Search Results (415)

Wearable electronics, particularly dry epidermal electrodes, provide human-connected interfaces for recording biopotential signals. However, their practical utility is often hindered by their limited operational longevity and the resulting environmental burden of electronic waste, as most conventional electrodes are discarded after a single use because of performance degradation. Herein, a reusable, soft, and conductive epidermal electrode is reported, fabricated through the precise incorporation of functional additives. By intentionally modulating the polymer chain architecture, a homogeneous composite is developed that exhibits exceptional flexibility, high conductivity (~100 S/cm), softness (~649 kPa), and stretchability (~234%). This molecular-level design promotes strong intermolecular interactions at the skin–electrode interface, facilitating persistent adhesion and conformability to challenging surfaces, including wet, wrinkled, and stretched skin. These properties enable reliable electrocardiography acquisition through 50 repeated attachment and detachment cycles, over which a commercial Ag/AgCl gel electrode became unmeasurable after 20. The applicability of the electrode to human–machine interfaces is further demonstrated by capturing clear electromyography signals of muscle activity during a rock–paper–scissors game. This low-modulus electrode platform offers a route towards repeated-use wearable healthcare systems and soft-robotics applications, with the potential to reduce the waste associated with single-use electrodes. Full article

As a crucial intersection of flexible electronics and embodied intelligent robotics, electronic skin is evolving from single flexible sensors toward a skin-like intelligent system integrating flexible support, signal sensing, environmental protection, signal transmission, and intelligent feedback. With expanding application scenarios, materials must simultaneously meet requirements for softness, stretchability, high strength, self-healing, wear resistance, and long-term stability. Bio-based self-healing polyurethane, leveraging tunable soft–hard segment structures, a wide range of mechanical properties, facile dynamic bond formation, and renewable raw materials, offers a novel material design pathway for highly reliable electronic skin. This review examines the structural and performance modulation of bio-based components—such as castor oil, nanocellulose, lignin, chitosan, tannic acid, and vanillin—in polyurethane coatings, analyzes the mechanisms of non-covalent interactions, dynamic covalent bonds, and multi-dynamic networks in segment motion, energy dissipation, damage repair, and interface reconstruction, and further discusses their adaptation strategies in encapsulation layers, sensing layers, circuit layers, and base layers. Particular attention is paid to polyurethane coatings as protective and functional interface layers, where coating structure, adhesion, mechanical durability, and damage recovery determine the long-term reliability of electronic skin devices. Finally, this review summarizes current challenges in multi-performance synergy, conductive network stability, bio-based component consistency, long-term service, and large-scale fabrication, while envisioning future directions such as intelligent encapsulation, multi-layer synergy, and data-driven material design. Full article

Mechanically compliant aerogels are increasingly important for wearable systems that require lightweight porous materials to retain function under repeated deformation. However, compressibility and stretchability impose different structural demands and should not be treated as equivalent manifestations of flexibility. This review provides a loading-mode-specific framework of compressible and stretchable aerogels. It summarizes how network chemistry, interfacial interactions, and multiscale architectures govern deformation, recovery, strength, and fatigue resistance under compression and tension. The relationships between these mechanical characteristics and thermal, spectral, and electrical functions are subsequently discussed in the context of wearable personal thermal management sensors, biosensors, and flexible energy-storage devices. Finally, current challenges are summarized in terms of mechanical–functional balancing, long-term durability, and scalable fabrication, providing guidance for the future development of mechanically reliable aerogel-based wearable materials. Full article

Soft robotic and wearable systems increasingly require actuators that conform to curved surfaces and stretch with the structures they are mounted on, yet conventional shape memory alloy (SMA) form factors—wires, springs, and sheets—remain limited to one-dimensional contraction or out-of-plane bending. This paper presents the Mesh-Structured Shape Memory Alloy (MeSMA) actuator, a thin, planar, and stretchable actuator in which flat SMA wire spans form a periodic mesh clamped by 3D-printed insulating beads; the beads are fabricated by a print–pause–insert process and define the effective beam length ($L_e$) of each span. Isotonic characterization over $L_e$ = 3–7 mm shows that the peak contraction stroke (30–81 mm) and the corresponding optimal payload (7.8–3.9 N) are well approximated by linear functions of $L_e$ over the tested range, consistent with a constant critical bending moment at the span level, establishing a single-parameter design rule for tailoring the actuator operating point. Isothermal tests show that temperature tunes the passive secant stiffness approximately threefold. Separately fabricated specimens exhibit a stroke coefficient of variation of about 1% over 30 thermal cycles with matching degradation trajectories. A tubular compression sleeve demonstrates conformal donning and spatially selective compression enabled by the planar, stretchable form factor. Full article

