A Breathable, Passive-Cooling, Non-Inflammatory, and Biodegradable Aerogel Electronic Skin for Wearable Physical-Electrophysiological-Chemical Analysis

Wearable Aerogels for Personal Thermal Management and Smart Devices

Extreme climates have become frequent nowadays, causing increased heat stress in human daily life. Personal thermal management (PTM), a technology that controls the human body's microenvironment, has become a promising strategy to address heat stress. While effective in ordinary environments, traditional high-performance fibers, such as ultrafine, porous, highly thermally conductive, and phase change materials, fall short when dealing with harsh conditions or large temperature fluctuations. Aerogels, a third-generation superinsulation material, have garnered extensive attention among researchers for their thermal management applications in building energy conservation, transportation, and aerospace, attributed to their extremely low densities and thermal conductivity. While aerogels have historically faced challenges related to weak mechanical strength and limited secondary processing capacity, recent advancements have witnessed notable progress in the development of wearable aerogels for PTM. This progress underscores their potential applications within extremely harsh environments, serving as self-powered smart devices and sensors. This Review offers a timely overview of wearable aerogels and their PTM applications with a particular focus on their wearability and suitability. Finally, the discussion classifies five types of PTM applications based on aerogel function: thermal insulation, heating, cooling, adaptive regulation (involving thermal insulation, heating, and cooling), and utilization of aerogels as wearable smart devices.

Photonics-powered augmented reality skin electronics for proactive healthcare: multifaceted opportunities

Rapid technological advancements have created opportunities for new solutions in various industries, including healthcare. One exciting new direction in this field of innovation is the combination of skin-based technologies and augmented reality (AR). These dermatological devices allow for the continuous and non-invasive measurement of vital signs and biomarkers, enabling the real-time diagnosis of anomalies, which have applications in telemedicine, oncology, dermatology, and early diagnostics. Despite its many potential benefits, there is a substantial information vacuum regarding using flexible photonics in conjunction with augmented reality for medical purposes. This review explores the current state of dermal augmented reality and flexible optics in skin-conforming sensing platforms by examining the obstacles faced thus far, including technical hurdles, demanding clinical validation standards, and problems with user acceptance. Our main areas of interest are skills, chiroptical properties, and health platform applications, such as optogenetic pixels, spectroscopic imagers, and optical biosensors. My skin-enhanced spherical dichroism and powerful spherically polarized light enable thorough physical inspection with these augmented reality devices: diabetic tracking, skin cancer diagnosis, and cardiovascular illness: preventative medicine, namely blood pressure screening. We demonstrate how to accomplish early prevention using case studies and emergency detection. Finally, it addresses real-world obstacles that hinder fully realizing these materials' extraordinary potential in advancing proactive and preventative personalized medicine, including technical constraints, clinical validation gaps, and barriers to widespread adoption.

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

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

A Fully Integrated Handheld Electrochemical Sensing Platform for Point-of-Care Testing of Escherichia coli O157:H7

Fully integrated devices that enable full functioning execution without or with minimum external accessories or equipment are deemed to be one of the most desirable and ultimate objectives for modern device design and construction. Escherichia coli O157:H7 (E. coli O157:H7) is often linked to outbreaks caused by contaminated water and food. However, the sensors that are currently used for point-of-care E. coli O157:H7 (E. coli O157:H7) detection are often large and cumbersome. Herein, we demonstrate the first example of a handheld and pump-free fully integrated electrochemical sensing platform with the capability to point-of-care test E. coli O157:H7 in the actual samples of E. coli O157:H7-spiked tap water and E. coli O157:H7-spiked watermelon juice. This platform was made possible by overcoming major engineering challenges in the seamless integration of a microfluidic module for pump-free liquid sample collection and transportation, a sensing module for efficient E. coli O157:H7 testing, and an electronic module for automatically converting and wirelessly transmitting signals into a single and compact electrochemical sensing platform that retains its inimitable stand-alone, handheld, pump-free, and cost-effective feature. Although our primary emphasis in this study is on detecting E. coli O157:H7, this pump-free fully integrated handheld electrochemical sensing platform may also be used to monitor other pathogens in food and water by including specific antipathogen antibodies.

