Search

Respiratory diseases are currently monitored through traditional pulmonary function tests, such as spirometry. However, the restrictions of these procedures, particularly in the context of the COVID‐19 pandemic, have underscored the need for alternative approaches to respiratory health assessment. Wearable devices have emerged as a promising solution, providing continuous data collection, and overcoming the limitations posed by conventional methods. This review explores the multifaceted field of wearable devices for respiratory monitoring, presenting the most common sensing technologies applied to pulmonary ventilation, their constituent materials, fabrication techniques, and diverse morphologies to enhance sensor performance. The role of machine learning algorithms and ethical data sharing is highlighted, contributing to the forthcoming patient‐centered healthcare landscape. Ultimately, the importance of validation and calibration protocols for wearable devices is underlined. In anticipation of evolving healthcare needs, this in‐depth study addresses the current challenges in wearable respiratory monitoring while laying a robust foundation for a personalized, connected, and ethically sound future for respiratory care. [ABSTRACT FROM AUTHOR]

Highlights: Vertical 1D GaN nanorod arrays/2D MoS2/PEDOT:PSS heterostructures in wafer scale have been fabricated for flexible photodetection firstly. Self-powered flexible photodetector at compressive strain reveals a significantly enhanced photoresponse with a responsivity of 2.47 A W−1 and response times of 40/45 µs, which are superior to the state-of-the-art flexible devices. This work not only provides a valuable strategy for the design and construction of tunable van der Waals heterostructures, but also opens a new opportunity for flexible sensors. van der Waals (vdW) heterostructures constructed by low-dimensional (0D, 1D, and 2D) materials are emerging as one of the most appealing systems in next-generation flexible photodetection. Currently, hand-stacked vdW-type photodetectors are not compatible with large-area-array fabrication and show unimpressive performance in self-powered mode. Herein, vertical 1D GaN nanorods arrays (NRAs)/2D MoS2/PEDOT:PSS in wafer scale have been proposed for self-powered flexible photodetectors arrays firstly. The as-integrated device without external bias under weak UV illumination exhibits a competitive responsivity of 1.47 A W−1 and a high detectivity of 1.2 × 1011 Jones, as well as a fast response speed of 54/71 µs, thanks to the strong light absorption of GaN NRAs and the efficient photogenerated carrier separation in type-II heterojunction. Notably, the strain-tunable photodetection performances of device have been demonstrated. Impressively, the device at − 0.78% strain and zero bias reveals a significantly enhanced photoresponse with a responsivity of 2.47 A W−1, a detectivity of 2.6 × 1011 Jones, and response times of 40/45 µs, which are superior to the state-of-the-art self-powered flexible photodetectors. This work presents a valuable avenue to prepare tunable vdWs heterostructures for self-powered flexible photodetection, which performs well in flexible sensors. [ABSTRACT FROM AUTHOR]

Flexible strain sensors that combine high sensitivity and wide range are important for developing wearable electronics. In this paper, AgNWs/MXene/SEBS flexible strain sensor with high sensitivity and wide strain range was prepared using a thermoplastic elastomer (styrene-ethylene-butene-styrene) SEBS as the polymer matrix and AgNWs and MXene as the composite conductive fillers. The sensitivity of the AgNWs/MXene/SEBS sensor is significantly higher than that of the AgNWs/SEBS and MXene/SEBS sensors based on a single conductive filler. At 100% strain, the AgNWs/MXene/SEBS sensor has a sensitivity of 176.25. The sensor detects small strains of 0.5-5% as well as large strains of 5–50% with high linearity. The sensors remained stable after 200 cycles. The AgNWs/MXene/SEBS tensile sensors were subjected to array testing and finger bending recognition, and the sensors have promising applications in human motion monitoring. [ABSTRACT FROM AUTHOR]

Tactile sensors have garnered considerable interest for their capacity to detect and quantify tactile information. The incorporation of microstructural designs into flexible tactile sensors has emerged as a potent strategy to augment their sensitivity to pressure variations, thereby enhancing their linearity, response spectrum, and mechanical robustness. This review underscores the imperative for progress in microstructured flexible tactile sensors. Subsequently, the discourse transitions to the prevalent materials employed in the fabrication of sensor electrodes, encapsulation layers, and active sensing mediums, elucidating their merits and limitations. In‐depth discussions are devoted to tactile sensors adorned with microstructures, including but not limited to, micropyramids, microhemispheres, micropillars, microporous configurations, microcracks, topological interconnections, multilevel constructs, random roughness, biomimetic microstructures inspired by flora and fauna, accompanied by exemplar studies from each category. Moreover, the utility of flexible tactile sensors within the realm of intelligent environments is explicated, highlighting their application in the monitoring of physiological signals, the detection of sliding motions, and the discernment of surface textures. The review culminates in a critical examination of the paramount challenges and predicaments that must be surmounted to further the development and enhance the functional performance of tactile sensors, paving the way for their integration into advanced sensory systems. [ABSTRACT FROM AUTHOR]

Flexible bending sensors have emerged as a technology with significant potential for a wide range of applications, including human-machine interaction, healthcare monitoring, and soft robotics. This paper provides a comprehensive review of the working principles, performance evaluation, application areas, and future trends of flexible bending sensors. The challenges faced by these sensors, such as anti-interference, adaptive detection, and multidirectional sensing, are discussed, along with potential solutions and future developmental directions. The paper highlights the importance of materials development, structural design, and manufacturing processes in advancing flexible bending sensor technology. Overall, this review aims to provide valuable insights and guidance for further research and development in the field of flexible bending sensors. [ABSTRACT FROM AUTHOR]

