Integrated Smart Janus Textile Bands for Self-Pumping Sweat Sampling and Analysis

Porous Microneedles Through Direct Ink Drawing with Nanocomposite Inks for Transdermal Collection of Interstitial Fluid

Interstitial fluid (ISF) is an attractive alternative to regular blood sampling for health checks and disease diagnosis. Porous microneedles (MNs) are well suited for collecting ISF in a minimally invasive manner. However, traditional methods of molding MNs from microfabricated templates involve prohibitive fabrication costs and fixed designs. To overcome these limitations, this study presents a facile and economical additive manufacturing approach to create porous MNs. Compared to traditional layerwise build sequences, direct ink drawing with nanocomposite inks can define sharp MNs with tailored shapes and achieve vastly improved fabrication efficiency. The key to this fabrication strategy is the yield-stress fluid ink that is easily formulated by dispersing silica nanoparticles into the cellulose acetate polymer solution. As-printed MNs are solidified into interconnected porous microstructure inside a coagulation bath of deionized water. The resulting MNs exhibit high mechanical strength and high porosity. This approach also allows porous MNs to be easily integrated on various substrates. In particular, MNs on filter paper substrates are highly flexible to rapidly collect ISF on non-flat skin sites. The extracted ISF is used for quantitative analysis of biomarkers, including glucose, = calcium ions, and calcium ions. Overall, the developments allow facile fabrication of porous MNs for transdermal diagnosis and therapy.

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.

Stretchable and Sweat-Wicking Patch for Skin-Attached Colorimetric Analysis of Sweat Biomarkers

Stretchable sweat sensors are promising technology that can acquire biomolecular insights for health and fitness monitoring by intimate integration with the body. However, current sensors often require microfabricated microfluidic channels to control sweat flow during lab-on-body analysis, which makes effective and affordable sweat sampling a significant practical challenge. Here, we present stretchable and sweat-wicking patches that utilize bioinspired smart wettable membranes for the on-demand manipulation of sweat flow. In a scalable process, the membrane is created by stacking hydrophobic elastomer nanofibers onto soft microfoams with predefined two-dimensional superhydrophobic and superhydrophilic patterns. The engineered heterogeneous wettability distribution allows these porous membranes to achieve enhanced extraction and selective collection of sweat in embedded assays. Despite the simplified architecture, the color reactions between sweat and chemical indicators are inhibited from directly contacting the skin to achieve a largely improved operation safety. The sensing patches can simultaneously quantify pH, urea, and calcium in sweat through digital colorimetric analysis with smartphone images. The construction with all compliant materials renders these patches soft and stretchy to achieve conformal attachment to the skin. Successfully analyzing sweat compositions after physical exercises illustrates the practical suitability of these skin-attachable sensors for health tracking and point-of-care diagnosis.

A Fully Elastic Wearable Electrochemical Sweat Detection System of Tree-Bionic Microfluidic Structure for Real-Time Monitoring

Fresh sweat contains a diverse range of physiological indicators that can effectively reflect changes in the body. However, existing wearable sweat detection systems face challenges in efficiently collecting and detecting fresh sweat in real-time. Additionally, they often lack the necessary deformation capabilities, resulting in discomfort for the wearer. Here, a fully elastic wearable electrochemical sweat detection system is developed that integrates a sweat-collecting microfluidic chip, a multi-parameter electrochemical sensor, a micro-heater, and a sweat detection elastic circuit board system. The unique tree-bionic structure of the microfluidic chip significantly enhances the efficiency of fresh sweat collection and discharge, enabling real-time detection by the electrochemical sensors. The sweat multi-parameter electrochemical sensor offers high-precision and high-sensitivity measurements of sodium ions, potassium ions, lactate, and glucose. The electronic system is built on an elastic circuit board that matches perfectly to wrinkled skin, ensuring improved wearing comfort and enabling multi-channel data sampling, processing, and wireless transmission. This state-of-the-art system represents a significant advancement in the field of elastic wearable sweat detection and holds promising potential for extending its capabilities to the detection of other sweat markers or various wearable applications.

Porous Conductive Textiles for Wearable Electronics

Over the years, researchers have made significant strides in the development of novel flexible/stretchable and conductive materials, enabling the creation of cutting-edge electronic devices for wearable applications. Among these, porous conductive textiles (PCTs) have emerged as an ideal material platform for wearable electronics, owing to their light weight, flexibility, permeability, and wearing comfort. This Review aims to present a comprehensive overview of the progress and state of the art of utilizing PCTs for the design and fabrication of a wide variety of wearable electronic devices and their integrated wearable systems. To begin with, we elucidate how PCTs revolutionize the form factors of wearable electronics. We then discuss the preparation strategies of PCTs, in terms of the raw materials, fabrication processes, and key properties. Afterward, we provide detailed illustrations of how PCTs are used as basic building blocks to design and fabricate a wide variety of intrinsically flexible or stretchable devices, including sensors, actuators, therapeutic devices, energy-harvesting and storage devices, and displays. We further describe the techniques and strategies for wearable electronic systems either by hybridizing conventional off-the-shelf rigid electronic components with PCTs or by integrating multiple fibrous devices made of PCTs. Subsequently, we highlight some important wearable application scenarios in healthcare, sports and training, converging technologies, and professional specialists. At the end of the Review, we discuss the challenges and perspectives on future research directions and give overall conclusions. As the demand for more personalized and interconnected devices continues to grow, PCT-based wearables hold immense potential to redefine the landscape of wearable technology and reshape the way we live, work, and play.

Electrospinning Nanofibers as Stretchable Sensors for Wearable Devices

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

Hydrogel-Functionalized Bandages with Janus Wettability for Efficient Unidirectional Drug Delivery and Wound Care

Chronic wounds have imposed a severe physical and economic burden on the global healthcare system, which are usually treated by the delivery of drugs or bioactive molecules to the wound bed through wound dressings. In this work, we have demonstrated a hydrogel-functionalized bandage with Janus wettability in a bilayer structure to achieve unidirectional drug delivery and multifunctional wound care. The Janus patterned bandage with porous gradient wetting channels on the upper layer is responsible for the unidirectional transport of the drug from the outside to the wound bed (up to 90% drug transport efficiency) while preventing drug diffusion in unwanted directions (<8%). The hydrogel composed of chitosan quaternary ammonium salt (HACC), poly(vinyl alcohol) (PVA), and poly(acrylic acid) (PAA) at the bottom layer further functionalized such a bandage with biocompatibility, excellent antibacterial properties, and hemostatic ability to promote wound healing. Especially, the hydrogel-functionalized bandage with Janus wettability exhibits excellent mechanical flexibility (∼198% strain), which can comply well with skin deformation (stretching, bending, or twisting) and maintain unidirectional drug delivery behavior without any leakage. The in vivo full-thickness skin wound model confirms that the hydrogel-functionalized bandage can significantly facilitate epithelialization and collagen deposition and improve drug delivery efficiency, thus promoting wound closure and healing (the wound healing ratio was 98.10% at day 15). Such a synergistic strategy of unidirectional drug delivery and multifunctional wound care provides a more efficient, economical, and direct method to promote wound healing, which could be used as a potential high-performance wound dressing for clinical application.