A Bionic Skin for Health Management: Excellent Breathability, In Situ Sensing, and Big Data Analysis

Developing an intelligent wearable system is of great significance to human health management. An ideal health-monitoring patch should possess key characteristics such as high air permeability, moisture-wicking function, high sensitivity, and a comfortable user experience. However, such a patch that encompasses all these functions is rarely reported. Herein, an intelligent bionic skin patch for health management is developed by integrating bionic structures, nano-welding technology, flexible circuit design, multifunctional sensing functions, and big data analysis using advanced electrospinning technology. By controlling the preparation of nanofibers and constructing bionic secondary structures, the resulting nanofiber membrane closely resembles human skin, exhibiting excellent air/moisture permeability, and one-side sweat-wicking properties. Additionally, the bionic patch is endowed with a high-precision signal acquisition capabilities for sweat metabolites, including glucose, lactic acid, and pH; skin temperature, skin impedance, and electromyographic signals can be precisely measured through the in situ sensing electrodes and flexible circuit design. The achieved intelligent bionic skin patch holds great potential for applications in health management systems and rehabilitation engineering management. The design of the smart bionic patch not only provides high practical value for health management but also has great theoretical value for the development of the new generation of wearable electronic devices.

A three-dimensional liquid diode for soft, integrated permeable electronics

Wearable electronics with great breathability enable a comfortable wearing experience and facilitate continuous biosignal monitoring over extended periods1-3. However, current research on permeable electronics is predominantly at the stage of electrode and substrate development, which is far behind practical applications with comprehensive integration with diverse electronic components (for example, circuitry, electronics, encapsulation)4-8. Achieving permeability and multifunctionality in a singular, integrated wearable electronic system remains a formidable challenge. Here we present a general strategy for integrated moisture-permeable wearable electronics based on three-dimensional liquid diode (3D LD) configurations. By constructing spatially heterogeneous wettability, the 3D LD unidirectionally self-pumps the sweat from the skin to the outlet at a maximum flow rate of 11.6 ml cm-2 min-1, 4,000 times greater than the physiological sweat rate during exercise, presenting exceptional skin-friendliness, user comfort and stable signal-reading behaviour even under sweating conditions. A detachable design incorporating a replaceable vapour/sweat-discharging substrate enables the reuse of soft circuitry/electronics, increasing its sustainability and cost-effectiveness. We demonstrated this fundamental technology in both advanced skin-integrated electronics and textile-integrated electronics, highlighting its potential for scalable, user-friendly wearable devices.

Wettability Gradient-Induced Diode: MXene-Engineered Membrane for Passive-Evaporative Cooling

Thermoregulatory textiles, leveraging high-emissivity structural materials, have arisen as a promising candidate for personal cooling management; however, their advancement has been hindered by the underperformed water moisture transportation capacity, which impacts on their thermophysiological comfort. Herein, we designed a wettability-gradient-induced-diode (WGID) membrane achieving by MXene-engineered electrospun technology, which could facilitate heat dissipation and moisture-wicking transportation. As a result, the obtained WGID membrane could obtain a cooling temperature of 1.5 °C in the "dry" state, and 7.1 °C in the "wet" state, which was ascribed to its high emissivity of 96.40% in the MIR range, superior thermal conductivity of 0.3349 W m-1 K-1 (based on radiation- and conduction-controlled mechanisms), and unidirectional moisture transportation property. The proposed design offers an approach for meticulously engineering electrospun membranes with enhanced heat dissipation and moisture transportation, thereby paving the way for developing more efficient and comfortable thermoregulatory textiles in a high-humidity microenvironment.

Ultrastretchable E-Skin Based on Conductive Hydrogel Microfibers for Wearable Sensors

Conductive microfibers play a significant role in the flexibility, stretchability, and conductivity of electronic skin (e-skin). Currently, the fabrication of conductive microfibers suffers from either time-consuming and complex operations or is limited in complex fabrication environments. Thus, it presents a one-step method to prepare conductive hydrogel microfibers based on microfluidics for the construction of ultrastretchable e-skin. The microfibers are achieved with conductive MXene cores and hydrogel shells, which are solidified with the covalent cross-linking between sodium alginate and calcium chloride, and mechanically enhanced by the complexation reaction of poly(vinyl alcohol) and sodium hydroxide. The microfiber conductivities are tailorable by adjusting the flow rate and concentration of core and shell fluids, which is essential to more practical applications in complex scenarios. More importantly, patterned e-skin based on conductive hydrogel microfibers can be constructed by combining microfluidics with 3D printing technology. Because of the great advantages in mechanical and electrical performance of the microfibers, the achieved e-skin shows impressive stretching and sensitivity, which also demonstrate attractive application values in motion monitoring and gesture recognition. These characteristics indicate that the ultrastretchable e-skin based on conductive hydrogel microfibers has great potential for applications in health monitoring, wearable devices, and smart medicine.

