Self-powered multifunctional sensing based on super-elastic fibers by soluble-core thermal drawing

Scalable Production of Functional Fibers with Nanoscale Features for Smart Textiles

Functional fibers, retaining nanoscale characteristics or nanomaterial properties, represent a significant advance in nanotechnology. Notably, the combination of scalable manufacturing with cutting-edge nanotechnology further expands their utility across numerous disciplines. Manufacturing kilometer-scale functional fibers with nanoscale properties are critical to the evolution of smart textiles, wearable electronics, and beyond. This review discusses their design principles, manufacturing technologies, and key advancements in the mass production of such fibers. In addition, it summarizes the current applications and state of progress in scalable fiber technologies and provides guidance for future advances in multifunctional smart textiles, by highlighting the upcoming impending demands for evolving nanotechnology. Challenges and directions requiring sustained effort are also discussed, including material selection, device design, large-scale manufacturing, and multifunctional integration. With advances in functional fibers and nanotechnology in large-scale production, wearable electronics, and smart textiles could potentially enhance human-machine interaction and healthcare applications.

Transformable 3D curved high-density liquid metal coils - an integrated unit for general soft actuation, sensing and communication

Rigid solenoid coils have long been indispensable in modern intelligent devices. However, their sparse structure and challenging preparation of flexible coils for soft robots impose limitations. Here, a transformable 3D curved high-density liquid metal coil (HD-LMC) is introduced that surpasses the structural density level of enameled wire. The fabrication technique employed for high-density channels in elastomers is universally applicable. Such HD-LMCs demonstrated excellent performance in pressure, temperature, non-contact distance sensors, and near-field communication. Soft electromagnetic actuators thus achieved significantly improved the electromagnetic force and power density. Moreover, precise control of swinging tail motion enables a bionic pufferfish to swim. Finally, HD-LMC is further utilized to successfully implement a soft rotary robot with integrated sensing and actuation capabilities. This groundbreaking research provides a theoretical and experimental basis for expanding the applications of liquid metal-based multi-dimensional complex flexible electronics and is expected to be widely used in liquid metal-integrated robotic systems.

Fibres-threads of intelligence-enable a new generation of wearable systems

Fabrics represent a unique platform for seamlessly integrating electronics into everyday experiences. The advancements in functionalizing fabrics at both the single fibre level and within constructed fabrics have fundamentally altered their utility. The revolution in materials, structures, and functionality at the fibre level enables intimate and imperceptible integration, rapidly transforming fibres and fabrics into next-generation wearable devices and systems. In this review, we explore recent scientific and technological breakthroughs in smart fibre-enabled fabrics. We examine common challenges and bottlenecks in fibre materials, physics, chemistry, fabrication strategies, and applications that shape the future of wearable electronics. We propose a closed-loop smart fibre-enabled fabric ecosystem encompassing proactive sensing, interactive communication, data storage and processing, real-time feedback, and energy storage and harvesting, intended to tackle significant challenges in wearable technology. Finally, we envision computing fabrics as sophisticated wearable platforms with system-level attributes for data management, machine learning, artificial intelligence, and closed-loop intelligent networks.

Bioinspired Liquid Metal Based Soft Humanoid Robots

The pursuit of constructing humanoid robots to replicate the anatomical structures and capabilities of human beings has been a long-standing significant undertaking and especially garnered tremendous attention in recent years. However, despite the progress made over recent decades, humanoid robots have predominantly been confined to those rigid metallic structures, which however starkly contrast with the inherent flexibility observed in biological systems. To better innovate this area, the present work systematically explores the value and potential of liquid metals and their derivatives in facilitating a crucial transition towards soft humanoid robots. Through a comprehensive interpretation of bionics, an overview of liquid metals' multifaceted roles as essential components in constructing advanced humanoid robots-functioning as soft actuators, sensors, power sources, logical devices, circuit systems, and even transformable skeletal structures-is presented. It is conceived that the integration of these components with flexible structures, facilitated by the unique properties of liquid metals, can create unexpected versatile functionalities and behaviors to better fulfill human needs. Finally, a revolution in humanoid robots is envisioned, transitioning from metallic frameworks to hybrid soft-rigid structures resembling that of biological tissues. This study is expected to provide fundamental guidance for the coming research, thereby advancing the area.

A temperature-responsive intravenous needle that irreversibly softens on insertion

The high stiffness of intravenous needles can cause tissue injury and increase the risk of transmission of blood-borne pathogens through accidental needlesticks. Here we describe the development and performance of an intravenous needle whose stiffness and shape depend on body temperature. The needle is sufficiently stiff for insertion into soft tissue yet becomes irreversibly flexible after insertion, adapting to the shape of the blood vessel and reducing the risk of needlestick injury on removal, as we show in vein phantoms and ex vivo porcine tissue. In mice, the needles had similar fluid-delivery performance and caused substantially less inflammation than commercial devices for intravenous access of similar size. We also show that an intravenous needle integrated with a thin-film temperature sensor can monitor core body temperature in mice and detect fluid leakage in porcine tissue ex vivo. Temperature-responsive intravenous needles may improve patient care.

