A Self-Supporting, Conductor-Exposing, Stretchable, Ultrathin, and Recyclable Kirigami-Structured Liquid Metal Paper for Multifunctional E-Skin

AI-Driven TENGs for Self-Powered Smart Sensors and Intelligent Devices

Triboelectric nanogenerators (TENGs) are emerging as transformative technologies for sustainable energy harvesting and precision sensing, offering eco-friendly power generation from mechanical motion. They harness mechanical energy while enabling self-sustaining sensing for self-powered devices. However, challenges such as material optimization, fabrication techniques, design strategies, and output stability must be addressed to fully realize their practical potential. Artificial intelligence (AI), with its capabilities in advanced data analysis, pattern recognition, and adaptive responses, is revolutionizing fields like healthcare, industrial automation, and smart infrastructure. When integrated with TENGs, AI can overcome current limitations by enhancing output, stability, and adaptability. This review explores the synergistic potential of AI-driven TENG systems, from optimizing materials and fabrication to embedding machine learning and deep learning algorithms for intelligent real-time sensing. These advancements enable improved energy harvesting, predictive maintenance, and dynamic performance optimization, making TENGs more practical across industries. The review also identifies key challenges and future research directions, including the development of low-power AI algorithms, sustainable materials, hybrid energy systems, and robust security protocols for AI-enhanced TENG solutions.

Cellulose Nanocrystal Stabilized Liquid Metal Pickering Emulsion as Photothermal and Conductive Direct-Writing Ink

Gallium-based liquid metal (LM) has attracted great attention for constructing flexible electronic devices due to its excellent deformability and electrical conductivity. However, its large surface tension makes it difficult to be uniformly dispersed in polymers, which severely limits its wide applications. Hence, a surfactant-free approach is proposed to prepare stable LM microspheres against precipitation and coalesce by facile ultrasonication via cellulose nanocrystal (CNC) stabilized LM-in-water Pickering emulsion (PE), where CNCs are employed as Pickering emulsifiers due their partial wettability with both LM and water phases, strong electrostatic adsorption and hydrogen bonding interactions with LM. So far, reports about LM PE and CNC-stabilized inorganic material PE are still rare. CNC/LM PE is employed as direct-writing inks on various substrates for delicate patterns. The pristine CNC/LM patterns show excellent photothermal conversion due to localized surface plasma resonance effect of CNC/LM microspheres. After activation by friction sintering, the LM patterns are highly electric conductive (1666.7 S m-1) due to the formation of LM connection. The activated LM patterns also displayed excellent Joule heating (83.2 °C at 0.9 V) and electromagnetic interference (EMI) shielding ability (585.7 dB mm-1) in X-band range.

3D Soft Liquid Metal Electrodes for High-Resolution and Long-Term Electromyography in Muscle Trauma Assessment

Electromyography (EMG) is a widely used diagnostic technique for evaluating the electrical activity of muscles and their controlling nerves. However, conventional surface electrodes with planar structures often suffer from low spatial resolution and suboptimal signal quality. Here, 3D-shaped, substrate-free, soft, and biocompatible liquid metal electrodes (LMe) are presented as a wearable interface for neuromuscular signal recording. These electrodes enable the acquisition of high-quality EMG signals while their intrinsic mechanical softness supports long-term use in clinical settings. In a human pilot study, continuous, high-spatial-resolution EMG monitoring of musculoskeletal activity over 25 days is achieved. Furthermore, in vivo EMG monitoring in mouse models of ischemia and volumetric muscle loss demonstrated the therapeutic effects of extracellular muscle-rehabilitative drugs. This work highlights the potential of LMe for advanced drug screening and long-term clinical diagnostics.

Multifunctional starch-based conductive hydrogels for smart sensors and flexible supercapacitors

In order to overcome harsh working environments and meet eco-friendly demands, the development of environmentally tolerant and recyclable hydrogels is necessary. Herein, multifunctional conductive hydrogel was successfully constructed by introducing starch into polyvinyl alcohol (PVA)/glycerin (Gly)/lithium chloride (LiCl) hydrogel. Starch is rich in active sites (-OH groups) that provide a variety of physical interactions for the construction of polymer hydrogels. PSGL hydrogel exhibited high conductivity (40.65 mS cm-1) and outstanding anti-freezing properties (-40 °C). Meanwhile, PSGL hydrogel retained 82.6 % initial weight after 30 days of exposure and 80 % conductivity retention after recycling. The mechanism of Gly and LiCl in inhibiting the freezing and dehydration of hydrogels was further revealed by density functional theory simulations. Moreover, PSGL hydrogel-based sensors had a satisfactory sensitivity (GF = 1.68 at 0-100 %) and accurately detected human motion. Further, by linking the PSGL hydrogel sensors with Internet of Things technology, human-computer interaction was accomplished. Besides, the PSGL hydrogel-based supercapacitors had a specific capacitance of 120.0 mF cm-2 (0.2 mA cm-2) and 98.17 % capacitance retention after 10,000 cycles. PSGL hydrogel-based devices also worked steadily in extreme environments. Therefore, the PSGL hydrogels have great potential for flexible electronics, soft robotics, energy storage etc.

Robustly Repeatable, Permeable, and Multi-Axially Stretchable, Adhesive Bioelectronics With Super-adaptive Conductive Suction Cups for Continuously Deformable Biosurfaces

Skin-integrated wearable bioelectronics offer immense potential for continuous health monitoring, diagnosis, and personalized therapy. However, robustly repeatable and permeable adhesive interfaces with omnidirectional stretchability for adaptability to continuously deforming skin surface remain a critical challenge and often results in issues such as delamination, void, and signal degradation. This study presents a highly adaptable bioelectronic device with a repeatable, robust and biocompatible adhesive interfaces designed for dynamic wet skin surfaces. The device integrates a conductive softened-double-layered octopus-inspired nanocomposites adhesive and kirigami metastructure (cs-OIA_k). The cs-OIA_k achieves skin-like softness, electrical stability (ΔR/R0 < 10, under 10 000 cycles) and omnidirectional stretchability (a maximum of 200%) to accommodate skin deformation. Additionally, the hierarchical structural design of cs-OIA_k enables repeatable robust adhesion (> 10 000 cycles) and vertical alignment to ensure reversible adhesion against dynamically deforming surface (-30% to 100%, depending on skin thickness, site, and age) without skin irritation. Based on these characteristics, the highly adaptable skin-adhesive bioelectronics are demonstrated to achieve reliable electrocardiogram (ECG) and electromyogram (EMG) signal measurements even under shoulder movements with extreme skin deformation. This approach utilizing multi-axially stretchable, repeatable robust adhesives, permeable and biocompatible bioelectronics provides new insights for the development of advanced wearable systems and human-machine interfaces.