Stretchable and Smart Wettable Sensing Patch with Guided Liquid Flow for Multiplexed in Situ Perspiration Analysis

Stretchable sweat sensors have become a personalized wearable platform for continuous, noninvasive health monitoring through conformal integration with the human body. Typically, these devices are coupled with soft microfluidic systems to control sweat flow during advanced analysis processes. However, the implementation of these soft microfluidic devices is limited by their high fabrication costs and the need for skin adhesives to block natural perspiration. To overcome these limitations, a stretchable and smart wettable patch has been proposed for multiplexed in situ perspiration analysis. The patch includes a porous membrane in the form of a patterned microfoam and a nanofiber layer laminate, which extracts sweat selectively from the skin and directs its continuous flow across the device. The integrated electrochemical sensor array measures multiple biomarkers simultaneously such as pH, K+, and Na+. The soft sensing patch comprises compliant materials and structures that allow deformability of up to 50% strain, which enables a stable and seamless interface with the curvilinear human body. During continuous physical exercise, the device has demonstrated a special operating mode by actively accumulating sweat from the skin for multiplex electrochemical analysis of biomarker profiles. The smart wettable membrane provides an affordable solution to address the sampling challenges of in situ perspiration analysis.

Sweat Sensor Based on Wearable Janus Textiles for Sweat Collection and Microstructured Optical Fiber for Surface-Enhanced Raman Scattering Analysis

Wearable sweat sensors provide real-time monitoring of biomarkers, enabling individuals to gain real-time insight into their health status. Current sensors primarily rely on electrochemical mechanisms, limiting their capacity for the concurrent detection of multiple analytes. Surface-enhanced Raman scattering spectroscopy offers an alternative approach by providing molecular fingerprint information to facilitate the identification of intricate analytes. In this study, we combine a wearable Janus fabric for efficient sweat collection and a grapefruit optical fiber embedded with Ag nanoparticles as a sensitive SERS probe. The Janus fabric features a superhydrophobic side in contact with the skin and patterned superhydrophilic regions on the opposite surface, facilitating the unidirectional flow of sweat toward these hydrophilic zones. Grapefruit optical fibers feature sharp tips with the ability to penetrate transparent dressings. Its microchannels extract sweat through capillary force, and nanoliter-scale volumes of sweat are sufficient to completely fill them. The Raman signal of sweat components is greatly enhanced by the plasmonic hot spots and accumulates along the fiber length. We demonstrate sensitive detection of sodium lactate and urea in sweat with a detection limit much lower than the physiological concentration levels. Moreover, the platform shows its capability for multicomponent detection and extends to the analysis of real human sweat.

Access and Management of Sweat for Non-Invasive Biomarker Monitoring: A Comprehensive Review

Sweat is an important biofluid presents in the body since it regulates the internal body temperature, and it is relatively easy to access on the skin unlike other biofluids and contains several biomarkers that are also present in the blood. Although sweat sensing devices have recently displayed tremendous progress, most of the emerging devices primarily focus on the sensor development, integration with electronics, wearability, and data from in vitro studies and short-term on-body trials during exercise. To further the advances in sweat sensing technology, this review aims to present a comprehensive report on the approaches to access and manage sweat from the skin toward improved sweat collection and sensing. It is begun by delineating the sweat secretion mechanism through the skin, and the historical perspective of sweat, followed by a detailed discussion on the mechanisms governing sweat generation and management on the skin. It is concluded by presenting the advanced applications of sweat sensing, supported by a discussion of robust, extended-operation epidermal wearable devices aiming to strengthen personalized healthcare monitoring systems.

Dual detection of human motion and glucose in sweat with polydopamine and glucose oxidase doped self-healing nanocomposite hydrogels

The detection of human motion and sweat composition are important for human health or sports training, so it is necessary to develop flexible sensors for monitoring exercise processes and sweat detection. Mussel secretion of adhesion proteins enables self-healing of byssus and adhesion to surfaces. We prepared Au nanoparticles@polydopamine (AuNPs@PDA) nanomaterials based on mussel-inspired chemistry and compounded them with polyvinyl alcohol (PVA) hydrogels to obtain PVA/AuNPs@PDA self-healing nanocomposite hydrogels. Dopamine (DA) was coated on the surface of AuNPs to obtain AuNPs based composite (AuNPs@PDA) and the AuNPs@PDA was implanted into the PVA hydrogels to obtain nanocomposite hydrogel through facile freeze-thaw cycle. Glucose oxidase (GOD) was added to the hydrogel matrix to achieve specific detection of glucose in sweat. The obtained hydrogels exhibit high deformability (573.7 %), excellent mechanical strength (550.3 KPa) and self-healing properties (85.1 %). The PVA/AuNPs@PDA hydrogel sensors exhibit quick response time (185.0 ms), wide strain sensing range (0-500 %), superior stability and anti-fatigue properties in motion detection. The detection of glucose had wide concentration detection range (1.0 μmol/L-200.0 μmol/L), low detection limits (0.9 μmol/L) and high sensitivity (24.4 μA/mM). This work proposes a reference method in dual detection of human exercise and sweat composition analysis.

A monolithically integrated in-textile wristband for wireless epidermal biosensing

Textile bioelectronics that allow comfortable epidermal contact hold great promise in noninvasive biosensing. However, their applications are limited mainly because of the large intrinsic electrical resistance and low compatibility for electronics integration. We report an integrated wristband that consists of multifunctional modules in a single piece of textile to realize wireless epidermal biosensing. The in-textile metallic patterning and reliable interconnect encapsulation contribute to the excellent electrical conductivity, mechanical robustness, and waterproofness that are competitive with conventional flexible devices. Moreover, the well-maintained porous textile architectures deliver air permeability of 79 mm s-1 and moisture permeability of 270 g m-2 day-1, which are more than one order of magnitude higher than medical tapes, thus ensuring superior wearing comfort. The integrated in-textile wristband performed continuous sweat potassium monitoring in the range of 0.3 to 40 mM with long-term stability, demonstrating its great potential for wearable fitness monitoring and point-of-care testing.