Functional fibers/textiles for smart sensing devices and applications in personal healthcare systems

Personalized medical diagnostics and monitoring have become increasingly important due to inefficient and delayed medical services of traditional centralized healthcare systems. To enhance the comfort and portability, flexible health monitoring systems have been developed in recent years. In particular, smart fiber/textile-based sensing devices show superiority for continuously monitoring personal health and vital physiological parameters owing to their light weight, good flexibility and inherent miniaturization. This review focuses on the recent advances in smart fiber/textile-based sensing devices for wearable electronic applications. First, fabrication strategies of smart sensing fibers/textiles are introduced in detail. In addition, sensing performances, working principles and applications of smart sensing fibers/textiles such as pressure sensing fibers/textiles, stretchable strain sensing fibers/textiles, temperature sensing fibers/textiles, and biofluid, gas and humidity sensing fibers/textiles in health monitoring are also reviewed systematically. Finally, we propose current challenges and future prospects in the area of fiber/textile-based sensors for wearable healthcare monitoring and diagnosis systems. In general, this review aims to give an overall perspective of the promising field by reviewing various fiber/textile-based sensing devices and highlighting the importance for researchers to keep up with the sequential exploration of soft sensing fibers/textiles for applications in wearable smart systems.

Dynamic interfacial electrostatic energy harvesting via a single wire

Spontaneously occurred electrostatic breakdown releases enormous energy, but harnessing the energy remains a notable challenge due to its irregularity and instantaneity. Here, we propose a revolutionary method that effectively harvests the energy of dynamic interfacial electrostatic breakdown by simply imbedding a conductive wire (diameter, 25 micrometers) beneath dielectric materials to regulate the originally chaotic and distributed electrostatic energy resulted from contact electrification into aggregation, effectively transforming mechanical energy into electricity. A point-charge physical model is proposed to explain the power generation process and output characteristics, guide structural design, and enhance output performance. Furthermore, a quantified triboelectric series including 72 dielectric material pairs is established for materials choice and optimization. In addition, a high voltage of over 10 kilovolts is achieved using polytetrafluoroethylene and polyethylene terephthalate. This work opens a door for effectively using electrostatic energy, offering promising applications ranging from novel high-voltage power sources, smart clothing, and internet of things.

Self-Healable Multifunctional Fibers via Thermal Drawing

The development of soft electronics and soft fiber devices has significantly advanced flexible and wearable technology. However, they still face the risk of damage when exposed to sharp objects in real-life applications. Taking inspiration from nature, self-healable materials that can restore their physical properties after external damage offer a solution to this problem. Nevertheless, large-scale production of self-healable fibers is currently constrained. To address this limitation, this study leverages the thermal drawing technique to create elastic and stretchable self-healable thermoplastic polyurethane (STPU) fibers, enabling cost-effective mass production of such functional fibers. Furthermore, despite substantial research into the mechanisms of self-healable materials, quantifying their healing speed and time poses a persistent challenge. Thus, transmission spectra are employed as a monitoring tool to observe the real-time self-healing process, facilitating an in-depth investigation into the healing kinetics and efficiency. The versatility of the fabricated self-healable fiber extends to its ability to be doped with a wide range of functional materials, including dye molecules and magnetic microparticles, which enables modular assembly to develop distributed strain sensors and soft actuators. These achievements highlight the potential applications of self-healable fibers that seamlessly integrate with daily lives and open up new possibilities in various industries.

In-situ forming ultra-mechanically sensitive materials for high-sensitivity stretchable fiber strain sensors

Fiber electronics with flexible and weavable features can be easily integrated into textiles for wearable applications. However, due to small sizes and curved surfaces of fiber materials, it remains challenging to load robust active layers, thus hindering production of high-sensitivity fiber strain sensors. Herein, functional sensing materials are firmly anchored on the fiber surface in-situ through a hydrolytic condensation process. The anchoring sensing layer with robust interfacial adhesion is ultra-mechanically sensitive, which significantly improves the sensitivity of strain sensors due to the easy generation of microcracks during stretching. The resulting stretchable fiber sensors simultaneously possess an ultra-low strain detection limit of 0.05%, a high stretchability of 100%, and a high gauge factor of 433.6, giving 254-folds enhancement in sensitivity. Additionally, these fiber sensors are soft and lightweight, enabling them to be attached onto skin or woven into clothes for recording physiological signals, e.g. pulse wave velocity has been effectively obtained by them. As a demonstration, a fiber sensor-based wearable smart healthcare system is designed to monitor and transmit health status for timely intervention. This work presents an effective strategy for developing high-performance fiber strain sensors as well as other stretchable electronic devices.

Triboelectric micro-flexure-sensitive fiber electronics

Developing fiber electronics presents a practical approach for establishing multi-node distributed networks within the human body, particularly concerning triboelectric fibers. However, realizing fiber electronics for monitoring micro-physiological activities remains challenging due to the intrinsic variability and subtle amplitude of physiological signals, which differ among individuals and scenarios. Here, we propose a technical approach based on a dynamic stability model of sheath-core fibers, integrating a micro-flexure-sensitive fiber enabled by nanofiber buckling and an ion conduction mechanism. This scheme enhances the accuracy of the signal transmission process, resulting in improved sensitivity (detectable signal at ultra-low curvature of 0.1 mm-1; flexure factor >21.8% within a bending range of 10°.) and robustness of fiber under micro flexure. In addition, we also developed a scalable manufacturing process and ensured compatibility with modern weaving techniques. By combining precise micro-curvature detection, micro-flexure-sensitive fibers unlock their full potential for various subtle physiological diagnoses, particularly in monitoring fiber upper limb muscle strength for rehabilitation and training.

