A high performance wearable strain sensor with advanced thermal management for motion monitoring

Advances in Machine Learning-Driven Flexible Strain Sensors: Challenges, Innovations, and Applications

Flexible strain sensors have garnered significant attention due to their high sensitivity, rapid response, and flexibility. Recent innovations, particularly those incorporating machine learning, have significantly enhanced their stability, sensitivity, and adaptability, positioning these sensors as promising solutions in health monitoring, human-computer interaction, and smart home applications. However, challenges remain in optimizing sensor materials for enhanced responsiveness, durability, and stability. Moreover, the development of machine learning-based strain sensors faces obstacles, including algorithmic limitations, low noise tolerance in complex environments, and limited model interpretability. This review systematically evaluates the latest advancements in flexible strain sensors, emphasizing the critical role of machine learning in performance enhancement. It further explores the shift from traditional machine learning methods to deep learning approaches, elucidating the potential applications that these algorithms facilitate. Finally, we discuss future research trajectories, highlighting both opportunities and challenges that may guide the next wave of innovations in this dynamic field.

Advancing Thermal Management Technology for Power Semiconductors through Materials and Interface Engineering

Power semiconductors and chips are essential in modern electronics, driving applications from personal devices and data centers to energy technologies, vehicles, and Internet infrastructure. However, efficient heat dissipation remains a critical challenge, directly affecting their performance, reliability, and lifespan. High-power electronics based on wide- and ultrawide-bandgap semiconductors can exhibit power densities exceeding 10 kW/cm2, hundreds of times higher than digital electronics, posing significant thermal management challenges. Addressing this issue requires advanced materials and interface engineering, alongside a comprehensive understanding of materials physics, chemistry, transport dynamics, and various electronic, thermal, and mechanical properties. Despite progress in thermal management solutions, the complex interplay of phonons, electrons, and their interactions with material lattices, defects, boundaries, and interfaces presents persistent challenges. This Account highlights key advancements in thermal management for power semiconductors and chips, with a focus on our group's recent contributions. Our approach addresses several critical issues: (1) developing materials with ultrahigh thermal conductivity for enhanced heat dissipation, (2) reducing thermal boundary resistance between power semiconductors and emerging 2D materials, (3) improving thermal and mechanical contacts between chips and heat sinks, (4) innovating dynamic thermal management solutions, and (5) exploring novel principles of thermal transport and design for future technologies. Our research philosophy integrates multiscale theoretical predictions with experimental validation to achieve a paradigm shift in thermal management. By leveraging first-principles calculations, the recent studies redefined traditional criteria for high-thermal-conductivity materials. Guided by these insights, we developed boron arsenide and boron phosphide, which exhibit record-high thermal conductivities of up to 1300 W/mK. Through phonon band structure engineering, we reduced TBR in GaN/BAs interfaces by over 8-fold compared to GaN/diamond interfaces. The combination of low TBR and high thermal conductivity significantly reduced hotspot temperatures, setting new benchmarks in thermal design for power electronics. We further explored the anisotropic TBR properties of two-dimensional materials and Moiré patterns in twisted graphene, expanding the thermal design landscape. To address challenges at device-heat sink interfaces, we developed self-assembled boron arsenide composites with a thermal conductivity of 21 W/mK and exceptional mechanical compliance (∼100 kPa). These composites provide promising solutions for thermal management in flexible electronics and soft robotics. In dynamic thermal management, we pioneered the concept of solid-state thermal transistors, enabling electrically controlled heat flow with unparalleled tunability, speed, reliability, and compatibility with integrated circuit fabrication. These innovations not only enhance thermal performance but also enable the exploration of novel transport physics, improving our fundamental understanding of thermal energy transport under extreme conditions. Looking forward, we reflect on remaining challenges and identify opportunities for further advancements. These include scaling up the production of high-performance materials, integrating thermal solutions with existing manufacturing processes, and uncovering new physics to inspire next-generation power electronics technologies. By addressing these challenges, we aim to inspire future codesign strategies that enable the development of more efficient, reliable, sustainable, and high-performance electronic systems.

Stretchable multifunctional wearable system for real-time and on-demand thermotherapy of arthritis

Thermotherapy is a conventional and effective physiotherapy for arthritis. However, the current thermotherapy devices are often bulky and lack real-time temperature feedback and self-adjustment functions. Here, we developed a multifunctional wearable system for real-time thermotherapy of arthritic joints based on a multilayered flexible electronic device consisting of homomorphic hollow thin-film sensors and heater. The kirigami-serpentine thin-film sensors provide stretchability and rapid response to changes in environmental temperature and humidity, and the homomorphic design offers easy de-coupling of dual-modal sensing signals. Based on a closed-loop control, the thin-film Joule heater exhibits rapid and stable temperature regulation capability, with thermal response time < 1 s and maximum deviation < 0.4 °C at 45 °C. Based on the multifunctional wearable system, we developed a series of user-friendly gears and demonstrated programmable on-demand thermotherapy, real-time personal thermal management, thermal dehumidification, and relief of the pain via increasing blood perfusion. Our innovation offers a promising solution for arthritis management and has the potential to benefit the well-being of thousands of patients.

Triboelectric Nanogenerators Based on 2D Conductive and High-Dielectric Material Heterostructures for Self-Powered Digital Medicine Applications

With the accelerating advancement of health monitoring and intelligent motion detection technologies, wearable flexible sensors have emerged as indispensable tools for real-time human activity monitoring. Self-powered systems centered on triboelectric nanogenerators (TENGs), which obviate the requirement for external power sources, have garnered substantial attention. However, attaining both high electrical performance and mechanical flexibility persists as a pivotal challenge. To tackle this, we propose a groundbreaking strategy that incorporates two-dimensional (2D) graphene as a conductive template with amino-modified BaTiO3 nanoparticles (BaTiO3-NH2), a high-dielectric-constant material, to develop a high-performance flexible TENG for human motion detection. The dual role of graphene is maximized: its superior electrical conductivity facilitates the formation of microcapacitive structures, while its 2D sheet structure promotes the uniform dispersion of BaTiO3-NH2, mitigating agglomeration issues and maintaining mechanical integrity. The fabricated TENG exhibited remarkable performance, attaining a high power output of 0.48 W/m2 in single-electrode mode for energy harvesting and a peak open-circuit voltage of 380 V for wearable sensing. These augmented properties permitted precise detection of diverse human motion patterns in real-world wearable scenarios and broadened its application to precise sensing in ball sports. This study illustrates the synergistic advantages of integrating 2D conductive materials with high-dielectric nanoparticles, offering a promising strategy for developing next-generation self-powered sensors. The designed TENG possesses significant potential for energy harvesting, wearable sensing, and advanced electronic skin applications in human-machine interfaces.

Lignin-containing nanofiber-reinforced flexible strain sensors with excellent mechanical properties and ionic conductivity for human motion detection

A multifunctional hydrogel with outstanding mechanical properties and excellent ionic conductivity holds immense potential for applications in various fields, such as healthcare monitoring, and various devices, such as wearable devices and flexible electronics. However, developing hydrogels that combine high mechanical strength with efficient electrical conductivity remains a considerable challenge. Herein, an ion-conductive hydrogel with excellent mechanical properties and ionic conductivity is successfully created. This hydrogel integrates sensing capabilities, freeze tolerance, and long-term solvent retention through a synergistic combination of lignin-containing cellulose nanofibers (LCNF), polyvinyl alcohol chains, ethylene glycol, and aluminum chloride. The resulting hydrogel demonstrates exceptional mechanical performance in terms of various factors, including tensile strength (1.28 MPa), strain capacity (794.94 %), toughness (6.32 MJ/m3), and fatigue resistance. In addition, the incorporation of enhanced LCNF fillers harmonizes the mechanical properties and ionic conductivity of the ion-conductive hydrogel, effectively addressing the inherent trade-off between these two attributes-a common challenge associated with ionic hydrogels. Moreover, the ion-conductive hydrogel exhibits exceptional sensing stability (300 cycles at 80 % strain), ionic conductivity (0.82 S/m), and sensitivity along with near real-time response (300 ms), freeze tolerance (-24 °C), and prolonged solvent retention (180 d). This multifunctional ion-conductive hydrogel opens new pathways for designing advanced wearable sensors.