Temperature-dependent characterization of nanomaterials is commonly performed through electrical measurements, and many temperature-sensing applications similarly rely on electrical readout signals. Although these approaches are simple and widely used, they require direct sample contact and may lose sensitivity when the electrical response is weak, saturated, or only weakly dependent on temperature. In this study, a photoacoustic (PA) measurement system was used to evaluate the temperature-dependent response of AgNW networks. PA measurement system detects ultrasonic waves generated through transient thermoelastic expansion after optical absorption, which enables sensitive probing of temperature-dependent optothermal responses beyond conventional electrical measurements. Silver nanowire (AgNW) films with different surface coverage were fabricated through one to four repeated spin-coating cycles using a 1% AgNW ethanol dispersion containing nanowires with diameters of 20–40 nm and lengths of 10–20 µm. The photoacoustic (PA) signals of the fabricated films were measured at various temperatures using a customized PA measurement system and were compared with sheet resistance values obtained using a four-point probe. Both sheet resistance and PA signals increased with increasing temperature, regardless of AgNW surface coverage. Notably, AgNW films with higher surface coverages showed only weak temperature dependence in sheet resistance but pronounced temperature-dependent PA response. These results indicate that PA analysis is particularly useful for characterizing AgNW networks with higher surface coverage, including those used in stretchable electrodes. All samples showed linear relationships for both sheet resistance and PA signals, with coefficients of determination (R²) exceeding 0.9. Overall, these findings suggest that PA measurement may provide complementary information on temperature-dependent behavior that is not fully reflected in sheet-resistance measurements. Full article

The development of antibacterial hydrogel with stretchable and self-healing properties is an urgent problem in the field of biomedical engineering. Herein, a series of hydrogels with antibacterial activity was successfully fabricated using polyvinyl alcohol (PVA), borax, 4-formylphenyl-β-D-allopyranoside (HLC), 3,3′-dithiobis (propionohydrazide) (DPH) and ionic liquid, 1-aminopropyl-3-methylimidazolium bromide (C₃MimNBr). The hydrogels were formed via in situ crosslinking through multiple dynamic covalent bonds, primarily including borate ester bonds, imine bonds and acylhydrazone bonds. A Field Emission Scanning Electron Microscope (FE-SEM) revealed that the formed hydrogels possessed a typical three-dimensional network structure. Notably, the interpenetrating network structure endowed the hydrogels with excellent stretchability and self-healing capability, as demonstrated by their ability to be molded into various shapes and stretched up to five times their original length. Furthermore, the mechanical properties of the hydrogel were affected by the amount of the ionic liquid added. Antibacterial evaluation using the colony counting method showed that the hydrogels exhibited outstanding antibacterial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). In summary, the multifunctional hydrogels, with favorable stretchability and antibacterial activity, represent promising alternative materials for biomedical engineering applications. Full article

Recently, flexible electronics have attracted widespread attention in personalized health monitoring, soft robotics, and smart human-machine interactions due to intrinsic high stretchability. Among them, constructing buckled structures in flexible devices is one of the most effective strategies to achieve flexibility and stretchability. Flexible electronic devices based on buckled structure (FEDB) have gained significant research progress, owing to their outstanding advantages such as simple fabrication processes, excellent structural stability, and broad applicability. Furthermore, its application areas are expanding to emerging scenarios, including the human body, underwater environments, the oceans, and space. However, there are few systematic reviews concerning their progresses, although researchers show increasing interest in the emerging applications of FEDB. This review summarizes recent research progress in FEDB. First, this review explains the buckled instability mechanism, listing the common conductive and substrate materials. The polymeric substrates discussed mainly include PDMS, TPU, SBS, PC, and hydrogel, which provide the flexibility and deformability required for FEDB. In addition, this review summarizes several methods for constructing buckled structures, including prestretch-release, solvent swelling, thermal, mold, and 3D printing as well as techniques for controlling morphology. Second, this review summarizes the applications of FEDB, such as flexible electrodes, strain and pressure sensors, and energy devices. Particularly, it provides a detailed introduction to the expansion of emerging scenarios, involving underwater monitoring, in vitro and in vivo physiological signal detection, human-machine interactions, and portable capsule devices. Finally, this review points out the current challenges of FEDB, including long-term service stability, adaptability to extreme environments, conformal attachment to complex curved surfaces, and large-scale manufacturing. Full article