Rational electrolyte design and electrode regulation for boosting high-capacity Zn-iodine fiber-shaped batteries with four-electron redox reactions

Aqueous Zn ion-based fiber-shaped batteries (AZFBs) with the merits of high flexibility and safety have received much attention for powering wearable electronic devices. However, the relatively low specific capacity provided by cathode materials limits their practical application. Herein, we first propose a simple strategy for fabricating high-capacity Zn-iodine fiber-shaped batteries with a high concentration electrolyte and a reduced graphene oxide fiber (GF) cathode. It was found that oxygen functional groups in the graphene sheet demonstrate strong interaction with polyiodides but hinder electron conductivity; thus, the optimal balance between the specific capacity and coulombic efficiency of the GF electrode can be a function of the surface properties at different hydrothermal temperatures. Besides, the regulated high concentration electrolyte effectively suppresses the diffusion of polyiodides, which is attributed to the constrained freedom of water. More importantly, a four-electron redox mechanism was experimentally revealed through in situ Raman spectra. As a result, this fiber-shaped battery delivers a superior high reversible capacity of 390 mA h cm-3 at 1 A cm-3, an excellent rate performance of 125.7 mA h cm-3 at a high current density of 8 A cm-3 and outstanding cycling life with 82% capacitance retention after 2500 cycles.

Electrospinning Nanofibers as Stretchable Sensors for Wearable Devices

Wearable devices attract great attention in intelligent medicine, electronic skin, artificial intelligence robots, and so on. However, boundedness of traditional sensors based on rigid materials unconstrained self-multilayer structure assembly and dense substrate in stretchability and permeability limits their applications. The network structure of the elastomeric nanofibers gives them excellent air permeability and stretchability. By introducing metal nanofillers, intrinsic conductive polymers, carbon materials, and other methods to construct conductive paths, stretchable conductors can be effectively prepared by elastomeric nanofibers, showing great potential in the field of flexible sensors. This perspective briefly introduces the representative preparations of conductive thermoplastic polyurethane, nylon, and hydrogel nanofibers by electrospinning and the application of integrated electronic devices in biological signal detection. The main challenge is to unify the stretchability and conductivity of the fiber structure.

Liquid Metal-Based Stable and Stretchable Zn-Ion Battery for Electronic Textiles

Electronic textiles harmoniously interact with the human body and the surrounding environment, offering tremendous interest in smart wearable electronics. However, their wide application faces challenges due to the lack of stable and stretchable power electrodes/devices with multifunctional design. Herein, an intrinsically stretchable liquid metal-based fibrous anode for a stable Zn-ion battery (ZIB) is reported. Benefiting from the liquid feature and superior deformability of the liquid metal, optimized Zn ion concentration distribution and Zn (002) deposition behavior are observed, which result in dendrite-free performance even under stretching. With a strain of 50%, the ZIB maintains a high capacity of 139.8 mAh cm-3 (corresponding to 83.0% of the initial value) after 300 cycles, outperforming bare Zn fiber-based ZIB. The fibrous ZIB seamlessly integrates with the sensor, Joule heater, and wirelessly charging device, which provides a stable power supply for human signal monitoring and personal thermal management, holding promise for the application of wearable multifunctional electronic textiles.

A 33nW Fully Autonomous SoC With Distributed Cooperative Energy Harvesting and Multi-Chip Power Management for mm-Scale System-in-Fiber

This article presents a fully autonomous system-on-chip (SoC) that can be distributed along a fiber strand, capable of simultaneously harvesting energy, cooperatively scaling performance, sharing power, and booting-up with other in-fiber SoCs for ultra-low-power (ULP) sensing applications. Utilizing a custom switched capacitor energy harvesting and power management unit (EHPMU), the SoC can efficiently redistribute and reuse harvested energy along the fiber. Integrated on-chip, the ULP RISC-V digital core and temperature sensor enable energy-efficient sensing and computation at nanowatt power levels. A dedicated ripple boot-up and cooperative dynamic voltage and frequency scaling (DVFS) further optimize the operation and physical size of the system. Fabricated in 65 nm, measurement results show that the proposed SoC achieves 33 nW power consumption for the whole chip under 92 Lux lighting condition and can reduce control power down to 2.7 nW for the EHPMU. With the proposed power sharing and cooperative DVFS techniques, the SoC reduces the illuminance needed to stay alive by >7× down to 12 Lux. Integrated into a mm-scale polymer fiber, our SoC demonstrates the feasibility of fully autonomous and ULP on-body sensing systems in resource-constrained fiber environments.