Soft Materials and Devices Enabling Sensorimotor Functions in Soft Robots

Sensorimotor functions, the seamless integration of sensing, decision-making, and actuation, are fundamental for robots to interact with their environments. Inspired by biological systems, the incorporation of soft materials and devices into robotics holds significant promise for enhancing these functions. However, current robotics systems often lack the autonomy and intelligence observed in nature due to limited sensorimotor integration, particularly in flexible sensing and actuation. As the field progresses toward soft, flexible, and stretchable materials, developing such materials and devices becomes increasingly critical for advanced robotics. Despite rapid advancements individually in soft materials and flexible devices, their combined applications to enable sensorimotor capabilities in robots are emerging. This review addresses this emerging field by providing a comprehensive overview of soft materials and devices that enable sensorimotor functions in robots. We delve into the latest development in soft sensing technologies, actuation mechanism, structural designs, and fabrication techniques. Additionally, we explore strategies for sensorimotor control, the integration of artificial intelligence (AI), and practical application across various domains such as healthcare, augmented and virtual reality, and exploration. By drawing parallels with biological systems, this review aims to guide future research and development in soft robots, ultimately enhancing the autonomy and adaptability of robots in unstructured environments.

Advances in Crack-Based Strain Sensors on Stretchable Polymeric Substrates: Crack Mechanisms, Geometrical Factors, and Functional Structures

This review focuses on deepening the structural understanding of crack-based strain sensors (CBSS) on stretchable and flexible polymeric substrates and promoting sensor performance optimization. CBSS are cutting-edge devices that purposely incorporate cracks into their functional elements, thereby achieving high sensitivity, wide working ranges, and rapid response times. To optimize the performance of CBSS, systematic research on the structural characteristics of cracks is essential. This review comprehensively analyzes the key factors determining CBSS performance such as the crack mechanism, geometrical factors, and functional structures and proposes optimization strategies grounded in these insights. In addition, we explore the potential of numerical analysis and machine learning to offer novel perspectives for sensor optimization. Following this, we introduce various applications of CBSS. Finally, we discuss the current challenges and future prospects in CBSS research, providing a roadmap for next-generation technologies.

A Bioinspired Defect-Tolerant Hydrogel Medical Patch for Abdominal Wall Defect Repair

Point-wise suturing is the standard method for ensuring that patches effectively perform mechanically supportive functions in tissue repair. However, stress concentrations around suture holes can compromise the mechanical stability of patches. In this study, we develop a suturable hydrogel patch with flaw-tolerance capabilities by leveraging multiscale stress deconcentration, inspired by natural silk. This design mitigates stress concentration across two scales through the synergistic integration of nanoscale high-energy crystalline domains and intermolecular interactions. The resulting integral hydrogel patch exhibits superior flaw resistance compared to conventional patches and effectively addresses tissue adhesion issues. To validate the efficacy of the patch, we demonstrate successful in vivo repair of abdominal wall defects in rats, comparing the performance of the proposed patch to commercial mesh patches (Prolene). The integral patch design strategy present here offers a valuable approach for developing patches that can be tailored to meet the mechanical support needs of various tissue repair applications.

Enhanced thermal management of mats and yarns from polystyrene fibers through incorporation of exfoliated graphite

The energy crisis, driven by modern electronics and global warming from population growth, underscores the need for advanced textiles to regulate thermal environments. Researchers stress the need to improve high-performance polymer mats with enhanced thermal conductivity. This report delves into the morphological, mechanical, and thermal properties of exfoliated graphite (EG) when incorporated into polystyrene (PS) fiber mats and yarns through blend electrospinning. The incorporation of EG inside the fibers allowed us to obtain approximately twofold improvement in maximum stress and toughness compared to pristine PS mats. Thermal camera measurement showed significant improvement in heat transport for PS-EG fibers. The heating test showed a temperature increase of ∼2.5 °C for an EG-loaded PS mat, and in the case of a resistance wire coated with a PS fiber yarn, the increase reached 17 °C. The incorporation of EG into electrospun mats enables the recovery of more energy in the form of heat by enhancing the heating of the sample through infrared radiation. The temperature increased by 2 °C for PS and by 27 °C for PS-EG, respectively. The obtained results exhibit a great potential for the application of electrospun hybrid systems with EG in further advancement in the field of next-generation thermal management.

Core-shell structured BN/SiO2 nanofiber membrane featuring with dual-effect thermal management and flame retardancy for extreme space thermal protection

With the rapid progress of aerospace frontier engineering, the extreme space thermal environment has brought severe challenges to astronauts' space suits, putting forward higher requirements for thermal protection materials. On this basis, a unique core-shell structured hexagonal boron nitride (h-BN)/silicon dioxide (SiO2) nanofiber membrane (HS) was prepared using the coaxial electrospinning method, of which both the thermal insulation SiO2 nanofiber cortex and the passive radiation cooling (PRC) h-BN nanofiber core make it a promising dual-effect thermal management material. Especially, when the amount of h-BN is 0.9 g, the resultant HS (HS0.9) exhibits astonishing low thermal conductivity of 0.026 W m-1 K-1 and high reflectivity and emissivity of exceeding 90% over an extremely wide range. The expected dual-effect thermal management performance enables the HS to have an ideal cooling effect under both high sunlight intensity and strong light radiation. In addition, HS also shows excellent flame retardant performance arising from the excellent high-temperature stability of h-BN and SiO2. What is more, the tensile strength of HS0.9 was also significantly increased from 0.42 to 7.2 MPa by encapsulating polyimide through vacuum filtration. Therefore, the research results of this work provide innovative highlights for high-temperature protection in daily life and even extreme space environments.

Spider Silk-Inspired Conductive Hydrogels for Enhanced Toughness and Environmental Resilience via Dense Hierarchical Structuring

Conductive hydrogels, known for their biocompatibility and responsiveness to external stimuli, hold promise for biomedical applications like wearable sensors, soft robotics, and implantable electronics. However, their broader use is often constrained by limited toughness and environmental resilience, particularly under mechanical stress or extreme conditions. Inspired by the hierarchical structures of natural materials like spider silk, a strategy is developed to enhance both toughness and environmental tolerance in conductive hydrogels. By leveraging multiscale dynamics including pores, crystallization, and intermolecular interactions, a dense hierarchical structure is created that significantly improves toughness, reaching ≈90 MJ m⁻3. This hydrogel withstands temperatures from -150 to 70 °C, pressure of 12 psi, and one-month storage under ambient conditions, while maintaining a lightweight profile of 0.25 g cm⁻3. Additionally, its tunable rheological properties allow for high-resolution printing of desired shapes down to 220 µm, capable of supporting loads exceeding 164 kg m⁻2. This study offers a versatile framework for designing durable materials for various applications.