Stretchable and adhesive bilayers for electrical interfacing

Integrated stretchable devices, containing soft modules, rigid modules, and encapsulation modules, are of potential use in implantable bioelectronics and wearable devices. However, such systems often suffer from electrical deterioration due to debonding failure at the connection between rigid and soft modules induced by severe stress concentration, limiting their practical implementation. Here, we report a highly conductive and adhesive bilayer interface that can reliably connect soft-soft modules and soft-rigid modules together by simply pressing without conductive pastes. This interface configuration features a nanoscale styrene-ethylene-butylene-styrene (SEBS) elastomer layer and a SEBS-liquid metal (LM) composite layer. The top SEBS layer enables a strong adhesion with different modules. The connections between soft-soft and soft-rigid modules can be stretched to high strains of 400% and 250%, respectively. Coupling electron tunneling through an ultrathin SEBS layer with LM particle networks in a SEBS-LM composite layer renders continuous pathways for electrical conductivity. Such a bilayer interface exhibits a strain-insensitive high conductivity (3.7 × 105 S m-1) over a wide strain range from 0 to 680%, which can be facilely fabricated in a self-organized manner by sedimentation of LM particles. We present a proof-of-concept demonstration of this bilayer interface as an electrode, interconnect, and self-solder for monitoring physiological signals.

Non-Secondary Activating Flexible Liquid Metal Sensors with Excellent Waterproof Capability for Detection of Human Signals

In recent years, flexible sensors have gained increasing attention due to their excellent flexibility. Liquid metal (LM) has gradually become an ideal material for fabricating flexible sensors, thanks to its outstanding electrical conductivity and low-temperature fluidity. However, oxidation and the need for secondary activation of LM present significant technical challenges in the development of flexible LM sensors. In this paper, we introduce a simple method that integrates the flexibility of polydimethylsiloxane (PDMS) to fabricate flexible LM sensors with a sandwich structure. The sandwich-structured sensor demonstrates superior conductivity and effectively prevents LM oxidation and the need for secondary mechanical activation. Additionally, the PDMS-LM sensor exhibits excellent performance under various conditions, with a fast response time to mechanical stimuli (0.5 s), as well as outstanding durability and stability (>10,000 s of cycling). These remarkable properties give the sandwich PDMS-LM sensor great potential for the field of human motion monitoring, bringing further development and direction for intelligent sensing technology.

Deep-Learning-Based Analysis of Electronic Skin Sensing Data

E-skin is an integrated electronic system that can mimic the perceptual ability of human skin. Traditional analysis methods struggle to handle complex e-skin data, which include time series and multiple patterns, especially when dealing with intricate signals and real-time responses. Recently, deep learning techniques, such as the convolutional neural network, recurrent neural network, and transformer methods, provide effective solutions that can automatically extract data features and recognize patterns, significantly improving the analysis of e-skin data. Deep learning is not only capable of handling multimodal data but can also provide real-time response and personalized predictions in dynamic environments. Nevertheless, problems such as insufficient data annotation and high demand for computational resources still limit the application of e-skin. Optimizing deep learning algorithms, improving computational efficiency, and exploring hardware-algorithm co-designing will be the key to future development. This review aims to present the deep learning techniques applied in e-skin and provide inspiration for subsequent researchers. We first summarize the sources and characteristics of e-skin data and review the deep learning models applicable to e-skin data and their applications in data analysis. Additionally, we discuss the use of deep learning in e-skin, particularly in health monitoring and human-machine interactions, and we explore the current challenges and future development directions.

Stretchable and High-Performance Fibrous Sensors Based on Ionic Capacitive Sensing for Wearable Healthcare Monitoring

Electronic textiles with remarkable breathability, lightweight, and comfort hold great potential in wearable technologies and smart human-machine interfaces. Ionic capacitive sensors, leveraging the advantages of the electric double layer, offer higher sensitivity compared to traditional capacitive sensors. Current research on wearable ion-capacitive sensors has focused mainly on two-dimensional (2D) or three-dimensional (3D) device architectures, which show substantial challenges for direct integration with textiles and compromise their wearing experience on conformability and permeability. One-dimensional (1D) stretchable fiber materials serve as vital components in constructing electronic textiles, allowing for rich structural design, patterning, and device integration through mature textile techniques. Here, a stretchable functional fiber with robust mechanical and electrical performances is fabricated based on semi-solid metal and ionic polymer, which provided a high stretchability and good electrical conductivity, enabling seamless integration with textiles. Consequently, high-performance stretchable fiber sensors are developed through different device architecture designs, including pressure sensors with high sensitivity (7.21 kPa-1), fast response (60 ms/30 ms), and excellent stability, as well as strain sensors with high sensitivity (GF = 1.05), wide detection range (0-300% strain), and excellent sensing stability under dynamic deformations.

Liquid Metal-Enabled Epidermal Interfaces

Soft materials are crucial for epidermal interfaces in biomedical devices due to their capability to conform to the body compared to rigid inorganic materials. Gels, liquids, and polymers have been extensively explored, but they lack sufficient electrical and thermal conductivity required for many application settings. Gallium-based alloys are molten metals at room temperature with exceptional electrical and thermal conductivity. These liquid metals and their composites can be directly applied onto the skin as interface materials. In this Spotlight on Applications, we focus on the rapidly evolving field of liquid metal-enabled epidermal interfaces featuring unique physical properties beyond traditional gels and polymers. We delve into the role of liquid metal in electrical and thermal biointerfaces in various epidermal applications. Current challenges and future directions in this active area are also discussed.

Breathable and Stretchable Epidermal Electronics for Health Management: Recent Advances and Challenges

Advanced epidermal electronic devices, capable of real-time monitoring of physical, physiological, and biochemical signals and administering appropriate therapeutics, are revolutionizing personalized healthcare technology. However, conventional portable electronic devices are predominantly constructed from impermeable and rigid materials, which thus leads to the mechanical and biochemical disparities between the devices and human tissues, resulting in skin irritation, tissue damage, compromised signal-to-noise ratio (SNR), and limited operational lifespans. To address these limitations, a new generation of wearable on-skin electronics built on stretchable and porous substrates has emerged. These substrates offer significant advantages including breathability, conformability, biocompatibility, and mechanical robustness, thus providing solutions for the aforementioned challenges. However, given their diverse nature and varying application scenarios, the careful selection and engineering of suitable substrates is paramount when developing high-performance on-skin electronics tailored to specific applications. This comprehensive review begins with an overview of various stretchable porous substrates, specifically focusing on their fundamental design principles, fabrication processes, and practical applications. Subsequently, a concise comparison of various methods is offered to fabricate epidermal electronics by applying these porous substrates. Following these, the latest advancements and applications of these electronics are highlighted. Finally, the current challenges are summarized and potential future directions in this dynamic field are explored.