Interlocking-Governed Ultra-Strong and Highly Conductive MXene Fibers Through Fluidics-Assisted Thermal Drawing

High-performance MXene fibers are always of significant interest for flexible textile-based devices. However, achieving high mechanical property and electrical conductivity remains challenging due to the uncontrolled loose microstructures of MXene (Ti3 C2 Tx and Ti3 CNTx ) nanosheets. Herein, high-performance MXene fibers directly obtained through fluidics-assisted thermal drawing are demonstrated. Tablet interlocks are formed at the interface layer between the outer cyclic olefin copolymer and inner MXene nanosheets due to the thermal drawing induced stresses, resulting in thousands of meters long macroscopic compact MXene fibers with ultra-high tensile strength, toughness, and outstanding electrical conductivity. Further, large-scale woven textiles constructed by these fibers offer exceptional electromagnetic interference shielding performance with excellent durability and stability. Such an effective and sustainable approach can be applied to produce functional fibers for applications in both daily life and aerospace.

Fiber Crossbars: An Emerging Architecture of Smart Electronic Textiles

Smart wearables have a significant impact on people's daily lives, enabling personalized motion monitoring, realizing the Internet of Things, and even reshaping the next generation of telemedicine systems. Fiber crossbars (FCs), constructed by crossing two fibers, have become an emerging architecture among the accessible structures of state-of-the-art smart electronic textiles. The mechanical, chemical, and electrical interactions between crossing fibers result in extensive functionalities, leading to the significant development of innovative electronic textiles employing FCs as their basic units. This review provides a timely and comprehensive overview of the structure designs, material selections, and assembly techniques of FC-based devices. The recent advances in FC-based devices are summarized, including multipurpose sensing, multiple-mode computing, high-resolution display, high-efficient power supply, and large-scale textile systems. Finally, current challenges, potential solutions, and future perspectives for FC-based systems are discussed for their further development in scale-up production and commercial applications.

Recent Progress of Advanced Materials for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) have received intense attention due to their broad application prospects in the new era of internet of things (IoTs) as distributed power sources and self-powered sensors. Advanced materials are vital components for TENGs, which decide their comprehensive performance and application scenarios, opening up the opportunity to develop efficient TENGs and expand their potential applications. In this review, a systematic and comprehensive overview of the advanced materials for TENGs is presented, including materials classifications, fabrication methods, and the properties required for applications. In particular, the triboelectric, friction, and dielectric performance of advanced materials is focused upon and their roles in designing the TENGs are analyzed. The recent progress of advanced materials used in TENGs for mechanical energy harvesting and self-powered sensors is also summarized. Finally, an overview of the emerging challenges, strategies, and opportunities for research and development of advanced materials for TENGs is provided.

Fluorescent Fiber-Shaped Aqueous Zinc-Ion Batteries for Bifunctional Multicolor-Emission/Energy-Storage Textiles

Wearable smart textiles are natural carriers to enable imperceptible and highly permeable sensing and response to environmental conditions via the system integration of multiple functional fibers. However, the existing massive interfaces between different functional fibers significantly increase the complexity and reduce the wearability of the textile system. Thus, it is significant yet challenging to achieve all-in-one multifunctional fibers for realizing miniaturized and lightweight smart textiles with high reliability. Herein, as bifunctional electrolyte additives, fluorescent carbon dots with abundant zincophilic functional groups are introduced into electrolytes to develop fluorescent fiber-shaped aqueous zinc-ion batteries (FFAZIBs). Originating from effective dendrite suppression of Zn anodes and multiple active sites of freestanding Prussian blue cathodes, high energy density (0.17 Wh·cm-3) and long-term cyclability (78.9% capacity retention after 1500 cycles) are achieved for FFAZIBs. More importantly, the one-dimensional structure ensures the same luminance in all directions of FFAZIBs, enabling the form of multicolor display-in-battery textiles.

Fibrous wearable and implantable bioelectronics

Fibrous wearable and implantable devices have emerged as a promising technology, offering a range of new solutions for minimally invasive monitoring of human health. Compared to traditional biomedical devices, fibers offer a possibility for a modular design compatible with large-scale manufacturing and a plethora of advantages including mechanical compliance, breathability, and biocompatibility. The new generation of fibrous biomedical devices can revolutionize easy-to-use and accessible health monitoring systems by serving as building blocks for most common wearables such as fabrics and clothes. Despite significant progress in the fabrication, materials, and application of fibrous biomedical devices, there is still a notable absence of a comprehensive and systematic review on the subject. This review paper provides an overview of recent advancements in the development of fibrous wearable and implantable electronics. We categorized these advancements into three main areas: manufacturing processes, platforms, and applications, outlining their respective merits and limitations. The paper concludes by discussing the outlook and challenges that lie ahead for fiber bioelectronics, providing a holistic view of its current stage of development.

Ambient-conditions spinning of functional soft fibers via engineering molecular chain networks and phase separation

Producing functional soft fibers via existing spinning methods is environmentally and economically costly due to the complexity of spinning equipment, involvement of copious solvents, intensive consumption of energy, and multi-step pre-/post-spinning treatments. We report a nonsolvent vapor-induced phase separation spinning approach under ambient conditions, which resembles the native spider silk fibrillation. It is enabled by the optimal rheological properties of dopes via engineering silver-coordinated molecular chain interactions and autonomous phase transition due to the nonsolvent vapor-induced phase separation effect. Fiber fibrillation under ambient conditions using a polyacrylonitrile-silver ion dope is demonstrated, along with detailed elucidations on tuning dope spinnability through rheological analysis. The obtained fibers are mechanically soft, stretchable, and electrically conductive, benefiting from elastic molecular chain networks via silver-based coordination complexes and in-situ reduced silver nanoparticles. Particularly, these fibers can be configured as wearable electronics for self-sensing and self-powering applications. Our ambient-conditions spinning approach provides a platform to create functional soft fibers with unified mechanical and electrical properties at a two-to-three order of magnitude less energy cost under ambient conditions.