Recent Advances in Skin-Interfaced Wearable Sweat Sensors: Opportunities for Equitable Personalized Medicine and Global Health Diagnostics

Recent advances in skin-interfaced wearable sweat sensors enable the noninvasive, real-time monitoring of biochemical signals associated with health and wellness. These wearable platforms leverage microfluidic channels, biochemical sensors, and flexible electronics to enable the continuous analysis of sweat-based biomarkers such as electrolytes, metabolites, and hormones. As this field continues to mature, the potential of low-cost, continuous personalized health monitoring enabled by such wearable sensors holds significant promise for addressing some of the formidable obstacles to delivering comprehensive medical care in under-resourced settings. This Perspective highlights the transformative potential of wearable sweat sensing for providing equitable access to cutting-edge healthcare diagnostics, especially in remote or geographically isolated areas. It examines the current understanding of sweat composition as well as recent innovations in microfluidic device architectures and sensing strategies by showcasing emerging applications and opportunities for innovation. It concludes with a discussion on expanding the utility of wearable sweat sensors for clinically relevant health applications and opportunities for enabling equitable access to innovation to address existing health disparities.

Expanded Carbon Nanotube Fiber at the Liquid-Air Interface for High-Performance Fiber-Based Supercapacitors and Electrochemical Sensors

Carbon nanotube fibers (CNTFs) are widely utilized in flexible and wearable electronics due to their outstanding electrical and mechanical properties. However, the spinning process of CNTFs has limited the CNTs from exposure, leading to an ultralow usage efficiency of individual CNTs. Here, we propose an electrochemical expansion strategy of a single CNTF at the liquid-air interface, forming a macroscopic spindle-shaped CNTF (SS-CNTF) with an enlarged volume of up to 5000-fold upon the spindle. The obtained spindle-shaped structure endows CNTF with a high specific surface area together with excellent conductivity and good mechanical properties. Therefore, the SS-CNTF-based devices exhibit outstanding performances both in energy storage (electrical double-layer supercapacitor, energy density: 11.22 Wh kg-1, power density: 203.9 kW kg-1) and electrochemical sensing (ascorbic acid: 1.26 μA μM-1 cm-2; dopamine: 103.91 μA μM-1 cm-2; uric acid: 11.53 μA μM-1 cm-2). The novel architecture of SS-CNTF prepared by one-step electrochemical expansion at the liquid-air interface enabled its high performance in multiple applications, providing new insight into the development of CNTF-based devices.

Flexible and Wearable Biosensors for Monitoring Health Conditions

Flexible and wearable biosensors have received tremendous attention over the past decade owing to their great potential applications in the field of health and medicine. Wearable biosensors serve as an ideal platform for real-time and continuous health monitoring, which exhibit unique properties such as self-powered, lightweight, low cost, high flexibility, detection convenience, and great conformability. This review introduces the recent research progress in wearable biosensors. First of all, the biological fluids often detected by wearable biosensors are proposed. Then, the existing micro-nanofabrication technologies and basic characteristics of wearable biosensors are summarized. Then, their application manners and information processing are also highlighted in the paper. Massive cutting-edge research examples are introduced such as wearable physiological pressure sensors, wearable sweat sensors, and wearable self-powered biosensors. As a significant content, the detection mechanism of these sensors was detailed with examples to help readers understand this area. Finally, the current challenges and future perspectives are proposed to push this research area forward and expand practical applications in the future.

All fabric and flexible wearable sensors for simultaneous sweat metabolite detection and high-efficiency collection

Wearable sweat electrochemical sensors have attracted wide attention due to their advantages of non-invasive, portable, real-time monitoring, etc. However, existing sensors still have some problems with efficient sweat collection. Microfluidic channel technology and electrospinning technology are commonly used to collect sweat efficiently, but there are some limitations such as complex channel design and multiple spinning parameters. Besides, existing sensors are mostly based on flexible polymers, such as, PET, PDMS, PI and PI, which have limited wearability and permeability. Based on the above, all fabric and dual-function flexible wearable sweat electrochemical sensor is proposed in this paper. This sensor uses fabric as the raw material to implement the directional transport of sweat and the multi-component integrated detection dual functions. Meanwhile, the high-efficiency collection of sweat is obtained by a Janus fabric, wherein one side of the selected silk is superhydrophobic graft treated and the other side is hydrophilic plasma treated. Therefore, the resulting Janus fabric can effectively transfer sweat from the skin side to the electrode, and the minimum sweat droplet can reach 0.2 μL to achieve micro-volume collection. Besides, the patterned sensor, made of silk-based carbon cloth, is fabricated using a simple laser engraving, which could detect Na⁺, pH, and glucose instantaneously. As a result, these proposed sensors can achieve good sensing performance and high-efficiency sweat collection dual functionality; moreover, it has good flexibility and comfortable wearability.

Skin-Interfaced Wearable Sweat Sensors for Precision Medicine

Wearable sensors hold great potential in empowering personalized health monitoring, predictive analytics, and timely intervention toward personalized healthcare. Advances in flexible electronics, materials science, and electrochemistry have spurred the development of wearable sweat sensors that enable the continuous and noninvasive screening of analytes indicative of health status. Existing major challenges in wearable sensors include: improving the sweat extraction and sweat sensing capabilities, improving the form factor of the wearable device for minimal discomfort and reliable measurements when worn, and understanding the clinical value of sweat analytes toward biomarker discovery. This review provides a comprehensive review of wearable sweat sensors and outlines state-of-the-art technologies and research that strive to bridge these gaps. The physiology of sweat, materials, biosensing mechanisms and advances, and approaches for sweat induction and sampling are introduced. Additionally, design considerations for the system-level development of wearable sweat sensing devices, spanning from strategies for prolonged sweat extraction to efficient powering of wearables, are discussed. Furthermore, the applications, data analytics, commercialization efforts, challenges, and prospects of wearable sweat sensors for precision medicine are discussed.

Ultra-thin 2D bimetallic MOF nanosheets for highly sensitive and stable detection of glucose in sweat for dancer

The measurement of glucose concentration in sweat is expected to replace the existing blood glucose detection, which realize the effective way of non-invasive monitoring of human glucose concentration in dancing. High precision glucose detection can be achieved by adjusting the electrode material of the sensor. Thus, in this work, the bimetallic organic frameworks (bi-MOFs) materials containing Mn and Ni ions (NiMn-MOF) with ultrathin nanosheets have been exquisitely designed. The ultrathin nanosheet and heterogeneous metal ions in the structure optimize the electronic structure, which improves the electrical conductivity of MOFs. The success of the preparation strategy leads the good electrocatalytic performance of NiMn-MOF for glucose detection. Detailedly, NiMn-MOF shows high sensitivity of 1576 μA mM-1 cm-2 in the linear range from 0 to 0.205 mM and the wide linear region of 0.255-2.655 mM and 3.655-5.655 mM were also observed. In addition, the high repeatability, reproductivity, long-term stability and ultra-low limited of detection (LOD, 0.28 μM, S/N = 3) provide foundation for the practical sensor application of this NiMn-MOF nanosheets. Remarkably, as designed NiMn-MOF sensor can accurately measure glucose in sweat showing great potential in the field of wearable glucose monitoring during dancing.

