Search Results (641)

Flexible sensors are important for wearable health monitoring, strain detection, and temperature sensing because of their mechanical flexibility and functional versatility. Here, a femtosecond laser direct scanning method was used to fabricate porous laser-induced graphene (LIG) and further modify it with platinum nanoparticles (PtNPs), forming Pt/LIG. This mask-free and rapid process enables simultaneous patterning and functionalization of flexible sensors. The introduction of PtNPs improves the electron transport and surface adsorption properties of LIG. As a result, the sheet resistance of Pt/LIG is reduced to 2.41 Ω/sq, enhancing electrical conductivity and suitability for sensing applications. Based on this method, highly sensitive strain and temperature sensors were fabricated. The Pt/LIG strain sensor shows a ΔR/R₀ of 1141.8 at a bending angle of 90°, about 213% higher than that of pristine LIG, with fast response and recovery times of 36 and 56 ms, respectively. The temperature sensitivity also improved by about 650%, with a temperature coefficient of resistance of 0.240%/°C, compared with −0.032%/°C for pristine LIG. Overall, this work provides a fast and precise strategy for fabricating nanoparticle–graphene composites for flexible electronics, wearable health monitoring, and environmental sensing. Full article

Ionogels combining ionic liquids with polymer networks show promise for flexible electronics, but their mechanical and functional performance often needs enhancement. Here, we report a series of magnetic nanocomposite ionogels fabricated by doping triiron tetraoxid (Fe₃O₄) nanoparticles into a [C₂mim]⁺[EtSO₄]⁻-dispersed cross-linked PAA matrix. The effect of PAA content (10–20 wt%) on the optical, mechanical, and dielectric properties of pure imidazolium ionogels was first investigated. Increasing PAA concentration enhanced tensile strength (up to ~0.7 MPa) and compressive modulus (~0.65 MPa) while reducing optical transmittance; dielectric relaxation peaks around 6–8 GHz were observed, with the 15 wt% sample showing the highest permittivity. Subsequently, Fe₃O₄ nanoparticles (0–20 wt%) were incorporated into the 10 wt% PAA ionogel. The resulting magnetic ionogels exhibited reduced tensile strength, but significantly increased elongation (up to ~12 strain), indicating network softening. Magnetic hysteresis measurements confirmed superparamagnetic behavior with saturation magnetization reaching ~2.5 emu/g at 20 wt% Fe₃O₄ loading. This work demonstrates a facile strategy to simultaneously tune mechanical, dielectric, and magnetic properties in imidazolium ionogels, providing guidelines for designing soft multifunctional materials for microwave absorption, magnetic actuation, and flexible sensor applications. Full article

With the rapid advancement of wearable technologies, high-performance flexible sensors have garnered significant research interest. This study presents a PAM-5 hydrogel characterized by exceptional tensile strain (425%), superior compressive modulus (325 kPa), and notable ionic conductivity (1.1 S/m), serving as a robust mechanical framework and electrical foundation for developing advanced sensors. The PNP-5 integrated hydrogel sensor fabricated from this material demonstrates an extensive sensing range (2–53 kPa), remarkable sensitivity, and rapid response time (~321 ms), with its outstanding performance attributed to the synergistic structural design. Furthermore, the sensor exhibits excellent durability, maintaining consistent voltage output (~6.5 mV) across 1000 compression cycles, confirming its long-term operational stability. Through real-time monitoring of physiological signals and biomechanical movements including finger bending, respiration, and grasping, combined with spatial pressure mapping experiments using a 5 × 5 array touchpad, the device’s potential applications in wearable sensing platforms and human–machine interface systems are effectively demonstrated. This self-powered hydrogel sensor not only advances the performance metrics of flexible electronic devices but also establishes a solid experimental basis for future development of intelligent materials in health monitoring and interactive technologies. Full article