Density-of-States Matching-Induced Ultrahigh Current Density and High-Humidity Resistance in a Simply Structured Triboelectric Nanogenerator

Triboelectric nanogenerators (TENGs) can covert mechanical energy into electricity in a clean and sustainable manner. However, traditional TENGs are mainly limited by the low output current, and thus their practical applications are still limited. Herein, a new type of TENG is developed by using conductive materials as the triboelectric layers and electrodes simultaneously. Because of the matched density of states between the two triboelectric layers, this simply structured device reaches an open-circuit voltage of 1400 V and an ultrahigh current density of 1333 mA m^-2 when poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film and copper (Cu) or aluminum (Al) foil are used as the triboelectric pair. The current density increases by nearly three orders of magnitude compared with traditional TENGs. More importantly, this device can work stably in high-humidity environments, which is always a big challenge for traditional TENGs. Surprisingly, this TENG can even perform well in the presence of water droplets. This work provides a new and effective strategy for constructing high-performance TENGs, which can be used in many practical applications in the near future.

Piezoelectric fibers for flexible and wearable electronics

Flexible and wearable electronics represent paramount technologies offering revolutionized solutions for medical diagnosis and therapy, nerve and organ interfaces, fabric computation, robot-in-medicine and metaverse. Being ubiquitous in everyday life, piezoelectric materials and devices play a vital role in flexible and wearable electronics with their intriguing functionalities, including energy harvesting, sensing and actuation, personal health care and communications. As a new emerging flexible and wearable technology, fiber-shaped piezoelectric devices offer unique advantages over conventional thin-film counterparts. In this review, we survey the recent scientific and technological breakthroughs in thermally drawn piezoelectric fibers and fiber-enabled intelligent fabrics. We highlight the fiber materials, fiber architecture, fabrication, device integration as well as functions that deliver higher forms of unique applications across smart sensing, health care, space security, actuation and energy domains. We conclude with a critical analysis of existing challenges and opportunities that will be important for the continued progress of this field.

Stretchable Woven Fabric-Based Triboelectric Nanogenerator for Energy Harvesting and Self-Powered Sensing

With the triboelectric nanogenerator developing in recent years, it has gradually become a promising alternative to fossil energy and batteries. Its rapid advancements also promote the combination of triboelectric nanogenerators and textiles. However, the limited stretchability of fabric-based triboelectric nanogenerators hindered their development in wearable electronic devices. Here, in combination with the polyamide (PA) conductive yarn, polyester multifilament, and polyurethane yarn, a highly stretchable woven fabric-based triboelectric nanogenerator (SWF-TENG) with the three elementary weaves is developed. Different from the normal woven fabric without elasticity, the loom tension of the elastic warp yarn is much larger than non-elastic warp yarn in the weaving process, which results in the high elasticity of the woven fabric coming from the loom. Based on the unique and creative woven method, SWF-TENGs are qualified with excellent stretchability (up to 300%), flexibility, comfortability, and excellent mechanical stability. It also exhibits good sensitivity and fast responsibility to the external tensile strain, which can be used as a bend-stretch sensor to detect and identify human gait. Its collected power under pressure mode is capable of lighting up 34 light-emitting diodes (LEDs) by only hand-tapping the fabric. SWF-TENG can be mass-manufactured by using the weaving machine, which decreases fabricating costs and accelerates industrialization. Based on these merits, this work provides a promising direction toward stretchable fabric-based TENGs with wide applications in wearable electronics, including energy harvesting and self-powered sensing.

Scalable Fabrication of MXene-PVDF Nanocomposite Triboelectric Fibers via Thermal Drawing

In the data-driven world, textile is a valuable resource for improving the quality of life through continuous monitoring of daily activities and physiological signals of humans. Triboelectric nanogenerators (TENG) are an attractive option for self-powered sensor development by coupling energy harvesting and sensing ability. In this study, to the best of the knowledge, scalable fabrication of Ti₃ C₂ T_x MXene-embedded polyvinylidene fluoride (PVDF) nanocomposite fiber using a thermal drawing process is presented for the first time. The output open circuit voltage and short circuit current show 53% and 58% improvement, respectively, compared to pristine PVDF fiber. The synergistic interaction between the surface termination groups of MXene and polar PVDF polymer enhances the performance of the fiber. The flexibility of the fiber enables the weaving of fabric TENG devices for large-area applications. The fabric TENG (3 × 2 cm² ) demonstrates a power density of 40.8 mW m^-2 at the matching load of 8 MΩ by maintaining a stable performance over 12 000 cycles. Moreover, the fabric TENG has shown the capability of energy harvesting by operating a digital clock and a calculator. A distributed self-powered sensor for human activities and walking pattern monitoring are demonstrated with the fabric.