Smart Janus fabrics for one-way sweat sampling and skin-friendly colorimetric detection

Functionalized textiles with biofluid management capability have attracted tremendous attention in recent years due to their significant roles in health monitoring and dehydration prevention. Here we propose a one-way colorimetric sweat sampling and sensing system based on a Janus fabric using interfacial modification techniques. The opposite wettability of Janus fabric enables sweat to be quickly moved from the skin surface to the hydrophilic side and colorimetric patches. The unidirectional sweat-wicking performance of Janus fabric not only facilitates adequate sweat sampling but also inhibits the backflow of hydrated colorimetric regent from the assay patch toward the skin, eliminating potential epidermal contaminations. On this basis, visual and portable detection of sweat biomarkers including chloride, pH, and urea is also achieved. The results show that the true concentrations of chloride, pH, and urea in sweat are ∼10 mM, ∼7.2, and ∼10 mM, respectively. The detection limits of chloride and urea are 1.06 mM and 3.05 mM. This work bridges the gap between sweat sampling and a friendly epidermal microenvironment, providing a promising way for multifunctional textiles.

Quasi-Homogeneous and Hierarchical Electronic Textiles with Porosity-Hydrophilicity Dual-Gradient for Unidirectional Sweat Transport, Electrophysiological Monitoring, and Body-Temperature Visualization

On-skin electronics based on impermeable elastomers and stacking structures often suffer from inferior sweat-repelling capabilities and severe mechanical mismatch between sub-layers employed, which significantly impedes their lengthy wearing comfort and functionality. Herein, inspired by the transpiration system of vascular plants and the water diode phenomenon, a hierarchical nonwoven electronic textile (E-textile) with multi-branching microfibers and robust interlayer adhesion is rationally developed. The layer-by-layer electro-airflow spinning method and selective oxygen plasma treatment are utilized to yield a porosity-hydrophilicity dual-gradient. The resulting E-textile shows unidirectional, nonreversible, and anti-gravity water transporting performance even upon large-scale stretching (250%), excellent mechanical matching between sub-layers, as well as a reversible color-switching ability to visualize body temperature. More importantly, the conducting and skin-conformal E-textile demonstrates accurate and stable detecting capability for biomechanical and bioelectrical signals when applied as an on-skin bioelectrode, including different human activities, electrocardiography, electromyogram, and electrodermal activity signals. Further, the E-textile can be efficiently implemented in human-machine interfaces to build a gesture-controlled dustbin and a smart acousto-optic alarm. Hence, this hierarchically-designed E-textile with integrated functionalities offers a practical and innovative method for designing comfortable and daily applicable on-skin electronics.

2D bimetallic organic framework nanosheets for high-performance wearable power source and real-time monitoring of glucose

Diabetics often prick their fingertips to measure the glucose levels in their blood. However, this traditional method not only causes prolonged pain but also increases the risk of infection. Hence, in this study, a non-invasive flexible glucose biosensor with high sensitivity was fabricated. Specifically, NiCo metal-organic frameworks (NiCo-MOFs) served as the electrode material of a micro-supercapacitor and sensing material of a glucose sensor. The electrochemical tests verified that the prominent sensitivity of the NiCo bimetal product is 1422.2 μA mM^-1 cm^-2. The micro-supercapacitor based on the as-fabricated NiCo-MOFs showed a high energy density of 11.5 mW h cm^-2 at the power density 0.26 mW cm^-2. In addition, the as-designed glucose device exhibited an excellent sensitivity of 0.31 μA μM^-1. Furthermore, a flexible energy storage and glucose detection system was successfully prepared by further integrating the micro-supercapacitor and glucose sensor. The smart detector could accurately and conveniently measure the glucose concentration in sweat in real-time. Therefore, the wearable real-time sensing device displays feasible application for non-invasive glucose monitoring and health management.

Flexible Sweat Sensors: From Films to Textiles

Flexible sweat sensors have found widespread potential applications for long-term wear and tracking and real-time monitoring of human health. However, the main substrate currently used in common flexible sweat sensors is thin film, which has disadvantages such as poor air permeability and the need for additional wearables. In this Review, the recent progress of sweat sensors has been systematically summarized by the types of monitoring methods of sweat sensors. In addition, this Review introduces and compares the performance of sweat sensors based on thin film and textile substrates such as fiber/yarn. Finally, opportunities and suggestions for the development of flexible sweat sensors are presented by summarizing the integration methods of sensors and human body monitoring sites.

Electrochemical-based remote biomarker monitoring: Toward Internet of Wearable Things in telemedicine

Internet of Wearable Things (IoWT) will be a major breakthrough for remote medical monitoring. In this scenario, wearable biomarker sensors have been developing not only to diagnose point-of-care (POC) of diseases, but also to continuously manage them. On-body tracking of biomarkers in biofluids is regarded as a proper substitution of conventional biomarker sensors for dynamic sampling and analyzing due to their high sensitivity, conformability, and affordability, creating ever-rising the market demand for them. In a wireless body area network (WBAN), data is captured from all sensors on the body to a smartphone/laptop, and sent the sensed data to a cloud for storing, processing, and retrieving, and ultimately displayed the data on custom applications (Apps). Wearable IoT biomarker sensors are used for early diseases diagnosis and continuous monitoring in developing countries in which people hardly access to healthcare systems. In this review, we aim to highlight a wide range of wearable electrochemical biomarker sensors, accompanied by microfluidics for continuous sampling, which will pave the way toward developing wearable IoT biomarker sensors to track health status. The current challenges and future perspective in skin-conformal biomarker sensors will be discussing their potential applicability for IoWT in cloud-based telemedicine.

Mechanical Janus Structures by Soft-Hard Material Integration

Engineering Janus structures that possess anisotropic features in functions have attracted growing attention for a wide range of applications in sensors, catalysis, and biomedicine, and are yet usually designed at the nanoscale with distinct physical or chemical functionalities in their opposite sides. Inspired by the seamless integration of soft and hard materials in biological structures, here a mechanical Janus structure composed of soft and hard materials with a dramatic difference in mechanical properties at an additively manufacturable macroscale is presented. In the combination of extensive experimental, theoretical, and computational studies, the design principle of soft-hard materials integrated mechanical Janus structures is established and their unique rotation mechanism is addressed. The systematic studies of assembling the Janus structure units into superstructures with well-ordered organizations by programming the local rotations are further shown, providing a direct route of designing superstructures by leveraging mechanical Janus structures with unique soft-hard material integration. Applications are conducted to demonstrate the features and functionalities of assembled superstructures with local ordered organizations in regulating and filtering acoustic wave propagations, thereby providing exemplification applications of mechanical Janus design in functional structures and devices.

