development of flexible and stretchable electronic devices. In this field, silver‐based silicone rubber composites have emerged as promising materials due to their commendable conductivity, stretchability, and printability. However, the manufacturing of stretchable silver electrode materials at room temperature faced significant challenges, including intricate ink preparation methods, phase separation requiring high‐temperature annealing, and subpar conductivity. To address these issues, SP‐RTV ink was developed by mechanically blending room‐temperature vulcanized silicone rubber (RTV) with commercial conductive silver paste (SP). Subsequently, the 3D‐printed SP‐RTV electrodes were both stretchable and curable at room temperature, demonstrating excellent conductivity across various substrates. By optimizing the ink ratio, we achieved outstanding electrical conductivity of 5.17 × 105 S/m for the SP‐RTV electrode comprising 90 wt% silver paste. Moreover, the SP‐RTV electrodes containing 70 wt% silver paste exhibited excellent stretchability of 110% along with a gauge factor of 14.87, making them suitable for detecting finger and wrist movements. Additionally, the 80 wt% SP‐RTV maintained stable relative resistance changes during stretching, positioning it aptly for intrinsic stretchable organic electrochemical transistor applications. Overall, this study offers valuable insights into the room‐temperature manufacturing of flexible electrodes, paving the way for advancements in this burgeoning field. [ABSTRACT FROM AUTHOR]

Flexible strain sensors capable of acquiring tiny mechanical signals and attaching to various irregular surfaces are becoming prevalent in physiological measurement, soft robotics, and human‐machine interaction. However, the advancement of flexible strain sensors is substantially impeded by the intrinsic compromise between sensitivity and the range of detectable signals. Inspired by the multilayer structure of nacre in nature, a carbon nanotubes (CNTs)/graphene (GR)/graphene (GR)/thermoplastic polyurethane (TPU) mat (CGGTM) is prepared by electrospinning and high‐pressure spraying technology. By designing a multilayer structure with mutually non‐interfering conductive networks, the resulting CGGTM possesses a low detection limit (0.05% strain), high sensitivity (gauge factor, GF > 152537), large detection range (up to 364% strain), fast response/recovery time (80 ms/100 ms), and excellent cyclic durability (up to 1000 cycles). Furthermore, the CGGTM also exhibits satisfactory triboelectric performances when assembled into a triboelectric nanogenerator (TENG, 3 × 3 cm2), including high triboelectric output (open‐circuit voltage Voc = 135.4 V, short‐circuit current Isc = 1.25 µA) and power density (88 mW m−2), enabling reliable power supply, self‐powered sensing, and pulse monitoring capability. Finally, CGGTM is successfully applied to the collection of biological signals and multi‐gesture motion recognition assisted by machine learning algorithms, which holds promise for intelligent interaction with gestures in the future. [ABSTRACT FROM AUTHOR]

The one-step direct laser writing process has been an efficient strategy for constructing flexible metal structures. However, the effect of laser wavelength on the structuring process remains unclear, thus restricting the universal manufacturing process development. In this work, the feasibility of one-step writing of flexible Cu structures with different wavelength continuous diode lasers has been verified. Here, photothermal reactions dominate in the decomposition of the reducing agent to form copper structures. Differences in the wavelength primarily affect the photothermal reaction amplitude for structuring, resulting in a variation in the formation of Cu structures. Under our processing conditions, the photothermal reaction induced by 532 nm laser is higher than 808 nm laser, a higher reduced-joining degree of the Cu structure can be achieved by 532 nm laser. This results in a superior conductivity, adhesion, and bendability of Cu structures fabricated by 532 nm laser than that of 808 nm laser. Furthermore, strain sensors that can detect different bending angles and bending frequencies have been fabricated by 532 nm laser-written structures to demonstrate their practical applications. [ABSTRACT FROM AUTHOR]

Integrating superior mechanical performance, anisotropic conductivity, and biocompatibility into conductive hydrogels as all‐in‐one human‐machine interaction device remains challenging. Herein, by mimicking the anisotropic structures of human muscles, a robust anisotropic conductive hydrogel is developed by initially aligning polyvinyl alcohol with polypyrrole decorated cellulose nanofibrils to form an anisotropically oriented polymer networks, followed by post‐crosslinking with tannic acid (TA). Introducing TA into hydrogel network permanently secures its hierarchically anisotropic structure through multiple hydrogen bonds, thus endowing the hydrogel with exceptional mechanical properties (tensile strength of 11.41 MPa, toughness of 12.44 MJ m−3), anisotropic adhesive property, and direction‐dependent conductivity. With these attributes, a hydrogel strain sensor with excellent multidirectional sensitivity is developed, enabling stable monitoring of multi‐degrees of freedom joint movements in the human body and facilitating the control of a multiaxial virtual robot manipulator. Moreover, the in vitro/vivo tests demonstrate exceptional biocompatibility and anti‐biofouling properties of the as‐prepared hydrogel sensor, maintaining stable electronic response signals for over 14 days after successful implantation into the Achilles tendon of mice. Overall, this study presents a promising approach for designing conductive hydrogels with superior mechanical properties and anisotropic functionality for emerging applications in both in vitro and in vivo human‐machine interface materials. [ABSTRACT FROM AUTHOR]