Two-dimensional (2D) materials have emerged as a key platform for next-generation electronics due to their atomic thickness and tunable properties. Iron disulfide (FeS₂), known as pyrite, with a bandgap of ~0.95 eV, is suitable for solar energy applications. However, its performance is limited by defects in bulk crystals. Reducing FeS₂ to a single layer eliminates bulk defects and enables strain engineering of the bandgap. In this study, First-principles density functional theory (DFT) calculations are performed using the CASTEP code and the PBEsol functional to examine the structural, electronic, and optical properties of a distorted 1T′-phase FeS₂ monolayer. Full geometry optimization yields lattice parameters a′ = 17.594 Å, b′ = 3.20231 Å, c′ = 5.28091 Å, and Fe–S bond angles of ~75.8° and ~98.2°, confirming symmetry-breaking distortion. The monolayer is dynamically stable, showing no imaginary modes in the phonon dispersion, and remains structurally intact up to 1000 K in molecular dynamics simulations. The unstrained system has an indirect bandgap of 0.70 eV, with the valence band maximum at the Γ point (dominated by S-p states) and conduction band minimum near the X point (Fe-d states). Under mechanical strain (±4%), the bandgap decreases significantly: from 0.70 eV to 0.44 eV under +4% tensile strain along the y-axis, and to 0.53 eV under −4% compressive strain. Biaxial strain causes weaker modulation, reducing the gap to 0.66 eV (+4%) and 0.62 eV (−4%). Optical absorption exceeds 10⁴ cm⁻¹ for photon energies above the bandgap, with tensile strain causing redshifts and compressive strain inducing blueshifts. These findings demonstrate that 2D FeS₂ is mechanically robust, electronically tunable, and optically active, making it a promising candidate material for flexible strain sensors and photovoltaic devices. This work is intended to motivate and inform future synthesis efforts. Full article

High-entropy alloys (HEAs), composed of five or more principal elements in near-equimolar ratios, have emerged as a groundbreaking class of materials for next-generation flexible electronics. This review systematically examines the unique potential of HEAs as sensing materials, moving beyond their traditional role as structural components. We first elucidate the fundamental mechanisms—core effects including lattice distortion, sluggish diffusion, and the cocktail effect—that endow HEAs with an exceptional synergy of high strength, good ductility, tunable electrical resistivity, and superior electrocatalytic activity. Subsequently, we critically analyze the state-of-the-art strategies for processing HEA-based micro/nano structures, including mechanical alloying, wet-chemical synthesis, and non-equilibrium deposition techniques, with an emphasis on their compatibility with flexible substrates. The core of the review categorizes and discusses the latest advances in HEA-based flexible sensors for strain/stress, gas, and electrochemical (e.g., glucose, biomarkers, heavy metals) detection, highlighting the structure–property–performance relationships. Representative studies have demonstrated that HEA flexible strain sensors achieve a temperature coefficient of resistance as low as 45.59 ppm/K with no signal drift over 6000 stretching cycles; room-temperature hydrogen sensors reach a detection limit down to 31 ppb with a response time of 19 s; and non-enzymatic glucose sensors deliver a sensitivity up to 3043 μA·mM⁻¹·cm⁻². Finally, we summarize the key challenges—such as manufacturing scalability, long-term stability under dynamic deformation, and cost-effectiveness—and provide a forward-looking perspective on promising research directions, including high-throughput compositional screening, multi-functional sensor arrays, and the integration of machine learning for rational material design. Full article

Conductive hydrogels are promising materials for fabricating flexible wearable strain sensors. However, their practical application remains limited by several challenges, including poor mechanical strength, unstable sensitivity, restricted stretchability, and poor structural durability. In this study, a zirconium-reinforced conductive hydrogel (PSPZr) with a dual chemical–physical cross-linked network was designed and developed. In the structural framework, polypyrrole-decorated silk fibroin (SF/PPy) functioned as a conductive reinforcing component, acrylamide and sulfobetaine methacrylate constituted the flexible polymer basis, and zirconium ions (Zr⁴⁺) acted as ionic cross-linkers to construct a dual cross-linked structure and improve mechanical stability. Due to the synergistic contributions of hydrogen bonding, ionic coordination interactions, and SF/PPy, the optimized PSPZr hydrogel exhibited a tensile strength of 166 kPa and a maximum strain 559%. Additionally, it achieved improved elasticity and reliable shape recovery. Furthermore, the optimized PSPZr hydrogel exhibited a broad working range, sensitivity with a gauge factor of 2.8, rapid response, recovery kinetics, and exceptional cycling stability over 1000 stretching–releasing cycles as wearable strain sensors. This performance enabled real-time and accurate monitoring of diverse human motions. Therefore, this study presents a feasible and versatile strategy for developing mechanically robust and electrically stable conductive hydrogel, providing a new pattern for advanced applications in wearable sensors. Full article

