为推进智能可穿戴纺织品的研发和应用,基于纺织基应变传感器的研究现状,从纤维、纱线、织物3个结构尺度介绍了柔性应变传感器的设计思路和制备方法。概述了纺丝法、表面涂层和炭化改性制备纤维基应变传感器的关键问题及优缺点,总结了螺旋纱、皮芯结构复合纱等特殊纱线结构在应变传感器中的应用,对比了不同织物结构作为应变传感器基材的传感机制和性能特征。最后讨论了纺织基柔性应变传感器发展过程存在的问题和挑战:通过纺织结构设计实现传感器高灵敏度和大应变范围的要求;建立多尺度结构与传感性能之间的理论关系,充分发挥纺织材料的结构和性能优势;进一步推动纺织基应变传感器在可穿戴电子领域的实际应用。

<p id="p00010"><strong>Significance</strong> Wearable flexible strain sensors can facilitate all-round monitoring of human activities and thus have broad application prospects in fields such as healthcare, public health and human-computer interaction. Compared with traditional embedded rigid strain sensors, textile structures become an ideal structural platform for flexible strain sensors with the advantages of flexibility, comfort and hyperbolic effect. However, since the raw materials used in traditional textiles generally have electrical insulating properties, they should be modified into electrically sensitive materials before being used to construct flexible strain sensors. In addition, the textile structure design is targeted on the basis of the strain sensing mechanism. Although there are some basic researches on the application of textile technology in the field of smart wearables, it is still in its infancy in the actual market application. In order to further promote the development and application of smart wearable textiles and make full use of the textile structural advantages, this paper summarizes the design concepts and preparation methods of flexible textile-based strain sensors based on the current research progress. The paper is organized on progress made in fibers, yarns and fabrics. </p> <p id="p00113"><strong>Progress</strong> For fiber-based strain sensors, integrating fibers with electrically sensitive materials to achieve conductive fiber preparation is the primary issue which needs to be addressed in the preparation of strain sensors. Currently, there are three mainstream technologies to prepare fiber materials with good electrical conductivity which are fiber spinning, fiber surface coating and carbonization modification of fibers. Compared to fiber-based strain sensors, yarn-based sensors pay more attention to the macroscopic structural design to assemble multiple functional materials, achieving multi-dimensional upgrading of sensing performance. Yarn spinning technology, on the other hand, is an effective way to integrate functional fibers into yarns to achieve a good combination of structure and function. Spiral yarn and core-spun yarn are two commonly used yarn structures in strain sensors. Different fabric structures have their own advantages and disadvantages for creating strain sensors. Knitted fabrics have high stretchability, which can meet the size change ability required for strain sensors, but the structural stability is relatively poor. In comparison, woven fabrics have stable structure but the deformation is limited. The most common method for preparing strain sensors with braided structure is to use elastic yarns as core and conductive yarns as the braided sheath. Nonwoven structures provide an ideal template for the deposition of conductive materials, which can effectively construct three-dimensional interconnected conductive paths. The disadvantage however is that the strength is low and thus nonwoven fabrics are rarely used as a separate substrate for strain sensor. Finally, embedding flexible conductive yarn into textiles through the sewing process is also one way to prepare textile-based strain sensors. In principle, it can be embedded anywhere in clothing, providing preparation flexibility and potentially reducing costs.</p> <p id="p00112"><strong>Conclusion and Prospect</strong> Although significant progress has been made in the research of textile-based strain sensors, there are still some key issues that need to be further investigated in terms of structural design, mechanism analysis, and performance optimization before academic research can be used for practical applications. 1) In order to meet the requirements of high sensitivity and large strain range of sensors, the design concept is that any slight deformation will cause changes in the conductive network inside the material, and the conductive network is always connected under different strain levels. At the same time, the interfacial properties of the conductive filler and the substrate need to be improved to ensure the repeatability and stability of the sensor. 2)The inherent insulation, viscoelasticity, and complexity of the multi-scale structure make the mechanism study of textile-based strain sensors very complex. Establishing a theoretical relationship between the multi-scale structure and the sensing performance is a necessary foundation for optimization design and performance improvement of textile-based strain sensors. 3) The performance improvement of materials in terms of washability, comfort, and adaptability with the human body is an important research direction. It is also a key issue to fully leverage the structural and performance advantages of textile materials, and consequently promoting the practical application of textile sensors in the field of wearable electronics.</p>