Some creatures have periodic nanostructures and chromophores in their flexible organs that allow them to control the color and shape of their skin. Artificial photonic structures that can mimic the aforementioned ability of these natural structures are researched extensively. In this study, polydopamine‐incorporated core–interlayer–shell (CIS‐PDA) nanoparticles capable of shape reconfiguration and expressing vivid structural colors are designed. These nanoparticles can be readily assembled to produce colloidal photonic crystals (CPhCs) and can exhibit vivid structural colors by virtue of their light‐absorbing capability. Soft CPhC films prepared with these nanoparticles undergo stable elastic deformation at 15% strain and exhibit mechanochromic properties. Specifically, the PDA in the CIS nanoparticles can absorb broadband light and exhibit a photothermal effect resembling that of melanosomes in living organisms, which enables self‐healing between multiple CPhC films. Due to their favorable properties, the CPhC films prepared in this study represent promising photothermally reconfigurable photonic materials. Moreover, arbitrarily shaped 2D or 3D surfaces are conformally coated with the films via microimprinting or vacuum wrapping, courtesy of the reconfigurability of these films. These findings suggest that CPhC films prepared with CIS‐PDA nanoparticles can be used as form‐free mechanochromic strain sensors and nonfading optical films for industrial products. [ABSTRACT FROM AUTHOR]

The following work explores the creation and advancement of a highly sensitive piezoresistive strain sensor. This sensor is composed of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with a layer of interconnected Ni microparticles (NiMPs) on its surface. The interconnection of NiMPs was achieved through a new simple and cost-effective method using a magnetic bar. Additionally, the elasticity of the PEDOT:PSS membrane is enhanced by incorporating polyvinyl alcohol (PVA). The piezoresistive strain sensor, consisting of PEDOT:PSS, PVA, and NiMPs, was examined to assess its electrical signal, stability, and response time under various strains and bending angles, ranging from 0 to 28%. This range covers typical human body movements. The results demonstrated that the pristine PEDOT:PSS membrane has no piezoresistive effect, while the modified one with NiMPs, it shows a gauge factor value of 174 at high strain levels. Additionally, the sensor's performance was tested with human finger motions, revealing a significant response to changes in finger movement. The modified method of evenly distributing metallic particles can be used with various magnetic particles such as iron, cobalt, steel, or manganese. [ABSTRACT FROM AUTHOR]

Non-contact and full-field strain mapping captures strain across an entire surface, providing a complete two-dimensional (2D) strain distribution without attachment to sensors. It is an essential technique with wide-ranging applications across various industries, significantly contributing to experimental mechanics and structural health monitoring. Although there have been reviews that focus on specific methods, such as interferometric techniques or carbon nanotube-based strain sensors, a comprehensive comparison that evaluates these diverse methods together is lacking. This paper addresses this gap by focusing on strain mapping techniques specifically used in experimental mechanics and structural health monitoring. The fundamental principles of each method are illustrated with specific applications. Their performance characteristics are compared and analyzed to highlight strengths and limitations. The review concludes by discussing future challenges in strain mapping, providing insights into potential advancements and developments in this critical field. [ABSTRACT FROM AUTHOR]

Nowadays, conductive hydrogels show significant prospects as strain sensors due to their good stretchability and signal transduction abilities. However, traditional hydrogels possess poor anti-freezing performance at low temperatures owing to the large number of water molecules, which limits their application scope. To date, constructing a hydrogel-based sensor with balanced stretchability, conductivity, transparency, and anti-freezing properties via simple methods has proven challenging. Here, a fully physically crosslinked poly(hydroxyethyl acrylamide)–glycerol–sodium chloride (PHEAA–Gl–NaCl) hydrogel was obtained by polymerizing hydroxyethyl acrylamide in deionized water and then soaking it in a saturated NaCl solution of glycerol and water. The PHEAA–Gl–NaCl hydrogel had good transparency (~93%), stretchability (~1300%), and fracture stress (~287 kPa). Owing to the presence of glycerol and sodium chloride, the PHEAA–Gl–NaCl hydrogel had good anti-freezing properties and conductivity. Furthermore, the PHEAA–Gl–NaCl hydrogel-based strain sensor possessed good sensitivity and cyclic stability, enabling the detection of different human motions stably and in a wide temperature range. Based on the above characteristics, the PHEAA–Gl–NaCl hydrogel has broad application prospects in flexible electronic materials. [ABSTRACT FROM AUTHOR]