E-Skin and Its Advanced Applications in Ubiquitous Health Monitoring

E-skin is a bionic device with flexible and intelligent sensing ability that can mimic the touch, temperature, pressure, and other sensing functions of human skin. Because of its flexibility, breathability, biocompatibility, and other characteristics, it is widely used in health management, personalized medicine, disease prevention, and other pan-health fields. With the proposal of new sensing principles, the development of advanced functional materials, the development of microfabrication technology, and the integration of artificial intelligence and algorithms, e-skin has developed rapidly. This paper focuses on the characteristics, fundamentals, new principles, key technologies, and their specific applications in health management, exercise monitoring, emotion and heart monitoring, etc. that advanced e-skin needs to have in the healthcare field. In addition, its significance in infant and child care, elderly care, and assistive devices for the disabled is analyzed. Finally, the current challenges and future directions of the field are discussed. It is expected that this review will generate great interest and inspiration for the development and improvement of novel e-skins and advanced health monitoring systems.

Wearable Sensors, Data Processing, and Artificial Intelligence in Pregnancy Monitoring: A Review

Pregnancy monitoring is always essential for pregnant women and fetuses. According to the report of WHO (World Health Organization), there were an estimated 287,000 maternal deaths worldwide in 2020. Regular hospital check-ups, although well established, are a burden for pregnant women because of frequent travelling or hospitalization. Therefore, home-based, long-term, non-invasive health monitoring is one of the hot research areas. In recent years, with the development of wearable sensors and related data-processing technologies, pregnancy monitoring has become increasingly convenient. This article presents a review on recent research in wearable sensors, physiological data processing, and artificial intelligence (AI) for pregnancy monitoring. The wearable sensors mainly focus on physiological signals such as electrocardiogram (ECG), uterine contraction (UC), fetal movement (FM), and multimodal pregnancy-monitoring systems. The data processing involves data transmission, pre-processing, and application of threshold-based and AI-based algorithms. AI proves to be a powerful tool in early detection, smart diagnosis, and lifelong well-being in pregnancy monitoring. In this review, some improvements are proposed for future health monitoring of pregnant women. The rollout of smart wearables and the introduction of AI have shown remarkable potential in pregnancy monitoring despite some challenges in accuracy, data privacy, and user compliance.

The impact of traditional Chinese paper-cutting in digital protection for intangible cultural heritage under virtual reality technology

Under the impact of the digital wave, traditional paper-cutting art faces unprecedented challenges in preservation and dissemination. Given the urgent need for Intangible Cultural Heritage (ICH) protection, this study explores the application of Virtual Reality (VR) technology in the preservation of paper-cutting art. VR efficiently digitizes and widely disseminates paper-cutting art by skillfully integrating modern technological elements. The study not only deeply analyzes how VR technology can safeguard and inherit traditional Chinese paper-cutting art but also focuses on the meticulous design and optimization of the paper-cutting VR system. The constructed VR system integrates cutting-edge technologies such as 3D modeling and modular design. It showcases outstanding performance in virtual environment rendering and user interaction, rigorously validated through precise evaluation methods. Experimental results demonstrate the paper-cutting VR system's response time of only 10 ms and a high frame rate of 90 frames per second, highlighting its exceptional performance. Furthermore, comprehensive research on the profound impact of the VR system on various stakeholders contributes a new perspective and profound insights into the digital preservation of ICH. In summary, this study successfully innovatively applies VR technology to the protection and dissemination of paper-cutting art, achieving digital preservation goals and injecting new vitality into its inheritance. This pioneering research path opens a hopeful new channel for the digital preservation of ICH and provides a valuable reference for the conservation of other traditional cultures. The study holds critical academic value and significant practical implications. Moreover, the extensive prospects of VR technology in the cultural heritage conservation field urgently require further exploration and investigation.

Robust and Environmentally Friendly MXene-Based Electronic Skin Enabling the Three Essential Functions of Natural Skin: Perception, Protection, and Thermoregulation

The development of electronic skin (e-skin) emulating the human skin's three essential functions (perception, protection, and thermoregulation) has great potential for human-machine interfaces and intelligent robotics. However, existing studies mainly focus on perception. This study presents a novel, eco-friendly, mechanically robust e-skin replicating human skin's three essential functions. The e-skin is composed of Ti3C2Tx MXene, polypyrrole, and bacterial cellulose nanofibers, where the MXene nanoflakes form the matrix, the bacterial cellulose nanofibers act as the filler, and the polypyrrole serves as a conductive "cross-linker". This design allows customization of the electrical conductivity, microarchitecture, and mechanical properties, integrating sensing (perception), EMI shielding (protection), and thermal management (thermoregulation). The optimal e-skin can effectively sense various motions (including minuscule artery pulses), achieve an EMI shielding efficiency of 63.32 dB at 78 μm thickness, and regulate temperature up to 129 °C in 30 s at 2.4 V, demonstrating its potential for smart robotics in complex scenarios.

Recent Advances of Stretchable Nanomaterial-Based Hydrogels for Wearable Sensors and Electrophysiological Signals Monitoring

Electrophysiological monitoring is a commonly used medical procedure designed to capture the electrical signals generated by the body and promptly identify any abnormal health conditions. Wearable sensors are of great significance in signal acquisition for electrophysiological monitoring. Traditional electrophysiological monitoring devices are often bulky and have many complex accessories and thus, are only suitable for limited application scenarios. Hydrogels optimized based on nanomaterials are lightweight with excellent stretchable and electrical properties, solving the problem of high-quality signal acquisition for wearable sensors. Therefore, the development of hydrogels based on nanomaterials brings tremendous potential for wearable physiological signal monitoring sensors. This review first introduces the latest advancement of hydrogels made from different nanomaterials, such as nanocarbon materials, nanometal materials, and two-dimensional transition metal compounds, in physiological signal monitoring sensors. Second, the versatile properties of these stretchable composite hydrogel sensors are reviewed. Then, their applications in various electrophysiological signal monitoring, such as electrocardiogram monitoring, electromyographic signal analysis, and electroencephalogram monitoring, are discussed. Finally, the current application status and future development prospects of nanomaterial-optimized hydrogels in wearable physiological signal monitoring sensors are summarized. We hope this review will inspire future development of wearable electrophysiological signal monitoring sensors using nanomaterial-based hydrogels.

Materials, Structure, and Interface of Stretchable Interconnects for Wearable Bioelectronics

Since wearable technologies for telemedicine have emerged to tackle global health concerns, the demand for well-attested wearable healthcare devices with high user comfort also arises. Skin-wearables for health monitoring require mechanical flexibility and stretchability for not only high compatibility with the skin's dynamic nature but also a robust collection of fine health signals from within. Stretchable electrical interconnects, which determine the device's overall integrity, are one of the fundamental units being understated in wearable bioelectronics. In this review, a broad class of materials and engineering methodologies recently researched and developed are presented, and their respective attributes, limitations, and opportunities in designing stretchable interconnects for wearable bioelectronics are offered. Specifically, the electrical and mechanical characteristics of various materials (metals, polymers, carbons, and their composites) are highlighted, along with their compatibility with diverse geometric configurations. Detailed insights into fabrication techniques that are compatible with soft substrates are also provided. Importantly, successful examples of establishing reliable interfacial connections between soft and rigid elements using novel interconnects are reviewed. Lastly, some perspectives and prospects of remaining research challenges and potential pathways for practical utilization of interconnects in wearables are laid out.