Room-Temperature Liquid Metals for Flexible Electronic Devices

Room-temperature gallium-based liquid metals (RT-GaLMs) have garnered significant interest recently owing to their extraordinary combination of fluidity, conductivity, stretchability, self-healing performance, and biocompatibility. They are ideal materials for the manufacture of flexible electronics. By changing the composition and oxidation of RT-GaLMs, physicochemical characteristics of the liquid metal can be adjusted, especially the regulation of rheological, wetting, and adhesion properties. This review highlights the advancements in the liquid metals used in flexible electronics. Meanwhile related characteristics of RT-GaLMs and underlying principles governing their processing and applications for flexible electronics are elucidated. Finally, the diverse applications of RT-GaLMs in self-healing circuits, flexible sensors, energy harvesting devices, and epidermal electronics, are explored. Additionally, the challenges hindering the progress of RT-GaLMs are discussed, while proposing future research directions and potential applications in this emerging field. By presenting a concise and critical analysis, this paper contributes to the advancement of RT-GaLMs as an advanced material applicable for the new generation of flexible electronics.

Polymeric Conductive Adhesive-Based Ultrathin Epidermal Electrodes for Long-Term Monitoring of Electrophysiological Signals

Electrophysiology, exploring vital electrical phenomena in living organisms, anticipates broader integration into daily life through wearable devices and epidermal electrodes. However, addressing the challenges of the electrode durability and motion artifacts is essential to enable continuous and long-term biopotential signal monitoring, presenting a hurdle for its seamless implementation in daily life. To address these challenges, an ultrathin polymeric conductive adhesive, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/polyvinyl alcohol/d-sorbitol (PPd) electrode with enhanced adhesion, stretchability, and skin conformability, is presented. The skin conformability and stability of electrodes is designed by theoretical criteria obtained by mechanical analysis. Thus, impedance stability is obtained over 1-week of daily life, and the PPd electrode addresses the challenges related to durability during prolonged usage. Proving stability in electromyography (EMG) signals during high-intensity exercise, the wireless PPd measurement system exhibits high signal-to-noise ratio (SNR) signals even in situations involving significant and repetitive skin deformation. Throughout continuous 1 week-long electrocardiogram (ECG) monitoring in daily life, the system consistently preserves signal quality, underscoring the heightened durability and applicability of the PPd measurement system.

Self-sustained and Insulated Radiative/Evaporative Cooler for Daytime Subambient Passive Cooling

Passive cooling technologies are one of the promising solutions to the global energy crisis due to no consumption of fossil fuels during operation. However, the existing radiative and evaporative coolers still have problems achieving daytime subambient cooling while maintaining evaporation over the long term. Here, we propose a self-sustained and insulated radiative/evaporative cooler (SIREC), which consists of a porous polyethylene film (P-PE) at the top, an air layer in the middle, and poly(vinyl alcohol) hydrogel with lithium bromide (PLH) at the bottom. In particular, the P-PE shows high solar reflectance (R̅solar = 0.91) and long-wave infrared transmittance (τ̅LWIR = 0.92), which reflects sunlight while enhancing the direct radiative heat transfer between outer space and PLH (ε̅LWIR = 0.96) for sky radiative cooling. In addition, the desirable vapor permeability (579 s m-1) of the P-PE also results in good compatibility with PLH for evaporative cooling (EC). Moreover, the PLH's ability to harvest atmospheric water at night provides self-sustainment for daytime EC. The air layer between P-PE and PLH further enhances the subambient cooling performance of the SIREC. These findings indicate promising prospects for the integration of passive cooling technologies.