Flexible strain sensors have attracted considerable attention in gait recognition owing to their ability to adhere directly to the skin near joints and transduce local deformation. In existing work, however, sensor placement and orientation are largely determined by anatomical experience, while multi-channel classification still relies on back-end digital processors, whose power consumption and latency constrain system practicality in wearable scenarios. This paper presents an integrated design path that proceeds from skin-mechanics theory through sensor-layout optimization to analog-domain front-end inference. On the layout side, the lines-of-non-extension (LoNE) theory is employed to convert the selection of sensor attachment angles from empirical judgment into a calculable mechanics problem; guided by the spatial course of LoNE in the ankle and knee regions, the positions and angles of the nine sensors are determined individually—channels perpendicular to the LoNE capture maximum strain, channels offset by 45 degrees supplement non-sagittal-plane information, and a channel aligned along the LoNE provides a near-zero-strain reference. On the circuit side, the mathematical equivalence between the weighted summation of a linear classifier and Kirchhoff’s current law (KCL) nodal current superposition is exploited to map the classification operation onto current aggregation in an analog circuit, yielding an in-sensor computing (ISC) front end in which the nine-channel weighted summation is completed in a single analog step. The sensors are fabricated by screen-printing a liquid-metal–polymer composite conductive ink onto a TPU film substrate, with a gauge factor RSD of $6.8\%$ and a tensile linearity $R^2>0.99$. Using walking, running, and stair descent as verification targets, the analog classifier reaches 99% accuracy at the circuit-level functional-verification stage. On real multi-subject data, it achieves $87.0\%\pm 8.4\%$ accuracy under intra-subject cross-session validation, with an analog-domain inference response faster than $100\mathsf{\mu }\mathrm{s}$. This design path is not bound to a specific joint or sensor material; when the layout methodology is extended to additional joint regions and the circuit architecture incorporates multiple outputs to cover more classification categories, the same workflow remains applicable, offering a promising low-power, lightweight technical solution for wearable motion monitoring. Full article

Recently, conductive hydrogels have gained extensive applications in flexible wearable electronics and have garnered considerable attention. However, their inherent swelling behaviour and limited mechanical strength have hindered their further development. In this study, a polyacrylamide/sodium alginate (PAM/SA, PS)-based hydrogel with high mechanical strength and anti-swelling properties was prepared by combining mechanical stretching–drying pretreatment with a bimetallic ion (Li⁺/multivalent metal ion) post-soaking strategy. Among multivalent metal ions (Ca²⁺, Al³⁺, and Zr⁴⁺), the Al³⁺-crosslinked hydrogel (PS-Al³⁺) demonstrated outstanding overall performance. It exhibited excellent mechanical properties, with tensile strength, elongation at break, and impact strength reaching 9.71 MPa, 993.53%, and 75 MJ/m³, respectively. Its dense network structure also gave it excellent anti-swelling properties (swelling ratio of 14%). As a strain sensor, the PS-Al³⁺ hydrogel displayed good conductivity (1.33 S/m), high sensitivity (GF = 2.25), fast response (response time of 403 ms), and negligible hysteresis (recovery time of 407 ms). Benefiting from its exceptional resistance to expansion, the material’s sensor response signals in underwater environments are highly consistent with those in air. Furthermore, this sensor has been successfully applied to swimming motion monitoring and data transmission in underwater environments. This study proposes a novel, low-cost, and simple approach for developing flexible sensors suitable for underwater environments. Full article