High-Fidelity Bioelectrodes with Bidirectional Ion-Electron Transduction Capability by Integrating Multiple Charge-Transfer Processes

Bioelectronics is an exciting field that bridges the gap between physiological activities and external electronic devices, striving for high resolution, high conformability, scalability, and ease of integration. One crucial component in bioelectronics is bioelectrodes, designed to convert neural activity into electronic signals or vice versa. Previously reported bioelectrodes have struggled to meet several essential requirements simultaneously: high-fidelity signal transduction, high charge injection capability, strain resistance, and multifunctionality. This work introduces a novel strategy for fabricating superior bioelectrodes by merging multiple charge-transfer processes. The resulting bioelectrodes offer accurate ion-to-electron transduction for capturing electrophysiological signals, dependable charge injection capability for neuromodulation, consistent electrode potential for artifact rejection and biomolecule sensing, and high transparency for seamless integration with optoelectronics. Furthermore, the bioelectrode can be designed to be strain-insensitive by isolating signal transduction from electron transportation. The innovative concept presented in this work holds great promise for extending to other electrode materials and paves the way for the advancement of multimodal bioelectronics.

Electronic Skin for Health Monitoring Systems: Properties, Functions, and Applications

Electronic skin (e-skin), a skin-like wearable electronic device, holds great promise in the fields of telemedicine and personalized healthcare because of its good flexibility, biocompatibility, skin conformability, and sensing performance. E-skin can monitor various health indicators of the human body in real time and over the long term, including physical indicators (exercise, respiration, blood pressure, etc.) and chemical indicators (saliva, sweat, urine, etc.). In recent years, the development of various materials, analysis, and manufacturing technologies has promoted significant development of e-skin, laying the foundation for the application of next-generation wearable medical technologies and devices. Herein, the properties required for e-skin health monitoring devices to achieve long-term and precise monitoring and summarize several detectable indicators in the health monitoring field are discussed. Subsequently, the applications of integrated e-skin health monitoring systems are reviewed. Finally, current challenges and future development directions in this field are discussed. This review is expected to generate great interest and inspiration for the development and improvement of e-skin and health monitoring systems.

Electronic Skin: Opportunities and Challenges in Convergence with Machine Learning

Recent advancements in soft electronic skin (e-skin) have led to the development of human-like devices that reproduce the skin's functions and physical attributes. These devices are being explored for applications in robotic prostheses as well as for collecting biopotentials for disease diagnosis and treatment, as exemplified by biomedical e-skins. More recently, machine learning (ML) has been utilized to enhance device control accuracy and data processing efficiency. The convergence of e-skin technologies with ML is promoting their translation into clinical practice, especially in healthcare. This review highlights the latest developments in ML-reinforced e-skin devices for robotic prostheses and biomedical instrumentations. We first describe technological breakthroughs in state-of-the-art e-skin devices, emphasizing technologies that achieve skin-like properties. We then introduce ML methods adopted for control optimization and pattern recognition, followed by practical applications that converge the two technologies. Lastly, we briefly discuss the challenges this interdisciplinary research encounters in its clinical and industrial transition.

High internal phase emulsions gel ink for direct-ink-writing 3D printing of liquid metal

3D printing of liquid metal remains a big challenge due to its low viscosity and large surface tension. In this study, we use Carbopol hydrogel and liquid gallium-indium alloy to prepare a liquid metal high internal phase emulsion gel ink, which can be used for direct-ink-writing 3D printing. The high volume fraction (up to 82.5%) of the liquid metal dispersed phase gives the ink excellent elastic properties, while the Carbopol hydrogel, as the continuous phase, provides lubrication for the liquid metal droplets, ensuring smooth flow of the ink during shear extrusion. These enable high-resolution and shape-stable 3D printing of three-dimensional structures. Moreover, the liquid metal droplets exhibit an electrocapillary phenomenon in the Carbopol hydrogel, which allows for demulsification by an electric field and enables electrical connectivity between droplets. We have also achieved the printing of ink on flexible, non-planar structures, and demonstrated the potential for alternating printing with various materials.

Recent advances in wearable flexible electronic skin: types, power supply methods, and development prospects

In recent years, wearable e-skin has emerged as a prominent technology with a wide range of applications in healthcare, health surveillance, human-machine interface, and virtual reality. Inspired by the properties of human skin, arrayed wearable e-skin is a novel technology that offers multifunctional sensing capabilities. It can detect and quantify various stimuli, mimicking the human somatosensory system, and record a wide range of physical and physiological parameters in real time. By combining flexible electronic device units with a data acquisition system, specific functional sensors can be distributed in targeted areas to achieve high sensitivity, resolution, adjustable sensing range, and large-area expandability. This review provides a comprehensive overview of recent advances in wearable e-skin technology, including its development status, types of applications, power supply methods, and prospects for future development. The emphasis of current research is on enhancing the sensitivity and stability of sensors, improving the comfort and reliability of wearable devices, and developing intelligent data processing and application algorithms. This review aims to serve as a scientific reference for the intelligent development of wearable e-skin technology.

Materials and Structural Designs toward Motion Artifact-Free Bioelectronics

Bioelectronics encompassing electronic components and circuits for accessing human information play a vital role in real-time and continuous monitoring of biophysiological signals of electrophysiology, mechanical physiology, and electrochemical physiology. However, mechanical noise, particularly motion artifacts, poses a significant challenge in accurately detecting and analyzing target signals. While software-based "postprocessing" methods and signal filtering techniques have been widely employed, challenges such as signal distortion, major requirement of accurate models for classification, power consumption, and data delay inevitably persist. This review presents an overview of noise reduction strategies in bioelectronics, focusing on reducing motion artifacts and improving the signal-to-noise ratio through hardware-based approaches such as "preprocessing". One of the main stress-avoiding strategies is reducing elastic mechanical energies applied to bioelectronics to prevent stress-induced motion artifacts. Various approaches including strain-compliance, strain-resistance, and stress-damping techniques using unique materials and structures have been explored. Future research should optimize materials and structure designs, establish stable processes and measurement methods, and develop techniques for selectively separating and processing overlapping noises. Ultimately, these advancements will contribute to the development of more reliable and effective bioelectronics for healthcare monitoring and diagnostics.

Thermogalvanic hydrogel-based e-skin for self-powered on-body dual-modal temperature and strain sensing

Sensing of both temperature and strain is crucial for various diagnostic and therapeutic purposes. Here, we present a novel hydrogel-based electronic skin (e-skin) capable of dual-mode sensing of temperature and strain. The thermocouple ion selected for this study is the iodine/triiodide (I-/I3-) redox couple, which is a common component in everyday disinfectants. By leveraging the thermoelectric conversion in conjunction with the inherent piezoresistive effect of a gel electrolyte, self-powered sensing is achieved by utilizing the temperature difference between the human body and the external environment. The composite hydrogels synthesized from polyvinyl alcohol (PVA) monomers using a simple freeze‒thaw method exhibit remarkable flexibility, extensibility, and adaptability to human tissue. The incorporation of zwitterions further augments the resistance of the hydrogel to dehydration and low temperatures, allowing maintenance of more than 90% of its weight after 48 h in the air. Given its robust thermal current response, the hydrogel was encapsulated and then integrated onto various areas of the human body, including the cheeks, fingers, and elbows. Furthermore, the detection of the head-down state and the monitoring of foot movements demonstrate the promising application of the hydrogel in supervising the neck posture of sedentary office workers and the activity status. The successful demonstration of self-powered on-body temperature and strain sensing opens up new possibilities for wearable intelligent electronics and robotics.