Electrochemical Nanosensors for Sensitization of Sweat Metabolites: From Concept Mapping to Personalized Health Monitoring

Sweat contains a broad range of important biomarkers, which may be beneficial for acquiring non-invasive biochemical information on human health status. Therefore, highly selective and sensitive electrochemical nanosensors for the non-invasive detection of sweat metabolites have turned into a flourishing contender in the frontier of disease diagnosis. A large surface area, excellent electrocatalytic behavior and conductive properties make nanomaterials promising sensor materials for target-specific detection. Carbon-based nanomaterials (e.g., CNT, carbon quantum dots, and graphene), noble metals (e.g., Au and Pt), and metal oxide nanomaterials (e.g., ZnO, MnO2, and NiO) are widely used for modifying the working electrodes of electrochemical sensors, which may then be further functionalized with requisite enzymes for targeted detection. In the present review, recent developments (2018-2022) of electrochemical nanosensors by both enzymatic as well as non-enzymatic sensors for the effectual detection of sweat metabolites (e.g., glucose, ascorbic acid, lactate, urea/uric acid, ethanol and drug metabolites) have been comprehensively reviewed. Along with this, electrochemical sensing principles, including potentiometry, amperometry, CV, DPV, SWV and EIS have been briefly presented in the present review for a conceptual understanding of the sensing mechanisms. The detection thresholds (in the range of mM-nM), sensitivities, linear dynamic ranges and sensing modalities have also been properly addressed for a systematic understanding of the judicious design of more effective sensors. One step ahead, in the present review, current trends of flexible wearable electrochemical sensors in the form of eyeglasses, tattoos, gloves, patches, headbands, wrist bands, etc., have also been briefly summarized, which are beneficial for on-body in situ measurement of the targeted sweat metabolites. On-body monitoring of sweat metabolites via wireless data transmission has also been addressed. Finally, the gaps in the ongoing research endeavors, unmet challenges, outlooks and future prospects have also been discussed for the development of advanced non-invasive self-health-care-monitoring devices in the near future.

Flexible Textile-Based Sweat Sensors for Wearable Applications

The current physical health care system has gradually evolved into a form of virtual hospitals communicating with sensors, which can not only save time but can also diagnose a patient's physical condition in real time. Textile-based wearable sensors have recently been identified as detection platforms with high potential. They are developed for the real-time noninvasive detection of human physiological information to comprehensively analyze the health status of the human body. Sweat comprises various chemical compositions, which can be used as biomarkers to reflect the relevant information of the human physiology, thus providing references for health conditions. Combined together, textile-based sweat sensors are more flexible and comfortable than other conventional sensors, making them easily integrated into the wearable field. In this short review, the research progress of textile-based flexible sweat sensors was reviewed. Three mechanisms commonly used for textile-based sweat sensors were firstly contrasted with an introduction to their materials and preparation processes. The components of textile-based sweat sensors, which mainly consist of a sweat transportation channel and collector, a signal-selection unit, sensing elements and sensor integration and communication technologies, were reviewed. The applications of textile-based sweat sensors with different mechanisms were also presented. Finally, the existing problems and challenges of sweat sensors were summarized, which may contribute to promote their further development.

Ultra-Small Wearable Flexible Biosensor for Continuous Sweat Analysis

In the field of wearable sensing, small and precise sensors can greatly reduce the burden on the wearer and improve the sense of experience, which is the future direction of sensing development. Herein, we introduce an ultra-small wearable biosensor system that integrates an MS02 chip for real-time and highly accurate sweat detection. The whole system mainly includes flexible electrodes and a printed circle board (PCB). The size of the PCB is only 1.5 cm × 0.8 cm, which greatly minimizes the size of the sweat system and improves wearing comfort. Notably, this miniaturized system is comparable to a commercial electrochemical workstation, ensuring the reliability and accuracy of real-time analysis. The core processing MS02 chip, with a dimension of 1.2 mm × 1.1 mm, is used to perform electrochemical signal processing. By performing electrochemical characterization and measurements of the ultra-small wearable biosensor system, on-body monitoring of four biomarkers (glucose, lactate, Na⁺, and K⁺) in sweat of human volunteers has been successfully achieved. With the help of this electrochemical sensor system, mass of biochemical data from perspiration can be acquired to better understand the body's response to daily activities, which will facilitate the early prediction of abnormal physiological changes in the future.

Perspiration-Wicking and Luminescent On-Skin Electronics Based on Ultrastretchable Janus E-Textiles

Stretchable electronics have attracted surging attention for next-generation smart wearables, yet traditional flexible devices fabricated on hermetical elastic substrates cannot satisfy lengthy wearing comfort and signal stability due to their poor moisture and air permeability. Herein, perspiration-wicking and luminescent on-skin electrodes are fabricated on superelastic nonwoven textiles with a Janus configuration. Through the electrospin-assisted face-to-face assembly of all-SEBS microfibers with differentiated diameters and composition, porosity and wettability asymmetry are constructed across the textile, endowing it with antigravity water transport capability for continuous sweat release. Also, the phosphor particles evenly encapsulated in the elastic fibers empower the Janus textile with stable light-emitting capability under extreme stretching in a dark environment. Additionally, the precise printing of highly conductive liquid metal (LM) circuits onto the matrix not only equips the electronic textile with broad detectability for various biophysical and electrophysiological signals but also enables successful implementation of human-machine interface (HMIs) to control a mechanical claw.

Utilizing Gradient Porous Graphene Substrate as the Solid-Contact Layer To Enhance Wearable Electrochemical Sweat Sensor Sensitivity

Wearable sweat monitoring represents an attractive opportunity for personalized healthcare and for evaluating sports performance. One of the limitations with such monitoring, however, is water layer formation upon cycling of ion-selective sensors, leading to degraded sensitivity and long-term instability. Our report is the first to use chemical vapor deposition-grown, three-dimensional, graphene-based, gradient porous electrodes to minimize such water layer formation. The proposed design reduces the ion diffusion path within the polymeric ion-selective membrane and enhances the electroactive surface for highly sensitive, real-time detection of Na⁺ ions in human sweat with high selectivity. We obtained a 7-fold enhancement in electroactive surface against 2D electrodes (e.g., carbon, gold), yielding a sensitivity of 65.1 ± 0.25 mV decade^-1 (n = 3, RSD = 0.39%), the highest to date for wearable Na⁺ sweat sensors. The on-body sweat sensing performance is comparable to that of ICP-MS, suggesting its feasibility for health evaluation through sweat.