A biomimetic strain sensor was designed and constructed based on Ir nanoparticles-modified multi-wall carbon nanotubes (Ir NPs@MWCNTs) and parallel Pt layer/dragon skin with carbonized butterfly wing patterns. This sensor exhibits high gauge factor (∼515.4), extensive tensile range (0%–96%), and swift response (∼300 ms), especially remarkable stability up to 60 000 cycles. The work mechanism has been proposed based on the experimental test and finite-element method. Some important applications such as human motion and micro-expression recognition have been confirmed using 3 × 3 flexible biomimetic sensor array. [ABSTRACT FROM AUTHOR]

Poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) is a promising material for organic thermoelectric (TE) applications. However, it is challenging to achieve PEDOT: PSS composites with stretchable, self‐healable, and high TE performance. Furthermore, some existing self‐healing TE materials employ toxic reagents, posing risks to human health and the environment. In this study, a novel intrinsically self‐healable and wearable composite is developed by incorporating environmentally friendly, highly biocompatible, and biodegradable materials of polyvinyl alcohol (PVA) and citric acid (CA) into PEDOT: PSS. This results in the formation of double hydrogen bonding networks among CA, PVA, and PEDOT: PSS, inducing microstructure alignment and leading to simultaneous enhancements in both TE performance and stretchability. The resulting composites exhibit a high electrical conductivity and power factor of 259.3 ± 11.7 S·cm−1, 6.9 ± 0.4 µW·m−1·K−2, along with a tensile strain up to 68%. Furthermore, the composites display impressive self‐healing ability, with 84% recovery in electrical conductivity and an 85% recovery in tensile strain. Additionally, the temperature and strain sensors based on the PEDOT: PSS/PVA/CA are prepared, which exhibit high resolution suitable for human–machine interaction and wearable devices. This work provides a reliable and robust solution for the development of environmentally friendly, self‐healing and wearable TE thermoelectrics. [ABSTRACT FROM AUTHOR]

Stretchable film strain sensors show potential applications in healthcare and human‐machine interfacing, while poor signal linearity restricts their practical applications owing to inaccurate and instable strain indication. Signal sensitivity and linearity can be improved via constructing hetero‐modulus microstructure on elastomeric substrate to some extent, though it is challenging to construct hetero‐structure with distinct modulus differences for electrical signal linearity modulation over a wide strain range. Herein, a simple strategy is proposed to tune signal sensitivity, linearity, and detection range of stretchable strain sensors by adjusting the distribution of rigid polystyrene (PS) nanospheres coated on electrospun thermoplastic polyurethane (TPU) fiber mats. Heterostructure characteristics can be controlled by spray coating times of PS nanospheres, which are immobilized onto the fiber mats by weak swelling of TPU and the linking layer of reduced graphene oxide (rGO) between TPU and PS induced by hydrogen bonding and π–π stacking. Relatively, the sensors with moderate spray coating times of PS nanospheres show balanced signal sensitivity and linearity over a strain range of 0–80%, as well as fast response to tensile strain and good signal reproducibility. Such elastomeric film strain sensors can be used for monitoring physiological activities and interfacing human hand and bionic fingers. [ABSTRACT FROM AUTHOR]

Monitoring stress and strain at the critical details of steel bridges is essential for ensuring structural integrity. This study introduces a three‐layer flexible strain sensor produced through a spraying process, using flake‐shaped silver‐coated copper powder as the conductive filler and modified acrylic emulsion as the matrix material. The study investigated the impact of size parameters on sensor sensitivity, determining optimal dimensions of 20 mm in length, 2 mm in width, and an initial resistance value ranging from 1.0 Ω to 1.8 Ω. Analysis of the optimized sensor's performance unveiled high sensitivity and linear response capabilities under low strain conditions with a gauge factor (GF) value of up to 25.6 and a linear correlation coefficient R2 ≥ 0.971 under 300 με. Notably, the sensor exhibits an extremely low strain detection limit of 0.005% and a broad response range spanning from 0.005% to 0.19% strain. It demonstrates swift response and recovery times of 500–800 ms, showcases directional strain response, exhibits good repeatability, and endures durability tests (withstanding 3000 cycles). Furthermore, a fitting formula is proposed to accurately depict the strain and relative resistance change relationship across a wide response range. The study and initial application of this sensor's sensing characteristics and performance signify its potential for practical engineering applications. [ABSTRACT FROM AUTHOR]

