Liquid metals (LMs) combine metallic conductivity with fluid-like deformability, making them promising for stretchable electronics. However, their low viscosity, surface oxidation, and interfacial instability hinder precise printing and reliable device integration. This review examines how LM properties govern printing behavior, discusses modification strategies and methods spanning two to four dimensions, evaluates applications in stretchable electronics, and establishes material-process-performance relationships to guide future device design and practical manufacturing strategies.
Flexible sensors that can be laminated on curved surfaces are a desired form for aircraft surface impact monitoring. Sensors for such applications must withstand the wide range of temperature fluctuations on aircraft surfaces during flight and exhibit excellent extensibility to attach to and monitor large-scale curved surfaces, whereas existing flexible sensors fail to meet these demands. Here, we report a wide temperature range, ultra-extensible piezoelectric sensor. The sensor employs a flexible piezoelectric film based on polydopamine@barium titanate/cellulose as the sensing layer, enabling excellent temperature stability across a wide range from −50 to 80 °C. The tensile axial interconnects and horizontal connections linking external contact to sensor units, together with a sequential stacking process for the row arrays, enable the overall dual-axis extension of the sensor array with a strain ratio of up to 2500%. The ultra-extensible sensor array is attached to the aircraft surface to monitor impact signals continuously. Via an embedded impact localization algorithm, the response times of 25-channel impact signal data were analyzed to achieve localization of the impact. The ultra-extensible piezoelectric sensor with a wide temperature range holds significant practical value for monitoring unexpected impacts on aircraft surfaces, and will greatly advance the development of structural health monitoring technology for aviation equipment.
Color-selective photodetector arrays are essential for imaging, optical communication, and vision systems. Although advances have demonstrated filterless architectures using wavelength-selective materials, most approaches still depend on vacuum-deposition, rigid substrates, or complex multistep fabrication processes, which hinder scalability and compatibility with flexible or wearable platforms. Here, a fully inkjet-printed, flexible photodetector array is demonstrated, enabling wavelength-selective visible-light detection without external filters, vacuum processes, or lithographic patterning. All components, including electrodes, semiconducting channels, and wavelength-selective absorbers, are printed on a substrate using an office inkjet printer under ambient conditions. Multi-walled carbon nanotubes (CNTs) serve as printable electrodes, while semiconducting single-walled CNTs form the active channels. Color selectivity is achieved by integrating three organic macrocycles with distinct absorption bands, spatially patterned using a tri-color ink cartridge. Each of the three photodetectors exhibits a unique photoresponse, enabling the array to resolve the wavelength and intensity of incident light. The devices maintain stable operation under mechanical deformation and after 1000 cycles of repeated illumination. A lightweight neural network model is incorporated into the system to perform real-time spectral classification with high accuracy under varying illumination conditions. This work introduces a scalable, low-cost route to fabricating flexible, color-selective optoelectronic devices entirely through ambient, additive manufacturing.
Soft bioelectronics have emerged as a transformative platform for wound care by enabling continuous, intimate, and multimodal interfacing with dynamic skin environments. This review systematically elaborates the underlying principles of biophysical and biochemical sensors for capturing critical wound parameters. We further discuss therapeutic soft bioelectronics, including electrical stimulation, phototherapy, and acoustic stimulation strategies, together with responsive drug delivery systems that leverage wound microenvironmental cues. Building upon these foundations, we highlight the development of smart wound care architectures that integrate wireless communication, data interpretation and real-time wound assessment with on-demand transdermal therapeutic actuation in both open-loop and closed-loop systems. Finally, we outline the major challenges facing the field, particularly long-term operational stability and the development of truly intelligent closed-loop platforms, and highlight future opportunities for next-generation soft bioelectronic systems capable of autonomously monitoring and managing complex wounds.
