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Flexible hydrogel film sensors have great advantages as human–machine interfaces for conformal contact with bio‐tissues, but suffer from weakness and dehydration, compromising flexibility and performance. Here, a breathable, highly stretchable, and anti‐dehydrating ultrathin organohydrogel film as a skin‐attachable strain sensor for long‐term motion monitoring is developed. An electrospun TPU (eTPU) nanomesh with hidden strength is used as skeleton to host in situ free radical polymerization of 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) and acrylamide (AAm) to form an interpenetrating double network organohydrogel with glycerol and water as solvent. Extensive hydrogen bonding between eTPU nanomesh and P(AMPS‐co‐AAm) network yields ultrathin organohydrogel film (≈200 µm) with synergetic deformation and energy dissipation upon stretching, leading to record‐high stretchability up to 920%, fracture toughness of 20.14 MJ m−3, fracture energy of 10 000 J m−2, and robustness over 4000 notched stretching cylcles to 50% strain. The binary glycerol/water solvent imparts excellent anti‐dehydration at room temperature for 10 d, and stable sensory performance from −20 to 60 °C. With a high water vapor transmission rate of 1.3 kg m−2 d−1, the film sensor ensures comfortable skin contact for continuous knee flexion monitoring throughout the day with stable signals. These organohydrogel film strain sensors are promising for wearable and long‐term motion monitoring applications. [ABSTRACT FROM AUTHOR]

Hydrogels, as valuable biomaterials, have limited applications owing to their mechanical fragility. This study presents a structural modification approach to strengthen hydrogels mechanically. First, the precursor hydrogel undergoes deformation through stretching and twisting, resulting in a helical polymer structure and a deformation gradient. This deformed structure is then stabilized by densification and additional crosslinking. The twisted hydrogel shows improved extensibility and toughness owing to enhanced stress transfer in its unique structure. Additionally, multiple hydrogel strands are assembled hierarchically into ropes and cables, exhibiting advantageous mechanical properties such as high energy dissipation and durability. These reinforced mechanical features lead to considerable performance improvements in applications such as strain sensing and impact absorption. Furthermore, practical utility is demonstrated in areas including posture correction and injury prevention. The hydrogel reinforced by this method has the potential to be used in various fields where both mechanical properties and biocompatibility are crucial. [ABSTRACT FROM AUTHOR]

Conductive fiber membranes have received widespread attention due to their excellent physical and chemical properties. However, developing conductive fiber membranes for both strain sensing and energy harvesting remains a challenge. Herein, a novel thermoplastic polyurethane (TPU)/polydopamine (PDA)/MXene/carbon black (CB) (TPMC) conductive fibrous membrane is developed by combining electrospinning and layer‐by‐layer dip‐coating processes. The TPMC fibrous membrane can be used as a component of strain sensors and triboelectric nanogenerators (TENG) to achieve dual‐mode human motion detection and energy harvesting. The strain sensor boasts a wide operating range (0.5%‐195%), excellent sensitivity (with a gauge factor (GF) up to 54 at 50% strain and maximum GF of 6.5×104), fast response (80 ms) and excellent cycle durability (over 10 000 cycles), making it possible to detect slight or heavy human activities under various conditions effectively. Additionally, a single‐electrode TENG utilizing the TPMC membrane achieves an output voltage of 115 V, a current of 0.8 µA, and a power density of 68 mW m⁻2, also serving as a self‐powered sensor for various movements. The excellent dual‐mode sensing and energy harvesting properties make it promising for future high‐performance wearable devices. [ABSTRACT FROM AUTHOR]

Deep eutectic solvent (DES)‐based eutectogels show significant promise for flexible sensors due to their high ionic conductivity, non‐volatility, biocompatibility, and cost‐effectiveness. However, achieving tough and stretchable eutectogels is challenging, as the highly polar DES tends to screen noncovalent bonds, such as hydrogen and ionic bonds, between polymer chains, limiting their mechanical strength. In this work, this issue is addressed by leveraging the limited solubility of zwitterionic polymers in a specific DES to induce phase separation, promoting dipole–dipole interactions between polymer chains. These interactions improve energy dissipation under mechanical stress, allowing the creation of tough and stretchable P(MAA‐co‐VIPS)/TBAC‐EG eutectogels through a copolymerization‐induced phase separation approach. Methacrylic acid (MAA) and sulfobetaine vinylimidazole (VIPS) are copolymerized within a tetrabutylammonium chloride‐ethylene glycol (TBAC‐EG) DES, resulting in a bicontinuous network. The bicontinuous structure consists of a PVIPS‐rich phase that enhances toughness via dipole–dipole interactions, and a PMAA solvent‐rich phase that enables high stretchability. The resulting eutectogel demonstrates excellent mechanical properties, including a strength of 1.76 MPa, toughness of 16.61 MJ m⁻3, and remarkable stretchability of 1293%, along with self‐recovery, self‐healing, and shape‐memory capabilities. The zwitterionic polymer‐specific DES design opens up broad application potential for these eutectogels in diverse fields. [ABSTRACT FROM AUTHOR]

High‐performance piezoresistive strain sensors (PSS) are important components of wearable electronics for human health management and are considered a key technology for future applications in fields such as artificial intelligence and human medical monitoring. Recently, many PSS have been developed based on a variety of electrosensitive materials. Among them, 3D graphene foams (GrF) have attracted significant attention owing to their excellent thermal conductivity, tensile properties, and light weight. Herein, a novel GrF‐based composite is developed by growing 2D molybdenum disulfide (MoS2) nanosheets directly. Many lathy nanosheets stand vertically on the GrF, similar to silkworms creeping on the leaf, making the composite more sensitive to mechanical deformation stimuli. The obtained MoS2@GrF composite is processed into PSS with a wide sensing range (0%–80%), high gauge factor values (16 below 1% and 39 over 40%), detection limit of 0.1% strain with 106/123 ms response/recovery time, and good cyclic stability (≥3000 cycles). Moreover, the as‐fabricated strain sensors exhibit excellent Joule heating performance, which can be adjusted by strain. As such, the PSS allows for full‐range body motion monitoring and thermal management, which has great potential for next‐generation smart wearable electronics. [ABSTRACT FROM AUTHOR]