Urban pipelines are essential infrastructure components in modern cities. Their curved and confined structures make sensing difficult to achieve. In conventional flexible sensing devices, pressure and bending signals often interfere with each other. To address this problem, we propose an integration strategy for multi-array sensors on flexible printed circuits. The approach integrates laser-induced graphene pressure sensors and bending sensors on a polydimethylsiloxane substrate with flexible printed circuits. This integration enables stable and reliable signal acquisition and the device shows good performance under pressure loading. It has high linearity (R² > 0.99), low hysteresis (2.68%), and a fast response time (~50 ms) in the range of 0–120 kPa. The sensing architecture is based on geometry-induced strain-field differentiation, which suppresses pressure–bending cross-interference and improves multimodal signal discrimination through structural design. Pressure mainly produces isotropic signals, while bending generates anisotropic strain signals. We test the device in simulated pipeline environments. Protrusion defects and corrosion defects generate different signal patterns. These differences allow clear defect identification. The device further supports spatial posture sensing and bending-state monitoring in complex curved pipeline conditions. Full article

This study focused on a three-dimensional cross-linked hydrophobic association (PS) hydrogel framework. Phytic acid (PA) was selected as both a dopant and an antifreeze agent, and it was combined with an ethylene glycol/water binary solvent to construct a dual antifreeze system. The resulting composite conductive hydrogel, E/PS/PA-PPy, exhibited synergistically enhanced electrical conductivity, mechanical strength, and antifreeze properties. At a PA concentration of 0.1 M, a structurally uniform and ordered three-dimensional network was formed. The PS/PA-PPy hydrogel exhibited an elongation at break of 2595.7% and a high conductivity of 1.8 S/m, while maintaining excellent flexibility and adhesion. Owing to the synergistic antifreeze effect, the freezing point of the E/PS/PA-PPy hydrogel was reduced to −42.3 °C, and after 35 days of room-temperature storage, the weight loss was less than 7%, indicating outstanding water retention. The assembled flexible strain sensor exhibited a sensitivity of 2.09, with response and recovery times both less than 0.25 s. Notably, it exhibited good cyclic stability and accurately monitored human movements. Furthermore, the sensing performance remained stable without significant attenuation even at −20 °C. The results demonstrate the broad application prospects of the hydrogel in flexible electronics such as wearable health monitoring systems and human–machine interfaces in extreme environments. Full article

Micro- and nanoscale mass sensing is crucial for applications such as molecular detection and wearable monitoring. However, the observation of mass perturbations in flexible composite structures requires systematic theoretical evaluation. This study develops a dual-mode vibration-based mass-sensing model based on a film–substrate composite strip. By releasing and re-stretching pre-strain in the soft substrate, the ribbon can reversibly switch between a two-dimensional flat configuration (Mode 1) and a three-dimensional buckled configuration (Mode 2), leading to distinct dynamic responses. Under a finite-deformation Euler–Bernoulli beam assumption, displacement fields and kinematic relations are formulated for both configurations. An energy-based approach is employed to decompose the total energy into stretching and bending contributions, while an added-mass block is incorporated into the kinetic energy as a lumped mass. The governing equations of motion are derived using the Lagrange equations and the Hamiltonian function. Based on these results, the influence of the added mass on displacement signatures is examined, and the mode-dependent observability in the flat versus buckled states is compared, providing an analytical basis for mass sensor evaluation. Full article

This study proposes a knee joint motion detection method based on overlapping spectrum demodulation using fiber Bragg grating (FBG) technology. A flexible FBG encapsulated with polydimethylsiloxane (PDMS) is attached to the joint surface. Axial strain in the FBG sensor is generated due to the bending and extension movements of the joint, which leads to a central reflection wavelength shift of the FBG sensor. The overlapping spectrum between the FBG reflection and the output of a tunable fiber laser is related to the wavelength shift of the FBG. The variation is expressed as the changes in reflected optical power received by an optical power meter. It transforms complex spectral analysis into intuitive optical power measurement for demodulating the reflected wavelength of the FBG sensor. The relationship between the optical power of the overlapping spectrum and wavelength shift of the FBG induced by joint motion is theoretically and experimentally analyzed. The real-time demodulation of joint motion is realized based on this relationship. Experimental results demonstrate that the system exhibits good repeatability in monitoring knee joint motion. The performance and practical potential of the system are evaluated through a quantitative comparison with existing techniques and an analysis of its current limitations. Full article