Skin-integrated electronics that directly interact with machines are transforming our ways of life toward the emerging trend of the metaverse. Consequently, developing a wearable and skin-conformal interface that simultaneously features waterproofness, low cost, and low power consumption for human–machine interaction remains highly desired. Herein, a stretchable, inexpensive, and waterproof magnetoelastic sensor array has been developed as a secondary skin for self-powered human–machine interaction. The magnetoelastic sensor array utilizes the giant magnetoelastic effect in a soft system, which converts mechanical pressure to magnetic field variation and, when coupled with the magnetic induction, can generate electricity. In such a way, our magnetoelastic sensor array comprises the giant magnetomechanical coupling layer made up of nanomagnets and a porous silicone rubber matrix, and the magnetic induction layer, which are coils patterned by liquid metal. With programmable functionalities, the soft magnetoelastic sensor array can supply different commands by producing bespoke electric signals from human finger touch with an optimal signal-to-noise ratio of 34 dB and a rapid response time of 0.2s. To pursue a practical application, the soft magnetoelastic sensor array can wirelessly turn on and off a household lamp and control a music speaker via Bluetooth continuously in real time, even with contact with high-humidity environments such as heavy perspiration. With a collection of compelling features, the soft magnetoelastic sensor array puts forth a unique and savvy avenue of self-powered bioelectronic technology that practically enables a wider variety of applications for wearable human–machine interaction.

Wearable sensors have recently seen a large increase in both research and commercialization. However, success in wearable sensors has been a mix of both progress and setbacks. Most of commercial progress has been in smart adaptation of existing mechanical, electrical and optical methods of measuring the body. This adaptation has involved innovations in how to miniaturize sensing technologies, how to make them conformal and flexible, and in the development of companion software that increases the value of the measured data. However, chemical sensing modalities have experienced greater challenges in commercial adoption, especially for non-invasive chemical sensors. There have also been significant challenges in making significant fundamental improvements to existing mechanical, electrical, and optical sensing modalities, especially in improving their specificity of detection. Many of these challenges can be understood by appreciating the body's surface (skin) as more of an information barrier than as an information source. With a deeper understanding of the fundamental challenges faced for wearable sensors and of the state-of-the-art for wearable sensor technology, the roadmap becomes clearer for creating the next generation of innovations and breakthroughs.

Soft electromagnetic devices have great potential in soft robotics and biomedical applications. However, existing soft-magneto-electrical devices would have limited hybrid functions and suffer from damaging stress concentrations, delamination or material leakage. Here, we report a hybrid magnetic-mechanical-electrical (MME) core-sheath fiber to overcome these challenges. Assisted by the coaxial printing method, the MME fiber can be printed into complex 2D/3D MME structures with integrated magnetoactive and conductive properties, further enabling hybrid functions including programmable magnetization, somatosensory, and magnetic actuation along with simultaneous wireless energy transfer. To demonstrate the great potential of MME devices, precise and minimally invasive electro-ablation was performed with a flexible MME catheter with magnetic control, hybrid actuation-sensing was performed by a durable somatosensory MME gripper, and hybrid wireless energy transmission and magnetic actuation were demonstrated by an untethered soft MME robot. Our work thus provides a material design strategy for soft electromagnetic devices with unexplored hybrid functions.© 2023. The Author(s).