In liquid-electrolyte lithium-ion batteries, separators prevent internal short circuits while enabling ion transport. However, commercial polyethylene (PE) separators exhibit severe thermal shrinkage and poor mechanical flexibility, limiting their use in stretch-tolerant batteries. To address these challenges, a coaxial electrospinning approach was employed to fabricate core-shell nanofibers with a polyimide (PI) shell and a PI/thermoplastic polyurethane (TPU) core, yielding a PI@PI/TPU (P@PT) separator that combines thermal stability with elasticity. The P@PT separator exhibited excellent thermal dimensional stability (4.03% shrinkage) compared with PE (96.14% shrinkage) at 150 °C and higher stretchability (66.6% strain at 7.6 MPa) than PI separators. At 25 °C, electrochemical tests showed comparable performance to PE, with higher coulombic efficiency and improved capacity retention at 65–90 °C. Using pre-stretched separators, we clarified the role of separator mechanics, independent of electrode effects, and linked strain history to electrochemical performance, demonstrating viability as a high-temperature stretch-tolerant separator.
Continuous monitoring of vocal cord vibrations and laryngeal movements is essential for early diagnosis of speech disorders and dysphagia, yet existing approaches suffer from noise susceptibility and limited spatial resolution. Here, we present a flexible piezoelectric sensor array based on screen-printed PZT nanocomposites with a heterogeneous epoxy matrix for noise-robust voice monitoring and swallowing detection. By blending bisphenol A and bisphenol F epoxies, we resolved the trade-off between piezoelectric performance and fine-pattern printability. An optimal 4:6 BPA:BPF ratio enabled 100 µm-gap patterns with a d₃₃ of 105 pC/N and sensitivity of 5.80 mV/kPa. The 60 µm-thick sensor array (on a 20 µm-thick polyimide base) maintained structural integrity without cracking at a 0.5 mm bending radius and delivered bending-insensitive output (<3.5% deviation) under a 5 mm bending radius. When attached to the neck, the multi-channel array tracked laryngeal elevation during swallowing (24 ± 1 mm for saliva; 33 ± 1 mm for water) and captured vocal vibrations with a signal-to-noise ratio of 32.06 dB under hair dryer noise—a 29.97 dB improvement over a conventional microphone. AI-assisted classification using convolutional neural networks achieved 95.93% accuracy across four voice states. Worn continuously throughout a full day, the device maintained conformal adhesion and enabled motion-robust, crosstalk-free simultaneous swallowing and voice monitoring across diverse daily activities. These results provide a proof-of-concept for wearable oropharyngeal health monitoring.
With growing interest in free-form displays, stretchable OLEDs have attracted significant attention. Among various approaches, the island–interconnector architecture is widely adopted for its compatibility with well-established materials that ensure high performance and reliability. While laser patterning is considered a simple and scalable approach to the formation of island-interconnectors in micro- to macroscales, the adhesion of laser-generated residues onto the substrate and rough interfaces has prevented its wide adoption in the manufacturing of free-form electronics. In this work, we introduce a sacrificial-layer-assisted laser patterning strategy that enables the lift-off removal of laser-generated residues and realizes a low-roughness substrate, realizing stretchable OLEDs with external quantum efficiency exceeding 30%. The devices sustain 30% stretchability over 1000 cycles and show temporal luminance decay comparable to that of encapsulated glass-based rigid counterparts, illustrating the feasibility of the proposed method as a scalable approach to the facile realization of free-form displays.
Plant-wearable sensors that enable real-time, non-invasive monitoring of physiological information have the potential to transform precision agriculture. However, designing these sensors for fragile grass-like plants presents challenges. In this study, we introduce the first wearable sap flow sensor specifically engineered for rice, a vital crop for human survival. This innovative sensor continuously monitors the plant’s sap flow, enabling real-time assessment of its water status in actual agricultural environments. The sensor integrates sensing components into a thin, stretchable magnetic kirigami substrate, resulting in a highly compact design (3 × 1.6 cm) and a lightweight (0.44 g). Unlike conventional polymer-based wearable sensors (such as PDMS), our kirigami-based sensor offers greater breathability to maintain plant health during long-term operation. Its magnetic feature also facilitates rapid self-attachment to plants, simplifying field deployment. Based on these designs, we successfully achieved long-term sap flow monitoring for 8 weeks under real farming conditions. Additionally, we developed a high-precision drought stress prediction method based on sap flow, achieving an accuracy of 93.22%, significantly outperforming traditional soil moisture-based approaches (57.69%). We believe our sensor represents a promising advancement in precision agriculture by enabling timely detection of plant drought stress, thereby improving water-use efficiency and enhancing agricultural productivity.