E-Tattoos: Toward Functional but Imperceptible Interfacing with Human Skin

The human body continuously emits physiological and psychological information from head to toe. Wearable electronics capable of noninvasively and accurately digitizing this information without compromising user comfort or mobility have the potential to revolutionize telemedicine, mobile health, and both human-machine or human-metaverse interactions. However, state-of-the-art wearable electronics face limitations regarding wearability and functionality due to the mechanical incompatibility between conventional rigid, planar electronics and soft, curvy human skin surfaces. E-Tattoos, a unique type of wearable electronics, are defined by their ultrathin and skin-soft characteristics, which enable noninvasive and comfortable lamination on human skin surfaces without causing obstruction or even mechanical perception. This review article offers an exhaustive exploration of e-tattoos, accounting for their materials, structures, manufacturing processes, properties, functionalities, applications, and remaining challenges. We begin by summarizing the properties of human skin and their effects on signal transmission across the e-tattoo-skin interface. Following this is a discussion of the materials, structural designs, manufacturing, and skin attachment processes of e-tattoos. We classify e-tattoo functionalities into electrical, mechanical, optical, thermal, and chemical sensing, as well as wound healing and other treatments. After discussing energy harvesting and storage capabilities, we outline strategies for the system integration of wireless e-tattoos. In the end, we offer personal perspectives on the remaining challenges and future opportunities in the field.

Liquid Metal-Polymer Conductor-Based Conformal Cyborg Devices

Gallium-based liquid metal (LM) exhibits exceptional properties such as high conductivity and biocompatibility, rendering it highly valuable for the development of conformal bioelectronics. When combined with polymers, liquid metal-polymer conductors (MPC) offer a versatile platform for fabricating conformal cyborg devices, enabling functions such as sensing, restoration, and augmentation within the human body. This review focuses on the synthesis, fabrication, and application of MPC-based cyborg devices. The synthesis of functional materials based on LM and the fabrication techniques for MPC-based devices are elucidated. The review provides a comprehensive overview of MPC-based cyborg devices, encompassing their applications in sensing diverse signals, therapeutic interventions, and augmentation. The objective of this review is to serve as a valuable resource that bridges the gap between the fabrication of MPC-based conformal devices and their potential biomedical applications.

Materials-Driven Soft Wearable Bioelectronics for Connected Healthcare

In the era of Internet-of-things, many things can stay connected; however, biological systems, including those necessary for human health, remain unable to stay connected to the global Internet due to the lack of soft conformal biosensors. The fundamental challenge lies in the fact that electronics and biology are distinct and incompatible, as they are based on different materials via different functioning principles. In particular, the human body is soft and curvilinear, yet electronics are typically rigid and planar. Recent advances in materials and materials design have generated tremendous opportunities to design soft wearable bioelectronics, which may bridge the gap, enabling the ultimate dream of connected healthcare for anyone, anytime, and anywhere. We begin with a review of the historical development of healthcare, indicating the significant trend of connected healthcare. This is followed by the focal point of discussion about new materials and materials design, particularly low-dimensional nanomaterials. We summarize material types and their attributes for designing soft bioelectronic sensors; we also cover their synthesis and fabrication methods, including top-down, bottom-up, and their combined approaches. Next, we discuss the wearable energy challenges and progress made to date. In addition to front-end wearable devices, we also describe back-end machine learning algorithms, artificial intelligence, telecommunication, and software. Afterward, we describe the integration of soft wearable bioelectronic systems which have been applied in various testbeds in real-world settings, including laboratories that are preclinical and clinical environments. Finally, we narrate the remaining challenges and opportunities in conjunction with our perspectives.

Kirigami-Structured, Low-Impedance, and Skin-Conformal Electronics for Long-Term Biopotential Monitoring and Human-Machine Interfaces

Epidermal dry electrodes with high skin-compliant stretchability, low bioelectric interfacial impedance, and long-term reliability are crucial for biopotential signal recording and human-machine interaction. However, incorporating these essential characteristics into dry electrodes remains a challenge. Here, a skin-conformal dry electrode is developed by encapsulating kirigami-structured poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/polyvinyl alcohol (PVA)/silver nanowires (Ag NWs) film with ultrathin polyurethane (PU) tape. This Kirigami-structured PEDOT:PSS/PVA/Ag NWs/PU epidermal electrode exhibits a low sheet resistance (≈3.9 Ω sq-1 ), large skin-compliant stretchability (>100%), low interfacial impedance (≈27.41 kΩ at 100 Hz and ≈59.76 kΩ at 10 Hz), and sufficient mechanoelectrical stability. This enhanced performance is attributed to the synergistic effects of ionic/electronic current from PEDOT:PSS/Ag NWs dual conductive network, Kirigami structure, and unique encapsulation. Compared with the existing dry electrodes or standard gel electrodes, the as-prepared electrodes possess lower interfacial impedance and noise in various conditions (e.g., sweat, wet, and movement), indicating superior water/motion-interference resistance. Moreover, they can acquire high-quality biopotential signals even after water rinsing and ultrasonic cleaning. These outstanding advantages enable the Kirigami-structured PEDOT:PSS/PVA/Ag NWs/PU electrodes to effectively monitor human motions in real-time and record epidermal biopotential signals, such as electrocardiogram, electromyogram, and electrooculogram under various conditions, and control external electronics, thereby facilitating human-machine interactions.

Recent Advances in Flexible Multifunctional Sensors

Wearable electronics have received extensive attention in human-machine interactions, robotics, and health monitoring. The use of multifunctional sensors that are capable of measuring a variety of mechanical or environmental stimuli can provide new functionalities for wearable electronics. Advancements in material science and system integration technologies have contributed to the development of high-performance flexible multifunctional sensors. This review presents the main approaches, based on functional materials and device structures, to improve sensing parameters, including linearity, detection range, and sensitivity to various stimuli. The details of electrical, biocompatible, and mechanical properties of self-powered sensors and wearable wireless systems are systematically elaborated. Finally, the current challenges and future developmental directions are discussed to offer a guide to fabricate advanced multifunctional sensors.