3D printing has shown promise in the development of notable sensing and health detection devices. Nonetheless, challenges remain in the concurrent development of highly durable wearable sensors with low‐friction surfaces. This challenge serves as a limiting factor in the operational lifespans of these sensors. In this study, a magnetically assisted 3D printing technique is developed to fabricate composites reinforced with magnetic Fe3O4@SiO2 nanochains (NCs) with dimensions of 60.2 µm in length (L) and 0.2 µm in diameter (D), indicating an L:D ratio exceeding 300. By applying a vertical magnetic field and extrusion flow field to the sensor's surface layer, the NCs can be arranged differently (together with the printed textures), reducing the coefficient of friction by 27.7% and improving the wear resistance. This approach is inspired by nacre, known for its impressive durability and resilience. A motion monitoring sensor with an extended lifespan is successfully fabricated by using liquid metal ink integrated with an anti‐wear layer. These findings offer significant insights into the evolution of wearable sensors, demonstrating their adaptability to multi‐material printing and resulting in improved performance and service lives. [ABSTRACT FROM AUTHOR]

The combination of fluidity and metallic conductivity has attracted considerable attention to liquid metal (LM), but its development remains challenging due to enormous surface tension. Here, vinyl‐terminated silicone oil and platinum catalyst are added to LM to reduce its surface tension, which develops a special type of liquid‐metal‐silicone (LMS) ink with a catalyst diffusion effect. Combined with an embedded three‐dimentional (3D) printing method, the LMS ink is printed on the support matrix, and the catalyst diffuses outward along the print path to cure the silicone around it, directly constructing self‐encapsulated conductive composites with excellent conductivity and self‐encapsulated flexible tactile sensors based on triboelectric nanogenerator (TENG). The sensor exhibits excellent sensitivity (0.308 V kPa−1), high linearity (≈0.99), and good durability (over 10 000 cycles). Furthermore, when used in flexible wearable electronics, the sensor demonstrates a good performance with an accuracy of ≈96% in classifying different human postures using a convolutional neural network. Finally, through embedded 3D printing with LMS ink and silicone ink, a somatosensory soft robotic gripper with complex cavity structures is designed and manufactured in one step, achieving the all‐in‐one integration of sensors and actuators. This study shows great application potential in flexible electronics and soft robotic systems. [ABSTRACT FROM AUTHOR]

Endowing artificial muscles with perceptual function, as an octopus does, is highly desired but still suffering from interfacing mismatch between actuating and sensing units in a thin fiber. Herein, an artificial neuromuscular fiber capable of electrically responding to external strain/temperature and actuation path with power supply is reported by using polymer‐assisted metal deposition to firmly coat Cu nanoparticles on the surface of liquid crystal elastomer (LCE). The LCE core acts as an actuator, while the wrinkled Cu sheath provides environment interaction and actuation monitoring. Benefiting from the levodopa/polyethyleneimine interface design, this fiber exhibits large reversible contraction (47.61%), fast strain rate (370% s−1), high output power density (663.75 W kg−1) and reliable durability (1000 cycles) under electrical stimulation. Furthermore, by combining as‐made fiber arrays with electronic system and computing algorithm, this machine learning‐assisted artificial neuromuscular system can actuate the Chinese shadow puppetry and recognize its body movements with high accuracy. This work paves a revolutionary way for fabricating next‐generation flexible robots. [ABSTRACT FROM AUTHOR]

The evaluation of the upkeep and freshness of aquatic products within the cold chain is crucial due to their perishable nature, which can significantly impact both quality and safety. Conventional methods for assessing freshness in the cold chain have inherent limitations regarding specificity and accuracy, often requiring substantial time and effort. Recently, advanced sensor technologies have been developed for freshness assessment, enabling real-time and non-invasive monitoring via the detection of volatile organic compounds, biochemical markers, and physical properties. The integration of sensor technologies into cold chain logistics enhances the ability to maintain the quality and safety of aquatic products. This review examines the advancements made in multifunctional sensor devices for the freshness assessment of aquatic products in cold chain logistics, as well as the application of pattern recognition algorithms for identification and classification. It begins by outlining the categories of freshness criteria, followed by an exploration of the development of four key sensor devices: electronic noses, electronic tongues, biosensors, and flexible sensors. Furthermore, the review discusses the implementation of advanced pattern recognition algorithms in sensor devices for freshness detection and evaluation. It highlights the current status and future potential of sensor technologies for aquatic products within the cold chain, while also addressing the significant challenges that remain to be overcome. [ABSTRACT FROM AUTHOR]

With the rapid development of the internet of things, the simple preparation of sensors has become a challenge. The present work presents the simple preparation of flexible sensors by using the fused deposition modeling (FDM) 3D printing combined with the microwave radiation‐assisted treatment of the thermoplastic polyurethane (TPU) with carbon nanotubes (CNTs) as conductive fillers to create the flexible sensors. The as‐prepared TPU/CNT composites exhibit the 7.27 MPa tensile strength and 401% elongation at break, similar to those of the pure TPU. After 200 tensile cycles, the TPU/CNT composites can still stably convert pressure into electrical signals, which can be used as flexible sensors with high sensitivity (0.879 kPa−1). In addition, shoe insoles and finger cover with sensing performance are fabricated through the FDM 3D printing technology, demonstrating the potential of the sensors to monitor human gait, finger straightening, and bending movements. The as‐proposed method involves the embedding CNTs as conductive fillers on the surface of TPU to form the TPU/CNT composite conductive layers on the surface of TPU, which is beneficial for maintaining the elasticity of the polymer matrix. The challenges in preparing stable, low‐cost, and scalable flexible sensors and highlights of the advantages of 3D printing technology in manufacturing flexible piezoresistive sensors are also deeply discussed. [ABSTRACT FROM AUTHOR]

Flexible bending sensors have emerged as a technology with significant potential for a wide range of applications, including human-machine interaction, healthcare monitoring, and soft robotics. This paper provides a comprehensive review of the working principles, performance evaluation, application areas, and future trends of flexible bending sensors. The challenges faced by these sensors, such as anti-interference, adaptive detection, and multidirectional sensing, are discussed, along with potential solutions and future developmental directions. The paper highlights the importance of materials development, structural design, and manufacturing processes in advancing flexible bending sensor technology. Overall, this review aims to provide valuable insights and guidance for further research and development in the field of flexible bending sensors.