Near-infrared and short-wave infrared (NIR–SWIR) light reveals molecular signatures and penetrates scattering media, advantages that are greatest in direct contact with target. Rigid, conventional imagers cannot meet this requirement. Flexible imagers, by contrast, conform to skin, tissue, and curved surfaces. Here, we review the materials, architectures, and readout mechanisms enabling them, then examine in depth their applications in wearable diagnostics, system monitoring, and human–computer interaction, and remaining challenges.
Conformal, high-density, and high-power integration for radio frequency systems is critical to future wireless communications. Alumina ceramic offers significant potential owing to its ultra-low dielectric loss tangent. However, wireless systems that exploit alumina’s thermal advantages remain unexplored. In this work, we developed a flexible alumina-based radio frequency system that integrates active components and antenna patches on a single substrate, achieving intrinsic heat spreading and high electromagnetic performance simultaneously, while maintaining its mechanical flexibility. An X-band array prototype demonstrated uniform temperature distribution with an average reduction of 11.5 °C in the power amplifier temperature at 1.1 W dissipation, and a larger mm-wave array further validated the scalability of our strategy and its robustness at higher frequencies. These results confirm flexible alumina as a promising substrate that is a suitable electromagnetic medium with heat-spreading capability. This work also demonstrates the use of material-circuit co-optimization in which electromagnetic performance and thermal behaviors are jointly engineered.
In this study, we have thoroughly investigated the intrinsic polarity-mediated optimization of multiple parameters, such as the piezoelectric coefficient, surface roughness, and surface work function, through the strategic incorporation of thermally exfoliated graphene oxide (TEGO) in poly(vinylidene fluoride) (PVDF) matrix, and its effect on piezoelectricity and triboelectricity. A higher density of delocalized π-electrons and oxygen-containing functional groups on the surface of TEGO regulated the electrostatic anchoring of -CH₂ dipoles in PVDF through π-dipole, dipole-dipole interaction to simultaneously induce a maximum polar phase content of ~89% at 2 wt.% TEGO concentration and a negative surface potential. This has resulted in a significant dual enhancement of charge generation and charge transfer through mechanical stimuli. The hybrid device yielded an instantaneous output power density of ~43.5 µW/cm², and a maximum external efficiency of ~42.4%, which was utilized to harvest various bio-mechanical energies, followed by the development of a smart health-monitoring system that calculates calories from footsteps in real time.
Stretchable electrodes with strain-insensitive performance across arbitrary directions and geometries are essential for next-generation customizable wearable electronics. However, conventional designs based on ordered structures such as serpentines, kirigami, and island-bridge generally exhibit directional limitations and geometry constraints, restricting their applicability in complex scenarios. Here, we report a universal machine-learning-guided design strategy that generates bioinspired disordered structures for direction- and geometry-independent, strain-insensitive stretchable electrodes. By integrating a neural network model with an evolutionary algorithm, an optimization framework is established to discover disordered structures with enhanced stretchability and minimized resistance variation under unidirectional, bidirectional, and omnidirectional deformation. Remarkably, this approach also proves effective for irregular geometries, exemplified by hand-shaped electrodes. The optimized disordered structures fabricated via 3D printing achieve a 20–50% reduction in relative resistance compared with the ordered counterparts. Leveraging these electrodes, we further develop a novel stretchable wireless electroencephalography (EEG) cap that replaces conventional rigid, wired designs, accommodates diverse head sizes, suppresses motion artifacts, and achieves a high recognition accuracy in brain-computer interaction tasks. The successful demonstration highlights a robust and universal design paradigm for geometrically adaptive wearable electronics, advancing data-driven innovation in stretchable structures.