A Review of Structure Engineering of Strain-Tolerant Architectures for Stretchable Electronics

Stretchable electronics possess significant advantages over their conventional rigid counterparts and boost game-changing applications such as bioelectronics, flexible displays, wearable health monitors, etc. It is, nevertheless, a formidable task to impart stretchability to brittle electronic materials such as silicon. This review provides a concise but critical discussion of the prevailing structural engineering strategies for achieving strain-tolerant electronic devices. Not only the more commonly discussed lateral designs of structures such as island-bridge, wavy structures, fractals, and kirigami, but also the less discussed vertical architectures such as strain isolation and elastoplastic principle are reviewed. Future opportunities are envisaged at the end of the paper.

All Resistive Pressure-Temperature Bimodal Sensing E-Skin for Object Classification

Electronic skin (E-skin) with multimodal sensing ability demonstrates huge prospects in object classification by intelligent robots. However, realizing the object classification capability of E-skin faces severe challenges in multiple types of output signals. Herein, a hierarchical pressure-temperature bimodal sensing E-skin based on all resistive output signals is developed for accurate object classification, which consists of laser-induced graphene/silicone rubber (LIG/SR) pressure sensing layer and NiO temperature sensing layer. The highly conductive LIG is employed as pressure-sensitive material as well as the interdigital electrode. Benefiting from high conductivity of LIG, pressure perception exhibits an excellent sensitivity of -34.15 kPa-1 . Meanwhile, a high temperature coefficient of resistance of -3.84%°C-1 is obtained in the range of 24-40 °C. More importantly, based on only electrical resistance as the output signal, the bimodal sensing E-skin with negligible crosstalk can simultaneously achieve pressure and temperature perception. Furthermore, a smart glove based on this E-skin enables classifying various objects with different shapes, sizes, and surface temperatures, which achieves over 92% accuracy under assistance of deep learning. Consequently, the hierarchical pressure-temperature bimodal sensing E-skin demonstrates potential application in human-machine interfaces, intelligent robots, and smart prosthetics.

Flexible triboelectric nanogenerators of Au-g-C3N4/ZnO hierarchical nanostructures for machine learning enabled body movement detection

Here we report the development of triboelectric nanogenerator (TENG) based self-powered human motion detector with chemically developed Au-g-C3N4/ZnO based nanocomposite on common cellulose paper platform. Compared to bare g-C3N4, the nanocomposite in the form of hierarchical morphology is found to exhibit higher output voltage owing to the contribution of Au and ZnO in increasing the dielectric constant and surface roughness. While generating power ∼3.5μW cm-2and sensitivity ∼3.3 V N-1, the flexible TENG, is also functional under common biomechanical stimuli to operate as human body movement sensor. When attached to human body, the flexible TENG is found to be sensitive towards body movement as well as the frequency of movement. Finally upon attaching multiple TENG devices to human body, the nature of body movement has been traced precisely using machine learning (ML) techniques. The execution of the learning algorithms like artificial neural network and random forest classifier on the data generated from these multiple sensors can yield an accuracy of 99% and 100% respectively to predict body movement with great deal of precision. The exhibition of superior sensitivity and ML based biomechanical motion recognition accuracy by the hierarchical structure based flexible TENG sensor are the prime novelties of the work.

Highly Stable Liquid Metal Conductors with Superior Electrical Stability and Tough Interface Bonding for Stretchable Electronics

Ga-based liquid metal stretchable conductors have recently gained interest in flexible electronic devices such as electrodes, antennas, and sensors. It is essential to maintain electrical stability under strain or cyclic strain for reliable data acquisition and exhibit tough interfacial bonding between liquid metal and polymers to prevent performance loss and device failure. Herein, a highly stable conductor with superior electrical stability and tough interface bonding is introduced by casting curable polymers and a peeling-activated process from liquid metal particles. Based on the compensating effect of liquid metal, similar to the recharge relationship of water between rivers and lakes in nature, the conductor is not only strain-insensitive (ΔR/R₀ < 10% for 100% strain) but also immune to cyclic deformation (ΔR/R₀ < 7% with 5000 stretching cycles at 50% strain). Embedding liquid metal within the elastomer to create stretchable conductors effectively improves interfacial adhesion properties (the fluid-solid interfacial adhesion force increases from 0.48 to 0.62 mN/mm²). The constructed tough interface could even withstand sonication treatment. Finally, by combining strategies in material design and fabrication, an integrated array composed of vertical interconnect access and robust electrodes is fabricated, which simultaneously holds tough interfacial bonding with the upper and lower layers.

Ultra-Stretchable Spiral Hybrid Conductive Fiber with 500%-Strain Electric Stability and Deformation-Independent Linear Temperature Response

Stretchable configuration occupies priority in devising flexible conductors used in intelligent electronics and implantable sensors. While most conductive configurations cannot suppress electrical variations against extreme deformation and ignore inherent material characteristics. Herein, a spiral hybrid conductive fiber (SHCF) composed of aramid polymeric matrix and silver nanowires (AgNWs) coating is fabricated through shaping and dipping processes. The homochiral coiled configuration mimicked by plant tendrils not only enables its high elongation (958%), but also generates a superior deformation-insensitive effect to existing stretchable conductors. The resistance of SHCF maintains remarkable stability against extreme strain (500%), impact damage, air exposure (90 days), and cyclic bending (150 000 times). Moreover, the thermal-induced densification of AgNWs on SHCF achieves precise and linear temperature response toward a broad range (-20 to 100 °C). Its sensitivity further manifests high independence to tensile strain (0%-500%), allowing for flexible temperature monitoring of curved objects. Such unique strain-tolerant electrical stability and thermosensation hold broad prospects for SHCF in lossless power transferring and expeditious thermal analysis.

Liquid Metal Droplets-Based Elastomers from Electric Toothbrush-Inspired Revolving Microfluidics

Liquid metal (LM)-based elastomers have a demonstrated value in flexible electronics. Attempts in this area include the development of multifunctional LM-based elastomers with controllable morphology, superior mechanical performances, and great stability. Herein, inspired by the working principle of electric toothbrushes, a revolving microfluidic system is presented for the generation of LM droplets and construction of desired elastomers. The system involves revolving modules assembled by a needles array and 3D microfluidic channels. LM droplets can be generated with controllable size in a high-throughput manner due to the revolving motion-derived drag force. It is demonstrated that by employing a poly(dimethylsiloxane) (PDMS) matrix as the collection phase, the generated LM droplets can act as conductive fillers for the construction of flexible electronics directly. The resultant LM droplets-based elastomers exhibit high mechanical strength, stable electrical performance, as well as superior self-healing property benefiting from the dynamic exchangeable urea bond of the polymer matrix. Notably, due to the flexible programmable feature of the LM droplets embedded within the elastomers, various patterned LM droplets-based elastomers can be easily achieved. These results indicate that the proposed microfluidic LM droplets-based elastomers have a great potential for promoting the development of flexible electronics.