Advances in Wearable Biosensors for Wound Healing and Infection Monitoring

Wound healing is a complicated biological process that is important for restoring tissue integrity and function after injury. Infection, usually due to bacterial colonization, significantly complicates this process by hindering the course of healing and enhancing the chances of systemic complications. Recent advances in wearable biosensors have transformed wound care by making real-time monitoring of biomarkers such as pH, temperature, moisture, and infection-related metabolites like trimethylamine and uric acid. This review focuses on recent advances in biosensor technologies designed for wound management. Novel sensor architectures, such as flexible and stretchable electronics, colorimetric patches, and electrochemical platforms, enable the non-invasive detection of changes associated with wounds with high specificity and sensitivity. These are increasingly combined with AI and analytics based on smartphones that can enable timely and personalized interventions. Examples are the PETAL patch sensor that applies multiple sensing mechanisms for wide-ranging views on wound status and closed-loop systems that connect biosensors to therapeutic devices to automate infection control. Additionally, self-powered biosensors that tap into body heat or energy from the biofluids themselves avoid any external batteries and are thus more effective in field use or with limited resources. Internet of Things connectivity allows further support for remote sharing and monitoring of data, thus supporting telemedicine applications. Although wearable biosensors have developed relatively rapidly and their prospects continue to expand, regular clinical application is stalled by significant challenges such as regulatory, cost, patient compliance, and technical problems related to sensor accuracy, biofouling, and power, among others, that need to be addressed by innovative solutions. The goal of this review is to synthesize current trends, challenges, and future directions in wound healing and infection monitoring, with emphasis on the potential for wearable biosensors to improve patient outcomes and reduce healthcare burdens. These innovations are leading the way toward next-generation wound care by bridging advanced materials science, biotechnology, and digital health.

Directional Liquid Transport in Thin Fibrous Matrices: Enhancement of Advanced Applications

Directional liquid transport fibrous matrices (DLTFMs) have the unique ability to direct liquid movement in a single direction through their thickness. Beyond their inherent liquid transport function, DLTFMs can also enhance the effectiveness of additional functionalities. This review focuses on recent advances in DLTFMs, particularly the role of DLTs in enhancing secondary functions. We begin with a brief overview of the historical development and major achievements in DLTFM research, followed by an outline of the classification, fabrication techniques, and basic functions derived from their natural liquid transport properties. The integration of DLT to enhance secondary functionalities such as responsiveness, thermal regulation, and wearable technology for innovative applications in various sectors is then discussed. The review concludes with a discussion of key challenges and prospects in the field, including the durability and reliability of DLT performance, the precise regulation of fluid transport rates, the resilience and longevity of DLTFMs in harsh environments, and the impact of DLT variations on performance enhancement. The goal of this review is to stimulate further innovative studies on DLTFMs and to promote their practical implementation in a variety of industries.

Full Body-Worn Textile-Integrated Nanomaterials and Soft Electronics for Real-Time Continuous Motion Recognition Using Cloud Computing

Recognizing human body motions opens possibilities for real-time observation of users' daily activities, revolutionizing continuous human healthcare and rehabilitation. While some wearable sensors show their capabilities in detecting movements, no prior work could detect full-body motions with wireless devices. Here, we introduce a soft electronic textile-integrated system, including nanomaterials and flexible sensors, which enables real-time detection of various full-body movements using the combination of a wireless sensor suit and deep-learning-based cloud computing. This system includes an array of a nanomembrane, laser-induced graphene strain sensors, and flexible electronics integrated with textiles for wireless detection of different body motions and workouts. With multiple human subjects, we demonstrate the system's performance in real-time prediction of eight different activities, including resting, walking, running, squatting, walking upstairs, walking downstairs, push-ups, and jump roping, with an accuracy of 95.3%. The class of technologies, integrated as full body-worn textile electronics and interactive pairing with smartwatches and portable devices, can be used in real-world applications such as ambulatory health monitoring via conjunction with smartwatches and feedback-enabled customized rehabilitation workouts.

Ultraflexible Sensor Development via 4D Printing: Enhanced Sensitivity to Strain, Temperature, and Magnetic Fields

This paper addresses the trade-off between sensitivity and sensing range in strain sensors, while introducing additional functionalities through an innovative 4D printing approach. The resulting ultraflexible sensor integrates carbon nanotubes/liquid metal hybrids and iron powders within an Ecoflex matrix. The optimization of this composition enables the creation of an uncured resin ideal for Direct Ink Writing (DIW) and a cured sensor with exceptional electromechanical, thermal, and magnetic performance. Notably, the sensor achieves a wide linear strain range of 350% and maintains a stable Gauge Factor of 19.8, offering an ultralow detection limit of 0.1% strain and a rapid 83-ms response time. Beyond superior strain sensing capabilities, the sensor exhibits outstanding thermal endurance for temperatures exceeding 300 °C, enhanced thermal conductivity, and a consistent resistance-temperature relationship, making it well-suited for high-temperature applications. Moreover, the inclusion of iron particles provides magnetic responsiveness, enabling synergistic applications in location and speed detection, particularly in home care. Leveraging DIW facilitates the creation of complex-shaped sensors with multiple functional materials, significantly broadening the sensor's capabilities. This convergence of additive manufacturing and multifunctional materials marks a transformative step in advancing the performance of next-generation sensors across diverse domains.

Revolutionizing human healthcare with wearable sensors for monitoring human strain

With the rapid advancements in wearable sensor technology, healthcare is witnessing a transformative shift towards personalized and continuous monitoring. Wearable sensors designed for tracking human strain offer promising applications in rehabilitation, athletic performance, occupational health, and early disease detection. Recent advancements in the field have centered on the design optimization and miniaturization of wearable biosensors. Wireless communication technologies have facilitated the simultaneous, non-invasive detection of multiple analytes with high sensitivity and selectivity through wearable biosensors, significantly enhancing diagnostic accuracy. This review meticulously chronicles noteworthy advancements in wearable sensors tailored for healthcare and biomedical applications, spanning the current market landscape, challenges faced, and prospective trends, including multifunctional smart wearable sensors and integrated decision-support systems. The domain of flexible electronics has witnessed substantial progress over the past decade, particularly in flexible strain sensors, which are crucial for contemporary wearable and implantable devices. These innovations have broadened the scope of applications in human health monitoring and diagnostics. Continuous advancements in novel materials and device architectural methodologies aim to expand the utility of these sensors while meeting the increasingly stringent demands for enhanced sensing performance. This review explores the diverse array of wearable sensors-from piezoelectric, piezoresistive, and capacitive sensors to advanced optical and bioimpedance sensors-each distinguished by unique material properties and functionalities. We analyzed these technologies' sensitivity, accuracy, and response time, which were crucial for reliably capturing strain metrics in dynamic, real-world conditions. Quantitative performance comparisons across various sensor types highlighted their relative effectiveness, strengths, and limitations regarding detection precision, durability, and user comfort. Additionally, we discussed the current challenges in wearable sensor design, including energy efficiency, data transmission, and integration with machine learning models for enhanced data interpretation. Ultimately, this review emphasized the revolutionary potential of wearable strain sensors in advancing preventative healthcare and enabling proactive health management, ushering in an era where real-time health insights could lead to more timely interventions and improved health outcomes.

Electrospun multifunctional nanofibers for advanced wearable sensors

The multifunctional extension of fiber-based wearable sensors determines their integration and sustainable development, with electrospinning technology providing reliable, efficient, and scalable support for fabricating these sensors. Despite numerous studies on electrospun fiber-based wearable sensors, further attention is needed to leverage composite structural engineering for functionalizing electrospun fibers. This paper systematically reviews the research progress on fiber-based multifunctional wearable sensors in terms of design concept, device fabrication, mechanism exploration, and application potential. Firstly, the basics of electrospinning are briefly introduced, including its development, principles, parameters, and material selection. Tactile sensors, as crucial components of wearable sensors, are discussed in detail, encompassing their performance parameters, transduction mechanisms, and preparation strategies for pressure, strain, temperature, humidity, and bioelectrical signal sensors. The main focus of the article is on the latest research progress in multifunctional sensing design concepts, multimodal decoupling mechanisms, sensing mechanisms, and functional extensions. These extensions include multimodal sensing, self-healing, energy harvesting, personal thermal management, EMI shielding, antimicrobial properties, and other capabilities. Furthermore, the review assesses existing challenges and outlines future developments for multifunctional wearable sensors, highlighting the need for continued research and innovation.