Textiles have been concomitant of human civilization for thousands of years. With the advances in chemistry and materials, integrating textiles with energy harvesters will provide a sustainable, environmentally friendly, pervasive, and wearable energy solution for distributed on-body electronics in the era of Internet of Things. This article comprehensively and thoughtfully reviews research activities regarding the utilization of smart textiles for harvesting energy from renewable energy sources on the human body and its surroundings. Specifically, we start with a brief introduction to contextualize the significance of smart textiles in light of the emerging energy crisis, environmental pollution, and public health. Next, we systematically review smart textiles according to their abilities to harvest biomechanical energy, body heat energy, biochemical energy, solar energy as well as hybrid forms of energy. Finally, we provide a critical analysis of smart textiles and insights into remaining challenges and future directions. With worldwide efforts, innovations in chemistry and materials elaborated in this review will push forward the frontiers of smart textiles, which will soon revolutionize our lives in the era of Internet of Things.

Combining traditional textiles with triboelectric nanogenerators (TENGs) gives birth to self-powered electronic textiles (e-textiles). However, there are two bottlenecks in their widespread application, low power output and poor sensing capability. Herein, by means of the three-dimensional five-directional braided (3DB) structure, a TENG-based e-textile with the features of high flexibility, shape adaptability, structural integrity, cyclic washability, and superior mechanical stability, is designed for power and sensing. Due to the spatial frame-column structure formed between the outer braided yarn and inner axial yarn, the 3DB-TENG is also endowed with high compression resilience, enhanced power output, improved pressure sensitivity, and vibrational energy harvesting ability, which can power miniature wearable electronics and respond to tiny weight variations. Furthermore, an intelligent shoe and an identity recognition carpet are demonstrated to verify its performance. This study hopes to provide a new design concept for high-performance textile-based TENGs and expand their application scope in human-machine interfacing.

Fiber-based sensors, owing to their high flexibility, excellent breathability, and ease of integration into everyday clothing, have the potential to serve as a novel type of wearable electronic device. This paper presents a helical strain-sensing fiber using electromagnetic induction, made from Ecoflex and magnetic nanoparticles. It achieves up to 2485% strain and maintains stable voltage output (max 90 μV) over 2000 cycles. In conclusion, based on this novel intelligent sensing material, we developed a human-machine interaction (HMI) system operable underwater, enabling remote control of a submarine model through hand gestures. This system facilitates real-time gesture interaction, opening new research avenues for the development of wearable HMI systems and Internet of Things technology in the future.

Magnetoelastic effect characterizes the change of materials' magnetic properties under mechanical deformation, which is conventionally observed in some rigid metals or metal alloys. Here we show magnetoelastic effect can also exist in 1D soft fibers with stronger magnetomechanical coupling than that in traditional rigid counterparts. This effect is explained by a wavy chain model based on the magnetic dipole-dipole interaction and demagnetizing factor. To facilitate practical applications, we further invented a textile magnetoelastic generator (MEG), weaving the 1D soft fibers with conductive yarns to couple the observed magnetoelastic effect with magnetic induction, which paves a new way for biomechanical-to-electrical energy conversion with short-circuit current density of 0.63 mA cm, internal impedance of 180 Ω, and intrinsic waterproofness. Textile MEG was demonstrated to convert the arterial pulse into electrical signals with a low detection limit of 0.05 kPa,  even with heavy perspiration or in underwater situations without encapsulations.© 2021. The Author(s).

The excellent electronic and mechanical properties of graphene provide a perfect basis for high performance flexible electronic and sensor devices. Here, we present the fabrication and characterization of flexible graphene based Hall sensors. The Hall sensors are fabricated on 50 μm thick flexible Kapton foil using large scale graphene grown by chemical vapor deposition technique on copper foil. Voltage and current normalized sensitivities of up to 0.096 V VT(-1) and 79 V AT(-1) were measured, respectively. These values are comparable to the sensitivity of rigid silicon based Hall sensors and are the highest values reported so far for any flexible Hall sensor devices. The sensitivity of the Hall sensor shows no degradation after being bent to a minimum radius of 4 mm, which corresponds to a tensile strain of 0.6%, and after 1000 bending cycles to a radius of 5 mm.