The iron-containing porphyrin heme is of high interest for the food industry for the production of artificial meat as well as for medical applications. Recently, the biotechnological platform strain Corynebacterium glutamicum has emerged as a promising host for animal-free heme production. Beyond engineering of complex heme biosynthetic pathways, improving heme export offers significant yet untapped potential for enhancing production strains. In this study, a growth-coupled biosensor was designed to impose a selection pressure on the increased expression of the hrtBA operon encoding an ABC-type heme exporter in C. glutamicum. For this purpose, the promoter region of the growth-regulating genes pfkA (phosphofructokinase) and aceE (pyruvate dehydrogenase) was replaced with that of PhrtB, creating biosensor strains with a selection pressure for hrtBA activation. Resulting sensor strains were used for plate-based selections and for a repetitive batch f(luorescent)ALE using a fully automated laboratory platform. Genome sequencing of isolated clones featuring increased hrtBA expression revealed three distinct mutational hotspots: (i) chrS, (ii) chrA, and (iii) cydD. Mutations in the genes of the ChrSA two-component system, which regulates hrtBA in response to heme levels, were identified as a promising target to enhance export activity. Furthermore, causal mutations within cydD, encoding an ABC-transporter essential for cytochrome bd oxidase assembly, were confirmed by the construction of a deletion mutant. Reversely engineered strains showed strongly increased hrtBA expression as well as increased cellular heme levels. These results further support the proposed role of CydDC as a heme transporter in bacteria. Mutations identified in this study therefore underline the potential of biosensor-based growth coupling and provide promising engineering targets to improve microbial heme production. [ABSTRACT FROM AUTHOR]

As a soft material with biocompatibility and stimulation response, ionic conductive hydrogel‐based wearable strain sensors show great potential across a wide spectrum of engineering disciplines, but their mechanical toughness is limited in practical applications. In this study, freeze‐thawing techniques were utilized to fabricate double‐network hydrogels of poly(vinyl alcohol)/polyacrylamide (PVA/PAM) with both covalent and physical cross‐linking networks. These double‐network hydrogels demonstrate excellent mechanical performance, with an elongation at break of 2253% and tensile strength of 268.2 kPa. Simultaneously, they also display a high sensitivity (Gage factor, GF = 2.32 at 0%–200% strain), achieve a rapid response time of 368 ms without the addition of extra conductive fillers or ions, stable signal transmission even after multiple cycles, and fast response to human motion detection. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors are crucial force‐sensitive devices in wearable electronics, robotics, and other fields due to their stretchability, high sensitivity, and easy integration. However, a limitation of existing pressure sensors is their reduced sensing accuracy when subjected to stretching. This study addresses this issue by adopting finite element simulation optimization, using digital light processing (DLP) 3D printing technology to design and fabricate the force‐sensitive structure of flexible pressure sensors. This is the first systematic study of how force‐sensitive structures enhance tensile strain stability of flexible resistive pressure sensors. 18 types of force‐sensitive structures have been investigated by finite element design, simultaneously, the modulus of the force‐sensitive structure is also a critical consideration as it exerts a significant influence on the overall tensile stability of the sensor. Based on simulation results, a well‐designed and highly stretch‐stable flexible resistive pressure sensor has been fabricated which exhibits a resistance change rate of 0.76% and pressure sensitivity change rate of 0.22% when subjected to strains ranging from no tensile strain to 20% tensile strain, demonstrating extremely low stretching response characteristics. This study presents innovative solutions for designing and fabricating flexible resistive pressure sensors that maintain stable sensing performance even under stretch conditions. [ABSTRACT FROM AUTHOR]

The sense of touch and perception of hand motion form an essential part of the somatic sensory system. Although piezoelectric sensors demonstrate high sensitivity and linearity, they are traditionally not employed for electronic skins because of their limited stretchability. Here, a printed, skin‐conformal, electronic system consisting of stretchable piezoelectric pressure sensors and carbon nanotube strain gauges capable of identifying tactile sensations and joint movements on the hand is introduced. The pressure sensor demonstrates both high sensitivity (19.9 mV kPa−1) and linearity (0.1–1000 kPa) while being reliably stretchable to above 15%. To complement the pressure sensing functionality, a strain gauge is fabricated in a rapid stamp printing process and designed to demonstrate excellent mechanical reliability with up to 70% strain and high sensitivity (36.5‐gauge factor). These sensors can seamlessly conform to numerous anatomical regions and cover wide areas of the skin, making them ideal for deployment in an electronic skin. Finally, the sensors are integrated with a flexible microelectronic device to demonstrate their functionality in human touch and prosthetic hand applications. [ABSTRACT FROM AUTHOR]