Stretchable One-Dimensional Conductors for Wearable Applications

Continuous, one-dimensional (1D) stretchable conductors have attracted significant attention for the development of wearables and soft-matter electronics. Through the use of advanced spinning, printing, and textile technologies, 1D stretchable conductors in the forms of fibers, wires, and yarns can be designed and engineered to meet the demanding requirements for different wearable applications. Several crucial parameters, such as microarchitecture, conductivity, stretchability, and scalability, play essential roles in designing and developing wearable devices and intelligent textiles. Methodologies and fabrication processes have successfully realized 1D conductors that are highly conductive, strong, lightweight, stretchable, and conformable and can be readily integrated with common fabrics and soft matter. This review summarizes the latest advances in continuous, 1D stretchable conductors and emphasizes recent developments in materials, methodologies, fabrication processes, and strategies geared toward applications in electrical interconnects, mechanical sensors, actuators, and heaters. This review classifies 1D conductors into three categories on the basis of their electrical responses: (1) rigid 1D conductors, (2) piezoresistive 1D conductors, and (3) resistance-stable 1D conductors. This review also evaluates the present challenges in these areas and presents perspectives for improving the performance of stretchable 1D conductors for wearable textile and flexible electronic applications.

Elastic Fibers/Fabrics for Wearables and Bioelectronics

Wearables and bioelectronics rely on breathable interface devices with bioaffinity, biocompatibility, and smart functionality for interactions between beings and things and the surrounding environment. Elastic fibers/fabrics with mechanical adaptivity to various deformations and complex substrates, are promising to act as fillers, carriers, substrates, dressings, and scaffolds in the construction of biointerfaces for the human body, skins, organs, and plants, realizing functions such as energy exchange, sensing, perception, augmented virtuality, health monitoring, disease diagnosis, and intervention therapy. This review summarizes and highlights the latest breakthroughs of elastic fibers/fabrics for wearables and bioelectronics, aiming to offer insights into elasticity mechanisms, production methods, and electrical components integration strategies with fibers/fabrics, presenting a profile of elastic fibers/fabrics for energy management, sensors, e-skins, thermal management, personal protection, wound healing, biosensing, and drug delivery. The trans-disciplinary application of elastic fibers/fabrics from wearables to biomedicine provides important inspiration for technology transplantation and function integration to adapt different application systems. As a discussion platform, here the main challenges and possible solutions in the field are proposed, hopefully can provide guidance for promoting the development of elastic e-textiles in consideration of the trade-off between mechanical/electrical performance, industrial-scale production, diverse environmental adaptivity, and multiscenario on-spot applications.

3D stretchable and self-encapsulated multimaterial triboelectric fibers

A robust power device for wearable technologies and soft electronics must feature good encapsulation, high deformability, and reliable electrical outputs. Despite substantial progress in materials and architectures for two-dimensional (2D) planar power configurations, fiber-based systems remain limited to relatively simple configurations and low performance due to challenges in processing methods. Here, we extend complex 2D triboelectric nanogenerator configurations to 3D fiber formats based on scalable thermal processing of water-resistant thermoplastic elastomers and composites. We perform mechanical analysis using finite element modeling to understand the fiber's deformation and the level of control and engineering on its mechanical behavior and thus to guide its dimensional designs for enhanced electrical performance. With microtexture patterned functional surfaces, the resulting fibers can reliably produce state-of-the-art electrical outputs from various mechanical deformations, even under harsh conditions. These mechanical and electrical attributes allow their integration with large and stretchable surfaces for electricity generation of hundreds of microamperes.

Vanadium Dioxide Nanosheets Supported on Carbonized Cotton Fabric as Bifunctional Textiles for Flexible Pressure Sensors and Zinc-Ion Batteries

Flexible pressure sensors and aqueous batteries have been widely used in the rapid development of wearable electronics. The synergistic functionalities of versatile materials with multidimensional architectures are recognized to have a significant impact on the performance of flexible electronics. Herein, a facile hydrothermal strategy was demonstrated to conformally grow vanadium dioxide nanosheets on carbonized cotton fabrics (VO₂/CCotton), which is a candidate material used in flexible piezoresistive sensors. As a result, the VO₂/CCotton-based pressure sensor behaved with high sensitivity (S = 7.12 kPa^-1 in the pressure range of 0-2.0 kPa) and a stable sensing ability in a wide pressure scale of 0-120 kPa. Further practical applications were performed in monitoring delicate physiological signals as well, such as twisting, blowing, and voice vibration recognitions. In addition, another application for energy storage was investigated as well. A quasi-solid-state aqueous zinc-ion battery was assembled with VO₂/CCotton as the cathode and a film of Zn nanosheets/carbon nanotube as the anode. A capacity as high as 301.5 mAh g^-1 and remarkable durability of 88.7% capacity retention after 5000 cycles at 10 A g^-1 were found. These exceptional outcomes are attributed to the unique three-dimensional architecture and the prominent synergetic effects of CCotton and VO₂ and allow for the proposal of novel guidelines for next-generation multifunctional flexible electronics.