Hydrogel‐based flexible strain sensors have an enormous potential for applications in wearable electronics, but currently, realizing excellent mechanical properties and electrical conductivity of sensors is difficult. In this work, polyvinyl alcohol (PVA) hydrogels were augmented with positively charged silk nanofibers (PCSNF) and PEDOT:PSS, and the resultant PVA‐PEDOT:PSS‐PCSNF hydrogel fabric showed remarkable mechanical properties (4.38 MPa) and elevated electrical conductivity. The presence of ethylene glycol (EG) in the hydrogel fabric imparts antifreezing properties and sustains electrical conductivity even at frigid temperatures (−18°C). In addition, EG contributes to the improvement of the electrical conductivity of PEDOT:PSS. This PVA‐PEDOT:PSS‐PCSNF hydrogel fabric can be used as a precise and reliable strain sensor for detecting diverse human motions and facial expressions. Significantly, the PVA‐PEDOT:PSS‐PCSNF hydrogel fabric strain sensor exhibits a gauge factor of 1.02 and exceptional durability, withstanding 400 elbow bends. This study introduces an innovative method for creating high‐performance and resilient hydrogel‐based flexible sensors. [ABSTRACT FROM AUTHOR]

In fields such as wearable technology and soft robotics, sensors that detect bending and pressure using flexible materials are becoming essential. This study aims to develop textile sensors using stitching methods with conductive yarn. Four types of sensors introduced: tensile and tactile sensors with rubber bands, flex sensors with films, and volumetric sensors with balloons. High sewing density and multi‐layer design improve performance. Experiments reveale a gauge factor (GF) of 1.52 for the multi‐layered tensile sensor under 11% strain, indicating a 20% improvement over single‐layer sensors. Flex sensors effectively detect resistance changes due to curvature, varying with bending velocity. Volumetric sensors demonstrate their adaptability in many shapes and materials with response times under 1 s. There is significant potential for these flexible and adaptable soft sensors in the healthcare and medical industries, especially due to their easy integration with wearable devices. [ABSTRACT FROM AUTHOR]

Polymerizable deep eutectic solvents (PDES) represent a novel class of ionic liquids characterized by the presence of polymerizable groups in their hydrogen‐bond donor or acceptor components. Within the realm of flexible electronics, PDES is emerged as a promising material for the fabrication of sensors that exhibit both flexibility and stretchability. This research employs the UV‐initiated photocopolymerization of a ternary PDES composed of choline chloride (ChCl), 2‐hydroxyethyl acrylate (HEA), and itaconic acid (IA), to synthesize an ionic conductive elastomer (ICE) that boasts desirable comprehensive performances, which can be controlled by meticulously adjusting the ratios of these components. The fabrication process is streamlined and efficient, utilizing cost‐effective and eco‐friendly materials. This elastomer exhibits favorable ionic conductivity (1.70 × 10−2–5.45 × 10−2 S m−1), mechanical strength (0.48–1.21 MPa stress at break, 395–701% elongation at break), adhesion capacity (49–120 kPa adhesion strength), and sensing sensitivity toward human motions. [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]

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]

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]

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 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]

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]

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]

Real‐time monitoring of respiration plays a very important role in human health assessment, especially in monitoring and analyzing respiration during exercise and sleep. However, traditional humidity sensors still have problems in flexibility, sensitivity, and durability, so there is an urgent need to develop humidity sensors with high sensitivity, stretchability, and environmental resistance as respiratory monitoring applications. Here, based on the double network hydrogel structure of polyvinyl alcohol and polyacrylamide, a highly sensitive, highly stretchable, and environmentally stable organic hydrogel humidity sensor has been manufactured by using the synergistic effect of lithium chloride and MXene. The hydrogel humidity sensor shows rapid response in the humidity range of 40–85% RH, and has a high sensitivity of −103.4%/% RH. In addition, it exhibits more than 3000% mechanical strain and excellent environmental resistance, which is attributed to the chemical cross‐linking in the hydrogel network and the synergistic effect of multiple hydroxyl groups in glycerol forming rich hydrogen bonds with water and polymer chains. The hydrogel humidity sensor is used for real‐time monitoring of breathing and sleep processes. This work provides a new strategy for preparing high‐performance, extensibility, and environmental stability hydrogel‐based sensors for respiratory monitoring. [ABSTRACT FROM AUTHOR]

Bioplastic is an emerging candidate for replacing traditional fossil‐based plastics due to its fewer carbon emissions, ease of recycling, and high degradability. Current research has shown that bioplastics benefit many applications, such as packaging, kitchenware, drug delivery, and sensors. However, high electrical resistance and poor stability of bioplastic are barriers to electronic components in robotic, bionic, and exoskeleton applications. Here, we introduce a novel bioplastic application as a strain sensor to estimate elbow angles for controlling exoskeletons. This study utilized extracted agar from red algae as the matrix, incorporating various concentrations of carbon nanotube (CNT) as a filler. The results were remarkable, with the increase in filler concentration not only improving strain from 0.8 to 1.1 but also stress from 35.2 to 45.8 kPa, surpassing commercial plastic by approximately two times. The optimized sensors have a response time of 0.16 s, a recovery time of 0.25 s, and stability over 10,000 cycles. Furthermore, the CNT‐bioplastic sensor is seamlessly integrated with the exoskeleton. Our work is a significant step toward using bioplastic in electronic applications. [ABSTRACT FROM AUTHOR]