Smart textiles integrate fabric comfort and flexibility with electronic functionality, offering transformative potential in healthcare, sports monitoring, and human-machine interfaces. However, most existing wearable systems rely on external circuit boards that compromise comfort, washability, and mechanical robustness. Here, we present a scalable textile-electronics integration strategy based on custom-engineered ID-Yarns ( ~ 500 μm in diameter) that embed semiconductor Radio-Frequency Identification (RFID) chips and antennas and can be seamlessly incorporated into fabrics using standard knitting processes. Using parameterized knitting geometries, we demonstrate two functional fabrics: a stretchable, interference-resistant Sensing-Fabric for precise motion detection, and a stretchable, deformation-insensitive Identification-Fabric (ID-Fabric) for stable passive wireless communication. Both fabrics exhibit strong mechanical endurance, maintaining functionality after more than 10,000 stretching and twisting cycles and over 20 machine washes while preserving consistent wireless performance. This work establishes a passive, yarn-level fiber-chip integration framework and provides a scalable solution toward soft, durable, and high-performance e-textiles through the synergistic design of yarn architecture and knitting-based antenna engineering.
Chronic diabetic wounds present a significant clinical challenge due to antibiotic abuse and limited understanding of the wound microenvironment. Real-time monitoring of key biomarkers in the wound microenvironment can provide critical insights into wound status and guide therapeutic interventions. In this study, we developed an intelligent wound patch by integrating a near-infrared (NIR)-responsive photothermal antibiotic-releasing hydrogel (PPQTA) with a multichannel electrochemical biosensor array, which takes sensor monitoring-guided precise drug administration as its core. The sensing module can continuously monitor the key biomarkers in the wound in situ with high sensitivity and strong anti-interference capability within the physiological range (pH: 4–9; uric acid: 0–700 μM; glucose: 5–30 mM), providing a quantitative basis for drug release. The PPQTA hydrogel can release drugs on demand via NIR irradiation based on the sensing results, achieving 100% antibacterial efficacy against both Gram-negative and Gram-positive bacteria. Experiments in a diabetic rat wound model confirmed that this patch can monitor the dynamic changes of biomarkers in situ and guide drug administration within 7 days. After terminating drug administration on day 4, the bacteria in the wound were effectively eliminated on day 5, and the wound healing process was significantly promoted. By combining real-time diagnostics with responsive therapy, this patch offers a closed-loop strategy for personalized management of diabetic chronic wounds.
Occlusal dysfunction is a prevalent orofacial disorder characterized by aberrant occlusal force transmission and dysregulated masticatory muscle activity. Currently, quantitative characterization of occlusion-related neuromechanical activity remains challenging in clinical practice. In this study, we propose a skin-interfaced bimodal sensing patch that integrates serpentine-structured piezoelectric poly(vinylidene fluoride) (PVDF) films with conductive hydrogel electrodes for simultaneous monitoring of facial skin deformation and muscle electrophysiology during occlusal activities. The island-serpentine design ensures high mechanical compliance while preserving stable electromechanical performance over more than 14,000 loading cycles. The hydrogel interface serves not only as an adhesive layer ensuring conformal adhesion of the PVDF film to the skin but also functions as a low-impedance electrode, enabling high-fidelity surface electromyography (sEMG) acquisition with a signal-to-noise ratio of ~30 dB. Through combined analysis of piezoelectric and sEMG signals, the system distinguishes functional occlusal actions, including normal occlusion, deep overbite, crossbite, and mandibular deviation. This bimodal framework provides a preliminary proof-of-concept for multimodal functional characterization of occlusal biomechanics and suggests potential applicability in noninvasive occlusal function assessment.
Polarity engineering of transition metal dichalcogenide field-effect transistors (FETs) has become a key requirement for complementary logic. Here, we report the polarity control of flexible tungsten diselenide (WSe2) FETs with atomic layer deposited (ALD) top-gate dielectrics. We identify evaporated WOx as suitable seeds for ALD top-gates enabling p-channel WSe2 FETs, while evaporated Al seeds lead to n-channel FETs. Our flexible p-channel FETs achieve good drain current on/off ratio up to 106, enhancement-mode operation with a negative threshold voltage, and low off-current down to ~6 × 10−7 µA/µm, which are important for low-power operation. Combining both seed layers in one fabrication process, we demonstrate flexible WSe2 complementary metal-oxide-semiconductor (CMOS) inverters. Our inverters show good switching behavior with voltage gain up to 65 and total noise margin up to ~88%. Overall, this study provides a strategy on polarity engineering of flexible WSe2 FETs and highlights the potential of flexible complementary WSe2 electronics.