Flexible Accelerated-Wound-Healing Antibacterial Hydrogel-Nanofiber Scaffold for Intelligent Wearable Health Monitoring

Flexible epidermal sensors hold significant potential in personalized healthcare and multifunctional electronic skins. Nonetheless, achieving both robust sensing performance and efficient antibacterial protection, especially in medical paradigms involving electrophysiological signals for wound healing and intelligent health monitoring, remains a substantial challenge. Herein, we introduce a novel flexible accelerated-wound-healing biomaterial based on a hydrogel-nanofiber scaffold (HNFS) via electrostatic spinning and gel cross-linking. We effectively engineer a multifunctional tissue nanoengineered skin scaffold for wound treatment and health monitoring. Key features of HNFS include high tensile strength (24.06 MPa) and elasticity (214.67%), flexibility, biodegradability, and antibacterial properties, enabling assembly into versatile sensors for monitoring human motion and electrophysiological signals. Moreover, in vitro and in vivo experiments demonstrate that HNFS significantly enhances cell proliferation and skin wound healing, provide a comprehensive therapeutic strategy for smart sensing and tissue repair, and guide the development of high-performance "wound healing-health monitoring" bioelectronic skin scaffolds. Therefore, this study provides insights into crafting flexible and repairable skin sensors, holding potential for multifunctional health diagnostics and intelligent medical applications in intelligent wearable health monitoring and next-generation artificial skin fields.

Biomimetic Wearable Sensors: Emerging Combination of Intelligence and Electronics

Owing to the advancement of interdisciplinary concepts, for example, wearable electronics, bioelectronics, and intelligent sensing, during the microelectronics industrial revolution, nowadays, extensively mature wearable sensing devices have become new favorites in the noninvasive human healthcare industry. The combination of wearable sensing devices with bionics is driving frontier developments in various fields, such as personalized medical monitoring and flexible electronics, due to the superior biocompatibilities and diverse sensing mechanisms. It is noticed that the integration of desired functions into wearable device materials can be realized by grafting biomimetic intelligence. Therefore, herein, the mechanism by which biomimetic materials satisfy and further enhance system functionality is reviewed. Next, wearable artificial sensory systems that integrate biomimetic sensing into portable sensing devices are introduced, which have received significant attention from the industry owing to their novel sensing approaches and portabilities. To address the limitations encountered by important signal and data units in biomimetic wearable sensing systems, two paths forward are identified and current challenges and opportunities are presented in this field. In summary, this review provides a further comprehensive understanding of the development of biomimetic wearable sensing devices from both breadth and depth perspectives, offering valuable guidance for future research and application expansion of these devices.

Silver nanowire-infused carbon aerogel: A multifunctional nanocellulose-derived material for personal thermal management

Personal thermal management (PTM) textiles for outdoor activities have become increasingly important for addressing energy consumption and thermal comfortable. Cellulose nanofiber (CNF) aerogels have emerged as promising candidates for PTM due to the eco-friendliness, lightweight, and low thermal conductivity. However, the singular insulation capability may not be sufficient to accommodate the diverse and harsh outdoor conditions. Herein, we carbonized CNF-based aerogel to fabricate anisotropic carbon aerogels, and then incorporated silver nanowires (AgNWs) upon onside to fabricate the dual-function AgNWs/carbon aerogel. The resulting material inherits high porosity (99.3 %), high surface area (503.2 m2/g), low density (7.08 mg/cm3), and low thermal conductivity (18.2 mW·m-1·k-1 in the axial direction) to act as an ideal thermal insulator. The AgNWs coating side demonstrates low IR-emissivity (17.6 % at 7-14 μm) and the carbon aerogel side has high solar absorptivity (91.97 %). Moreover, the AgNWs/carbon aerogel shows Joule heating performance (∆T = 44.5 °C within 3 min at 5 V). The multi-heating modes enabling self-adaptable thermal comfortable under various harsh environment. Additionally, the material's breathability, permeability, and electromagnetic shielding characteristics also make it suitable candidate for advanced wearable textiles for PTM.