Stretchable conductive hydrogels have garnered considerable recognition due to their uses in strain sensors, electronic skins, soft robotics, and actuators. However, many hydrogels have poor mechanical properties limiting widespread implementation. While the development of ultrastretchable and mechanically robust hydrogels remains a challenge, the fabrication of these materials with customized designs is also highly desirable. Herein, a direct‐ink write 3D printable double‐network (DN) hydrogel is reported by integrating a physically cross‐linked κ‐carrageenan and a chemically cross‐linked poly(acrylamide‐co‐hydroxyethyl acrylate‐co‐Pluronic F127‐bisurethane methacrylate) with an ionically cross‐linked coordination between κ‐carrageenan and Fe3+ ions in water–glycerol binary solvent. The DN hydrogel demonstrates excellent stretchability (1770% strain), remarkable toughness (6.24 MJ m−3), high ionic conductivity (1.55 S m−1), biocompatibility, and nondrying behavior. A variety of 3D printed constructs including auxetic structures are fabricated and used as a strain sensor. The sensor exhibited real‐time electrical response to strain to detect human motions demonstrating the practicality of this system. These 3D printable DN hydrogels show great potential for on‐demand fabrication of flexible health‐monitoring devices. [ABSTRACT FROM AUTHOR]

Low mechanical properties and easy detachment from the hydration layer at the wet interface of hydrogel limit its application as an adhesive‐flexible sensor. In this study, the composition and structure of mussel mucoprotein are replicated using sulfonyl betaine (SBMA) containing zwitterion and N‐hydroxyethyl acrylamide to be polymerized in deep eutectic solvents and integrated with a polydopamine network to create a bionic eutectic gel with exceptionally strong and wet adhesion. Water erosion is effectively inhibited by the extensive hydrogen bond and electrostatic interactions. These dynamic bonds also impart self‐healing properties to the gel, showing a self‐healing efficiency of 55.45% after 48 h healing at room temperature. The zwitterion in SBMA can preferentially react with water to form a hydrated shell to protect the hydrogen bonds and enhance the exceptional water resistance and adhesion of the gel. The peel strength of the gel on a wet substrate is up to 220.71 N m−1, and its tensile strength can reach 1.01 MPa. It also has good mass stability at both low and high temperatures. This eutectic gel has the potential to be used in flexible electronic devices and can detect human movement and bioelectrical impulses on wet skin with great sensitivity. [ABSTRACT FROM AUTHOR]

Eutectogels have attracted increasing attention from researchers due to their broad application potential, good environmental stability, biocompatibility, and low cost. Currently reported eutectogels generally show large residue strain and hysteresis, which will cause output signal inconsistency between the loading and unloading processes and is not conducive to accurate strain monitoring. Besides, the low adhesiveness of available eutectogels brings about difficulties in the installation of the sensors and dynamic interfacial stability between the sensors and human skin. Herein, a dual ion regulation strategy is proposed to obtain eutectogels with high resilience, high adhesiveness, ultralow residue strain, wide temperature adaptability (−20–60 °C) and good environmental stability. Strain sensors based on gradient eutectogels exhibit high sensitivity, a wide linear response range, and good cycling stability. The response curve shows negligible electrical hysteresis, providing consistent output signals at the fixed strain regardless of stretch or release. Accurate micrometry with a step as minute as 50 µm is realized. Moreover, the sensors demonstrate higher signal intensity and stability in human physiological signals and motion detection due to the strong interfacial bonding. [ABSTRACT FROM AUTHOR]

A stretchable conductive Janus hydrogel with controllable porous structures is developed for highly sensitive monitoring of human motion. The Janus porous structure of the hydrogel is fabricated using patterned single‐layer droplets produced by microfluidics as pore‐forming templates. The hydrogel possess dual‐crosslinked polymeric networks to achieve good stretchability (480%), which allows fully cover the stretching range of human skin (usually <200%). Meanwhile, the hydrogel possess controllable Janus porous structures with local strain/stress enhancement to achieve high sensitivity (GF = 5.2) for strain‐sensing. The Janus hydrogel shows fast response for stretching (175 ms) and recovery (170 ms), and good durability (200 cycles at 50% strain). The conductive Janus hydrogel with high sensitivity and good mechanical properties are promising for developing soft wearable sensors in fields such as human health monitoring and human motion detection. [ABSTRACT FROM AUTHOR]

Carbon nanofibers have been widely studied as one of the promising materials for fabricating flexible electronic strain sensors. Surface modification of carbon nanofibers by conducting polymers is a simple yet effective approach to constructing strain sensors with good conductivity and sensitivity. In this work, composite nanofiber membranes composed of carbon nanofiber and conducting polymer are developed via in situ polymerization of pyrrole, aniline, and thiophene respectively on the surface of the carbon nanofiber which serves as a substrate. Different composite membranes, CNF@PANI, CNF/Ppy, and CNF@PTh, are successfully manufactured. The conducting polymer‐carbon nanofiber composite membranes exhibit improved conductivity as well as response sensitivity compared to pristine carbon nanofiber membranes. Among different composite membranes being studied, CNF/Ppy demonstrates the highest strain‐sensing performance. It shows good sensitivity, reproducibility, and stability in detecting both subtle (strain = 0.1%) and large (strain = 25%) deformation. The excellent strain‐sensing performance of CNF/Ppy endows the composite membrane with great potential for applications in wearable electronics. Highlights: Adding PANI, Ppy, and PTh could improve the conductivity of the CNF sensor.Ppy doping has a good effect on the performance of the CNF strain sensor.CNF/Ppy strain sensor has high sensitivity, stability, and durability.CNF/Ppy sensors can detect deformation caused by human movement.CP‐CNF composite material has good flexibility and mechanical properties. [ABSTRACT FROM AUTHOR]

Flexible strain sensors are essential components for wearable devices, human‐machine interaction systems, and intelligent soft robots. Current active strain sensors have high power consumption, while passive strain sensors exhibit limitations in detecting static or slowly‐varying stimulations. Here, inspired by the strain sensing behavior of Ruffini endings in natural skin, a new type of potentiometric, fully passive, and highly stretchable strain sensors are presented based on the mechanical regulation of ionically conductive percolating networks. Specifically, an artificial potential difference is first created with two electrochemical active electrodes, followed by encoding external strain stimulations into the potential difference variations using a new class of highly elastic and ionically conductive composites with configurable ionic percolating networks. Based on the proposed passive strain sensing mechanism, both static and slowly‐varying strain stimulations (up to 100%) can be monitored with ultralow power consumption (at nW level). Promising applications of the passive strain sensors in human motion monitoring, Morse code communication, and hand gesture recognition are demonstrated. This work opens up a new avenue to constructing novel strain sensing devices with high stretchability, ultralow power consumption, and desirable sensing performance. [ABSTRACT FROM AUTHOR]