High sensitivity flexible strain sensor for motion monitoring based on MWCNT@MXene and silicone rubber

Research on flexible strain sensors has grown rapidly and is widely applied in the fields of soft robotics, body motion detection, wearable sensors, health monitoring, and sports. In this study, MXene was successfully synthesized in powder form and combined with multi-walled carbon nanotube (MWCNT) to develop MWCNT@MXene conductive network-based flexible strain sensors with silicone rubber (SR) substrate. Combining MWCNTs with MXene as a conductive material has been shown to significantly improve the sensor performance, due to MXene's high conductivity properties that strengthen the MWCNT conductive pathway, increase sensitivity, and improve sensor stability. The sensor is fabricated by a sandwich method consisting of three layers, which enables more accurate and reliable detection of strain changes. The main innovation of this research is the utilization of MWCNT@MXene as a conductive material that optimizes the performance of flexible strain sensors, overcomes the limitations of previous materials, and makes it a more effective solution for long-term applications. Furthermore, the sensor was evaluated to test its performance through sensitivity, linearity, response time, and durability tests. The results showed that the sensor exhibited excellent performance with a high sensitivity of 39.97 over a strain range of 0-100% and excellent linearity (0.99) over a strain of 0-50%. The sensor also has a fast response time of about 70 ms, it also has good stability during low (1-5%) and high (20-100%) strain cycle testing and can withstand up to 1200 loading and unloading cycles. In addition, the sensor effectively detects a wide range of body movements, including finger, wrist and knee movements. These findings show that the electromechanical properties of strain sensors are significantly improved through the use of MWCNT@MXene as a conductive material, so these sensors are considered a promising solution for applications in wearables and body motion monitoring.

The effect of atomic vibration on thermal transport in diatomic semiconductors investigated via ab initio molecular dynamics

Based on the ab initio molecular dynamics (AIMD), the temperature and velocity statistics of diatomic semiconductors were proposed to be classified by atomic species. The phase differences resulting from lattice vibrations of different atoms indicated the presence of anharmonicity at finite atomic temperatures. To further explore the electronic properties, the effect of temperature on electrostatic potential field vibrations in semiconductors was studied, and the concept of electrostatic potential oscillation (EPO) at finite atomic temperature was introduced. It was confirmed that EPO in semiconductors was driven by lattice vibrations at finite temperatures. As the temperature increased, both the intensity of EPO and the rate of EPO change in heavy and light atoms increased, influencing electron thermal transport. To characterize the uncertainties in atomic lattice vibrations and EPO, the entropies of atomic EPO, atomic velocity of EPO (VEPO), atomic temperature, and atomic velocity were defined, with results consistent with the principle of entropy increase. This study not only aids in understanding the fundamental physical picture of electronic properties in semiconductors at finite temperatures but also provides a method for describing their uncertainties. The new theoretical concepts and statistical methods presented here can advance the understanding of electron thermal transport issues in semiconductor devices.

Wearable Biodevices Based on Two-Dimensional Materials: From Flexible Sensors to Smart Integrated Systems

The proliferation of wearable biodevices has boosted the development of soft, innovative, and multifunctional materials for human health monitoring. The integration of wearable sensors with intelligent systems is an overwhelming tendency, providing powerful tools for remote health monitoring and personal health management. Among many candidates, two-dimensional (2D) materials stand out due to several exotic mechanical, electrical, optical, and chemical properties that can be efficiently integrated into atomic-thin films. While previous reviews on 2D materials for biodevices primarily focus on conventional configurations and materials like graphene, the rapid development of new 2D materials with exotic properties has opened up novel applications, particularly in smart interaction and integrated functionalities. This review aims to consolidate recent progress, highlight the unique advantages of 2D materials, and guide future research by discussing existing challenges and opportunities in applying 2D materials for smart wearable biodevices. We begin with an in-depth analysis of the advantages, sensing mechanisms, and potential applications of 2D materials in wearable biodevice fabrication. Following this, we systematically discuss state-of-the-art biodevices based on 2D materials for monitoring various physiological signals within the human body. Special attention is given to showcasing the integration of multi-functionality in 2D smart devices, mainly including self-power supply, integrated diagnosis/treatment, and human-machine interaction. Finally, the review concludes with a concise summary of existing challenges and prospective solutions concerning the utilization of 2D materials for advanced biodevices.

Self-powered strain sensing devices with wireless transmission: DIW-printed conductive hydrogel electrodes featuring stretchable and self-healing properties

With rapid advancements in health and human-computer interaction, wearable electronic skins (e-skins) designed for application on the human body provide a platform for real-time detection of physiological signals. Wearable strain sensors, integral functional units within e-skins, can be integrated with Internet of Things (IoT) technology to broaden the applications for human body monitoring. A significant challenge lies in the reliance of most existing wearable strain sensors on rigid external power supplies, limiting their practical flexibility. In this study, we present an innovative strategy to fabricate glutaraldehyde (GA)-poly(vinyl alcohol) (PVA)/cellulose nanocrystals (CNC)/Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) conductive hydrogels through multiple hydrogen bonding systems. Combining the advantageous rheological properties of the precursor solution and the high specific surface area after freeze-thaw cycling, we have created a self-powered sensing system prepared by large-area printing using direct ink writing (DIW) printing. The resulting conductive hydrogel exhibits commendable mechanical properties (411 KPa), impressive stretchability (580 %), and robust self-healing capabilities (>98.3 %). The strain sensor, derived from the conductive hydrogel, demonstrates a gauge factor (GF) of 2.5 within a stretching range of 0-580 %. Additionally, the resultant supercapacitor displays a peak energy density of 0.131 mWh/cm3 at a power density of 3.6 mW/cm3. Benefiting from its elevated strain response and remarkable power density features, this self-powered strain sensing system enables the real-time monitoring of human joint motion. The incorporation of a 5G transmission module enhances its capabilities for remote data monitoring, thereby contributing to the progress of wireless tracking technologies for self-powered electronic skin.

Revolutionizing Sports with Nanotechnology: Better Protection and Stronger Support

Modern sports activities have increasingly benefited from the development of nanotechnology, which is extensively applied in various sports events and associated activities and facilities. Nanotechnology deals with materials with nanoscale size, providing unique properties and functions compared with their bulk counterparts. Nanotechnology can not only provide better training feedback by tracking the athlete's physiological signals as well as performance details but also protect humans with nanomaterial-functionalized sports fabrics, equipment, and medicine. Nanotechnology has significantly advanced sports in various aspects, thereby leading to a rising research interest in this interdisciplinary field. This article highlights several representative nanotechnologies applied in sports such as nanomaterials in wearable sensors, personal heat management devices, functional sports fabrics, and sports medicine and discusses the principles, current challenges, as well as future opportunities.

Development of tough and stiff elastomers by leveraging hydrophilic-hydrophobic supramolecular segment interaction

The presence of supramolecular interactions plays a crucial role in the formation of resilient multifunctional elastomers. Nevertheless, achieving elastomers with fabulous mechanical properties remains a significant challenge due to the incomplete understanding of the underlying principles. In this study, we have presented a simple yet efficient approach for manipulating the microstructure, resulting in a significant enhancement of the mechanical properties of the elastomers. By utilizing hydrophobic and hydrophilic extended chain segments to elongate a hydrophilic oligomer, we successfully created elastomers with improved toughness and stiffness through supramolecular interactions. The elastomer with hydrophobic extended chain segments demonstrates a fracture energy (94 842 J m-2) and high tensile stress (16 MPa). In contrast, the elastomer with hydrophilic extended segments showed significantly lower tensile stress (0.18 MPa), even though their molecular chain structures are nearly identical. We conducted a systematic demonstration and investigation of the significant difference mentioned above and ultimately found that due to the hydrophobic-hydrophilic difference between the oligomer and extended chain segments, the hydrophobic chain segments are able to create hydrophobic association and the association can further facilitate the development of stronger and more abundant supramolecular interactions (hydrogen bonds). The resulting hydrogen bonds, combined with the hydrophobic association, effectively disperse energy and consequently improve the elastomer's capacity to withstand external forces. The hydrophilic-hydrophobic mechanism showcases the potential for creating durable supramolecular materials with promising applications in biology and electronics.