Ultra-compact MXene fibers by continuous and controllable synergy of interfacial interactions and thermal drawing-induced stresses

Recent advances in MXene (Ti₃C₂T_x) fibers, prepared from electrically conductive and mechanically strong MXene nanosheets, address the increasing demand of emerging yet promising electrode materials for the development of textile-based devices and beyond. However, to reveal the full potential of MXene fibers, reaching a balance between electrical conductivity and mechanical property is still the fundamental challenge, mainly due to the difficulties to further compact the loose MXene nanosheets. In this work, we demonstrate a continuous and controllable route to fabricate ultra-compact MXene fibers with an in-situ generated protective layer via the synergy of interfacial interactions and thermal drawing-induced stresses. The resulting ultra-compact MXene fibers with high orientation and low porosity exhibit not only excellent tensile strength and ultra-high toughness, but also high electrical conductivity. Then, we construct meter-scale MXene textiles using these ultra-compact fibers to achieve high-performance electromagnetic interference shielding and personal thermal management, accompanied by the high mechanical durability and stability even after multiple washing cycles. The demonstrated generic strategy can be applied to a broad range of nanostructured materials to construct functional fibers for large-scale applications in both space and daily lives.

Achieving Ultrahigh Effective Surface Charge Density of Direct-Current Triboelectric Nanogenerator in High Humidity

As an emerging energy-harvesting technology, the triboelectric nanogenerator (TENG) is considered a powerful driving force toward the new-era of Internet of Things and artificial intelligence, but its output performance is dramatically influenced by environmental humidity. Herein, a direct current TENG (DC-TENG) based on the triboelectrification effect and electrostatic breakdown is reported to address the problem of output attenuation in high humidity environments for the conventional TENGs. It is found that high humidity not only enhances the sliding triboelectrification effect of hydrophobic triboelectric materials, but also promotes the electrostatic breakdown process for DC-TENG, thus contributing to the improvement of DC-TENG output. Furthermore, taking poly(vinyl chloride) film as the friction layer, the effective surface charge density of DC-TENG with microstructure-designed electrode achieves a milestone value of ≈2.97 mC m^-2 under 90% relative humidity, which is almost 1.42-fold larger than that under 30% RH. This work not only establishes an effective methodology to boost the output performance of TENG in a high humidity environment, but also establishes a foundation for its practical applications in large-scale energy harvesting.

Digitally-embroidered liquid metal electronic textiles for wearable wireless systems

Electronic textiles capable of sensing, powering, and communication can be used to non-intrusively monitor human health during daily life. However, achieving these functionalities with clothing is challenging because of limitations in the electronic performance, flexibility and robustness of the underlying materials, which must endure repeated mechanical, thermal and chemical stresses during daily use. Here, we demonstrate electronic textile systems with functionalities in near-field powering and communication created by digital embroidery of liquid metal fibers. Owing to the unique electrical and mechanical properties of the liquid metal fibers, these electronic textiles can conform to body surfaces and establish robust wireless connectivity with nearby wearable or implantable devices, even during strenuous exercise. By transferring optimized electromagnetic patterns onto clothing in this way, we demonstrate a washable electronic shirt that can be wirelessly powered by a smartphone and continuously monitor axillary temperature without interfering with daily activities.

Recent progress of fiber-based transistors: materials, structures and applications

Wearable electronics on fibers or fabrics assembled with electronic functions provide a platform for sensors, displays, circuitry, and computation. These new conceptual devices are human-friendly and programmable, which makes them indispensable for modern electronics. Their unique properties such as being adaptable in daily life, as well as being lightweight and flexible, have enabled many promising applications in robotics, healthcare, and the Internet of Things (IoT). Transistors, one of the fundamental blocks in electronic systems, allow for signal processing and computing. Therefore, study leading to integration of transistors with fabrics has become intensive. Here, several aspects of fiber-based transistors are addressed, including materials, system structures, and their functional devices such as sensory, logical circuitry, memory devices as well as neuromorphic computation. Recently reported advances in development and challenges to realizing fully integrated electronic textile (e-textile) systems are also discussed.

Helical Fiber Strain Sensors Based on Triboelectric Nanogenerators for Self-Powered Human Respiratory Monitoring

Respiration is a major vital sign, which can be used for early illness diagnosis and physiological monitoring. Wearable respiratory sensors present an exciting opportunity to monitor human respiratory behaviors in a real-time, noninvasive, and comfortable way. Among them, fiber-shaped triboelectric nanogenerators (FS-TENGs) are attractive for their comfort and high degree of freedom. However, the single-electrode FS-TENGs cannot respond to their own tensile strains, and the coaxial double-electrode FS-TENGs show low sensitivity to strain due to structural limitations. Here, a type of helical fiber strain sensor (HFSS) is developed, which can respond to tiny tensile strains. In addition, a smart wearable real-time respiratory monitoring system is developed based on the HFSSs, which can measure some key breathing parameters for disease prevention and medical diagnosis. An intelligent alarm can automatically call a preset mobile phone for help in response to respiratory behavior changes. This work provides an effective helical structure for fabricating highly sensitive strain sensors based on FS-TENGs and develops wearable self-powered real-time respiratory monitoring systems.

Adaptive polymer fiber neural device for drug delivery and enlarged illumination angle for neuromodulation

OBJECTIVE

Optical fiber devices constitute significant tools for the modulation and interrogation of neuronal circuitry in the mid and deep brain regions. The illuminated brain area during neuromodulation has a direct impact on the spatio-temporal properties of the brain activity and depends solely on the material and geometrical characteristics of the optical fibers. In the present work, we developed two different flexible polymer optical fibers (POFs) with integrated microfluidic channels (MFCs) and an ultra-high numerical aperture (UHNA) for enlarging the illumination angle to achieve efficient neuromodulation.