Achieving highly efficient self‐powered fibrous sensing systems is desirable for smart electronic textiles but remains a great challenge. Here, a bifunctional hydrogel is proposed by introducing of polyacrylic acid grafted MXene (MXene‐g‐PAA) into polyacrylamide/chitosan, achieving high‐sensitivity sensor and a stable hydrogel electrolyte of battery. The MXene‐g‐PAA flakes act as ion transport "highway", significantly enhance ionic conductivity, thereby increasing the sensitivity of sensors and facilitating Zn2+ diffusion in Zn‐ion battery (ZIB). The rich hydrogen bonding network in the hydrogel improves its mechanical properties and limits water molecule movement, thus reducing side reactions and prolonging the stability of ZIB. As a result, the fibrous sensor exhibits high strain sensitivity (gauge factor of 2.4) with a wide detection range (0–800%), and the fibrous Zn‐ion battery exhibits high capacity (353 mAh cm−3) with long cycling stability (400 cycles). The hydrogel‐based sensor and ZIB can be easily integrated into a flexible self‐powered sensing system, which effectively detects human movement and 3D ball motion. The bifunctional hydrogel with the integrated fibrous system will shed light on the development of next‐generation smart electronic textiles. [ABSTRACT FROM AUTHOR]

Strain measurement is crucial for the safety and stability of engineering activities. With the increasing demand for sensors and large strain measurement in engineering monitoring, the study on the large strain measurement is deepening. However, the conventional strain sensors based on rigid conductive materials have limited flexibility and low stretchability, and the research of large strain and flexible sensors in engineering still lacks. In this work, a highly stretchable and sensitive flexible strain sensor based on liquid metal‐Nickle microparticles (LMN) composite is developed to detect large strain. The LMN composite, featuring uniformly dispersed Nickle microparticles within the liquid metal matrix, is deposited onto the elastomer Ecoflex base material.The LMN composite based‐sensor exhibits high sensitivity (GF = 16.14644 at strain of 200%), large stretchability (up to 200%) and low hysteresis. The theoretical relationship between the relative resistance changes and strain is derived, and the theoretical derivation is compared with experimental data to verify the accuracy of theoretical derivation. Additionally, the LMN composite based‐sensors can be used to detect pressure and bending signals in engineering. This work highlights the potential of LMN composite in broad applications and can facilitate the application of flexible sensing devices in engineering. [ABSTRACT FROM AUTHOR]

This research has developed a fabricating process of thin‐strain sensor by utilizing wafer‐level‐packaging (WLP) techniques. The thickness of sensor makes thinner, its performance is able to highly increase. However, the thinner sensor was fragile, and so it was difficult to handle in post processes. Thus, a thin sensor with lid by utilizing WLP techniques, which is tough to break even when handled, is proposed in this research. More than 250‐µm‐deep grooves were fabricated around the lid by deep reactive ion etching. After the lid substrate was bonded on the sensor substrate with a resin, the sensor and lid substrates were respectively polished to 50 and 200 µm thickness. The lids were released along the grooves, and the 50‐µm‐thick strain sensors were able to be fabricated by utilizing WLP techniques. This sensor was used as a diaphragm to measure pressure. The sensors were assembled on a stainless steel housing without breakage. The performance of the developed sensor was almost showed with a conventional pressure sensor. [ABSTRACT FROM AUTHOR]

Strain sensors which are embeded in AMOLED are introduced and studied in this paper. High accuray strain sensing are achieved, resolution of the sensors are about 0.05%. By combing the strain sensors in the panel, mechanical behaviors can be monitored and studied in real time. The snesors are used to conduct the foldable AMOLED mechanical and reliability study. Dynamic and static strains and related mechanism are introduced and discussed. Finite element simulation models considering the mechanical properties of materials including hyperelasticity, viscoelasticity and creep are established. Finally, the strain sensors and finite element anlysis are combined to study the mechanical response of AMOLED under dynamic folding, static folding, and different temperature and humidity environments. [ABSTRACT FROM AUTHOR]

Ionic conductive hydrogels attracted much attention for applying as wearable sensors, but most hydrogel sensors were not strong enough to withstand repeated sensing because of their low mechanical strength. Here, xanthan gum and sodium chloride were introduced into the polyvinyl alcohol hydrogel system for constructing hydrogels with high mechanical strength due to the hydrogen bonds formed between polyvinyl alcohol and gum xanthan as well as the chain entanglement of polyvinyl alcohol. Meanwhile, the hydrogel was highly sensitive to mechanical deformation because of the existence of free ions provided by sodium chloride. As a result, the hydrogel could serve as sensors for perceiving various body motions, with the advantages of fast response, reproducibility and durability for repeated stretching or compression. The strategy of xanthan gum‐enhanced hydrogel fuels an exciting new direction for hydrogel‐based wearable sensors. [ABSTRACT FROM AUTHOR]

Responsive hydrogels hold great promise for applications such as biological tissue engineering, controlled drug release, soft actuators, and intelligent sensors. However, the design and construction of robust responsive hydrogels using a simple method remains a significant challenge. Herein, a non‐covalently crosslinked responsive hydrogel was constructed by introducing carboxyl‐Zr4+ metal coordination to the hydrophobic association network of P(AA‐co‐LMA) hydrogel through a facile one‐pot polymerization method. The incorporation of multiple reversible interactions, including hydrogen bonding, metal coordination, and hydrophobic association, resulted in a responsive hydrogel with exceptional mechanical strength (≈2.92 MPa), outstanding flexibility (elongation>1000%), and rapid response to pH alterations. Furthermore, the hydrogel also presented good ionic conductivity due to the abundant movable ions, as well as high sensitivity and stability. As application demonstrations, the supermolecular hydrogel had been successfully used in actuating and strain sensing. This work establishes an effective design strategy for creating tough and multifunctional responsive hydrogel. [ABSTRACT FROM AUTHOR]