Wearable technology refers to the devices that are integrated with textiles, or implanted in the body or plants for smart monitoring. Hence, this wearable technology has attracted tremendous attention from researchers globally due to its smart functions to be useful for mankind. The key target of this review is to examine the potential of rubber composite materials for such wearable devices. The rubber composites reviewed explore silicone rubber as a rubber matrix (SR). Another objective includes the use of multi‐walled carbon nanotubes (MWCNTs) in pristine and functionalization forms explored as reinforcing fillers. Moreover, prospects of CNT including their structure, properties, and types are explored both in pristine and functionalized state are reviewed. Following this, the mechanical, and electrical, properties of such composites are reviewed. The reported results show that the reinforcing properties are strongly improved by adding functional groups to CNT in rubber composite. These improvements in reinforcing properties are assisted by the functional groups like carboxyl (OH), carbonyl (CO), epoxy, and alkoxy (CO) on the surface of filler are useful. They assist in improving the filler‐rubber compatibility thereby improving filler dispersion and thus finally mechanical and electrical properties. Following this, such improved properties are explored for specific real‐time wearable technologies. This real‐time monitoring includes nursing plant pulse growth monitoring, health monitoring, and humidity sensors. The review further proposes that the functionalized CNTs can be useful for obtaining robust real‐time strain‐sensing monitoring. Moreover, it assists in obtaining sharp response time, strain sensitivity, and good stretchability. Finally, the prospects and challenges are explored discussing the real‐time monitoring of these sensors. Highlights: Configurations for nursing plant growth and other monitoring parameters are reviewed.The properties of pristine and functionalized carbon nanotubes reinforced silicone rubber for wearable technology were reviewed.The mechanical, and electrical aspects of functionalized carbon nanotubes were comparatively reviewed.Applications such as wearable strain sensors, humidity sensors, and wearable plant pulse monitoring sensors were reported. [ABSTRACT FROM AUTHOR]

A fully biodegradable, ultra‐sensitive, and soft strain sensor is pivotal for temporary, real‐time monitoring of microdeformations, crucial in disease diagnosis, surgical precision, and prognosis of muscular, and vascular conditions. Nevertheless, the strain sensitivity of previous biodegradable sensors, denoted by gauge factor (GF) up to ≈100, falls short of requirements for complex biomedical monitoring scenarios, specifically monitoring cardio‐cerebrovascular diseases with microscale variations in vascular surface strain. Here, a fully biodegradable, ultra‐sensitive crack‐based flexible strain sensor is introduced achieving GF of 1355 at 1.5% strain through integration of molybdenum (Mo) film, molybdenum trioxide (MoO3) adhesion layer, and polycaprolactone (PCL) substrate. Analysis of crack morphology of biodegradable thin‐film metals, including Mo, tungsten (W), and magnesium (Mg), reveals material‐dependent sensitivity and repeatability of crack‐based strain sensors. The effect of the adhesion layer and polymer substrate is also investigated. Overall morphological studies on the sensor present a comprehensive understanding of metal film cracking behavior and corresponding performance characterization, showing significant potential for highly sensitive sensors. A hybrid membrane composed of candelilla wax (Cw), beeswax (Bw), and polybutylene adipate‐co‐terephthalate (PBAT) is introduced to provide hydrophobic, yet flexible encapsulation. In vivo, short‐term (≈3 days) monitoring of vascular pulsatility underscores the potential of the sensing tool for rapid, accurate, and temporal disease diagnosis and treatment. [ABSTRACT FROM AUTHOR]

Interest in flexible photonics has been motivated by the development of artificial smart skins. In particular, coupling of photonics and mechanics can offer opportunities to realize ultrasensitive strain sensor, however, low‐cost fabrication of flexible sensing device with desired photonic functionality remains a challenge. Hereby, the study reports an ultrasensitive strain‐gauge sensor based on the poly(ethylenenaphthalate (PEN))/monocrystal Au/MgF2/CsPbBr3 nanorod/Al2O3/polyacrylonitrile (in short P/mAu/M/CPB@Al2O3@PAN), which are sensitive to nanoscale structure alterations of PEN substrate via the stress response of the single‐mode laser based on the piezoelectric‐effect. Wherein a low‐threshold single‐mode lasing (Pth ≈ 170 nJ cm−2) is achieved through coating Al2O3 on the CsPbBr3 nanorod, producing the higher quality factor (Q ≈ 1637) to guarantee a much higher sensitivity in sensing application. Reversible spectral regulating of ≈3 nm in single‐mode‐lasing wavelength, with a subnanometre scale resolution <0.4 nm and the wavelength sensitivity (Sλ) as high as 160 nm RIU−1, is validated in response to applied strain ranging from −1.31% to 1.31%. This work not only represents essential progress in construction of ultrasensitive and cost‐effective flexible photonic sensor, but also lays the foundation for the potential application in smart photonic skins. [ABSTRACT FROM AUTHOR]