Stroke and other neurological injuries impair hand function. Although rehabilitation therapists encourage reintegration of the affected hand into daily activities, there are few tools that can be worn during everyday life that provide quantitative feedback on how much or how effectively the hand is used. Wearable sensors that can accurately track hand movements and are easily applied and removed can present intuitive feedback that could motivate hand use similarly to how pedometers encourage walking. While tracking all the hand and finger joints is needed for scientific studies, under-sensorization, or using fewer sensors than required for tracking all degrees of freedom, may suffice for providing users feedback about hand use in everyday life. Further, it may enable a wearable device to be more easily donned and doffed, more power efficient, and more cost efficient. Here we develop a low-cost, multi-sensor, wireless wearable system for tracking selected hand and wrist movements during everyday life. The system includes fabricated soft, stretchable “e-skin” bend sensors and off-the-shelf inertial measurement units (IMUs) that accurately measure finger bend angles and wrist movements. The system also includes an application and removal protocol that enabled naïve unimpaired participants to apply and remove the system in ~5 min and ~4 min, respectively. The system cost was $111 per device, with prices falling to an estimate of $55 when manufactured at scale. This hand wearable demonstrates accurate kinematic tracking and user-friendly donning/doffing workflows for unimpaired participants, making it a promising platform for everyday hand tracking. Future work will extend this platform to the movement-impaired population for neurorehabilitation applications. Full article

Flexible thermoelectric textiles have emerged as promising materials for wearable energy harvesting and electrothermal applications because they combine mechanical flexibility with the ability to convert low-grade heat into electrical energy. In this study, reduced graphene oxide/zinc oxide/copper oxide (rGO/ZnO/CuO) hybrid nanocomposites were synthesized and deposited onto Cotton–Nylon–Spandex (80:15:05) stretch fabrics using a silicone elastomer-assisted coating process to develop flexible conductive textiles. The influence of nanocomposite loading (2–8 g/100 mL elastomer) on the structural, electrical, thermal, and thermoelectric properties of the coated fabrics was systematically investigated. SEM, EDX, XRD, and Raman analyses confirmed the successful formation and uniform distribution of the rGO/ZnO/CuO hybrid coating on the textile substrate. Increasing the nanocomposite loading progressively reduced the electrical resistance from approximately 42 to 18 MΩ, indicating the formation of an interconnected conductive network, while the Seebeck coefficient increased from 0.049 to 0.056 mV K⁻¹ (49–56 μV K⁻¹). The measured effective thermal conductivity of the coated textile decreased from approximately 12 to 2.68 W m⁻¹ K⁻¹, reflecting changes in the thermal transport behavior of the composite coating. The coated fabrics also exhibited stable electrical performance under repeated bending, stretching (up to 80% strain), and washing, together with improved thermal stability and uniform Joule-heating behavior. These results demonstrate that the rGO/ZnO/CuO hybrid coating provides an effective strategy for developing flexible, mechanically durable, and multifunctional conductive textiles with potential applications in wearable thermoelectric energy harvesting and smart heating systems. Full article

Gallium (Ga)-based liquid metal (LM) composites, particularly those based on eutectic gallium–indium (EGaIn) and related alloys, have emerged as a promising materials platform for soft and deformable energy storage owing to their unique combination of metallic conductivity, fluidic deformability, and adaptive interfaces. Despite rapid advances in LM-enabled devices, binders remain insufficiently understood and are still commonly regarded as passive structural components. Here, we present a comprehensive binder-centered perspective for LM composites, establishing the binder as a key regulator of electro-chemo-mechanical coupling, interfacial stability, transport behavior, and processability in soft energy systems. We show that tailored binder chemistries in Ga-based LM systems—including stretchable batteries, printable conductors, and soft electrochemical devices—govern LM droplet dispersion, suppress coalescence and leakage, and preserve conductive percolation under large deformation, while enabling room-temperature fabrication and printability through rheological regulation and interfacial wetting. Beyond mechanical confinement, emerging binder functionalities—including dynamic bonding, supramolecular interactions, ionically conductive networks, and reversible polymer architectures—enable self-healing interfaces, adaptive transport pathways, and robust adhesion in deformable devices. By integrating recent advances in stretchable batteries, flexible supercapacitors, printable electronics, and multifunctional soft energy systems, we establish a unified multiscale framework linking binder molecular design to device-level electrochemical and mechanical performance. We further discuss sustainability and manufacturing considerations, including recyclable polymer networks, low-temperature fabrication, and scalable processing strategies. Finally, we outline current challenges and future opportunities toward programmable binder systems with tunable viscoelasticity, interfacial reactivity, and adaptive functionality. This Review establishes binder-centered engineering as a key pathway for transforming LM composites from proof-of-concept materials into resilient, manufacturable, and multifunctional soft energy technologies for wearable, stretchable, and biointegrated electronics. 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