Flexible wearable sensors have the characteristics of flexibility, comfort, and wearability, and have shown great potential in future electronic products. Despite significant efforts in developing stretchable electronic materials and structures, the development of flexible strain sensors with a wide temperature range, high sensitivity, broad detection range, and good interface stability remains challenging. Here, strain sensors with buckled structures are fabricated using high and low‐temperature resistant material Ti3C2Tx MXene/graphene, PDMS 184. The conductive material Ti3C2Tx MXene/graphene exhibits excellent interface interaction with PDMS 184, addressing not only the poor compatibility issue between the conductive material and the flexible substrate, but also demonstrating good stability and cycling performance. Buckled structure improves the stretchability and linearity of strain sensors. The fabricated strain sensor is suitable for a wide temperature range (−40 to 120 °C) and exhibits high stretchability (120% strain). The strain sensor demonstrates rapid response times at different temperatures: −40 (72.6 ms), 0 (62.7 ms), and 120 °C (52.7 ms). The strain sensor exhibits high sensitivity at different temperatures: −40 (GF = 0.38), 0 (GF = 0.24), 40 (GF = 0.66), and 120 °C (GF = 1.47). The strain sensor has a wide detection range (0.1% to 120%) and excellent cycling stability. In addition, Ti3C2Tx MXene/graphene strain sensors can accurately capture various human activities, such as blinking, speaking, finger bending, and wrist bending. [ABSTRACT FROM AUTHOR]

Conductive polymer composites use elastomers as a matrix for strain sensors. However, elastic polymer composites usually exhibit shoulder peak effects in their resistance response signals, limiting their applicability as strain sensors. In this study, we modified multiwalled carbon nanotubes (MWCNTs)/methyl vinyl silicone rubber (VMQ) by incorporating nanosilica (NSD) to eliminate the shoulder peak effect. The results showed that the addition of a suitable amount of NSD can improve the reconstruction of the conductive network of composite material and eliminated the shoulder peak effect of the composite material in the resistive response signal. The mechanism of eliminating the shoulder peak effect was elucidated, while the mechanical properties of the composite material were improved, which endowed the composite material with excellent strain sensing properties, including sensitivity (GF = 127) and response time (270 ms), and maintained excellent stability and recovery even in 15,000 cycles. These findings highlight the potential of our strain sensor for the real‐time strain monitoring of large‐deformation isolation bearings. Highlights: NSD eliminates shoulder peak effect in MWCNT/VMQ composites.Explained the shoulder peak effect elimination mechanism.NSD enhanced mechanical properties of MWCNT/VMQ composites.MWCNT‐NSD20/VMQ composites have stable resistive strain response properties. [ABSTRACT FROM AUTHOR]

Dexterity and perceptual abilities of the hand are crucial in virtual reality (VR) interactions. This necessitates haptic gloves capable of accurately measuring finger movements and ensuring comfort, a challenging combination that demands both high sensitivity and stretchability. A flexible sensor fabricated from semi‐solid material CNTs‐Inkpad composed of carbon nanotubes (CNTs) mixed with silica gel is proposed and its real‐time response can be achieved by controlling the ratio. Its semi‐solid form harnesses CNTs' high conductivity and sensitivity, avoiding structural cracking in solid CNTs during extensive stretching, thus the semi‐solid form can adapt to various hand gestures. This mechanism enables the CNTs‐Inkpad to function as strain sensors with high gauge factors (GF = 16.99) and high extensibility (350%). By integrating ten CNTs‐Inkpad sensors and five vibrators, a thin and lightweight haptic glove is developed with high sensitivity and stretchability. The glove enables collaborative measurement of all finger joints required for typical gestures in VR interactions, suitable for motion detection and haptic feedback. [ABSTRACT FROM AUTHOR]

Acquiring physical and mechanical strain information of the human body with wearable strain sensors can provide essential data from personal healthcare to human‐machine interfaces and others. Recent research reveals that CO2 laser scribing can convert polyimide films into porous graphene sponges under ambient atmospheres. However, the electrically conductive laser‐induced graphene (LIG) film mismatches with the tough and rigid plastic substrates when it is employed as stretchable strain sensors. In this work, by leveraging the advantageous properties of atoms‐level configured defects within crystalline LIG and heat transfer printing techniques, a flexible LIG‐SEBS (styrene‐ethylene‐butylene‐styrene) strain sensor is made. It is able to achieve exceptional electromechanical properties including a remarkable sensitivity in terms of gauge factor (413–3118), minimal hysteresis, and a broad strain range (>100% strain). Meanwhile, the SEBS‐LIG strain sensor has a stable and fast dynamic response and good repeatability. Additionally, the sensor can be integrated with a wireless communication module for remote monitoring of physiological signals in a real‐time manner with a smartphone App. [ABSTRACT FROM AUTHOR]

Herein, a polyurethane elastomer reinforced with SiO2 nanoparticles modified with 3‐(trimethoxysilyl) methacrylate was proposed, enabling outstanding tensile, tear resistance and suitability for a variety of complex applications. The introduction of modified SiO2 nanoparticles has augmented the crosslink density among the molecular chains. The prioritized fracture of sacrificial bonds and chain entanglement can extend the local damage at the crack tip to the whole elastomer network. This effect might significantly improve the efficiency of energy dissipation, as well as prevent the crack propagation. The polyurethane elastomer, which consists of 0.5% modified nano‐SiO2, demonstrated a tear strength of 23.4 N/mm and superior mechanical stability, surpassing most commercial photocurable 3D printed polyurethane elastomers available commercially. Subsequently, polyurethane composite nano‐SiO2/LiTFSI (PSL) strain sensors with various flexible architectures were fabricated using DLP 3D printing technology by incorporating LiTFSI ionic liquid. The PSL strain sensor exhibited long‐term operational stability and high sensitivity, showing a considerable potential in the field of electronics. Overall, this study has opened up new opportunities for 3D printing of smart structured wearable devices with high performance. Highlights: We constructed a SiO2 nanoparticle which can be used as a crosslinking agent of polyurethane molecular chain.The polyurethane elastomer doped with SiO2 nanoparticles is endowed with an excellent tear resistance.The LiTFSI composite PPU strain sensor constructed by DLP exhibited long‐term operational stability and high sensitivity. [ABSTRACT FROM AUTHOR]