Silk-Based Electrochemical Sensor for the Detection of Glucose in Sweat

The development of reliable glucose sensors for noninvasive monitoring is highly desirable and essential for diabetes detection. As a testing sample, sweat is voluminous and is easy to collect compared to blood. However, the application of sweat glucose sensors is generally limited because of their low stability and sensitivity compared to commercial glucometers. In this manuscript, a silk nanofibril (SNF)/reduced graphene oxide (RGO)/glucose oxidase (GOx) composite was developed as the working electrode of the sweat glucose sensor. The SNF/RGO/GOx composite was prepared via a facile two-step process, which involved the self-assembly of SNF from silk fibroin while reducing graphene oxide to RGO and immobilizing GOx on SNF. The SNF/RGO/GOx glucose sensor exhibited a low limit of detection (300 nM) and high sensitivity (18.0 μA/mM) in the sweat glucose range, covering both healthy people and diabetic patients (0-100 μM). Moreover, the SNF/RGO/GOx glucose sensors showed a long stability for at least 4 weeks. Finally, the SNF/RGO/GOx glucose sensor was applied to test the actual sweat samples from two volunteers and two sweating methods (by dry sauna and exercise). The results indicate the glucose data tested by the SNF/RGO/GOx glucose sensor were reliable, which correlated well to the data obtained from the commercial glucometer. Therefore, the SNF/RGO/GOx glucose sensor developed in this study may have a great potential for glucose control in personalized healthcare monitoring and chronic disease management.

Wireless Wearable Electrochemical Sensing Platform with Zero-Power Osmotic Sweat Extraction for Continuous Lactate Monitoring

Wearable and wireless monitoring of biomarkers such as lactate in sweat can provide a deeper understanding of a subject's metabolic stressors, cardiovascular health, and physiological response to exercise. However, the state-of-the-art wearable and wireless electrochemical systems rely on active sweat released either via high-exertion exercise, electrical stimulation (such as iontophoresis requiring electrical power), or chemical stimulation (such as by delivering pilocarpine or carbachol inside skin), to extract sweat under low-perspiring conditions such as at rest. Here, we present a continuous sweat lactate monitoring platform combining a hydrogel for osmotic sweat extraction, with a paper microfluidic channel for facilitating sweat transport and management, a screen-printed electrochemical lactate sensor, and a custom-built wireless wearable potentiostat system. Osmosis enables zero-electrical power sweat extraction at rest, while continuous evaporation at the end of a paper channel allows long-term sensing from fresh sweat. The positioning of the lactate sensors provides near-instantaneous sensing at low sweat volume, and the custom-designed potentiostat supports continuous monitoring with ultra-low power consumption. For a proof of concept, the prototype system was evaluated for continuous measurement of sweat lactate across a range of physiological activities with changing lactate concentrations and sweat rates: for 2 h at the resting state, 1 h during medium-intensity exercise, and 30 min during high-intensity exercise. Overall, this wearable system holds the potential of providing comprehensive and long-term continuous analysis of sweat lactate trends in the human body during rest and under exercising conditions.

Surface Wettability for Skin-Interfaced Sensors and Devices

The practical applications of skin-interfaced sensors and devices in daily life hinge on the rational design of surface wettability to maintain device integrity and achieve improved sensing performance under complex hydrated conditions. Various bio-inspired strategies have been implemented to engineer desired surface wettability for varying hydrated conditions. Although the bodily fluids can negatively affect the device performance, they also provide a rich reservoir of health-relevant information and sustained energy for next-generation stretchable self-powered devices. As a result, the design and manipulation of the surface wettability are critical to effectively control the liquid behavior on the device surface for enhanced performance. The sensors and devices with engineered surface wettability can collect and analyze health biomarkers while being minimally affected by bodily fluids or ambient humid environments. The energy harvesters also benefit from surface wettability design to achieve enhanced performance for powering on-body electronics. In this review, we first summarize the commonly used approaches to tune the surface wettability for target applications toward stretchable self-powered devices. By considering the existing challenges, we also discuss the opportunities as a small fraction of potential future developments, which can lead to a new class of skin-interfaced devices for use in digital health and personalized medicine.

Development of a textile based protein sensor for monitoring the healing progress of a wound

This article focuses on the design and fabrication of flexible textile-based protein sensors to be embedded in wound dressings. Chronic wounds require continuous monitoring to prevent further complications and to determine the best course of treatment in the case of infection. As proteins are essential for the progression of wound healing, they can be used as an indicator of wound status. Through measuring protein concentrations, the sensor can assess and monitor the wound condition continuously as a function of time. The protein sensor consists of electrodes that are directly screen printed using both silver and carbon composite inks on polyester nonwoven fabric which was deliberately selected as this is one of the common backing fabric types currently used in wound dressings. These sensors were experimentally evaluated and compared to each other by using albumin protein solution of pH 7. A comprehensive set of cyclic voltammetry measurements was used to determine the optimal sensor design the measurement of protein in solution. As a result, the best sensor design is comprised of silver conductive tracks but a carbon layer as the working and counter electrodes at the interface zone. This design prevents the formation of silver dioxide and protects the sensor from rapid decay, which allows for the recording of consecutive measurements using the same sensor. The chosen printed protein sensor was able to detect bovine serum albumin at concentrations ranging from 30 to 0.3 mg/mL with a sensitivity of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.0026 \mu $$\end{document}0.0026μA/M. Further testing was performed to assess the sensor’s ability to identify BSA from other interferential substances usually present in wound fluids and the results show that it can be distinguishable.

Bioinspired superwettable electrodes towards electrochemical biosensing

Superwettable materials have attracted much attention due to their fascinating properties and great promise in several fields. Recently, superwettable materials have injected new vitality into electrochemical biosensors. Superwettable electrodes exhibit unique advantages, including large electrochemical active areas, electrochemical dynamics acceleration, and optimized management of mass transfer. In this review, the electrochemical reaction process at electrode/electrolyte interfaces and some fundamental understanding of superwettable materials are discussed. Then progress in different electrodes has been summarized, including superhydrophilic, superhydrophobic, superaerophilic, superaerophobic, and superwettable micropatterned electrodes, electrodes with switchable wettabilities, and electrodes with Janus wettabilities. Moreover, we also discussed the development of superwettable materials for wearable electrochemical sensors. Finally, our perspective for future research is presented.