A flexible formaldehyde sensor with high sensitivity was successfully fabricated by integrating palladium (Pd) nanoparticles, polyvinylpyrrolidone (PVP), multi-walled carbon nanotubes (MWCNTs) and nanocellulose (NC) into composite films. The flexible composite films were fabricated via vacuum filtration. The morphology, structure, composition, crystallinity, and functional group of as-fabricated sensing materials were characterized by scanning electron microscopy, transmission electron microscopy, electron probe microanalyzer, Raman spectroscopy, and Fourier transform infrared spectrometer. Pd nanoparticles-PVP-MWCNTs-NC (Pd-PVP-MWCNTs-NC) composite films exhibited an 11-fold increase in formaldehyde sensitivity compared to MWCNTs-NC composite films. The excellent sensing performances of Pd-PVP-MWCNTs-NC sensors were attributed to the combination of Pd nanoparticles and PVP. The enhanced sensitivity is attributed to the synergistic effect of the high electron transfer from formaldehyde molecule to Pd nanoparticles and swelling of PVP due to sorption of formaldehyde molecule. Pd-PVP-MWCNTs-NC sensors still maintained good response under bending angle up to 30° and 300 bending cycles. The results demonstrate that the Pd-PVP-MWCNTs-NC composite films are highly promising in terms of sensitivity and flexibility for sub-ppm level formaldehyde detection at room temperature. [ABSTRACT FROM AUTHOR]

The intricate muscle arrangement structure endows the biological tissues with unique mechanical properties. Inspired by that, a mechanically robust and multifunctional anisotropic Polyacrylamide/Sodium alginate/Zirconium ion/Carbon dots (PAM/SA/Zr4+/CDs, PSZC) hydrogel is developed through the synergistic effect of mechanical‐assisted stretching, Zr4+ metal‐coordination and CDs embedding. The resulting hydrogel exhibited an impressive tensile strength of 2.56 MPa and exceptional toughness of 10.10 MJ m−3 along the stretching direction, attributing to the oriented alignment of PAM and SA molecular chains induced by mechanical‐assisted stretching and metal‐coordination. The dense network structure endowed the PSZC hydrogel with excellent anti‐swelling performance, achieving a swelling ratio of only 1.7% after being stored in water for 30 days. The presence of Zr4+ conferred remarkable electrical conductivity of 2.15 S m−1 to the PSZC hydrogel. Furthermore, the integration of carbon dots imparted the PSZC hydrogel fluorescence properties, rendering it visual sensing capabilities. Overall, a straightforward strategy is proposed for fabricating a mechanically robust and multifunctional hydrogel suitable for underwater sensing and visual sensing, offering valuable insights for the development of high‐performance underwater sensors. [ABSTRACT FROM AUTHOR]

Sleep plays a role in maintaining our physical well-being. However, sleep-related issues impact millions of people globally. Accurate monitoring of sleep is vital for identifying and addressing these problems. While traditional methods like polysomnography (PSG) are commonly used in settings, they may not fully capture natural sleep patterns at home. Moreover, PSG equipment can disrupt sleep quality. In recent years, there has been growing interest in the use of sensors for sleep monitoring. These lightweight sensors can be easily integrated into textiles or wearable devices using technology. The flexible sensors can be designed for skin contact to offer continuous monitoring without being obtrusive in a home environment. This review presents an overview of the advancements made in flexible sensors for tracking body movements during sleep, which focus on their principles, mechanisms, and strategies for improved flexibility, practical applications, and future trends. [ABSTRACT FROM AUTHOR]

The development of photo-/electro-chemical and flexible electronics has stimulated research in catalysis, informatics, biomedicine, energy conversion, and storage applications. Gels (e.g., aerogel, hydrogel) comprise a range of polymers with three-dimensional (3D) network structures, where hydrophilic polyacrylamide, polyvinyl alcohol, copolymers, and hydroxides are the most widely studied for hydrogels, whereas 3D graphene, carbon, organic, and inorganic networks are widely studied for aerogels. Encapsulation of functional species with hydrogel building blocks can modify the optoelectronic, physicochemical, and mechanical properties. In addition, aerogels are a set of nanoporous or microporous 3D networks that bridge the macro- and nano-world. Different architectures modulate properties and have been adopted as a backbone substrate, enriching active sites and surface areas for photo-/electro-chemical energy conversion and storage applications. Fabrication via sol–gel processes, module assembly, and template routes have responded to professionalized features and enhanced performance. This review presents the most studied hydrogel materials, the classification of aerogel materials, and their applications in flexible sensors, batteries, supercapacitors, catalysis, biomedical, thermal insulation, etc. [ABSTRACT FROM AUTHOR]

Drawing inspiration from the intricate soft structures found in nature, soft actuators possess the ability to incrementally execute complex tasks and adapt to dynamic and interactive environments. In particular, the integration of sensor data feedback allows actuators to respond to environmental stimuli with heightened intelligence. However, conventional rigid sensors are constrained by their inherent lack of flexibility. The current manufacturing processes for flexible sensors are complex and fail to align with the inherent simplicity of soft actuators. In this study, to facilitate the straightforward and consistent sensing of soft pneumatic actuators, carbon–polydimethylsiloxane (CPDMS) materials were employed, utilizing 3D printing and laser-cutting techniques to fabricate a flexible sensor with ease. The preparation of standard tensile specimens verified that the sensor exhibits a fatigue life extending to several hundred cycles and determined its gauge factor to be −3.2. Experimental results indicate that the sensor is suitable for application in soft pneumatic actuators. Additionally, a printed circuit board (PCB) was fabricated and the piecewise constant curvature (PCC) kinematic method was utilized to enable real-time pose estimation of the soft pneumatic actuator. Compared with computer vision methods, the pose estimation error obtained by the sensing method is as low as 4.26%. This work demonstrates that this easily fabricated sensor can deliver real-time pose feedback for flexible pneumatic actuators, thereby expanding the potential application scenarios for soft pneumatic actuators (SPAs). [ABSTRACT FROM AUTHOR]