In recent years, the smart hydrogels have gained much concern in the field of research specially related to flexible strain sensors because they exhibit many types of smart interactions that can be useful in wearable devices. However, the conventional hydrogels have poor electrical conductivity that affect the performance of the sensors, so it remains a challenge to achieve noncontact signal monitoring (e.g., for the detection of magnetic field changes). In this study, an ultra‐stretchable and magnetically responsive conductive hydrogel was fabricated by adding magnetic ferric tetroxide@polypyrrole composite nanoparticles (Fe3O4@PPy NPs) to polyacrylamide (PAm). The nanoparticles were easily agglomerated and improved the compatibility of PPy and hydrogel. The obtained PAm/Fe3O4@PPy hydrogel showed an ultra‐stretchability of (961%), a low elastic modulus of (87.8 kPa), and an excellent toughness of (1010.5 kJ m−3). Moreover, PAm/Fe3O4@PPy hydrogel also exhibited a high electrical conductivity of 0.34 S m−1, and the PAm/Fe3O4@PPy hydrogel sensor could detect human motions (such as bending of finger, bending of wrist) and muscle micromotion (such as pronouncing). In addition, it can also monitor the change in magnitude of magnetic field. [ABSTRACT FROM AUTHOR]

Two‐dimensional transition metal dichalcogenides (TMDs) are needed in high‐performance piezoresistive sensors due to their strong strain‐induced bandgap modification and thereby large gauge factors. However, integrating a conventional high‐temperature chemical vapor deposition (CVD)‐grown TMD with a flexible substrate necessitates a transfer process that inevitably degrades the sensing properties of the TMDs and increases the overall fabrication complexity. We present a high‐performance piezoresistive strain sensor that employs large‐area PdSe2 films grown directly on polyimide (PI) substrates via plasma‐assisted selenization of a sputtered Pd film. The reliable strain transfer from the substrate to the PdSe2 film ensures an outstanding strain‐sensing capability of the sensor. Specifically, the sensors have a gauge factor of up to −315 ± 2.1, a response time under 25 ms, a detection limit of 8 × 10−6, and an exceptional stability of over 104 loading–unloading cycles. By attaching the sensors to the skin surface, we demonstrate their application for measuring physiological parameters in health care monitoring, including motion, voice, and arterial pulse vibration. Furthermore, using the PdSe2 film sensor combined with deep learning technology, we achieved intelligent recognition of artery temperature from arterial pulse signals with only a 2% difference between predicted and actual temperatures. The excellent sensing performance, together with the advantages of low‐temperature fabrication and simple device structure, make the PdSe2 film sensor promising for wearable electronics and health care sensing systems. [ABSTRACT FROM AUTHOR]

This study reports the fabrication of a serious of anisotropic composite aerogels comprising polyimide and graphene (PI/G) through a simple and eco‐friendly technique. Poly(amic acid) ammonium salt/graphene dispersion, which was produced through the mixture of poly(amic acid), graphene aqueous dispersion, triethylamine, and water, was utilized in the process of creating PI/G composite aerogels employing unidirectional freezing, freeze‐drying, and thermal imidization. The PI/G aerogels displayed anisotropic mechanical properties, thermal insulation, and electrical conductivity. The PI/G aerogels with an anisotropic microstructure demonstrated notable rigidity and a high compressive modulus (52.7 MPa) along the axial direction, while displaying favorable flexibility and a low modulus (18.2 MPa) along the radial direction. Furthermore, the PI/G aerogel exhibited anisotropic thermal conductivity (axial: 64 mW m−1 K−1; radical: 55 mW m−1 K−1). These properties enable the PI/G aerogel to have a wider range of potential applications, especially strain sensors. The research presented herein establishes a simple and eco‐friendly strategy for the production of anisotropic PI/G‐based composite aerogels. [ABSTRACT FROM AUTHOR]

In this study, we fabricated strain sensors using a dip‐coating method on spandex fabric utilizing a mixed solvent of tetrahydrofuran/N,N‐dimethylformamide and carbon black. Scanning electron microscopy images demonstrated a positive correlation between the amount of adhered Carbon black (CB) particles and coating time. Thermogravimetric analysis revealed the thermodynamic behavior of the sensor as gradually heated up to 650°. Mechanical analysis indicated that the reported sensors exhibited a higher elongation at break compared to the original spandex fabric, but with a slight decrease in strength. Moreover, the dissipated energy of each fabric shows a stabilizing tendency after 10 cycles during a 300% stretching‐releasing cyclic tests, where no significant changes observed until the 50th cycle, demonstrating an excellent mechanical repeatability of the fabric sensors. In terms of sensing performance, the sensor exhibited a high sensing range of up to 300%, with the maximum sensitivity reaching 16. Furthermore, we conducted cyclic stretching tests up to 200% strain to characterize the long‐term stability of the fabric's sensing ability. The results demonstrated that our reported method enables a low‐cost and efficient fabrication of sensors with excellent performance. [ABSTRACT FROM AUTHOR]

In order to prepare a flexible strain sensor with a large monitoring range, high sensitivity and excellent stability, a polyolefin elastomer (POE)/carbon nanotubes (CNTs) conductive polymer composite with a bilayer structure was prepared by biaxially stretching in this work. The results showed that the bilayer structured nanocomposites had better processability and better stability than monolayer CNT/POE nanocomposites during biaxial stretching. The biaxial stretching process could promote the dispersion and planar orientation of CNTs within the polymer, improving the crystallinity of nanocomposites and the sensing performance of strain sensors. The optimal stretching ratios (SRs) of bilayer structured nanocomposites were studied. The 8 wt% CNT/POE‐POE strain sensor with an SR of 2.5 exhibited a high sensitivity (gauge factor/GF = 72604.7 at 900% strain), wide strain range (0%–900%), and stable cycling performance (1000 cycles at 30% strain), showing a broad application prospect in wearable electronic devices. This study provides a valuable method for efficiently manufacturing high performance and low‐cost flexible strain sensors. [ABSTRACT FROM AUTHOR]