Ultrastretchable High-Conductivity MXene-Based Organohydrogels for Human Health Monitoring and Machine-Learning-Assisted Recognition

Conductive hydrogels as promising candidates of wearable electronics have attracted considerable interest in health monitoring, multifunctional electronic skins, and human-machine interfaces. However, to simultaneously achieve excellent electrical properties, superior stretchability, and a low detection threshold of conductive hydrogels remains an extreme challenge. Herein, an ultrastretchable high-conductivity MXene-based organohydrogel (M-OH) is developed for human health monitoring and machine-learning-assisted object recognition, which is fabricated based on a Ti₃C₂T_x MXene/lithium salt (LS)/poly(acrylamide) (PAM)/poly(vinyl alcohol) (PVA) hydrogel through a facile immersion strategy in a glycerol/water binary solvent. The fabricated M-OH demonstrates remarkable stretchability (2000%) and high conductivity (4.5 S/m) due to the strong interaction between MXene and the dual-network PVA/PAM hydrogel matrix and the incorporation between MXene and LS, respectively. Meanwhile, M-OH as a wearable sensor enables human health monitoring with high sensitivity and a low detection limit (12 Pa). Furthermore, based on pressure mapping image recognition technology, an 8 × 8 pixelated M-OH-based sensing array can accurately identify different objects with a high accuracy of 97.54% under the assistance of a deep learning neural network (DNN). This work demonstrates excellent comprehensive performances of the ultrastretchable high-conductive M-OH in health monitoring and object recognition, which would further explore extensive potential application prospects in personal healthcare, human-machine interfaces, and artificial intelligence.

Smart Wearable Systems for Health Monitoring

Smart wearable systems for health monitoring are highly desired in personal wisdom medicine and telemedicine. These systems make the detecting, monitoring, and recording of biosignals portable, long-term, and comfortable. The development and optimization of wearable health-monitoring systems have focused on advanced materials and system integration, and the number of high-performance wearable systems has been gradually increasing in recent years. However, there are still many challenges in these fields, such as balancing the trade-off between flexibility/stretchability, sensing performance, and the robustness of systems. For this reason, more evolution is required to promote the development of wearable health-monitoring systems. In this regard, this review summarizes some representative achievements and recent progress of wearable systems for health monitoring. Meanwhile, a strategy overview is presented about selecting materials, integrating systems, and monitoring biosignals. The next generation of wearable systems for accurate, portable, continuous, and long-term health monitoring will offer more opportunities for disease diagnosis and treatment.

Liquid metal enabled conformal electronics

The application of three-dimensional common electronics that can be directly pasted on arbitrary surfaces in the fields of human health monitoring, intelligent robots and wearable electronic devices has aroused people's interest, especially in achieving stable adhesion of electronic devices on biological dynamic three-dimensional interfaces and high-quality signal acquisition. In recent years, liquid metal (LM) materials have been widely used in the manufacture of flexible sensors and wearable electronic devices because of their excellent tensile properties and electrical conductivity at room temperature. In addition, LM has good biocompatibility and can be used in a variety of biomedical applications. Here, the recent development of LM flexible electronic printing methods for the fabrication of three-dimensional conformal electronic devices on the surface of human tissue is discussed. These printing methods attach LM to the deformable substrate in the form of bulk or micro-nano particles, so that electronic devices can adapt to the deformation of human tissue and other three-dimensional surfaces, and maintain stable electrical properties. Representative examples of applications such as self-healing devices, degradable devices, flexible hybrid electronic devices, variable stiffness devices and multi-layer large area circuits are reviewed. The current challenges and prospects for further development are also discussed.

Liquid Metal Patterning and Unique Properties for Next-Generation Soft Electronics

Room-temperature liquid metal (LM)-based electronics is expected to bring advancements in future soft electronics owing to its conductivity, conformability, stretchability, and biocompatibility. However, various difficulties arise when patterning LM because of its rheological features such as fluidity and surface tension. Numerous attempts are made to overcome these difficulties, resulting in various LM-patterning methods. An appropriate choice of patterning method based on comprehensive understanding is necessary to fully utilize the unique properties. Therefore, the authors aim to provide thorough knowledge about patterning methods and unique properties for LM-based future soft electronics. First, essential considerations for LM-patterning are investigated. Then, LM-patterning methods-serial-patterning, parallel-patterning, intermetallic bond-assisted patterning, and molding/microfluidic injection-are categorized and investigated. Finally, perspectives on LM-based soft electronics with unique properties are provided. They include outstanding features of LM such as conformability, biocompatibility, permeability, restorability, and recyclability. Also, they include perspectives on future LM-based soft electronics in various areas such as radio frequency electronics, soft robots, and heterogeneous catalyst. LM-based soft devices are expected to permeate the daily lives if patterning methods and the aforementioned features are analyzed and utilized.

A review related to MXene preparation and its sensor arrays of electronic skins

MXenes have been flourishing over the last decade as a high-performance 2D material, which combines the advantages of high electrical conductivity, photothermal conversion, and easy dispersion. They have been used to create soft, highly conductive, self-healing, and tactile-simulating electronic skins (E-skins). However, these E-skins remain generally limited to one or two functions with a complex preparation process. Next-generation E-skins necessitate not only large-scale fabrication using simple and fast methods but also the integration of multiple sensing functions and signal analysis components in order to provide functionality that was not unattainable in the past. Starting with the synthesis of pure MXenes, we walk through the steps of designing MXene sensors, integrating electronic skin arrays, and determining the function of MXene-based electronic skins. We also summarise the problems with existing MXene-based E-skins and possible futuristic directions.

Engineering Triboelectric Charge in Natural Rubber-Ag Nanocomposite for Enhancing Electrical Output of a Triboelectric Nanogenerator

An environmentally friendly triboelectric nanogenerator (TENG) is fabricated from a natural rubber (NR)-Ag nanocomposite for harvesting mechanical energy from human motions. Ag nanoparticles (AgNPs) synthesized with two different capping agents are added to NR polymer for improving dielectric constant that contributes to the enhancement of TENG performance. Dielectric constant is modulated via interfacial polarization between AgNPs and NR matrix. The effects of AgNP concentration, particle size and dispersion in NR composite, and type of capping agents on dielectric properties and electrical output of the NR composite TENG are elucidated. It is found that, apart from AgNPs content in the NR-Ag nanocomposite, cations of CTAB capping agent play important roles not only on the dispersion of AgNPs in NR matrix but also on intensifying tribopositive charges in the NR composite. In addition, the application of the NR-Ag TENG as a shoe insole is also demonstrated to convert human footsteps into electricity to power small electronic devices. Furthermore, with the presence of Ag nanoparticles, the fabricated shoe insole also exhibits antibacterial property against Staphylococcus aureus that causes foot odor.