The significant impact of stress on health necessitates accurate assessment methods, where traditional questionnaires lack reliability and objectivity. Current advancements like wearables with electrocardiogram (ECG) and galvanic skin response (GSR) sensors face accuracy and artifact challenges. Molecular biosensors detecting cortisol, a critical stress hormone, present a promising solution. However, existing cortisol assays, requiring saliva, urine, or blood, are complex, expensive, and unsuitable for continuous monitoring. Our study introduces a passive, molecularly imprinted polymer-radio-frequency (MIP-RF) wearable sensing system for real-time, non-invasive sweat cortisol assessment. This system is wireless, flexible, battery-free, reusable, environmentally stable, and designed for long-term monitoring, using an inductance-capacitance transducer. The transducer translates cortisol concentrations into resonant frequency shifts with high sensitivity (∼ 160 kHz/(log (µM))) across a physiological range of 0.025–1 µM. Integrated with near-field communication (NFC) for wireless and battery-free operation, and three-dimensional (3D)-printed microfluidic channel for in-situ sweat collection, it enables daily activity cortisol level tracking. Validation of cortisol circadian rhythm through morning and evening measurements demonstrates its effectiveness in tracking and monitoring sweat cortisol levels. A 28-day stability test and the use of cost-effective 3D nanomaterials printing enhance its economic viability and reusability. This innovation paves the way for a new era in realistic, on-demand health monitoring outside the laboratory, leveraging wearable technology for molecular stress biomarker detection. [ABSTRACT FROM AUTHOR]

Elastic polymer-based conductive composites (EPCCs) are of great potential in the field of flexible sensors due to the advantages of designable functionality and thermal and chemical stability. As one of the popular choices for sensor electrodes and sensitive materials, considerable progress in EPCCs used in sensors has been made in recent years. In this review, we introduce the types and the conductive mechanisms of EPCCs. Furthermore, the recent advances in the application of EPCCs to sensors are also summarized. This review will provide guidance for the design and optimization of EPCCs and offer more possibilities for the development and application of flexible sensors. [ABSTRACT FROM AUTHOR]

Tactile sensing provides robots the ability of object recognition, fine operation, natural interaction, etc. However, in the actual scenario, robotic tactile recognition of similar objects still faces difficulties such as low efficiency and accuracy, resulting from a lack of high-performance sensors and intelligent recognition algorithms. In this paper, a flexible sensor combining a pyramidal microstructure with a gradient conformal ionic gel coating was demonstrated, exhibiting excellent signal-to-noise ratio (48 dB), low detection limit (1 Pa), high sensitivity (92.96 kPa−1), fast response time (55 ms), and outstanding stability over 15,000 compression-release cycles. Furthermore, a Pressure-Slip Dual-Branch Convolutional Neural Network (PSNet) architecture was proposed to separately extract hardness and texture features and perform feature fusion. In tactile experiments on different kinds of leaves, a recognition rate of 97.16% was achieved, and surpassed that of human hands recognition (72.5%). These researches showed the great potential in a broad application in bionic robots, intelligent prostheses, and precise human–computer interaction. [ABSTRACT FROM AUTHOR]

Flexible conductive films are a key component of strain sensors, and their performance directly affects the overall quality of the sensor. However, existing flexible conductive films struggle to maintain high conductivity while simultaneously ensuring excellent flexibility, hydrophobicity, and corrosion resistance, thereby limiting their use in harsh environments. In this paper, a novel method is proposed to fabricate flexible conductive films via centrifugal spinning to generate thermoplastic polyurethane (TPU) nanofiber substrates by employing carbon nanotubes (CNTs) and carbon nanofibers (CNFs) as conductive fillers. These fillers are anchored to the nanofibers through ultrasonic dispersion and impregnation techniques and subsequently modified with polydimethylsiloxane (PDMS). This study focuses on the effect of different ratios of CNTs to CNFs on the film properties. Research demonstrated that at a 1:1 ratio of CNTs to CNFs, with TPU at a 20% concentration and PDMS solution at 2 wt%, the conductive films crafted from these blended fillers exhibited outstanding performance, characterized by electrical conductivity (31.4 S/m), elongation at break (217.5%), and tensile cycling stability (800 cycles at 20% strain). Furthermore, the nanofiber-based conductive films were tested by attaching them to various human body parts. The tests demonstrated that these films effectively respond to motion changes at the wrist, elbow joints, and chest cavity, underscoring their potential as core components in strain sensors. [ABSTRACT FROM AUTHOR]

Cough is a common symptom of various respiratory diseases. However, recognizing a subject's cough using acoustic imaging can be challenging due to the complexity of coughing and the vulnerability of acoustic acquisition to external interference. This research aims to address these issues by utilizing a flexible piezoelectric ionic liquid‐doped poly(L‐lactic acid) (PLLA) sensor to gather the pressure signals from the human surface. 1‐butyl‐3‐methylimidazolium bis (trifluoromethylsulfonyl)imide ([BMIm]TFSI) ionic liquid (IL) can enhance the piezoelectric performance of PLLA thin film, the corresponding output voltage, and impact sensitivity are improved to three times and 105.1% for the PLLA/IL thin film with 1 wt% IL, 140 °C annealing 2 h and four times drawing ratio. The effect of IL on the crystallization behavior and piezoelectric properties of thin films during their preparation is investigated. The flexible PLLA/IL sensor is integrated into a wearable electronic system which collects and transmits piezoelectric signals from cough‐induced vibrations to the filter for denoising, then the acquired cough data are decomposed using the Empirical Mode Decomposition method and trained in a multi‐layer perception model to detect human coughing. It's evident that the flexible piezoelectric PLLA/IL sensors can be applied to human coughing recognition and show great potential applications in intelligent healthcare. [ABSTRACT FROM AUTHOR]