Flexible strain sensors are of great significance in health monitoring, wearable electronic devices, intelligent robot sensing, and other fields. Most of the reported works focus on the enhancement of sensitivity or working range, while linearity is ignored and exhibits strong nonlinearity. Conflict among performances remains a serious challenge for the development of flexible strain sensors. Herein, inspired by the architecture of butterfly's wings, a strain sensor with double conductive layers and wrinkles/holes structures is proposed. The fabricated sensor shows a high linearity of >0.98 over a full working strain range of 120%, and a linearity of up to 0.999 within a strain range of 0%–30%. Apart from that, the sensor also presents a sensitivity of 8.28, high stability over 40 000 cycles when subjected to a full‐scale strain, as well as a water contact angle of >167.4°. Meanwhile, strains as low as 0.075% can be identified, while a maximum frequency of 40 Hz can be responded to for the sensor. It is demonstrated that the sensor is capable of enabling flexible grippers to sense and monitor the motions of underwater vehicles, indicating its greater potential for diverse applications, such as human–machine interaction, marine environmental protection, and biological research. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-parameter strain/displacement safety monitoring technology for railway tunnel lining structures. An integrated monitoring system with FBG (Fiber Bragg grating) and VDM (video displacement meter) components was used to monitor both the strain and deformation of the tunnel cross-section. Initially, a comprehensive experimental study was carried out using FBG strain sensors with temperature-compensated grating. The temperature-compensated grating was used to further improve the monitoring accuracy. The data show that the stability and accuracy were better than the traditional electronic strain sensor. Secondly, high-precision and multipoint monitoring of railway tunnel lining deformation was achieved by using VDM technology. Three months of case study results taken from the Gansu Railway Tunnel in China demonstrated a tunnel cross-section strain accuracy for microstrain and crown deformation at the submillimeter level, respectively. The technology provides a new high-precision way to monitor the condition of tunnel lining structures. [ABSTRACT FROM AUTHOR]

The work is devoted to the consideration of methods for determining the strain of objects using fiber Bragg gratings under a high-frequency vibration or pulsed mechanical action, which is difficult to perform using widespread methods and devices. The methods are based on numerical processing of the time dependence of the radiation power reflected from the fiber Bragg grating at various wavelengths, which makes it possible to measure strain parameters in a wide range of magnitude and frequencies. The efficiency of the proposed methods is demonstrated by numerical simulation. It is shown that it is possible to restore the strain dependence on time in the range ± 1000   μ ϵ or more from simultaneously measured power dependencies reflected by the fiber Bragg grating using common fiber-optic components. The case of sequential registration of reflected radiation power at different wavelengths to determine the probability density of the distribution of the strain values is also considered. The results of signal processing obtained both by numerical simulation and experimentally for the case of a linear vibration are presented. The technical problems of using the proposed methods are discussed. [ABSTRACT FROM AUTHOR]

A robust strain sensor is demonstrated based on a microfiber Mach–Zehnder interferometer (MMZI) encapsulated by the polymer polydimethylsiloxane (PDMS). Benefiting from the low Young's modulus of PDMS, both a robust structure and high sensitivity can be realized based on three different encapsulations. In the experiment, the proposed sensors are fabricated and tested with strain sensitivities ranging from −20.95 pm/με to 127.00 pm/με within the wavelength range of 1200–1650 nm. Compared with the bare MMZI sensor, at least one order of magnitude higher sensitivity is reached. To further evaluate the performance of the sensor, the dependences of sensitivity on probing wavelength and the different types and quantities of polymers used in encapsulation are discussed. Results show that the sensitivity of the sensor will increase with the probing wavelength. The type and quantity of polymer used are also very critical to sensitivity. Additionally, a response time of 24.72 ms can be reached. Good recoverability and repeatability of the sensor are also demonstrated by repeated experiments. The strain sensor demonstrated here shows the advantages of simple fabrication, robust structure, high and tunable sensitivity, fast response, good recoverability and repeatability. [ABSTRACT FROM AUTHOR]