This study introduces and characterizes a family of quilling-inspired S-shaped unit-cell architectures intended as building blocks for mechanical metamaterials. In contrast to conventional lattice designs based mainly on straight struts, the proposed geometries use continuous curved elements inspired by paper quilling, enabling deformation mechanisms dominated by bending, rotation, and progressive opening of the curved members. By translating quilling’s coiled and spiraled patterns into engineered geometries, nine distinct S-shaped unit cells were fabricated by fused deposition modeling and tested experimentally under uniaxial tensile loading. Finite element analysis was performed to reproduce the tensile response and to assess the influence of geometry on stiffness, stretchability, and energy absorption. The results show that relatively small changes in radii, span lengths, angular distribution, and symmetry produce significant differences in mechanical response. Compact configurations such as S2, S3, and S5 exhibit high stiffness and limited elongation, whereas S9 shows the highest compliance and stretchability. The results indicate that these quilling-inspired architectures provide a tunable design space and have strong potential for applications in energy absorption, adaptive structures, and lightweight load-bearing systems. Full article

Gel-based flexible electronic sensors have emerged as a transformative class of materials for next-generation applications. These applications are wearable electronics, soft robotics, electronic skin (e-skin), and healthcare monitoring systems. Owing to their intrinsic softness, stretchability, and biocompatibility, gels provide an ideal platform for constructing highly deformable and skin-conformable sensing devices. This paper provides insight into emerging fabrication techniques, including 3D printing, bioprinting, and microfabrication. These techniques have facilitated the creation of complex architectures with improved sensitivity and scalability. The review also focuses on recent advancements that have focused on overcoming traditional limitations. These limitations are poor mechanical strength, dehydration, limited environmental stability, and low sensitivity. In particular, the incorporation of conductive fillers and ionic species has enabled a range of sensing mechanisms. These mechanisms include piezoresistive, capacitive, piezoelectric, and ionotronic responses. Therefore, it allows for the accurate detection of strain, pressure, temperature, and biochemical signals. Finally, this review provides a summary of future research, which is expected to focus on multifunctional integration, sustainable materials, and intelligent data processing. It provides pathways to the widespread adoption of gel-based flexible electronic sensors in both consumer and clinical applications. Full article

With the rapid advancement of artificial intelligence and wearable technologies, the demand for soft, multifunctional electronic materials has grown substantially. Hydrogels have emerged as a promising platform due to their intrinsic softness, stretchability, and biocompatibility. Among them, cellulose-based conductive hydrogels uniquely integrate the sustainability of natural polymers with tunable electrical functionality, offering significant potential for flexible and biointegrated electronics. This review provides a comprehensive and critical perspective on the recent progress in cellulose-based conductive hydrogels. We systematically summarize key design strategies, including physical and chemical crosslinking and interpenetrating network engineering. More importantly, we present a comparative analysis of distinct conductive mechanisms, including ionic conduction, conductive polymers, metallic nanostructures, and carbon-based fillers, highlighting the inherent trade-offs among electrical conductivity, mechanical robustness, and environmental stability. Emerging applications in flexible electronics, energy storage, bioelectronics, and self-powered systems are discussed through structure–property relationships. Finally, we outline current challenges and future directions, emphasizing multifunctional integration, scalable fabrication, and long-term operational stability, thereby providing a framework for the rational design of next-generation sustainable electronic materials. Full article

Precise monitoring of forearm muscle groups is crucial for decoding motor intentions in human–machine interfaces (HMIs) and rehabilitation. However, traditional surface electromyography (sEMG) electrodes face significant challenges in densely packed muscle regions with large skin deformations, leading to severe signal crosstalk and unstable contact. Here, we report a flexible, low-cost 16-channel copper electrode array system designed for the high-density monitoring of multiple forearm muscle activities. Through a facile fabrication process, rigid copper is transformed into a conformable sensing interface. The optimized serpentine interconnects endow the array with excellent stretchability and effectively isolate motion-induced stress, ensuring high-quality signal acquisition under complex deformations. The high-density 2 × 8 array enables the spatiotemporal mapping of distributed flexor and extensor muscle groups. Integrated with a customized wireless data acquisition system, the array successfully demonstrates real-time, multi-channel sEMG monitoring of various hand movements (e.g., fist clenching, wrist flexion/extension), clearly revealing specific muscle activation patterns. This low-cost, high-performance flexible sensor array provides a highly promising tool for complex gesture decoding, electromyographic imaging, and next-generation wearable HMIs. Full article