This study presents a wearable plant tattoo sensor array designed for continuous monitoring of leaf temperature, relative water content, and biopotential. Current plant wearable sensor technologies often require relatively bulky substrates for sensor support and adhesives for leaf attachment, which potentially can hinder plant growth and affect long‐term measurements. The multifunctional tattoo sensor array overcomes these issues by adhering directly to the leaf surface without the need for additional supporting structures or glues. This array includes a biopotential electrode, a resistive temperature sensor, and an impedimetric water content sensor, all constructed using laminated gold‐on‐polymer thin‐film patterns. Due to their mechanical flexibility, stretchability, and conformability, the sensors can seamlessly attach to leaves via van der Waals force. Performances of these sensors are evaluated to explore plant responses under diverse growth environments. This sensor array is capable of both short‐term and long‐term monitoring, offering continuous data and detailed insights into plant physiological responses to various stress conditions. [ABSTRACT FROM AUTHOR]

Since the 21st century, transparent flexible sensors (TFSs) have been widely employed in abundant fields, such as smart glasses, intelligent watches, robots, electronic skin, especially biomedicine. Presently, various materials have been developed, such as metal‐based, carbon‐based, conductive polymer‐based, and ionic liquid‐based (IL‐based) materials. Compared with the first three materials, IL, as a novel material, with the tendency of green chemistry development, has a high application prospect in TFSs. Based on this, this paper mainly discusses recent advances in TFSs based on ILs, with special emphasis on the role of ILs and the factors influencing transparency as well as electricity. The current challenges and opportunities for each type of sensors based on IL are also studied. [ABSTRACT FROM AUTHOR]

Measuring pH in oxidizing solutions is a crucial issue in areas such as aquaculture, water treatment, industrial chemistry, and environmental analysis. For this purpose, a low-cost potentiometric flexible sensor using a polymer film as a pH-sensitive material has been developed in this study. The sensor consists in a polyaniline film electrodeposited from a sulfuric acid solution on a gold electrode previously deposited on a flexible polyimide substrate. The resulting polyaniline-based pH sensors showed an interesting performance detection in aqueous solution, leading to sensitive (73.4 mV per unit pH) and reproducible (standard deviation of 1.75) responses over the entire pH range from 3 to 8. On the contrary, they were inoperative in the presence of oxidizing hypochlorite ions. Thus, other polyaniline films were electrodeposited in the presence of cetyltrimethylammonium bromide or Tritonx100 surfactant in an attempt to improve the sensing performance of the pH sensors in oxidizing solutions. The pH sensors based on polyaniline and Tritonx100 surfactant were then found to be sensitive (62.3 mV per unit pH) and reproducible (standard deviation of 1.52) in aqueous solutions containing hypochlorite ions. All polyaniline films were also characterized by profilometry and electronic microscopy to correlate the physicochemical features with the performance of the sensors. [ABSTRACT FROM AUTHOR]

This study investigated the influence of microstructure on the performance of Ag inkjet-printed, resistive temperature detectors (RTDs) fabricated using particle-free inks based on a silver nitrate (AgNO3) precursor and ethylene glycol as the ink solvent. Specifically, the temperature coefficient of resistance (TCR) and sensitivity for sensors printed using inks that use monoethylene glycol (mono-EG), diethylene glycol (di-EG), and triethylene glycol (tri-EG) and subjected to a low-pressure argon (Ar) plasma after printing were investigated. Scanning electron microscopy (SEM) confirmed previous findings that microstructure is strongly influenced by the ink solvent, with mono-EG inks producing dense structures, while di- and tri-EG inks produce porous structures, with tri-EG inks yielding the most porous structures. RTD testing revealed that sensors printed using mono-EG ink exhibited the highest TCR (1.7 × 10−3/°C), followed by di-EG ink (8.2 × 10−4/°C) and tri-EG ink (7.2 × 10−4/°C). These findings indicate that porosity exhibits a strong negative influence on TCR. Sensitivity was not strongly influenced by microstructure but rather by the resistance of RTD. The highest sensitivity (0.84 Ω/°C) was observed for an RTD printed using mono-EG ink but not under plasma exposure conditions that yield the highest TCR. [ABSTRACT FROM AUTHOR]

As a result of anthropogenic activities, the environment is polluted by heavy metals. The most important task is to find methods to control their content in water. Track-etched membranes (TeMs) can be relatively easily modified by nanometer layers of functional materials with using the Langmuir‒Blodgett technique, which makes it possible to specifically change the structural, selective properties of the membrane surface and obtain new materials with desired properties. The aim of the work was to develop flexible sensors for the analysis of lead ions in water based on poly(ethylene terephthalate) (PET) TeMs with perfluorodecanoic acid (PFDA) nanolayers. Techniques for modifying TeMs based on PET with a monolayer coating based on PFDA by the Langmuir‒Blodgett method, and with two-layer coatings, formed by soaking PET TeMs/PFDA in xylenol orange solutions have been developed. The microstructure and local mechanical properties of the sensor surface were studied by atomic force microscopy, and the wettability and values of the specific surface energy of PET TeMs before and after modification were evaluated using the ''sessile'' drop method. Based on the measurement of electrochemical characteristics, it was found that PET TeMs/PFDA have a higher response of electrochemical characteristics compared to PET TeMs and PET TeMs/PFDA/XO. The limit of detection for lead ions in aqueous solutions at pH = 12 was of 0.652 µg/l within 5 measurements.

As one of the important physiological signals of the human body, changes in respiration can provide an important reference for human health and is an early warning signal for some chronic respiratory diseases on heart or lung diseases. Usually, doctors combine such changes with electrocardiograph (ECG), electroencephalograph (EEG), electromyography (EMG), and electrooculogram (EOG) results of the patient to make a comprehensive analysis and judgment of the condition. Traditional respiratory monitoring methods have the limitation that portability and accuracy cannot be balanced; while the wearable respiratory monitoring sensors have come into the public's view due to their excellent performances, such as light weight, fast response, not interfering with the subject's daily movement, and maintaining excellent measurement accuracy, which provide more possibilities for the improvement of the performances of the wearable devices applied in the early stage of chronic diseases. [ABSTRACT FROM AUTHOR]