Recently the ever‐increasing demand for wearable electronics has greatly triggered the development of flexible strain sensors. However, it is still challenging to simultaneously achieve high sensitivity, wide working range, and good wearability. Herein, we developed a highly stretchable fiber strain sensor based on wet‐spun porous polyurethane (PU) fiber, and especially a unique conductive network of dual silver (Ag)/carbon black (CB) layers is constructed. Under strain, the rapid crack propagation on the brittle Ag layer brings a large resistance change and thus high sensitivity, while the tunneling‐effect dominated CB layer bridges the separated Ag islands to maintain the integrity of conductive pathways under large strain. By means of the synergistic effect of Ag/CB layers, this composite fiber of Ag/CB@PU presents not only high conductivity of 5139.9 S/m, but also ultrahigh sensitivity with a gauge factor of 2.52 × 106 and a wide working range of up to 200%. Besides that, it is also capable of detecting very tiny strain of 0.1% and working stably for over 8000 cycles. Using mature weaving technology, this fiber strain sensor can be seamlessly integrated into the textile to conformally track different movements of the human body. Together with the facile all‐solution‐based fabrication protocol, this work proposed a new strategy to prepare high‐performance fiber strain sensor, promising the textile‐based wearable applications. [ABSTRACT FROM AUTHOR]

In order to reduce the detection limit and improve the working range of flexible strain sensor, in this article, we reported a multi‐walled carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO) co‐decorated multifunctional core spurn yarn flexible strain sensor (CGY FSS). It was found that the well lapping between MWCNT and rGO endows sensor with high working range (> 300%), while the helical structure of core‐spun yarn makes it sensitive to very tiny deformation (0.1%). To improve its dynamic durability, polydopamine (PDA) was used to improve the interface bonding force between yarn and conductive materials, which ensures the sensor conduct stable electrical signals during 10,000 stretching cycles test at 10% strain. These features made it suitable for human motion detection and structural health monitoring. Moreover, due to the abundant carboxyl groups on the carbon material surface and the employment of polymer‐based yarn, CGY FSS also showed good responsiveness to water vapor and acetone gas. It can be conceived that this as prepared strain sensor shows promising potential in smart device application with multiple response mechanism. [ABSTRACT FROM AUTHOR]

Double‐network hydrogels have outstanding mechanical characteristics but mostly suffer from poor self‐healing performance since most hydrogels are chemically crosslinked via covalent links for each network. In this work, a tough and self‐healing double network hydrogel with multiple dynamic non‐covalent bonds is developed by combining the hydrophobically modified polyacrylamide (HPAM) with a thermally reversible potassium ion crosslinked κ‐carrageenan (K+C) network through a dual physical crosslinked network strategy. Being the multiple dynamic non‐covalent bond interactions and dual physical crosslink networks, the K+C/HPAM DN hydrogel exhibits excellent mechanical characteristics (tensile strength: 1.86 MPa, tensile strain: 1637%) and good self‐healing ability (maximum stress self‐healing efficiency: 87%, maximum tensile strength after self‐healing: 0.95 MPa). Due to the three‐dimensional pore structure and the conductive ions in the system, the K+C/HPAM DN hydrogel also achieves good strain sensing capabilities with a strain sensitivity of 2.98 (gauge factor, GF) in the 100% strain range. Even after being cut and self‐healed, the gel still exhibits good strain sensing capabilities (GF = 2.79), which is still better than the most similar DN hydrogel strain sensors in sensitivity. We believe this work offers a new material for self‐healing flexible strain sensors. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Flexible strain sensors are essential components of wearable electronic skins. Here we report a new kind of flexible strain sensor by filling conductive nanowires in elastomers featuring a concentration gradient. The fabrication method involves a fast photo‐induced copolymerization of acrylates in the presence of gradient deposited polypyrrole (PPy) nanowires, which is facile and cost‐effective in steadily doping PPy into elastomeric films. The combination of delicately selected polyacrylates as the matrix filled with entangled, nano‐sized PPy endows the sensor good stretchability, sensitive deformation‐electrical signal conversion and high fatigue resistance, which can be used repeatedly without scarifying the sensitivity of electrical signal. Besides, the lower side of the composite films exhibits high light absorption (> 98%) in a wide spectral range (250—2400 nm). Systematic characterizations of the sensors support that the excellent strain sensing and light‐heat conversion performances are essentially dependent on the gradient filling of PPy nanowires. Moreover, the applications of this flexible strain sensor for human motion monitoring and wearable thermotherapy are demonstrated, manifesting a promising option for wearable electronics and personalized healthcare. [ABSTRACT FROM AUTHOR]

Self‐healing conductive materials have become promising candidates for flexible sensor devices. However, the mechanical properties of the substrate elastomers are often poor due to the inherent performance of the materials. Here, a poly(vinyl alcohol) (PVA)‐based self‐healing material with high strength and good thermal stability was prepared by side‐linked grafting modification of PVA with a one‐step esterification reaction. Benefiting from the hydrogen bonds and ion coordination between iron ions and carboxyl groups, the synthesized elastomer exhibited excellent mechanical properties (tensile strength of 38.6 MPa, fracture elongation of 1565.0%) and good self‐healing performance (self‐healing efficiency of 53.4% at room temperature). In addition, the high sensitivity and self‐healing performance of a silver nanowire‐coated elastomer strain sensor demonstrated the wide potential applicability of the prepared PVA‐based elastomers in health care, electrocardiography and safety monitoring. © 2023 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