New Carbon Materials for Multifunctional Soft Electronics

Soft electronics are garnering significant attention due to their wide-ranging applications in artificial skin, health monitoring, human-machine interaction, artificial intelligence, and the Internet of Things. Various soft physical sensors such as mechanical sensors, temperature sensors, and humidity sensors are the fundamental building blocks for soft electronics. While the fast growth and widespread utilization of electronic devices have elevated life quality, the consequential electromagnetic interference (EMI) and radiation pose potential threats to device precision and human health. Another substantial concern pertains to overheating issues that occur during prolonged operation. Therefore, the design of multifunctional soft electronics exhibiting excellent capabilities in sensing, EMI shielding, and thermal management is of paramount importance. Because of the prominent advantages in chemical stability, electrical and thermal conductivity, and easy functionalization, new carbon materials including carbon nanotubes, graphene and its derivatives, graphdiyne, and sustainable natural-biomass-derived carbon are particularly promising candidates for multifunctional soft electronics. This review summarizes the latest advancements in multifunctional soft electronics based on new carbon materials across a range of performance aspects, mainly focusing on the structure or composite design, and fabrication method on the physical signals monitoring, EMI shielding, and thermal management. Furthermore, the device integration strategies and corresponding intriguing applications are highlighted. Finally, this review presents prospects aimed at overcoming current barriers and advancing the development of state-of-the-art multifunctional soft electronics.

Palm oil based stretchable piezoresistive strain sensors

The advancement of wearable devices and soft robots requires soft and stretchable sensors to detect their movements. This article proposes palm oil as an organic solvent for a stretchable piezoresistive strain sensor made from a composite consisting of elastomer (Ecoflex 00-30) filled with carbon black. The high content of palmitic acid in the palm oil increases the dispersity of carbon black in the composite, hence effectively improving the conductivity of the sensors. Furthermore, using palm oil as a natural plasticizer can lower the degree of crosslinking of the matrix, reducing the modulus elasticity but still producing a stretchable sensor with 500 % elongation at break. The presence of palm oil in the sensor also increases the gauge factor, showing a value of 2.43-4.75 and better repeatability during loading. These gauge factors are associated with two linear strain regions of the sensors (R2 > 0.99), which are 20-200 % and 0-20 % strain, respectively. The stretchable sensor also shows high durability that can withstand >1500 cycles at 60 % strain. The as-fabricated sensor can be deployed to detect the movement of the human body, such as for measuring a finger's joint angle and in soft robotics applications.

Highly Conducting and Ultra-Stretchable Wearable Ionic Liquid-Free Transducer for Wireless Monitoring of Physical Motions

Wearable strain transducers are poised to transform the field of healthcare owing to the promise of personalized devices capable of real-time collection of human physiological health indicators. For instance, monitoring patients' progress following injury and/or surgery during physiotherapy is crucial but rarely performed outside clinics. Herein, multifunctional liquid-free ionic elastomers are designed through the volume effect and the formation of dynamic hydrogen bond networks between polyvinyl alcohol (PVA) and weak acids (phosphoric acid, phytic acid, formic acid, citric acid). An ultra-stretchable (4600% strain), highly conducting (10 mS cm-1), self-repairable (77% of initial strain), and adhesive ionic elastomer is obtained at high loadings of phytic acid (4:1 weight to PVA). Moreover, the elastomer displayed durable performances, with intact mechanical properties after a year of storage. The elastomer is used as a transducer to monitor human motions in a device comprising an ESP32-based development board. The device detected walking and/or running biomechanics and communicated motion-sensing data (i.e., amplitude, frequency) wirelessly. The reported technology can also be applied to other body parts to monitor recovery after injury and/or surgery and inform practitioners of motion biomechanics remotely and in real time to increase convalescence effectiveness, reduce clinic appointments, and prevent injuries.

An Artificial Intelligence-Assisted Flexible and Wearable Mechanoluminescent Strain Sensor System

The complex wiring, bulky data collection devices, and difficulty in fast and on-site data interpretation significantly limit the practical application of flexible strain sensors as wearable devices. To tackle these challenges, this work develops an artificial intelligence-assisted, wireless, flexible, and wearable mechanoluminescent strain sensor system (AIFWMLS) by integration of deep learning neural network-based color data processing system (CDPS) with a sandwich-structured flexible mechanoluminescent sensor (SFLC) film. The SFLC film shows remarkable and robust mechanoluminescent performance with a simple structure for easy fabrication. The CDPS system can rapidly and accurately extract and interpret the color of the SFLC film to strain values with auto-correction of errors caused by the varying color temperature, which significantly improves the accuracy of the predicted strain. A smart glove mechanoluminescent sensor system demonstrates the great potential of the AIFWMLS system in human gesture recognition. Moreover, the versatile SFLC film can also serve as a encryption device. The integration of deep learning neural network-based artificial intelligence and SFLC film provides a promising strategy to break the "color to strain value" bottleneck that hinders the practical application of flexible colorimetric strain sensors, which could promote the development of wearable and flexible strain sensors from laboratory research to consumer markets.

Hybrid Integration of Wearable Devices for Physiological Monitoring

Wearable devices can provide timely, user-friendly, non- or minimally invasive, and continuous monitoring of human health. Recently, multidisciplinary scientific communities have made significant progress regarding fully integrated wearable devices such as sweat wearable sensors, saliva sensors, and wound sensors. However, the translation of these wearables into markets has been slow due to several reasons associated with the poor system-level performance of integrated wearables. The wearability consideration for wearable devices compromises many properties of the wearables. Besides, the limited power capacity of wearables hinders continuous monitoring for extended duration. Furthermore, peak-power operations for intensive computations can quickly create thermal issues in the compact form factor that interfere with wearability and sensor operations. Moreover, wearable devices are constantly subjected to environmental, mechanical, chemical, and electrical interferences and variables that can invalidate the collected data. This generates the need for sophisticated data analytics to contextually identify, include, and exclude data points per multisensor fusion to enable accurate data interpretation. This review synthesizes the challenges surrounding the wearable device integration from three aspects in terms of hardware, energy, and data, focuses on a discussion about hybrid integration of wearable devices, and seeks to provide comprehensive guidance for designing fully functional and stable wearable devices.

Notch-insensitive, tough and self-healing conductive bacterial cellulose nanocomposite hydrogel for flexible wearable strain sensor

To date, conductive hydrogels as an alternative to traditional rigid metallic conductors have attracted much attention in the field of flexible wearable electronic devices due to their inherent characteristics. Herein, a conductive bacterial cellulose (BC) nanocomposite hydrophobic-association (HA) hydrogel with highly stretchable, strong, self-healing, and notch-insensitive was fabricated by introducing the hydrophobic association. The obtained BCNC HA hydrogel shows excellent mechanical properties (∼ 2400 % of stress and ∼ 0.35 MPa of mechanical strength), superior notch-insensitive property with a fracture energy of ∼38 KJ.m-2, and good self-healing property (healing efficiency of ∼97 %). In addition, the hydrogel exhibits excellent ionic conductivity of ∼1.90 S.m-1 and high sensing sensitivity toward tensile deformation. The wearable strain sensor based on this material is assembled can detect both large-scale motions and subtle body motions in real time, which show excellent durability (1000 cycles with the strain of 30 %). Thus, the BCNC HA hydrogels have promising potential in various wearable flexible electronic devices for artificial intelligence and human-machine interface applications in the future.