Recently, eutectogels have emerged as ideal candidates for flexible wearable strain sensors. However, the development of eutectogels with robust mechanical strength, high stretchability, excellent transparency, and desirable conductivity remains a challenge. Herein, a covalently cross-linked eutectogel was prepared by exploiting the high solubility of oligoethylene glycol in a polymerizable deep eutectic solvent (DES) form of acrylic acid (AA) and choline chloride (ChCl). The resulting eutectogel exhibited high transparency (90%), robust mechanical strength (up to 1.5 MPa), high stretchability (up to 962%), and desirable ionic conductivity (up to 1.22 mS cm−1). The resistive strain sensor fabricated from the eutectogel exhibits desirable linear sensitivity (GF: 1.66), wide response range (1–200%), and reliable stability (over 1000 cycles), enabling accurate monitoring of human motions (fingers, wrists, and footsteps). We believe that our DES-based eutectogel has great potential for applications in wearable strain sensors with high sensitivity and reliability. [ABSTRACT FROM AUTHOR]

High electrical conductivity, along with high piezoresistive sensitivity and stretchability, are crucial for designing and developing nanocomposite strain sensors for damage sensing and on-line structural health monitoring of smart carbon fiber-reinforced polymer (CFRP) composites. In this study, the influence of the geometric features and loadings of carbon-based nanomaterials, including reduced graphene oxide (rGO) or carbon nanofibers (CNFs), on the tunable strain-sensing capabilities of epoxy-based nanocomposites was investigated. This work revealed distinct strain-sensing behavior and sensitivities (gauge factor, GF) depending on both factors. The highest GF values were attained with 0.13 wt.% of rGO at various strains. The stability and reproducibility of the most promising self-sensing nanocomposites were also evaluated through ten stretching/relaxing cycles, and a distinct behavior was observed. While the deformation of the conductive network formed by rGO proved to be predominantly elastic and reversible, nanocomposite sensors containing 0.714 wt.% of CNFs showed that new conductive pathways were established between neighboring CNFs. Based on the best results, formulations were selected for the manufacturing of pre-impregnated materials and related smart CFRP composites. Digital image correlation was synchronized with electrical resistance variation to study the strain-sensing capabilities of modified CFRP composites (at 90° orientation). Promising results were achieved through the incorporation of CNFs since they are able to form new conductive pathways and penetrate between micrometer-sized fibers. [ABSTRACT FROM AUTHOR]

A multifunctional sensor comprising flexible and transparent ultraviolet (UV) photodetectors (PDs) with strain gauges based on Ag nanowire (AgNW)@ZnO nanorods (ZnONRs) was fabricated using a cost-effective, simple, and efficient method. High-aspect ratio silver nanowires were synthesized using the polyol method. An AgNW@ZnONR composite was formed via the hydrothermal method to ensure the multifunctional capability of the flexible sensors. After refining the process parameters, the size of the ZnO nanorods was decreased to fabricate pliable multifunctional sensors using AgNW@ZnONRs. At a deposition of 0.207 g of AgNW@ZnONRs, the sensor achieves its maximum switching ratio and fastest response time under conditions of 2000 μW/cm2 UV optical power density. With a ton (rise time) of 2.7 s and a toff (fall time) of 2.3 s, the ratio of Ion to Ioff current is 1151. Additionally, the sensor's maximum optical current value correlates linearly with UV light's power density. The maximum response current increased from 222.5 pA to 588.1 pA, an increase of 164.3%, when the bending angle was increased from 15° to 90° for the sensor with a deposition of 0.276 g of AgNW@ZnONRs. There was no degradation in the response of the sensors after 10,000 bending cycles, as they have excellent stability and repeatability, which means they can meet the requirements of wearable sensor applications. Therefore, there is great potential for the practical application of multifunctional AgNW@ZnONRs in flexible sensors. [ABSTRACT FROM AUTHOR]

The flexible electronic sensor is a critical component of wearable devices, generally requiring high stretchability, excellent transmittance, conductivity, self‐healing capability, and strong adhesion. However, designing ion‐conducting elastomers meeting all these requirements simultaneously remains a challenge. In this study, a novel approach is presented to fabricate highly stretchable, transparent, and self‐healing ion‐conducting elastomers, which are synthesized via photo‐polymerization of two polymerizable deep eutectic solvents (PDESs) monomers, i.e., methacrylic acid (MAA)/choline chloride (ChCl) and itaconic acid (IA)/ChCl. The as‐prepared ion‐conducting elastomers possess outstanding properties, including high transparency, conductivity, and the capability to adhere to various substrates. The elastomers also demonstrate ultra‐stretchability (up to 3900%) owing to a combination of covalent cross‐linking and noncovalent cross‐linking. In addition, the elastomers can recover up to 3250% strain and over 94.5% of their original conductivity after self‐healing at room temperature for 5 min, indicating remarkable mechanical and conductive self‐healing abilities. When utilized as strain sensors to monitor real‐time motion of human fingers, wrist, elbow, and knee joints, the elastomers exhibit stable and strong repetitive electrical signals, demonstrating excellent sensing performance for large‐scale movements of the human body. It is anticipated that these ion‐conducting elastomers will find promising applications in flexible and wearable electronics. [ABSTRACT FROM AUTHOR]