Highly stretchable and robust strain sensors are rapidly emerging as promising candidates for a diverse of wearable electronics. The main challenge for the practical application of wearable electronics is the energy consumption and device aging. Energy consumption mainly depends on the conductivity of the sensor, and it is a key factor in determining device aging. Here, we design a liquid metal (LM)‐embedded hydrogel as a sensing material to overcome the barrier of energy consumption and device aging of wearable electronics. The sensing material simultaneously exhibits high conductivity (up to 22 S m−1), low elastic modulus (23 kPa), and ultrahigh stretchability (1500%) with excellent robustness (consistent performance against 12 000 mechanical cycling). A motion monitoring system is composed of intrinsically soft LM‐embedded hydrogel as sensing material, a microcontroller, signal‐processing circuits, Bluetooth transceiver, and self‐organizing map developed software for the visualization of multi‐dimensional data. This system integrating multiple functions including signal conditioning, processing, and wireless transmission achieves monitor hand gesture as well as sign‐to‐verbal translation. This approach provides an ideal strategy for deaf‐mute communicating with normal people and broadens the application of wearable electronics. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Flexible strain sensors are essential components of wearable electronic skins. Here we report a new kind of flexible strain sensor by filling conductive nanowires in elastomers featuring a concentration gradient. The fabrication method involves a fast photo‐induced copolymerization of acrylates in the presence of gradient deposited polypyrrole (PPy) nanowires, which is facile and cost‐effective in steadily doping PPy into elastomeric films. The combination of delicately selected polyacrylates as the matrix filled with entangled, nano‐sized PPy endows the sensor good stretchability, sensitive deformation‐electrical signal conversion and high fatigue resistance, which can be used repeatedly without scarifying the sensitivity of electrical signal. Besides, the lower side of the composite films exhibits high light absorption (> 98%) in a wide spectral range (250—2400 nm). Systematic characterizations of the sensors support that the excellent strain sensing and light‐heat conversion performances are essentially dependent on the gradient filling of PPy nanowires. Moreover, the applications of this flexible strain sensor for human motion monitoring and wearable thermotherapy are demonstrated, manifesting a promising option for wearable electronics and personalized healthcare. [ABSTRACT FROM AUTHOR]

Here, in comparison to indirect and nonvisualizable detections that usually convert strains from electrical signals, the strain sensors that show visible signals with operation simplicity and intuitive perception for practical applications in flexible, printed, and hybrid microelectronics are summarized. The sensors are categorized into four mechanisms of optical phenomena (diffraction, reflection, interference, and photonic crystal), fluorescent mapping (mechanochromism and mechanoluminescence), Moiré effect, and thermal imaging. In addition to their operating principles, three characteristics of sensitivity, dynamic window, and spatial resolution are examined. Furthermore, three types of strains (uniaxial, biaxial, and multiaxial) with subcategories in strain mode (tensile and compressive) and uniformity (isotropic and anisotropic) that are supported by corresponding sensors are also summarized here. With three potential applications and markets of healthcare and biomedical engineering, human motion detection (sports science), and roll‐to‐roll manufacturing listed at the end, a steppingstone is offered here for those who works or intends to work in this field by revisiting the outcomes from key literature published in recent years. [ABSTRACT FROM AUTHOR]

The representatively chronic problems of the piezoresistive‐type sensing media containing conductive fillers such as carbon nanotubes are dispersion problem when conductive fillers are composited with a high content for securing a certain conductivity and are low reliable sensor performance owing to the hysteresis of the sensing signals. Therefore, this study introduces a piezoresistive sensing medium with a multilayered parallel structure of resistors which effectively reduces the resistance and stabilizes the sensing signal. The multiparallel resistor (MPR) sensing medium with parallel‐connected structure shows an initial resistance ≈2.5 times lower compared to that of the typical single‐resistive type. When the proposed MPR sensing medium is applied as a strain sensor, GF value is 0.103 ± 0.009%−1 showing a remarkable improvement over 0.030 ± 0.018%−1 of the single type. The MPR strain sensor exhibits approximately the same GF values with no hysteresis and high linearity of the sensing signals in the forward and reverse strain directions. Finally, the developed MPR sensing medium is applied both as a strain sensor as well as a pressure sensor with excellent performance, thereby suggesting a new methodology to develop the high‐performance piezoresistive physical sensors. [ABSTRACT FROM AUTHOR]

Flexible sensors have versatile applications in a home environment to create better ambient intelligence, which still have high fabrication costs and disposable value. As a proof‐of‐concept example to resolve these problems, the graphite‐based sensors on a disposable paper cup by laser patterning to measure the water level and temperature are proposed. The optimal process parameters of graphitic film, sensing mechanisms, and the sensor performance are investigated in the experiments. Moreover, the paper cup with graphitic sensors is simulated by the finite element method to analyze the experimental results. This fast and low‐cost manufacturing method may open up avenues for the development of disposable flexible electronics in smart home necessities. [ABSTRACT FROM AUTHOR]

In this work, a stretchable and compressible strain sensor was fabricated from conductive porous carbon nanotubes/polydimethylsiloxane (CNT/PDMS‐P) high internal phase emulsion (HIPE), which was obtained by simple mechanical mixing of CNTs, PDMS, and water. Micropores were uniformly distributed in the PDMS matrix, with diameters mainly in the range of 3–9 μm and averaging 5.3 μm. Due to the confined dispersion of CNTs in the porous PDMS framework, the CNT/PDMS‐P achieved a lower percolation threshold of 0.29 wt%. Compared to the non‐porous composite (CNT/PDMS), its percolation threshold was reduced by 25%. Besides, the CNT/PDMS‐P showed excellent sensitivity and cyclic stability. The sensitivity of CNT/PDMS‐P was 50% higher than that of CNT/PDMS in the tensile strain range of 0%–10%. The stability tests for 1000 loading/unloading cycles showed that the maximum offset rate of CNT/PDMS‐P was 58% lower than that of CNT/PDMS. The sensitivity of CNT/PDMS‐P compression sensor was S = 0.00259 kPa−1, which could detect the stress up to 600 kPa and maintain the standard waveform even after 1000 compression cycles. Finally, the potential application scenarios of the sensor, such as perception of human body limb movement, facial movement, gesture transformation, and human‐computer interaction scenarios, were explored. [ABSTRACT FROM AUTHOR]