Real-Time Wireless Sensing of Cardiomyocyte Contractility by Integrating Magnetic Microbeam and Oriented Nanofibers

In vitro cardiomyocyte mechano-sensing platform is crucial for evaluating the mechanical performance of cardiac tissues and will be an indispensable tool for application in drug discovery and disease mechanism study. Magnetic sensing offers significant advantages in real-time, in situ wireless monitoring and resistance to ion interference. However, due to the mismatch between the stiffness of traditional rigid magnetic material and myocardial tissue, sensitivity is insufficient and it is difficult to achieve cell structure induction and three-dimensional cultivation. Herein, a magnetic sensing platform that integrates a neodymium-iron-boron/polydimethylsiloxane (NdFeB/PDMS) flexible microbeam with suspended and ordered polycaprolactone (PCL) nanofiber membranes was developed, providing a three-dimensional anisotropic culture environment for cardiomyocyte growth and simultaneously realizing in situ wireless contractility monitoring. The as-prepared sensor presented an ultrahigh sensitivity of 442.2 μV/μm and a deflection resolution of 2 μm. By continuously monitoring the cardiomyocyte growth status and drug stimulation feedback, we verified the capability of the platform to capture dynamic changes in cardiomyocyte contractility. This platform provides a perspective tool for evaluating cardiomyocyte maturity and drug performance.

Superhydrophobic Solar-to-Thermal Materials Toward Cutting-Edge Applications

Solar-to-thermal conversion is a direct and effective way to absorb sunlight for heat via the rational design and control of photothermal materials. However, when exposed to water-existed conditions, the conventional solar-to-thermal performance may experience severe degradation owing to the high specific heat capacity of water. To tackle with the challenge, the water-repellent function is introduced to construct superhydrophobic solar-to-thermal materials (SSTMs) for achieving stable heating, and even, for creating new application possibilities under water droplets, sweat, seawater, and ice environments. An in-depth review of cutting-edge research of SSTMs is given, focusing on synergetic functions, typical construction methods, and cutting-edge potentials based on water medium. Moreover, the current challenges and future prospects based on SSTMs are also carefully discussed.

Data-Driven Strain Sensor Design Based on a Knowledge Graph Framework

Wearable flexible strain sensors require different performance depending on the application scenario. However, developing strain sensors based solely on experiments is time-consuming and often produces suboptimal results. This study utilized sensor knowledge to reduce knowledge redundancy and explore designs. A framework combining knowledge graphs and graph representational learning methods was proposed to identify targeted performance, decipher hidden information, and discover new designs. Unlike process-parameter-based machine learning methods, it used the relationship as semantic features to improve prediction precision (up to 0.81). Based on the proposed framework, a strain sensor was designed and tested, demonstrating a wide strain range (300%) and closely matching predicted performance. This predicted sensor performance outperforms similar materials. Overall, the present work is favorable to design constraints and paves the way for the long-awaited implementation of text-mining-based knowledge management for sensor systems, which will facilitate the intelligent sensor design process.

Bioinspired High-Linearity, Wide-Sensing-Range Flexible Stretchable Bioelectronics Based on MWCNTs/GR/Nd2Fe14B/PDMS Nanocomposites for Human-Computer Interaction and Biomechanics Detection

In recent years, flexible and stretchable strain sensors have emerged as a prominent area of research, primarily due to their remarkable stretchability and extremely low strain detection threshold. Nevertheless, the advancement of sensors is currently constrained by issues such as complexity, high costs, and limited durability. To tackle the aforementioned issues, this study introduces a lepidophyte-inspired flexible, stretchable strain sensor (LIFSSS). The stretchable bioelectronics composites were composed of multiwalled carbon nanotubes, graphene, neodymium iron boron, and polydimethylsiloxane. Unique biolepidophyted microstructures and magnetic conductive nanocomposites interact with each other through synergistic interactions, resulting in the effective detection of tensile strain and magnetic excitation. The LIFSSS exhibits a 170% tensile range, a linearity of 0.99 in 50-170% strain (0.96 for full-scale range), and a fine durability of 7000 cycles at 110% tensile range. The sensor accurately detects variations in linear tensile force, human movement, and microexpressions. Moreover, LIFSSS demonstrates enhanced efficacy in sign language recognition for individuals with hearing impairments and magnetic grasping for robotic manipulators. Hence, the LIFSSS proposed in this study shows potential applications in various fields, including bioelectronics, electronic skin, and physiological activity monitoring.

Strong and ductile Resinvar alloys with temperature- and time-independent resistivity

Materials with well-defined electrical resistivity that does not change with temperature or time are important in robotics, communication and automation. However, the challenge of designing such materials has remained elusive due to the temperature-dependent electron-phonon scattering. Moreover, resistive electrical conductors used in flexible and mobile systems under high mechanical loads must possess both high strength and ductility. Achieving such multi-properties presents a fundamental challenge. Here, we solve this problem by combining multicomponent alloy design with atomic-scale chemistry tuning. We term the resultant material 'Resinvar' alloy, due to its invariable resistivity (148 μΩ·cm) over wide temperature ranges from room temperature to 723 K. The alloy also has high tensile strength (948 MPa) at large tensile elongation (53%). The distorted lattice, chemical short-range order and ordered coherent nanoprecipitates in the material enable the invariant resistivity via promoting temperature-independent inelastic electron scattering, and contribute to the excellent strength-ductility synergy by manipulating dislocation slip.

A Flexible Skin Bionic Thermally Comfortable Wearable for Machine Learning-Facilitated Ultrasensitive Sensing

Tremendous popularity is observed for multifunctional flexible electronics with appealing applications in intelligent electronic skins, human-machine interfaces, and healthcare sensing. However, the reported sensing electronics, mostly can hardly provide ultrasensitive sensing sensitivity, wider sensing range, and robust cycling stability simultaneously, and are limited of efficient heat conduction out from the contacted skin interface after wearing flexible electronics on human skin to satisfy thermal comfort of human skin. Inspired from the ultrasensitive tactile perception microstructure (epidermis/spinosum/signal transmission) of human skin, a flexible comfortably wearable ultrasensitive electronics is hereby prepared from thermal conductive boron nitride nanosheets-incorporated polyurethane elastomer matrix with MXene nanosheets-coated surface microdomes as epidermis/spinosum layers assembled with interdigitated electrode as sensing signal transmission layer. It demonstrates appealing sensing performance with ultrasensitive sensitivity (≈288.95 kPa-1), up to 300 kPa sensing range, and up to 20 000 sensing cycles from obvious contact area variation between microdome microstructures and the contact electrode under external compression. Furthermore, the bioinspired electronics present advanced thermal management by timely efficient thermal dissipation out from the contacted skin surface to meet human skin thermal comfort with the incorporated thermal conductive boron nitride nanosheets. Thus, it is vitally promising in wearable artificial electronic skins, intelligent human-interactive sensing, and personal health management.

Thermal Conductive Polymer Composites: Recent Progress and Applications

As microelectronics technology advances towards miniaturization and higher integration, the imperative for developing high-performance thermal management materials has escalated. Thermal conductive polymer composites (TCPCs), which leverage the benefits of polymer matrices and the unique effects of nano-enhancers, are gaining focus as solutions to overheating due to their low density, ease of processing, and cost-effectiveness. However, these materials often face challenges such as thermal conductivities that are lower than expected, limiting their application in high-performance electronic devices. Despite these issues, TCPCs continue to demonstrate broad potential across various industrial sectors. This review comprehensively presents the progress in this field, detailing the mechanisms of thermal conductivity (TC) in these composites and discussing factors that influence thermal performance, such as the intrinsic properties of polymers, interfacial thermal resistance, and the thermal properties of fillers. Additionally, it categorizes and summarizes methods to enhance the TC of polymer composites. The review also highlights the applications of these materials in emerging areas such as flexible electronic devices, personal thermal management, and aerospace. Ultimately, by analyzing current challenges and opportunities, this review provides clear directions for future research and development.

Polymeric Nanocomposites of Boron Nitride Nanosheets for Enhanced Directional or Isotropic Thermal Transport Performance

Polymeric composites with boron nitride nanosheets (BNNs), which are thermally conductive yet electrically insulating, have been pursued for a variety of technological applications, especially those for thermal management in electronic devices and systems. Highlighted in this review are recent advances in the effort to improve in-plane thermal transport performance in polymer/BNNs composites and also the growing research activities aimed at composites of enhanced cross-plane or isotropic thermal conductivity, for which various filler alignment strategies during composite fabrication have been explored. Also highlighted and discussed are some significant challenges and major opportunities for further advances in the development of thermally conductive composite materials and their mechanistic understandings.