Flexible coils are being developed to alleviate patient discomfort, reflecting ongoing trends in coil design. However, flexibility introduces challenges such as resonant frequency shifts, connection instability, and reduced durability, limiting dynamic and multi-posture imaging. In this study, we developed a flexible adaptive MRI receive coil integrating a deformation-driven frequency compensation structure and a modulus matching layer. The proposed coil achieves more than a 30-fold improvement in resonance frequency stability under 0–30% strain, as quantified by a frequency stability factor reaching several tens in the typical body-conforming strain range, and it maintains frequency stability within 30% stretching and achieves a 77% SNR (Signal-to-Noise Ratio) improvement over commercial coils. Utilizing flexible materials and robust interconnects, it enables high-quality imaging of multiple anatomical regions, including the neck, wrist, and knee joints, and supports continuous multi-posture and dynamic joint movement imaging. Beyond fulfilling routine clinical imaging demands, the proposed coil facilitates MRI in scenarios involving patient motion, potentially providing complementary diagnostic information to conventional designs.
Reconfigurable module-level interconnection across small-scale robotic systems and thin-film electronic systems remains limited, particularly in terms of active connection formation, reversible mechanical coupling, and electrical continuity. In this study, we report active electromechanical docking and undocking mechanisms for thin-film robotic and electronic modules based on kinetic electronics. We developed a single-plane probe assembly mechanism and a separation module assembly mechanism. These mechanisms operate at 5–12 V and establish simultaneous mechanical coupling and electrical continuity that persist in the unpowered state. During docking, the probe mechanism achieved 10 mm deformation at 1.1 W, whereas the separation module mechanism exhibited a mean operating power of 0.43 W and a mean maximum holding force of 618 mgf (6.1 mN). These results demonstrate a proof-of-concept for reversible active electromechanical interconnection for thin-film module systems.
This work introduces a novel electronic yarn (E-yarn) capable of delivering controlled vibrotactile feedback, offering a seamless haptic integration technique into wearable textiles. By embedding miniature vibrotactile motors at the yarn level and employing robust encapsulation techniques, the design ensures durability and compatibility with everyday wear. Prototypes, including a knitted glove incorporating these haptic E-yarns, demonstrated sustained functionality over 20 wash cycles with minimal resistance change (< 1%), and first signs of failure at cycle 23. Performance evaluation using a custom test rig revealed strong correlations between compression forces and vibrotactile output, with frequency and amplitude influenced by textile structure and dynamic loading. Haptic E-yarns achieved an average vibration of 282.6 ± 33.4 Hz at 0.34 ± 0.2 ms−2, with only 1–5% frequency variation and up to 40% amplitude increase post-integration to wearables. This technology enables reliable haptic feedback within textiles, paving the way for future applications in assistive communication and interactive wearables.
Ocular blood oxygen saturation is critical for detecting vision-threatening and systemic diseases. Existing wearable oxygen sensors are unsuitable for ocular use, and current ocular SpO₂ measurements rely on bulky equipment. This work introduces a flexible plasmonic nano-confinement (PNC) nanowire photodetector, based on a PNC nanowire array consisting of highly aligned and ordered PEDOT:PSS nanowires with embedded gold nanoparticles, for high-sensitivity oxygen saturation sensing. The PNC nanowire array acts as an anode interfacial modification layer, where nanowire-geometry-induced confinement and localized surface plasmon resonance synergistically lower the hole-extraction barrier, suppress interfacial recombination, and enhance photoconversion efficiency. Its flexible and transparent design, combined with a compact backend circuit using wavelet-threshold denoising, enables integration into a smart contact lens for accurate and stable non-invasive ocular oxygen monitoring. In vivo experiments demonstrate that this smart contact lens could provide a simple, non-invasive platform for continuous ocular SpO₂ monitoring, with potential relevance to systemic oxygen-status assessment.