Tactile recognition is among the basic survival skills of human beings, and advances in tactile sensor technology have been adopted in various fields, bringing benefits such as outstanding performance in manipulating objects and general human-robot interactions. However, promoting enhanced perception of the existing tactile sensors is limited by their sensor array arrangement and wire-connected design. Here we present a wireless flexible magnetic tactile sensor (FMTS) consisting of a multidirection magnetized flexible film (perception module) and a contactless Hall sensor (signal receiving module). The flexible magnetic film is composed of NdFeB microparticles and soft silicone elastomer microparticles, and it transfers the unambiguous transduction of external force position and magnitude into magnetic signals. Benefiting from the specific magnetization arrangement and clustering algorithm, only one Hall sensor is needed in FMTS to perceive the magnitude and position of the contact spot simultaneously with super-resolution (2.1 mm average error) on a large area (3600 mm), and the effective working distance is also greatly extended (∼30 mm), allowing for the full softness and adaptability to diverse conditions. We anticipate that this design will promote the development of soft tactile sensors and their integration into human-robot interaction and humanoid robot perception.

Graphene has shown considerable potential for sensing magnetic fields based on the Hall Effect, due to its high carrier mobility, low sheet carrier density, and low-temperature dependence. However, the cost of graphene in comparison to conventional materials has meant that its uptake in electronic manufacturing has been slow. To lower technological barriers and bring more widespread adoption of graphene Hall sensors, we are using a one-step laser scribing process that does not rely on multiple steps, toxic chemicals, and subsequent treatments. Laser-scribed graphene Hall sensors offer a linear response to magnetic fields with a normalized sensitivity of ~1.12 V/AT. They also exhibit a low constant noise voltage floor of ~ 50 nV/$$\\sqrt {{\\mathrm{Hz}}}$$\n \n \n Hz\n \n \n for a bias current of 100 µA at room temperature, which is comparable with state-of-the-art low-noise Hall sensors. The sensors combine a high bendability, come with high robustness and operating temperatures up to 400 °C. They enable device ideas in various areas, for instance, soft robotics. As an example, we combined a laser-scribed graphene sensor with a deformable elastomer and flexible magnet to realize low-cost, compliant, and customizable tactile sensors.

The magnetoelastic effect-the variation of the magnetic properties of a material under mechanical stress-is usually observed in rigid alloys, whose mechanical modulus is significantly different from that of human tissues, thus limiting their use in bioelectronics applications. Here, we observed a giant magnetoelastic effect in a soft system based on micromagnets dispersed in a silicone matrix, reaching a magnetomechanical coupling factor indicating up to four times more enhancement than in rigid counterparts. The results are interpreted using a wavy chain model, showing how mechanical stress changes the micromagnets' spacing and dipole alignment, thus altering the magnetic field generated by the composite. Combined with liquid-metal coils patterned on polydimethylsiloxane working as a magnetic induction layer, the soft magnetoelastic composite is used for stretchable and water-resistant magnetoelastic generators adhering conformably to human skin. Such devices can be used as wearable or implantable power generators and biomedical sensors, opening alternative avenues for human-body-centred applications.© 2021. The Author(s), under exclusive licence to Springer Nature Limited.

In conventional classification, soft robots feature mechanical compliance as the main distinguishing factor from traditional robots made of rigid materials. Recent advances in functional soft materials have facilitated the emergence of a new class of soft robots capable of tether-free actuation in response to external stimuli such as heat, light, solvent, or electric or magnetic field. Among the various types of stimuli-responsive materials, magnetic soft materials have shown remarkable progress in their design and fabrication, leading to the development of magnetic soft robots with unique advantages and potential for many important applications. However, the field of magnetic soft robots is still in its infancy and requires further advancements in terms of design principles, fabrication methods, control mechanisms, and sensing modalities. Successful future development of magnetic soft robots would require a comprehensive understanding of the fundamental principle of magnetic actuation, as well as the physical properties and behavior of magnetic soft materials. In this review, we discuss recent progress in the design and fabrication, modeling and simulation, and actuation and control of magnetic soft materials and robots. We then give a set of design guidelines for optimal actuation performance of magnetic soft materials. Lastly, we summarize potential biomedical applications of magnetic soft robots and provide our perspectives on next-generation magnetic soft robots.