APPROACH

Three distinct thermoplastic polymers: polysulfone (PSU), polycarbonate (PC), and fluorinated ethylene propylene (FEP) were used to fabricate two step-index UHNA POF neural devices using a scalable thermal drawing process. The POFs were characterized in terms of their illumination map as well as their fluid delivery capability in phantom and adult rat brain slices.

MAIN RESULTS

A 100-fold reduced bending stiffness of the proposed fiber devices compared to their commercially available counterparts has been found. The integrated MFCs can controllably deliver dye (trypan blue) on-demand over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min. Compared with commercial silica fibers, the proposed UHNA POFs exhibited an increased illumination area by 17% and 21% under 470 and 650 nm wavelength, respectively. In addition, a fluorescent light recording experiment has been conducted to demonstrate the ability of our UHNA POFs to be used as optical waveguides in fiber photometry.

SIGNIFICANCE

Our results overcome the current technological limitations of fiber implants that have limited illumination area and we suggest that soft neural fiber devices can be developed using different custom designs for illumination, collection, and photometry applications. We anticipate our work to pave the way towards the development of next-generation functional optical fibers for neuroscience.

Controlling the elasticity of polyacrylonitrile fibers via ionic liquids containing cyano-based anions

As the predominant precursor for high-performance carbon fiber manufacturing, the fabrication of polyacrylonitrile (PAN)-based composite fibers attracts great interest. Ionic liquids (ILs) have recently been investigated for melt-spinning of ultrafine PAN fibers. The plasticizing properties of ILs are significantly affected by the structure of ILs and can be influenced by electronegativity, steric effects, etc. Herein, we report a facile strategy to control the elasticity of the PAN/ILs fibers by tuning the anion structure of ILs. Particularly, the ILs containing nitrile-rich groups exhibited enhanced plasticizing effect and nucleating ability on dissolving PAN components, achieving highly stretchable PAN/ILs fibers.

Highly stretchable PAN/ILs fibers were fabricated through melt-spinning with ionic liquids containing cyano-based anions.

Recent Advances in Self-Powered Piezoelectric and Triboelectric Sensors: From Material and Structure Design to Frontier Applications of Artificial Intelligence

The development of artificial intelligence and the Internet of things has motivated extensive research on self-powered flexible sensors. The conventional sensor must be powered by a battery device, while innovative self-powered sensors can provide power for the sensing device. Self-powered flexible sensors can have higher mobility, wider distribution, and even wireless operation, while solving the problem of the limited life of the battery so that it can be continuously operated and widely utilized. In recent years, the studies on piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs) have mainly concentrated on self-powered flexible sensors. Self-powered flexible sensors based on PENGs and TENGs have been reported as sensing devices in many application fields, such as human health monitoring, environmental monitoring, wearable devices, electronic skin, human–machine interfaces, robots, and intelligent transportation and cities. This review summarizes the development process of the sensor in terms of material design and structural optimization, as well as introduces its frontier applications in related fields. We also look forward to the development prospects and future of self-powered flexible sensors.

Inorganic Perovskite Quantum Dot-Based Strain Sensors for Data Storage and In-Sensor Computing

Although remarkable improvement has been achieved in stretchable strain sensors, challenges still exist in aspects including intelligent sensing, simultaneous data processing, and scalable fabrication techniques. In this work, a strain-sensitive device is presented by fabricating a CsPbBr₃ quantum dots (QDs) floating-gate field-effect transistor (FET) sensing array on thin polyimide (PI) films. The FET exhibits an excellent on/off ratio (>10³) and a large memory window (>2 V). With the introduction of CsPbBr₃ QDs as the trapping layer, an additional UV response is obtained because of the photogenerated charge carriers that significantly enhance the source-drain current (I_DS) of the device. At each electrical state, the I_DS varies with the strains and the sensing range is from compressive +12.5% to tensile -10.8%. Excellent data retainability and mechanical durability demonstrate the high quality and reliability of the fabricated sensors. Furthermore, synapse functions including long-term potentiation (LTP), long-term depression (LTD), etc., are emulated at the device level. Linearity factor changes of LTP/LTD in different sensing scenarios demonstrate the reliability of the device and further confirm the different sensing mechanisms with/without UV illumination. Our results exhibit the potential of transistor-based devices for multifunctional intelligent sensing.

Inorganic Thermoelectric Fibers: A Review of Materials, Fabrication Methods, and Applications

Thermoelectric technology can directly harvest the waste heat into electricity, which is a promising field of green and sustainable energy. In this aspect, flexible thermoelectrics (FTE) such as wearable fabrics, smart biosensing, and biomedical electronics offer a variety of applications. Since the nanofibers are one of the important constructions of FTE, inorganic thermoelectric fibers are focused on here due to their excellent thermoelectric performance and acceptable flexibility. Additionally, measurement and microstructure characterizations for various thermoelectric fibers (Bi-Sb-Te, Ag₂Te, PbTe, SnSe and NaCo₂O₄) made by different fabrication methods, such as electrospinning, two-step anodization process, solution-phase deposition method, focused ion beam, and self-heated 3ω method, are detailed. This review further illustrates that some techniques, such as thermal drawing method, result in high performance of fiber-based thermoelectric properties, which can emerge in wearable devices and smart electronics in the near future.