Patterning Techniques Based on Metallized Electrospun Nanofibers for Advanced Stretchable Electronics

Stretchable electronics have experienced remarkable progress, especially in sensors and wireless communication systems, attributed to their ability to conformably contact with rough or uneven surfaces. However, the development of complex, multifunctional, and high-precision stretchable electronics faces substantial challenges, including instability at rigid-soft interfaces and incompatibility with traditional high-precision patterning technologies. Metallized electrospun nanofibers emerge as a promising conductive filler, offering exceptional stretchability, electrical conductivity, transparency, and compatibility with existing patterning technologies. Here, this review focuses on the fundamental properties, preparation processes, patterning technologies, and application scenarios of conductive stretchable composites based on metallized nanofibers. Initially, it introduces the fabrication processes of metallized electrospun nanofibers and their advantages over alternative materials. It then highlights recent progress in patterning technologies, including collector collection, vapor deposition with masks, and lithography, emphasizing their role in enhancing precision and integration. Furthermore, the review shows the broad applicability and potential influence of metallized electrospun nanofibers in various fields through their use in sensors, wireless systems, semiconductor devices, and intelligent healthcare solutions. Ultimately, this review seeks to spark further innovation and address the prevailing challenges in stretchable electronics, paving the way for future breakthroughs in this dynamic field.

Amineh R. Elbow Gesture Recognition with an Array of Inductive Sensors and Machine Learning

This work presents a novel approach for elbow gesture recognition using an array of inductive sensors and a machine learning algorithm (MLA). This paper describes the design of the inductive sensor array integrated into a flexible and wearable sleeve. The sensor array consists of coils sewn onto the sleeve, which form an LC tank circuit along with the externally connected inductors and capacitors. Changes in the elbow position modulate the inductance of these coils, allowing the sensor array to capture a range of elbow movements. The signal processing and random forest MLA to recognize 10 different elbow gestures are described. Rigorous evaluation on 8 subjects and data augmentation, which leveraged the dataset to 1270 trials per gesture, enabled the system to achieve remarkable accuracy of 98.3% and 98.5% using 5-fold cross-validation and leave-one-subject-out cross-validation, respectively. The test performance was then assessed using data collected from five new subjects. The high classification accuracy of 94% demonstrates the generalizability of the designed system. The proposed solution addresses the limitations of existing elbow gesture recognition designs and offers a practical and effective approach for intuitive human-machine interaction.

Organic-inorganic hybrid piezotronic bipolar junction transistor for pressure sensing

With the rapid development of the Internet of Things (IoTs), wearable sensors are playing an increasingly important role in daily monitoring of personal health and wellness. The signal-to-noise-ratio has become the most critical performance factor to consider. To enhance it, on the one hand, good sensing materials/devices have been employed; on the other hand, signal amplification and noise reduction circuits have been used. However, most of these devices and circuits work in an active sampling mode, requiring frequent data acquisition and hence, entailing high-power consumption. In this scenario, a flexible and wearable event-triggered sensor with embedded signal amplification without an external power supply is of great interest. Here, we report a flexible two-terminal piezotronic n-p-n bipolar junction transistor (PBJT) that acts as an autonomous and highly sensitive, current- and/or voltage-mediated pressure sensor. The PBJT is formed by two back-to-back piezotronic diodes which are defined as emitter-base and collector-base diodes. Upon force exertion on the emitter side, as a result of the piezoelectric effect, the emitter-base diode is forward biased while the collector-base diode is reverse biased. Due to the inherent BJT amplification effect, the PBJT achieves record-high sensitivities of 139.7 kPa-1 (current-based) and 88.66 kPa-1 (voltage-based) in sensing mode. The PBJT also has a fast response time of <110 ms under exertion of dynamic stimuli ranging from a flying butterfly to a gentle finger touch. Therefore, the PBJT advances the state of the art not only in terms of sensitivity but also in regard to being self-driven and autonomous, making it promising for pressure sensing and other IoT applications.

Stretchable MXene/Carbon Nanotube Bilayer Strain Sensors with Tunable Sensitivity and Working Ranges

Stretchable strain sensors have gained increasing popularity as wearable devices to convert mechanical deformation of the human body into electrical signals. Two-dimensional transition metal carbides (Ti3C2Tx MXene) are promising candidates to achieve excellent sensitivity. However, MXene films have been limited in operating strain ranges due to rapid crack propagation during stretching. In this regard, this study reports MXene/carbon nanotube bilayer films with tunable sensitivity and working ranges. The device is fabricated using a scalable process involving spray deposition of well-dispersed nanomaterial inks. The bilayer sensor's high sensitivity is attributed to the cracks that form in the MXene film, while the compliant carbon nanotube layer extends the working range by maintaining conductive pathways. Moreover, the response of the sensor is easily controlled by tuning the MXene loading, achieving a gauge factor of 9039 within 15% strain at 1.92 mg/cm2 and a gauge factor of 1443 within 108% strain at 0.55 mg/cm2. These tailored properties can precisely match the operation requirements during the wearable application, providing accurate monitoring of various body movements and physiological activities. Additionally, a smart glove with multiple integrated strain sensors is demonstrated as a human-machine interface for the real-time recognition of hand gestures based on a machine-learning algorithm. The design strategy presented here provides a convenient avenue to modulate strain sensors for targeted applications.

Wearable EMI Shielding Composite Films with Integrated Optimization of Electrical Safety, Biosafety and Thermal Safety

Biomaterial-based flexible electromagnetic interference (EMI) shielding composite films are desirable in many applications of wearable electronic devices. However, much research focuses on improving the EMI shielding performance of materials, while optimizing the comprehensive safety of wearable EMI shielding materials has been neglected. Herein, wearable cellulose nanofiber@boron nitride nanosheet/silver nanowire/bacterial cellulose (CNF@BNNS/AgNW/BC) EMI shielding composite films with sandwich structure are fabricated via a simple sequential vacuum filtration method. For the first time, the electrical safety, biosafety, and thermal safety of EMI shielding materials are optimized integratedly. Since both sides of the sandwich structure contain CNF and BC electrical insulation layers, the CNF@BNNS/AgNW/BC composite films exhibit excellent electrical safety. Furthermore, benefiting from the AgNW conductive networks in the middle layer, the CNF@BNNS/AgNW/BC exhibit excellent EMI shielding effectiveness of 49.95 dB and ultra-fast response Joule heating performance. More importantly, the antibacterial property of AgNW ensures the biosafety of the composite films. Meanwhile, the AgNW and the CNF@BNNS layers synergistically enhance the thermal conductivity of the CNF@BNNS/AgNW/BC composite film, reaching a high value of 8.85 W m‒1 K‒1, which significantly enhances its thermal safety when used in miniaturized electronic device. This work offers new ideas for fabricating biomaterial-based EMI shielding composite films with high comprehensive safety.

Building-Envelope-Inspired, Thermomechanically Robust All-Fiber Ceramic Meta-Aerogel for Temperature-Controlled Dominant Infrared Camouflage

The unsatisfactory properties of ceramic aerogels when subjected to thermal shock, such as strength degradation and structural collapse, render them unsuitable for use at large thermal gradients or prolonged exposure to extreme temperatures. Here, a building-envelope-inspired design for fabricating a thermomechanically robust all-fiber ceramic meta-aerogel with interlocked fibrous interfaces and an interwoven cellular structure in the orthogonal directions is presented, which is achieved through a two-stage physical and chemical process. Inspired by the reinforced concrete building envelope, a solid foundation composed of fibrous frames is constructed and enhanced through supramolecular in situ self-assembly to achieve high compressibility, retaining over 90% of maximum stress under a considerable compressive strain of 50% for 10 000 cycles, and showing temperature-invariance when compressed at 60% strain within the range of -100 to 500 °C. As a result of its distinct response to oscillation tolerance coupled with elastic recovery, the all-fiber ceramic meta-aerogel exhibits exceptional suitability for thermal shock resistance and infrared camouflage performance in cold (-196 °C) and hot (1300 °C) fields. This study provides an opportunity for developing ceramic aerogels for effective thermal management under extreme conditions.