Conductive hydrogel is considered a promising wearable sensor material. Developing flexible conductive hydrogel sensors with stretchability, adhesion, and stability remains challenging. In this study, a transparent, self‐adhesive, antifreeze, anti‐UV, stretchable, conductive, and reusable hydrogel with polyacrylamide/glycerol/gelatin/tannic acid/Fe3+ (PGGT‐Fe3+) structure is successfully constructed through a simple one‐pot polymerization method. The PGGT‐Fe3+ hydrogel is composed of dual networks of polyacrylamide and gelatin for organic cross‐linking, using water/glycerol as the dispersion medium, and incorporates a viscous substance: tannic acid, and a conductive substance: metal ions (Fe3+). Due to the introduction of the abundant amino, carboxylic acid, and hydroxyl functional groups on gelatin and tannic acid, the PGGT‐Fe3+ hydrogel exhibits excellent and repeatable adhesion capabilities on various surfaces (including glass, metal, plastic, and pigskin) with maximum adhesion strength of 98 kPa when attached to pigskin. Furthermore, based on the stable conductive network and high conductivity, the hydrogel not only exhibits strain sensitivity, fast response, and stability but also can stably collect epidermal bio signals. In conclusion, this work provides a new approach to the design and development of next‐generation multifunctional conductive hydrogels and opens up vast possibilities for their applications in the flexible electronics field. [ABSTRACT FROM AUTHOR]

Copyright of China Textile Leader is the property of China Textile Information Center and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A pressure sensor array fabricated on a flexible substrate using the printing method can be easily mounted in various locations by combining it with a wireless communication circuit. This is particularly advantageous for applications where wiring is difficult, such as the tip of a robot gripper. Additionally, printed devices are highly efficient in material utilization, facilitating large areas and low‐cost production. In recent years, there has been growing interest in the harmonious interaction between robots and humans, and the intelligentization of robots is a worthwhile research area. Herein, a method for realizing intelligent gripping force control and object recognition robots using a printed flexible pressure sensor array in combination with a wireless communication circuit is proposed. By mounting the sensor array on a robot gripper and performing arithmetic processing on software, these capabilities are achieved. [ABSTRACT FROM AUTHOR]

With the rapid advancement of modern technology, flexible and wearable electronics, particularly electromechanical sensors, have gained considerable attention for motion‐based applications in medical health monitoring and artificial intelligence. Correspondingly, extensive efforts have been dedicated to enhancing their performance and practicality. Electromechanical sensors based on functional composites and structures accurately detect and monitor the body, generating the corresponding output signals. However, there are several limitations in manufacturing composite sensors, such as the selection and combination of functional materials, geometrical structures, constructed conductive pathways, stability of output signals, and operational lifetime. Thus, this review summarizes notable trends in the electromechanical sensors using functional composites and structures. This also provides an overview of different types of electromechanical pressure and strain sensors, exploring their operational mechanisms regarding triboelectricity, piezoelectricity, piezocapacitance, and piezoresistivity. The unique characteristics of functional materials, including conductive polymers, nanostructured metals, and carbon nanomaterials and composites, are analyzed alongside various design concepts for highly flexible and stretchable sensors. Furthermore, potential applications concerning human motion and human–machine interfaces are also recommended. Additionally, several future outlooks are reviewed for insights into future prospects and strategies. Thus, this review can assist readers in understanding current electromechanical devices more accurately. [ABSTRACT FROM AUTHOR]

Human–machine interactions (HMIs) have advanced rapidly in recent decades in the fields of healthcare, work, and life. However, people with disabilities and other mobility problems do not have corresponding high-tech aids for them to enjoy the convenience of HMIs. In this paper, we propose a sensor with a wave-shaped (corrugated) electrode embedded in a friction layer, which exhibits high sensitivity to skin fold excitation and enormous potential in HMIs. Attributing to the wave-shaped electrode design, it has no built-in cavities, and its small size allows it to flexibly cope with folds at different angles. By specifying the carbon nanotube hybrid silicone film as the electrode layer material and silicone film as the friction layer, good electrical output performance, tensile properties, and biocompatibility can be achieved. Then, the sensor is tested on various joints and skin folds of the human body, the output signals of which can be distinguished between normal physiological behavior and test behavior. Based on this sensor, we designed a medical alarm system, a robotic arm assistive system, and a cell phone application control system for the disabled to help them in the fields of healthcare, work, and life. In conclusion, our research presents a feasible technology to enhance HMIs and makes a valuable contribution to the development of high-tech aids for the disabled. [ABSTRACT FROM AUTHOR]

Monitoring immune-supporting micronutrients such as vitamins C and D is relevant as these nutrients are involved in metabolic pathways to fight against viruses and bacteria. The simultaneous determination of these biomarkers in the same sample volume is challenging, with multistep protocols if labels and redox probes are required. In this paper, we report on a flexible bioelectronic chip combining a 25-hydroxyvitamin D3 metabolite (25-(OH)-D3) immunoassay with an electrocatalytic assay for vitamin C. One of the sensors in the chip was made with graphitic carbon nitride modified with the electroactive dye toluidine blue, decorated with electrodeposited 6.5 nm gold nanoparticles, and coated with a layer of anti-25-(OH)-D3 antibodies. With this sensor, 25-(OH)-D3 could be detected via chronoamperometry at concentrations ranging from 0.1 to 700 ng mL–1 with a limit of detection (LOD) of 0.01 ng mL–1. The other sensor had 24.7 nm Pearls carbon nanoparticles whose electroactivity permitted vitamin C detection in the range from 1 to 140 μM, with an LOD of 0.12 μM. Since the chip is flexible and does not contain labels or redox probes, it has the potential for use in wearable devices to track vitamins in bodily fluids, aiding personalized nutrition by preventing deficiencies and toxicity. [ABSTRACT FROM AUTHOR]