Ultrathin Aerogel Micro/Nanofiber Membranes with Hierarchical Cellular Architecture for High-Performance Warmth Retention

A low temperature environment poses significant challenges to the global economy and public health. However, the existing cold-protective materials still struggle with the trade-off between thickness and thermal resistance, resulting in poor thermal-wet comfort and limited personal cold protection performance. Here, a scalable strategy, based on electrospinning and solution casting, is developed to create aerogel micro/nanofiber membranes with a hierarchical cellular architecture by manipulating the phase separation of the charged jets and of the spreading casting solution. The integration of interconnected nanopores (30-60 nm), ultrafine fiber diameter, and high porosity, enables the aerogel micro/nanofiber membranes with lightweight, ultrathin thickness (∼0.5 mm), and superior warmth retention performance with ultralow thermal conductivity of 14.01 mW m-1 K-1. And the resultant membrane with customized semiclosed walls exhibits both striking wind resistance and satisfactory thermal-wet comfort (3.4 °C warmer than the cutting-edge thermal underwear). This work will inspire the design and development of high-performance fibrous materials for thermal management applications.

An All-In-One Transient Theranostic Platform for Intelligent Management of Hemorrhage

Developing theranostic devices to detect bleeding and effectively control hemorrhage in the prehospital setting is an unmet medical need. Herein, an all-in-one theranostic platform is presented, which is constructed by sandwiching silk fibroin (SF) between two silver nanowire (AgNW) based conductive electrodes to non-enzymatically diagnose local bleeding and stop the hemorrhage at the wound site. Taking advantage of the hemostatic property of natural SF, the device is composed of a shape-memory SF sponge, facilitating blood clotting, with ≈82% reduction in hemostatic time in vitro as compared with untreated blood. Furthermore, this sandwiched platform serves as a capacitive sensor that can detect bleeding and differentiate between blood and other body fluids (i.e., serum and water) via capacitance change. In addition, the AgNW electrode endows anti-infection efficiency against Escherichia coli and Staphylococcus aureus. Also, the device shows excellent biocompatibility and gradually biodegrades in vivo with no major local or systemic inflammatory responses. More importantly, the theranostic platform presents considerable hemostatic efficacy comparable with a commercial hemostat, Dengen, in rat liver bleeding models. The theranostic platform provides an unexplored strategy for the intelligent management of hemorrhage, with the potential to significantly improve patients' well-being through the integration of diagnostic and therapeutic capabilities.

Screen-Printed Textile-Based Electrochemical Biosensor for Noninvasive Monitoring of Glucose in Sweat

Wearable sweat biosensors for noninvasive monitoring of health parameters have attracted significant attention. Having these biosensors embedded in textile substrates can provide a convenient experience due to their soft and flexible nature that conforms to the skin, creating good contact for long-term use. These biosensors can be easily integrated with everyday clothing by using textile fabrication processes to enhance affordable and scalable manufacturing. Herein, a flexible electrochemical glucose sensor that can be screen-printed onto a textile substrate has been demonstrated. The screen-printed textile-based glucose biosensor achieved a linear response in the range of 20-1000 µM of glucose concentration and high sensitivity (18.41 µA mM^-1 cm^-2, R² = 0.996). In addition, the biosensors show high selectivity toward glucose among other interfering analytes and excellent stability over 30 days of storage. The developed textile-based biosensor can serve as a platform for monitoring bio analytes in sweat, and it is expected to impact the next generation of wearable devices.

Skin-interfaced electronics: A promising and intelligent paradigm for personalized healthcare

Skin-interfaced electronics (skintronics) have received considerable attention due to their thinness, skin-like mechanical softness, excellent conformability, and multifunctional integration. Current advancements in skintronics have enabled health monitoring and digital medicine. Particularly, skintronics offer a personalized platform for early-stage disease diagnosis and treatment. In this comprehensive review, we discuss (1) the state-of-the-art skintronic devices, (2) material selections and platform considerations of future skintronics toward intelligent healthcare, (3) device fabrication and system integrations of skintronics, (4) an overview of the skintronic platform for personalized healthcare applications, including biosensing as well as wound healing, sleep monitoring, the assessment of SARS-CoV-2, and the augmented reality-/virtual reality-enhanced human-machine interfaces, and (5) current challenges and future opportunities of skintronics and their potentials in clinical translation and commercialization. The field of skintronics will not only minimize physical and physiological mismatches with the skin but also shift the paradigm in intelligent and personalized healthcare and offer unprecedented promise to revolutionize conventional medical practices.