Interfacing with the human body, wearable and implantable bioelectronics are a compelling platform technology for healthcare monitoring and medical therapeutics. However, clinical adoption of these devices is largely shadowed by their weakness in humidity resistance, stretchability, durability, and biocompatibility. In this work, we report a self-powered waterproof biomechanical sensor with stretchability up to 440% using the giant magnetoelastic effect in a soft polymer system. By manipulating the magnetic dipole alignment, the sensor achieved a particularly broad sensing range from 3.5 Pa to 2000 kPa, with a response time of ∼3 ms. To validate the excellent performance of the magnetoelastic sensor in biomonitoring, both porcine heart testing and rat model testing were performed for cardiovascular monitoring and heart disease diagnosis. With the obtained sensing data, we have successfully detected ventricular arrhythmia and ventricular fibrillation in the Sprague-Dawley rat model. Holding a collection of compelling features, including minimal hysteresis, ultrawide sensing range, waterproofness, and biocompatibility, the magnetoelastic sensor represents a unique platform technology for self-powered biomonitoring in both wearable and implantable manners.

In this study, we present the observation of the giant magnetoelastic effect that occurs in soft elastomer systems without the need of external magnetic fields and possesses a magnetomechanical coupling factor that is four times larger than that of traditional rigid metal-based ferromagnetic materials. To investigate the fundamental scientific principles at play, we built a linear model by using COMSOL Multiphysics, which was consistent with the experimental observations. Next, by combining the giant magnetoelastic effect with electromagnetic induction, we developed a magnetoelastic generator (MEG) for biomechanical energy conversion. The wearable MEG demonstrates an ultrahigh output current of 97.17 mA, a low internal impedance of around ∼40 Ω, and an intrinsic waterproof property. We further leveraged the wearable MEG as an ultrahigh current power source to drive a Joule-heating textile for personalized thermoregulation, which increased the temperature of the fiber-shaped resistor by 0.2 °C. The development of the wearable MEG will act as an alternative and compelling approach for on-body electricity generation and arouse a wide range of possibilities in the renewable energy community.

Respiratory monitoring is crucial because it provides key insights into a person's health and physiological conditions. Conventional respiratory sensing is significantly challenged by the presence of water vapor in exhaled breath. An on-mask magnetoelastic sensor network is developed, featuring an ultralight, intrinsically waterproof architecture to achieve continuous, long-term respiratory monitoring and real-time, high-fidelity signal acquisition. Leveraging the giant magnetoelastic effect, each soft magnetoelastic sensor is miniaturized to only 3.2 g, which markedly enhances its sensitivity to airflow-induced mechanical fluctuations during respiration while also ensuring sufficient wearing comfort for daily use. Beyond mechanical compliance, the system achieves a signal-to-noise ratio exceeding 35 dB and a rapid response time of 80 ms under the optimal conditions, and it can reliably transduce the fluid dynamics generated during respiration in the mouth-mask microenvironment into high-fidelity electrical signals for continuous respiratory monitoring. With the aid of machine learning, the on-mask magnetoelastic sensor network achieves respiration pattern recognition with a classification accuracy of up to 94.03%. Furthermore, a user-friendly, custom-designed mobile application has been developed to process respiratory signals, enabling real-time, data-driven diagnosis and one-click health data sharing with clinicians. This machine-learning-enhanced magnetoelastic sensor network is expected to support personalized respiratory management in the Internet of Things era.