The remarkable flexibility and heightened sensitivity of flexible sensors have drawn significant attention, setting them apart from traditional sensor technology. Within this domain, hydrogels—3D crosslinked networks of hydrophilic polymers—emerge as a leading material for the new generation of flexible sensors, thanks to their unique material properties. These include structural versatility, which imparts traits like adhesiveness and self-healing capabilities. Traditional templating-based methods fall short of tailor-made applications in crafting flexible sensors. In contrast, 3D printing technology stands out with its superior fabrication precision, cost-effectiveness, and satisfactory production efficiency, making it a more suitable approach than templating-based strategies. This review spotlights the latest hydrogel-based flexible sensors developed through 3D printing. It begins by categorizing hydrogels and outlining various 3D-printing techniques. It then focuses on a range of flexible sensors—including those for strain, pressure, pH, temperature, and biosensors—detailing their fabrication methods and applications. Furthermore, it explores the sensing mechanisms and concludes with an analysis of existing challenges and prospects for future research breakthroughs in this field. [ABSTRACT FROM AUTHOR]

Physical sensors with distinctive characteristics such as extreme thinness, low modulus, lightweight design, and exceptional flexibility and stretchability are garnering considerable interest. This is due to their ability to effectively measure and quantify electrical signals generated by human activities. The current methods for making sensors are complicated and call for a lot of organic solvents, which are bad for the environment as well as human health. A flexible stretch sensor is proposed, utilizing a hierarchical layer of graphene nanoplates, and is prepared through a straightforward, solvent-free method. The flexible sensors obtained demonstrate remarkable characteristics, such as a nearly linear response, low strain detection limits down to 0.1%, a substantial strain gauge factor of up to 30, and exceptional cyclic stability enduring over 1000 cycles. Also, the sensors have been successfully employed in wearable devices to detect human motions, displaying excellent sensitivity to small-range movements such as swallowing, clicking, and other small-range movements in addition to large-scale movements of the wrists, ankles, and knees. The utilization of a completely eco-friendly technique in this study, devoid of any organic solvents unlike the majority of published graphene-based sensors, underscores the tremendous potential for wearable sensors. [ABSTRACT FROM AUTHOR]

In this article, a novel approach is presented for drift‐aware feature learning aimed at calibrating drift biases in soft sensors for long‐term use. The proposed method leverages an autoencoder for data preprocessing to extract expressive signal drift traces features, and incorporates drift characteristics through the latent space representation in a long short‐term memory (LSTM) regression neural network. In the results, it is demonstrated that the proposed approach outperforms other typical recurrent neural networks, such as LSTM, gated recurrent unit, and bidirectional LSTM, with a reduced root mean square error of 60% for the training dataset (≈2.5 h) and 80% for the testing dataset (≈20 h). The proposed approach has the potential to optimize the performance of soft sensors with long‐term drift and reduce the need for frequent recalibration. By compensating for sensor drift using existing prior information and limited time data, the proposed neural network can effectively reduce the complexity and computational burden of the system, without the need for additional settings or hyperparameter fine‐tuning. [ABSTRACT FROM AUTHOR]

Surface acoustic waves sensors are based on piezoelectric materials. These sensors are the best choice for sensing purposes due to their unprecedented accuracy. SAW sensors are often used in biochemical sensors, drug production, chemicals agents and gas analytes as sensing devices. These systems are extremely competitive due to their compact size, high thermal efficiency, stability, and capacity to integrate wirelessly. In the past two decades, considerable research has been conducted on the manufacturing of SAW on rigid substrates. These substrates of SAW sensors preclude their use in wearable technologies. The review will cover the research conducted on flexible saw sensors to highlight limitations in this research area for future applications sensors in wearable technology. In the end, future directions and strategies have been discussed to overcome the current challenges.

Abstract The widespread adoption of smart terminals has significantly boosted the market potential for wearable electronic devices. Two-dimensional (2D) nanomaterials show great promise for flexible, wearable electronics of next-generation electronic materials and have potential in energy, optoelectronics, and electronics. First, this review focuses on the importance of functionalization/defects in 2D nanomaterials, a discussion of different kinds of 2D materials for wearable devices, and the overall structure–property relationship of 2D materials. Then, in this comprehensive review, we delve into the burgeoning realm of emerging applications for 2D nanomaterial-based flexible wearable electronics, spanning diverse domains such as energy, medical health, and displays. A meticulous exploration is presented, elucidating the intricate processes involved in tailoring material properties for specific applications. Each research direction is dissected, offering insightful perspectives and dialectical evaluations that illuminate future trajectories and inspire fruitful investigations in this rapidly evolving field. Graphical Abstract

Wearable devices are currently of great importance in developing health management and care applications and devices especially for early breast cancer detection (BCD). This is supported by the novel innovations in materials and techniques to construct highly accurate and comfortable biosensors for wearables. In this paper, the proposed flexible sensor is integrated with a Bra to realize a wearable breast cancer detection system. The proposed antenna-based sensor is composed of a CPW monopole antenna with an overall compact size of $24\times45$ mm2 on flexible PCB Roger substrate with thickness 0.17 mm. The proposed sensors have enough bandwidth from 1.5 to 8 GHz at -6 dB reflection coefficient and conformal structure for biological structures and biocompatibility. The specific absorption rate (SAR) has been calculated and measured for the proposed sensor with a value of 0.75 W/kg at 0 dBm to ensure safety level. For testing, real shaped rubber phantoms from medical school enables the dynamic combination of breast and tumor to create test scenarios for breast cancer detection. $2\times 2$ antenna-based sensors elements are placed around the breast phantom to gather data on scattering parameters for tumor characterization. Several simulation and measurement scenarios are presented to validate detection, optimum number of sensors to be used as well as training data for developed detection algorithms. Artificial intelligence techniques are used among which the CAT-Boost technique for scanning collected data and identifying the undesired tumor component inside the breast.

Flexible sensors based on polymer materials have the potential to enable non-invasive health monitoring and exercise tracking. This review summarizes recent progress in developing flexible sensing platforms for healthcare and fitness applications. Key materials like conductive polymers and elastomeric substrates provide the basis for flexible strain, pressure, chemical and gas sensors. Advances in manufacturing techniques such as printing and photolithography have enabled the scalable fabrication of polymer-based sensor arrays. Flexible chemical sensors for sweat and breath analysis show promise for non-invasive diagnostics. Strain sensors integrated into wearables and textiles can map body motions during exercise. Challenges remain in improving sensor sensitivity, selectivity and long-term stability. However, polymer-based flexible sensors offer advantages like conformability, biocompatibility and low cost that make them well-suited for disposable and skin-mounted devices. With further refinements in materials, manufacturing and data analytics, flexible sensors have the potential to transform point-of-care health monitoring, nutrition guidance, fitness training and chronic disease management.