Wearable technologies are attracting increasing attention in the materials science field, prompting a quest for active components with beneficial functional attributes whilst ensuring human and environmental safety. Hydrogels are highly biocompatible platforms with interesting mechanical properties, which can be exploited for the construction of strain sensors. In order to improve the directionality of their strain response and combine it with electrical properties to fabricate piezoresistive devices, it is possible to incorporate various types of nanofillers within the polymeric network of the hydrogels. 2D materials are ideal nanofillers thanks to their intrinsic two‐dimensional anisotropy and unique electronic properties. Herein, the covalent functionalization of 2D 1T‐MoS2 is exploited to build robust hybrid cross‐linked networks with a polyethylene glycol diacrylate gel (PEGDA). The conductivity of this nanocomposite is also further improved by inducing the interfacial polymerization of aniline. The resulting free‐standing samples demonstrate a linear and highly reversible piezoresistive response in a pressure range compatible with that of peripheral blood, while also featuring good compatibility with human skin cells, thereby making them interesting options for incorporation into wearable strain sensors. [ABSTRACT FROM AUTHOR]

The demand for stretchable strain sensors with customizable sensitivities has increased across a spectrum of applications, spanning from human motion detection to plant growth monitoring. Nevertheless, a major challenge remains in the digital fabrication of scalable and cost‐efficient strain sensors with tailored sensitivity to diverse demands. Currently, there is a lack of simple digital fabrication approaches capable of adjusting strain sensitivity in a controlled way with no changes to the material and without affecting the linearity. In this study, parallel microgates‐based strain sensors whose strain sensitivity can be adjusted systematically throughout an all‐laser‐based fabrication process without any material replacement are presented. The technique employs a two‐step direct laser writing method that combines the well‐established capabilities of laser ablation and laser marking, boasting a varying gauge factor of up to 433% (GF = 168), while paving the way for the mass production of nanocomposite strain sensors. Parallel microgates‐based strain sensors exhibit a remarkable signal‐to‐noise ratio at ultralow strains (ɛ = 0.001), rendering them ideal for monitoring the gradual growth of plants. As an application demonstration, the proposed sensors are deployed on tomato plants to capture their growth under varying planting conditions including hydroponic and soil mediums, as well as diverse irrigation regimens. [ABSTRACT FROM AUTHOR]

Fiber‐based multimodal sensors with electrical/optical signals are highly desired for next‐generation wearable electronics. Despite the remarkable progress in this area, achieving large‐scale knittable, washable, and self‐healing performance in fiber‐based multimodal sensors simultaneously remains a great challenge. Here, a smart fiber capable of exhibiting piezoresistive/luminescent properties based on an H‐bonding connected multilayered core–shell nanostructure is developed. The core principle of this design involves constructing strong interfacial interactions between the fiber layers, which results in a sensor with high sensitivity (gauge factor = 12383500), exceptional water resistance, and robust self‐healing properties (tensile strength 30.9 MPa, healing efficiency 72.9%). Unlike traditional fiber‐based sensors where elaborate nanostructures are prone to shedding during knitting, this strategy enables the fiber sensors with excellent knittability to be patterned in the fabric, improving both optical and electrical sensitivities. This work is anticipated to make a significant contribution to the further development of wearable electronic products and visual human–computer interaction electronic devices. [ABSTRACT FROM AUTHOR]

Flexible and stretchable strain sensors are in high demand in sports performance monitoring, structural health monitoring, and biomedical applications. However, existing stretchable soft sensors, primarily based on soft polymer materials, often suffer from drawbacks, including high hysteresis, low durability, and delayed response. To overcome these limitations, a stretchable miniature fiber sensor comprised of a stretchable core tightly coiled with parallel conductive wires is introduced. This fiber sensor is flexible and stretchable while exhibiting low hysteresis, a remarkable theoretical resolution of 0.015%, a response time of <30 milliseconds, and excellent stability after extensive cycling tests of over 16 000 cycles. To understand and predict the capacitive sensor response of the proposed sensor, an analytical expression is derived and proved to have good agreements with both experimental results and numerical simulation. The potential of the strain sensor as a wearable device is demonstrated by embedding it into belts, gloves, and knee protectors. Additionally, the sensor can extend its applications beyond wearable devices, as demonstrated by its integration into bladder and life safety rope monitoring systems. The sensor is envisioned to have applications in the field of sports performance evaluations, health care monitoring, and structural safety assessments. [ABSTRACT FROM AUTHOR]