Spongy Ag Foam for Soft and Stretchable Strain Gauges

Strain gauges, particularly for wearable sensing applications, require a high degree of stretchability, softness, sensitivity, selectivity, and linearity. They must also steer clear of challenges such as mechanical and electrical hysteresis, overshoot behavior, and slow response/recovery times. However, current strain gauges face challenges in satisfying all of these requirements at once due to the inevitable trade-offs between these properties. Here, we present an innovative method for creating strain gauges from spongy Ag foam through a steam-etching process. This method simplifies the traditional, more complex, and costly manufacturing techniques, presenting an eco-friendly alternative. Uniquely, the strain gauges crafted from this method achieve an unparalleled gauge factor greater than 8 × 103 at strains exceeding 100%, successfully meeting all required attributes without notable trade-offs. Our work includes systematic investigations that reveal the intricate structure-property-performance relationship of the spongy Ag foam with practical demonstrations in areas such as human motion monitoring and human-robot interaction. These breakthroughs pave the way for highly sensitive and selective strain gauges, showing immediate applicability across a wide range of wearable sensing applications.

Permeable Bioelectronics toward Biointegrated Systems

Bioelectronics integrates electronics with biological organs, sustaining the natural functions of the organs. Organs dynamically interact with the external environment, managing internal equilibrium and responding to external stimuli. These interactions are crucial for maintaining homeostasis. Additionally, biological organs possess a soft and stretchable nature; encountering objects with differing properties can disrupt their function. Therefore, when electronic devices come into contact with biological objects, the permeability of these devices, enabling interactions and substance exchanges with the external environment, and the mechanical compliance are crucial for maintaining the inherent functionality of biological organs. This review discusses recent advancements in soft and permeable bioelectronics, emphasizing materials, structures, and a wide range of applications. The review also addresses current challenges and potential solutions, providing insights into the integration of electronics with biological organs.

Recent advances in smart wearable sensors for continuous human health monitoring

In recent years, the biochemical and biological research areas have shown great interest in a smart wearable sensor because of its increasing prevalence and high potential to monitor human health in a non-invasive manner by continuous screening of biomarkers dispersed throughout the biological analytes, as well as real-time diagnostic tools and time-sensitive information compared to conventional hospital-centered system. These smart wearable sensors offer an innovative option for evaluating and investigating human health by incorporating a portion of recent advances in technology and engineering that can enhance real-time point-of-care-testing capabilities. Smart wearable sensors have emerged progressively with a mixture of multiplexed biosensing, microfluidic sampling, and data acquisition systems incorporated with flexible substrate and bodily attachments for enhanced wearability, portability, and reliability. There is a good chance that smart wearable sensors will be relevant to the early detection and diagnosis of disease management and control. Therefore, pioneering smart wearable sensors into reality seems extremely promising despite possible challenges in this cutting-edge technology for a better future in the healthcare domain. This review presents critical viewpoints on recent developments in wearable sensors in the upcoming smart digital health monitoring in real-time scenarios. In addition, there have been proactive discussions in recent years on materials selection, design optimization, efficient fabrication tools, and data processing units, as well as their continuous monitoring and tracking strategy with system-level integration such as internet-of-things, cyber-physical systems, and machine learning algorithms.

Advanced Multiparallel-Connected Piezoresistive Physical Sensors: Elevating Performance Reliability of Flexible Strain and Pressure Sensors

A physical sensor with a sensing medium comprising multiparallel-connected (MPC) piezoresistive pathways in both the vertical and horizontal directions was developed to achieve improved sensing performance. The MPC sensing medium reduces the total resistance and offsets noise, offering enhanced signal stability and device reliability and providing a high-performance sensing platform. The signal change and gauge factor (GF) of the 3PW-5L strain sensor (comprising three lines and five layers of piezoresistive pathways horizontally and vertically, respectively) were, respectively, 5.9 and 4.7 times higher than those of the 1PW-1L sensor composed of a monosensing pathway; the hysteresis of the detected signal was also significantly reduced. The linearity of the detected signal increased from 0.912 for 1PW-1L to 0.995 for 3PW-5L, indicating a greater sensing reliability. The direction of the applied tensile strain was successfully detected using the MPC sensing medium with an orthogonal configuration. The MPC piezoresistive sensor composing vertically stacked piezoresistive pathways demonstrated excellent performance as a pressure sensor; the 3PW-5L pressure sensor afforded a GF of 0.121 ± 0.002 kPa-1 with a linearity of 0.998 under an applied pressure ≥16.4 kPa. The MPC piezoresistive physical sensor offers a superior sensing performance and should contribute to the future development of wearable sensors and electronic devices.

Substrate-Free Transfer of Silicon- and Metallic-Based Strain Sensors on Textile and in Composite Material for Structural Health Monitoring

New technologies to integrate electronics and sensors on or into objects can support the growth of embedded electronics. The method proposed in this paper has the huge advantage of being substrate-free and applicable to a wide range of target materials such as fiber-based composites, widely used in manufacturing, and for which monitoring applications such as fatigue, cracks, and deformation detection are crucial. Here, sensors are first fabricated on a donor substrate using standard microelectronic processes and then transferred to the host material by direct transfer printing. Results show the viability of composites instrumented by strain gauges. Indeed, dynamic and static measurements highlight that the deformations can be detected with high sensitivity both on the surface and at various points in the depth of the composite material. Thanks to this technology, for the first time, a substrate-free piezoresistive n-doped silicon strain sensor is transferred into a composite material and characterized as a function of strain applied on it. It is shown that the transfer process does not alter the electrical behavior of the sensors that are five times more sensitive than extensively used metallic ones. An application designed for monitoring the deformation of a rudder foil with a classic NACA profile in real time is presented.

Comparison of the Magnetic and Structural Properties of MnFePSi Microwires and MnFePSi Bulk Alloy

We provide comparative studies of the structural, morphological, microstructural, and magnetic properties of MnFePSi-glass-coated microwires (MnFePSi-GCMWs) and bulk MnFePSi at different temperatures and magnetic fields. The structure of MnFePSi GCMWs prepared by the Taylor-Ulitovsky method consists of the main Fe2P phase and secondary impurities phases of Mn5Si3 and Fe3Si, as confirmed by XRD analysis. Additionally, a notable reduction in the average grain size from 24 µm for the bulk sample to 36 nm for the glass-coated microwire sample is observed. The analysis of magnetic properties of MnFePSi-glass-coated microwires shows different magnetic behavior as compared to the bulk MnFePSi. High coercivity (450 Oe) and remanence (0.32) are observed for MnFePSi-GCMWs compared to low coercivity and remanent magnetization observed for bulk MnFePSi alloy. In addition, large irreversibility at low temperatures is observed in the thermal dependence of magnetization of microwires. Meanwhile, the bulk sample shows regular ferromagnetic behavior, where the field cooling and field heating magnetic curves show a monotonic increase by decreasing the temperature. The notable separation between field cooling and field heating curves of MnFePSi-GCMWs is seen for the applied field at 1 kOe. Also, the M/M5K vs. T for MNFePSi-GCMWs shows a notable sensitivity at a low magnetic field compared to a very noisy magnetic signal for bulk alloy. The common features for both MnFePSi samples are high Curie temperatures above 400 K. From the experimental results, we can deduce the substantial effect of drawing and quenching involved in the preparation of glass-coated MnFePSi microwires in modification of the microstructure and magnetic properties as compared to the same bulk alloy. The provided studies prove the suitability of the Taylor-Ulitovsky method for the preparation of MnFePSi-glass-coated microwires.