In this study, poly(vinylpyrrolidone) (PVP)-modified liquid metal (LM) particles were formulated into a mixed-solvent system comprising ethanol (EtOH), 1,2-propanediol (1,2-PG), and a trace amount of N,N-dimethylformamide (DMF). This design addresses the instability, poor wetting/adhesion on polydimethylsiloxane (PDMS), and limited rheological tunability of conventional LM inks for screen printing. By regulating solvent evaporation during drying, the system enables coordinated control over wettability, viscosity, shear-thinning behavior, and drying-induced film formation. At an LM:PVP weight ratio of 20:1, the contact angle on PDMS decreased from 115° to 17.8°. The ink exhibited pronounced shear-thinning characteristics with tunable viscosity in the range of 1000–3000 cP, meeting the screen-printing requirements of facile mesh passage and rapid setting. Following laser activation, the printed conductive patterns demonstrated stable electrical performance, with a resistance drift of less than 1% after 14 days of storage and a ΔR/R₀ of less than 1% after 3000 bending cycles at a bending diameter of 1 cm. Furthermore, a resistance drift of less than 3% was observed after 1000 stretching cycles at 30% strain. This study proposes a viable materials and processing strategy for the reliable screen printing of LM:PVP ink on PDMS substrates toward flexible conductive electronics. The motion-monitoring test is presented only as a preliminary proof-of-concept demonstration of motion-induced electrical resistance response, rather than as a sensor performance evaluation. Full article

With the rapid development of flexible electronics technology, flexible wearable sensors based on Lanthanum Strontium Manganese Oxide (La_1-xSr_xMnO₃) have garnered extensive attention in recent years due to their excellent multi-functional integration, environmental stability and biocompatibility. This review systematically analyzes the preparation methods, process optimization strategies, multi-performance integration technologies, and the expansion of the application field of La_1-xSr_xMnO₃-based flexible sensors. Firstly, the basic characteristics and sensing mechanism of the La_1-xSr_xMnO₃ material were presented, including its temperature sensitivity, strain response characteristics, and magnetoresistance effect. Secondly, the fabrication process of flexible sensors was elaborately discussed, with a focus on analyzing crucial technologies, such as laser induction and transfer printing technology. Subsequently, the strategies for regulating the electrical, thermal, and mechanical properties of materials through element doping, along with the multimodal sensing integration and signal decoupling methods, were expounded. Furthermore, the actual performance of this type of sensor in fields such as health monitoring, human–computer interaction, and extreme environment applications was summarized. Finally, the challenges and future development directions of La_1-xSr_xMnO₃-based flexible sensors are outlined, providing theoretical references for the design and optimization of next-generation flexible electronic devices. Full article

Polyvinyl alcohol (PVA)-based hydrogels suffer from insufficient mechanical strength, while aramid nanofibers (ANF) have intrinsic insulation that limits their sensing applications, and the synergistic effect of composite fillers remains underexplored. This study aims to develop a multifunctional PVA/ANF/NaCl composite organohydrogel for high-performance flexible sensors. The gel was fabricated via freeze–thaw crosslinking, solvent exchange and NaCl impregnation, with systematic investigations of its microstructure, mechanical, electrical and multifunctional sensing properties, and a corresponding triboelectric nanogenerator (TENG) and self-powered handwriting recognition system were constructed. Results show that 2% ANF significantly enhances the gel’s mechanical performance, 0.5 M NaCl achieves optimal mechanical-electrical balance, the gel-based sensor exhibits excellent distance, pressure and strain sensing with high cyclic stability, the TENG delivers stable electrical output, and the recognition system achieves 95% accuracy on the test set. This work provides a new material and design strategy for advanced flexible electronic devices. Full article