An epidermal wearable microfluidic patch for simultaneous sampling, storage, and analysis of biofluids with counterion monitoring

Simultaneous access to different biofluids enables an accurate analysis of multiple analytes, leading to a precision diagnosis and appropriate medication. Additionally, establishing a relationship between various markers in different biofluids and their correlation to biomarkers in blood allows the development of an algorithmic approach, which aids non-invasive diagnosis through single parameter monitoring. However, the main bottleneck that exists in multiple biofluid analyses for its clinical implementation is the requirement of an advanced microfluidic coupled device design, which empowers simultaneous collection and monitoring. To tackle this challenge, an epidermal wearable bio-fluidic patch that facilitates simultaneous on-demand extraction, sampling, and storage of sweat and interstitial fluid (ISF) together with monitoring of their corresponding counterions is presented. The clean room free development of a biofluidic patch is realized through 3D integration of laser patterned optimized microfluidic structures, a low-cost screen-printed stimulation module, and a potentiometric chloride (Cl^-) and calcium (Ca²⁺) ion sensing module for adequate dual biofluid sampling and analysis. The developed Cl^- and Ca²⁺ ion-selective sensors exhibit good repeatability, selectivity, acceptable stability, and sensitivity. The proof-of-concept demonstration of the fabricated patch for simultaneous dual-sampling, storage, and monitoring of the sweat Cl^- and ISF Ca²⁺ on a healthy volunteer during different periods of the day leverages its potential in real-time personalized healthcare clinical usages. Furthermore, the patch's electronic interface and use of wireless transmission facilitates a point-of-care non-invasive lab-on-skin application for monitoring the health status of individuals.

Validation of the Application of Solid Contact Ion-Selective Electrode for Off-Body Sweat Ion Monitoring

The solid contact ion-selective electrode (ISE) is a promising skin-interfaced monitoring system for sweat ions. Despite a growing number of on-body usages of ISE with fancy new materials and device fabrications, there are very few reports attempting to validate ISE results with a gold standard technique. For this purpose, this work uses inductively coupled plasma-optical emission spectrometry (ICP-OES) as a reference technique to conduct a direct evaluation of the sweat sodium and potassium ion levels obtained by ISE in an off-body approach. Eight healthy male subjects were recruited to collect exercise-induced sweat. It was found that sweat sodium and potassium ions present a rather wide concentration range. The sweat sodium concentration did not vary greatly in an exercise period of half an hour, while the sweat potassium concentration typically decreased with exercise. Mineral drink intake had no clear impact on the sweat sodium level, but increased the sweat potassium level. A paired t-test and mean absolute relative difference (MARD) analysis, a method typically used for evaluating the performance of glucometers, was employed to compare the results of ISE and ICP-OES. The statistical analysis validated the feasibility of ISE for measuring sweat ions, although better accuracy is required. Our data suggests that overweight subjects are likely to possess a higher sweat sodium level.

Smart Electronic Textiles for Wearable Sensing and Display

Increasing demand of using everyday clothing in wearable sensing and display has synergistically advanced the field of electronic textiles, or e-textiles. A variety of types of e-textiles have been formed into stretchy fabrics in a manner that can maintain their intrinsic properties of stretchability, breathability, and wearability to fit comfortably across different sizes and shapes of the human body. These unique features have been leveraged to ensure accuracy in capturing physical, chemical, and electrophysiological signals from the skin under ambulatory conditions, while also displaying the sensing data or other immediate information in daily life. Here, we review the emerging trends and recent advances in e-textiles in wearable sensing and display, with a focus on their materials, constructions, and implementations. We also describe perspectives on the remaining challenges of e-textiles to guide future research directions toward wider adoption in practice.

Wearable Microfluidic Sensor for the Simultaneous and Continuous Monitoring of Local Sweat Rates and Electrolyte Concentrations

Temperature elevation due to global warming increases the risks of dehydration, which can induce heat-related illness. Proper rehydration with appropriate amounts of water and electrolytes is essential to aid body fluid homeostasis. Wearable sweat sensors which can monitor both the sweat rate and sweat electrolyte concentration may be an effective tool for determining appropriate rehydration. Here, we developed a novel potentially wearable sensor that can monitor both the local sweat rate and sweat electrolyte concentration continuously. The new device includes a system with a short microfluidic pathway that guides the sweat appearing on the skin to a small space in the device to form a quantifiable droplet. The sweat rate is assessed from the time for the droplet to appear and droplet volume, while an integrated electric sensor detects the sodium chloride concentration in each sweat droplet. We demonstrated that this new device could record both the flow rates of artificial sweat and its sodium chloride concentration in ranges of human sweating with an accuracy within ±10%. This is equivalent to the accuracy of commercially available sweat rate meters and sweat ion sensors. The present study provides a new perspective for the design of wearable sensors that can continuously monitor sweat rates and sweat electrolyte concentrations for potential application to a healthcare device.

Textile-based electrochemical sensors and their applications

Textile and their composite-based functional sensors are extensively acknowledged and preferred detection platforms in recent times. Developing suitable methodologies for fabricating textile sensors can be achieved either by integration of conductive fibers and yarns into textiles using technologies such as weaving, knitting and embroidery; or by functionalization of textile materials with conductive nanomaterials/inks using printing or coating methods. Textile materials are gaining enormous attention for fabricating soft lab-on-fabric devices due to their unique features such as high flexibility, wear and wash resistance, mechanical strength and promising sensing performances. Owing to these collective properties, textile-based electrochemical transducers are now showcasing rapid and accurate electrical measurements towards real time point-of-care diagnostics and environmental monitoring applications. The present review provides a brief overview of key progress made in the field of developing textile materials and their composites-based electrochemical sensors and biosensors in recent years where electrode configurations are specifically based on either natural or synthetic fabrics. Different ways to fabricate and functionalize textiles for their application in electrochemical analysis are briefly discussed. The review ends with a conclusive note focusing on the current challenges in the fabrication of textile-based stable electrochemical sensors and biosensors.

Photosensitive-Stamp-Inspired Scalable Fabrication Strategy of Wearable Sensing Arrays for Noninvasive Real-Time Sweat Analysis

Wearable sweat sensing is essential to the development of personalized health monitoring in a noninvasive manner with molecular-level insight. Hence, there is an increasing demand for convenient, facile, and efficient fabrication of wearable sensing arrays. Inspired by a photosensitive stamp (PS), we present herein a simple, low-cost, and eco-friendly vacuum filtration-transfer printing method (termed PS-VFTP) for the scalable preparation of single-walled carbon nanotube (SWCNT) based flexible electrode arrays. This method can economically yield customized flexible SWCNT arrays with praiseworthy performance, such as high reproducibility, precision, uniformity, conductivity, and mechanical stability. In addition, the flexible SWCNT arrays can be easily functionalized into high-performance electrochemical sensors for the simultaneous monitoring of sweat metabolites (glucose, lactate) and electrolytes (Na⁺, K⁺). The integration of wearable sensing arrays with a signal acquisition and processing circuit system in the intelligent wearable sensors empowers them to realize noninvasive, real-time, and in situ sweat analysis during exercise. More meaningfully, such a PS-VFTP strategy can be easily expanded to the economical manufacturing of other flexible electronic devices.