Water-Modulated Biomimetic Hyper-Attribute-Gel Electronic Skin for Robotics and Skin-Attachable Wearables

Electronic skin (e-skin), mimicking the physical-chemical and sensory properties of human skin, is promising to be applied as robotic skins and skin-attachable wearables with multisensory functionalities. To date, most e-skins are dedicated to sensory function development to mimic human skins in one or several aspects, yet advanced e-skin covering all the hyper-attributes (including both the sensory and physical-chemical properties) of human skins is seldom reported. Herein, a water-modulated biomimetic hyper-attribute-gel (Hygel) e-skin with reversible gel-solid transition is proposed, which exhibits all the desired skin-like physical-chemical properties (stretchability, self-healing, biocompatibility, biodegradability, weak acidity, antibacterial activities, flame retardance, and temperature adaptivity), sensory properties (pressure, temperature, humidity, strain, and contact), function reconfigurability, and evolvability. Then the Hygel e-skin is applied as an on-robot e-skin and skin-attached wearable to demonstrate its highly skin-like attributes in capturing multiple sensory information, reconfiguring desired functions, and excellent skin compatibility for real-time gesture recognition via deep learning. This Hygel e-skin may find more applications in advanced robotics and even skin-replaceable artificial skin.

Liquid Metal-Based Electronics for On-Skin Healthcare

Wearable devices are receiving growing interest in modern technologies for realizing multiple on-skin purposes, including flexible display, flexible e-textiles, and, most importantly, flexible epidermal healthcare. A 'BEER' requirement, i.e., biocompatibility, electrical elasticity, and robustness, is first proposed here for all the on-skin healthcare electronics for epidermal applications. This requirement would guide the designing of the next-generation on-skin healthcare electronics. For conventional stretchable electronics, the rigid conductive materials, e.g., gold nanoparticles and silver nanofibers, would suffer from an easy-to-fail interface with elastic substrates due to a Young's modulus mismatch. Liquid metal (LM) with high conductivity and stretchability has emerged as a promising solution for robust stretchable epidermal electronics. In addition, the fundamental physical, chemical, and biocompatible properties of LM are illustrated. Furthermore, the fabrication strategies of LM are outlined for pure LM, LM composites, and LM circuits based on the surface tension control. Five dominant epidermal healthcare applications of LM are illustrated, including electrodes, interconnectors, mechanical sensors, thermal management, and biomedical and sustainable applications. Finally, the key challenges and perspectives of LM are identified for the future research vision.

Recent progress in fiber-based soft electronics enabled by liquid metal

Soft electronics can seamlessly integrate with the human skin which will greatly improve the quality of life in the fields of healthcare monitoring, disease treatment, virtual reality, and human-machine interfaces. Currently, the stretchability of most soft electronics is achieved by incorporating stretchable conductors with elastic substrates. Among stretchable conductors, liquid metals stand out for their metal-grade conductivity, liquid-grade deformability, and relatively low cost. However, the elastic substrates usually composed of silicone rubber, polyurethane, and hydrogels have poor air permeability, and long-term exposure can cause skin redness and irritation. The substrates composed of fibers usually have excellent air permeability due to their high porosity, making them ideal substrates for soft electronics in long-term applications. Fibers can be woven directly into various shapes, or formed into various shapes on the mold by spinning techniques such as electrospinning. Here, we provide an overview of fiber-based soft electronics enabled by liquid metals. An introduction to the spinning technology is provided. Typical applications and patterning strategies of liquid metal are presented. We review the latest progress in the design and fabrication of representative liquid metal fibers and their application in soft electronics such as conductors, sensors, and energy harvesting. Finally, we discuss the challenges of fiber-based soft electronics and provide an outlook on future prospects.

Laser-Patterned Hierarchical Aligned Micro-/Nanowire Network for Highly Sensitive Multidimensional Strain Sensor

Flexible multidirectional strain sensors capable of simultaneously detecting strain amplitudes and directions have attracted tremendous interest. Herein, we propose a flexible multidirectional strain sensor based on a newly designed single-layer hierarchical aligned micro-/nanowire (HAMN) network. The HAMN network is efficiently fabricated using a one-step femtosecond laser patterning technology based on a modulated line-shaped beam. The anisotropic performance is attributed to the significantly different morphological changes caused by an inhomogeneous strain redistribution among the HAMN network. The fabricated strain sensor exhibits high sensitivity (gauge factor of 65 under 2.5% strain and 462 under larger strains), low response/recovery time (140 and 322 ms), and good stability (over 1000 cycles). Moreover, this single-layer strain sensor with high selectivity (gauge factor differences of ∼73 between orthogonal strains) is capable of distinguishing multidimensional strains and exhibits decoupled responses under low strains (<1%). Therefore, the strain sensors enable the precise monitoring of subtle movements, including radial pulses and wrist bending, and the rectification of pen-holding posture. Benefitting from these remarkable performances, the HAMN-based strain sensors show potential applications, including healthcare and complex human motion monitoring.

The benefits of combining 1D and 3D nanofillers in a piezocomposite nanogenerator for biomechanical energy harvesting

Mechanical energy harvesting using piezoelectric nanogenerators (PNGs) offers an attractive solution for driving low-power portable devices and self-powered electronic systems. Here, we designed an eco-friendly and flexible piezocomposite nanogenerator (c-PNG) based on H₂(Zr_0.1Ti_0.9)₃O₇ nanowires (HZTO-nw) and Ba_0.85Ca_0.15Zr_0.10Ti_0.90O₃ multipods (BCZT-mp) as fillers and polylactic acid (PLA) as a biodegradable polymer matrix. The effects of the applied stress amplitude, frequency and pressing duration on the electric outputs in the piezocomposite nanogenerator (c-PNG) device were investigated by simultaneous recording of the mechanical input and the electrical outputs. The fabricated c-PNG shows a maximum output voltage, current and volumetric power density of 11.5 V, 0.6 μA and 9.2 mW cm^-3, respectively, under cyclic finger imparting. A high-pressure sensitivity of 0.86 V kPa^-1 (equivalent to 3.6 V N^-1) and fast response time of 45 ms were obtained in the dynamic pressure sensing. Besides this, the c-PNG demonstrates high-stability and durability of the electrical outputs for around three months, and can drive commercial electronics (charging capacitor, glowing light-emitting diodes and powering a calculator). Multi-physics simulations indicate that the presence of BCZT-mp is crucial in enhancing the piezoelectric response of the c-PNG. Accordingly, this work reveals that combining 1D and 3D fillers in a polymer composite-based PNG could be beneficial in improving the mechanical energy harvesting performances in flexible piezoelectric nanogenerators for application in electronic skin and wearable devices.

Roles of Low-Dimensional Nanomaterials in Pursuing Human-Machine-Thing Natural Interaction

A wide variety of low-dimensional nanomaterials with excellent properties can meet almost all the requirements of functional materials for information sensing, processing, and feedback devices. Low-dimensional nanomaterials are becoming the star of hope on the road to pursuing human-machine-thing natural interactions, benefiting from the breakthroughs in precise preparation, performance regulation, structural design, and device construction in recent years. This review summarizes several types of low-dimensional nanomaterials commonly used in human-machine-thing natural interactions and outlines the differences in properties and application areas of different materials. According to the sequence of information flow in the human-machine-thing interaction process, the representative research progress of low-dimensional nanomaterials-based information sensing, processing, and feedback devices is reviewed and the key roles played by low-dimensional nanomaterials are discussed. Finally, the development trends and existing challenges of low-dimensional nanomaterials in the field of human-machine-thing natural interaction technology are discussed.