Quantitative analysis of harmful patina components on the surface of bronzeware is crucial as patina can corrode artifacts. Surface-enhanced Raman spectroscopy (SERS) has a common application in surface analysis. However, there exists an absence of documented investigations concerning the quantitative analysis of detrimental patina, particularly the chloride patina. To achieve high sensitivity in targeting harmful patina, we report a fabrication method for constructing Ag/Au alloys in the pores and on the surface of UiO-66 (zirconium 1,4-dicarboxybenzene metal–organic framework) nanomaterials, resulting in Ag/Au/UiO-66 nanoparticle monolayers formed by self-assembly at the oil–water interface. By incorporating them onto the surface of PVA hydrogel, we obtained SERS sensor devices with excellent flexibility, outstanding optical transparency, and ultrahigh activity. These sensor devices efficiently sample irregular surfaces and detect micrometer-scale specimen. They significantly enhance the Raman characteristic peaks of measured objects, facilitating precise analysis of the patina composition on the surface of bronze artifacts. The Raman peak at 118 cm–1 was boosted from 367 to 11,909 for detecting harmful patina, and the enhancement factor of the SERS substrate was calculated to be 3.6 ×1010 for detecting the Raman peak of rhodamine 6G (R6G), which could be easily detected at 610 cm–1 at a concentration of 10–13 mol/L (M). The Raman peaks at 610 cm–1 from the SERS substrate could also be readily detected. By grafting the organic fluorescent group amino-MQAE onto the surface of Ag/Au/UiO-66 nanoparticles (NPs), the content of harmful patina on the surface of bronze artifacts treated for different durations was indirectly determined. These results indicate the successful construction of the Ag/Au alloy on the surface of UiO-66 NPs, resulting in SERS sensor devices with excellent flexibility, optical transparency, and ultrahigh sensitivity. [ABSTRACT FROM AUTHOR]

Porous conductive composites hold immense promise in flexible sensors and soft robotics due to their pressure‐responsive electrical conductivity. Unlike non‐porous composites whose pressure sensitivity is limited by relatively high elastic modulus, porous materials show improved pressure sensitivity owing to their lower stiffness. Despite this, existing porous composites still suffer from insufficient pressure sensitivity or narrow detection ranges, severely restricting their applications. This work presents a liquid metal hybrid filler porous composite to address these issues. Through experiment and simulation optimization, the composite exhibits a conductivity increase of five order‐of‐magnitude over 0–250 kPa, demonstrating a 900% higher pressure sensitivity than the best non‐porous counterpart in this work. The composite maintains a highly linear response (R2 of 0.999) over an exceptionally wide dynamic range up to 8.9 MPa, with a pressure sensitivity of 8.1 MPa–1, surpassing the state‐of‐the‐art in both pressure range and sensitivity. A proof‐of‐concept pressure sensor array further demonstrates the composite's excellent sensing performance, showing stable response under 100‐cycle loading with a measured pressure deviation of only 1.4%, outperforming existing commercial pressure sensors in terms of sensitivity, detection range and cyclic stability. The porous material design strategy opens doors for high sensitivity pressure sensors in wearable devices, flexible electronics, and soft robotics. [ABSTRACT FROM AUTHOR]

The field of continuum robotics is rapidly developing. The development of new kinematic structures, locomotion principles and control strategies is driving the development of new types of sensors and sensing methodologies. The sensing in continuum robots can be divided into shape perception and environment perception. The environment perception is focusing on sensing the interactions between the robot and environment. These sensors are often embedded on an outer layer of the robots, so the interactions can be detected. The shape perception is sensing the robot's shape using various principles. There are three main groups of sensors that use the properties of electricity, magnetism and optics to measure the shape of the continuum robots. The sensors based on measuring the properties of electricity are often based on measuring the electrical resistance or capacitance of the flexible sensor. Sensors based on magnetism use properties of permanent magnets or coils that are attached to the robot. Their magnetic field, flux or other properties are then tracked, and shape reconstruction can be performed. The last group of sensors is mostly based on leveraging the properties of traveling light through optical fibers. There are multiple objectives of this work. Objective number one is to clearly categorize the sensors and make a clear distinction between them. Objective number two is to determine the trend and progress of the sensors used in continuum robotics. And finally, the third objective is to define the challenges that the researchers are currently facing. The challenges of sensing the shape or the interaction with the environment of continuum robots are currently in the miniaturization of existing sensors and the development of novel sensing methods. [ABSTRACT FROM AUTHOR]

Microstrip crescent antennas offer compactness, conformability, low profile, high sensitivity, multi-band operability, cost-effectiveness and ease of fabrication in contrast to bulky, rigid horn, helical and Vivaldi antennas. This work presents crescent sensors for monitoring brain pathology associated with stroke and atrophy. Single- and multi-element crescent sensors are designed and validated by software simulations. The fabricated sensors are integrated with glasses and experimentally evaluated using a realistic brain phantom. The performance of the sensors is compared in terms of peak gain, directivity, radiation performance, flexibility and detection capability. The crescent sensors can detect the pathologies through the monitoring of backscattered electromagnetic signals that are triggered by dielectric variations in the affected tissues. The proposed sensors can effectively detect stroke and brain atrophy targets with a volume of 25 mm3 and 56 mm3, respectively. The safety of the sensors is examined through the evaluation of Specific Absorption Rate (peak SAR < 1.25 W/Kg, 100 mW), temperature increase within brain tissues (max: 0.155 °C, min: 0.115 °C) and electric field analysis. The results suggest that the crescent sensors can provide a flexible, portable and non-invasive solution to monitor degenerative brain pathology. [ABSTRACT FROM AUTHOR]