Dissolvable Polymer Valves for Sweat Chrono-Sampling in Wearable Paper-Based Analytical Devices

Paper sensors with colorimetric signal transduction mechanisms are promising for developing single-use wearable patches that only require a smartphone to quantify signals. However, measuring biomarker fluctuations with colorimetric wearable sensors requires implementing a chrono-sampling method for performing sequential measurements. In this article, we report on a chrono-sampling method that enables the fabrication of wearable devices made entirely of filter paper. It consists of using dried polymers as closed valves that deflect the flow of liquids to different transducers of a multisensor. As time passes by, the polymer dissolves and the valve opens. The sequential opening of the valves results in a succession of measurements that reveals fluctuations in the concentration of the target analyte. This concept was demonstrated with a paper multisensor capable of performing nine consecutive pH measurements. The device was also adapted for developing a urea biosensor that detects pH measurements generated by the hydrolysis of the analyte catalyzed by urease. The proposed analytical platform could monitor the pH of sweat with an accuracy and precision comparable to a laboratory-based method when worn during an exercise routine. The results shown here pave the way for developing colorimetric wearable biosensors that measure variations in the concentration of biomarkers such as glucose, lactate, creatinine, or uric acid over time.

Review on the Development and Application of Directional Water Transport Textile Materials

Moisture (sweat) management in textile products is crucial to regulate human thermo-physiological comfort. Traditional hydrophilic textiles, such as cotton, can absorb sweat, but they retain it, leading to undesired wet adhesion sensation and even excessive cooling. To address such issues, the development of functional textiles with directional water transport (DWT) has garnered great deal of interest. DWT textile materials can realize directional water transport and prevent water penetration in the reverse direction, which is a great application for sweat release in daily life. In this review article, the mechanism of directional water transport is analyzed. Then, three key methods to achieve DWT performance are reviewed, including the design of the fabric structure, surface modification and electrospinning. In addition, the applications of DWT textile materials in functional clothing, electronic textiles, and wound dressing are introduced. Finally, the challenges and future development trends of DWT textile materials in the textile field are discussed.

Hybrid Janus Membrane with Dual-Asymmetry Integration of Wettability and Conductivity for Ultra-Low-Volume Sweat Sensing

Highly sensitive and selective analysis of sweat at ultra-low sample volume remains a major challenge in the field of biosensing. Manipulation of small volumes of liquid for efficient sampling is essential to address this challenge. A hybrid Janus membrane with dual-asymmetry integration of wettability and conductivity is developed for regulated micro-volume liquid transport in wearable sweat biosensing. Unlike the uncontrollable liquid diffusion in a conventional porous membrane, the asymmetric wettability of porous Janus membrane leads to unique unidirectional liquid transport with high breakthrough pressure (1737.66 Pa) and fast self-pumping rate (35.94 μL/min) for micro-volume liquid sampling. The asymmetric conductive layer shows excellent flexible conductivity, anti-interference of friction, and efficient electrochemical interface due to the in situ generation of gold nanoparticles on one side of the membrane. The fabricated Pt-enzyme electrodes on the membrane promises effective testing range, great selectivity, and high sensitivity and accuracy (correlation efficiency, glucose: R² = 0.999, lactate: R² = 0.997), enabling ultra-low volume (∼0.15 μL) real time measurements on the skin surface. The innovative Janus membrane with unidirectional, self-pumping, and anti-interference performance provides a new strategy for miniaturized wearable microfluidic sweat electrochemical biosensor preparation in athletic performance evaluation, health monitoring, disease diagnosis, intelligent medicine, and so forth.

An integrated and conductive hydrogel-paper patch for simultaneous sensing of Chemical-Electrophysiological signals

Simultaneous monitoring of electrophysiological and biochemical signals is of great importance in healthcare and fitness management, while the fabrication of highly integrated and flexible devices is crucial to these applications. Herein, we devised a multifunctional and flexible hydrogel-paper patch (HPP) that was capable of simultaneously real-time monitoring of electrocardiogram (ECG) signal and biochemical signal (glucose content) in sweat during exercise. The self-assembly of the highly porous PEDOT:PSS hydrogel on paper fiber provided the HPP with good conductivity and hydrophilic wettability for efficient electron transmission and substance diffusion, thereby enabling it to serve as a low-impedance ECG electrode and a highly sensitive glucose sensor. Additionally, the spontaneous capillary flow effect allows the paper patch to be used as microfluidic channels for the collect and analysis of sweat. Moreover, the HPP is integrated with a flexible printed circuit board (FPCB) and works as a multifunctional wearable device mounted on the chest for real-time monitoring of electrophysiological and biochemical signals during exercise.

Differential Amperometric Microneedle Biosensor for Wearable Levodopa Monitoring of Parkinson's Disease

Levodopa (L-Dopa) is considered to be one of the most effective therapies available for Parkinson's disease (PD) treatment. The therapeutic window of L-Dopa is narrow due to its short half-life, and long-time L-Dopa treatment will cause some side effects such as dyskinesias, psychosis, and orthostatic hypotension. Therefore, it is of great significance to monitor the dynamic concentration of L-Dopa for PD patients with wearable biosensors to reduce the risk of complications. However, the high concentration of interferents in the body brings great challenges to the in vivo monitoring of L-Dopa. To address this issue, we proposed a minimal-invasive L-Dopa biosensor based on a flexible differential microneedle array (FDMA). One working electrode responded to L-Dopa and interfering substances, while the other working electrode only responded to electroactive interferences. The differential current response of these two electrodes was related to the concentration of L-Dopa by eliminating the common mode interference. The differential structure provided the sensor with excellent anti-interference performance and improved the sensor's accuracy. This novel flexible microneedle sensor exhibited favorable analytical performance of a wide linear dynamic range (0-20 μM), high sensitivity (12.618 nA μM^-1 cm^-2) as well as long-term stability (two weeks). Ultimately, the L-Dopa sensor displayed a fast response to in vivo L-Dopa dynamically with considerable anti-interference ability. All these attractive performances indicated the feasibility of this FDMA for minimal invasive and continuous monitoring of L-Dopa dynamic concentration for Parkinson's disease.

Lab on a body for biomedical electrochemical sensing applications: The next generation of microfluidic devices

This chapter highlights applications of microfluidic devices toward on-body biosensors. The emerging application of microfluidics to on-body bioanalysis is a new strategy to establish systems for the continuous, real-time, and on-site determination of informative markers present in biofluids, such as sweat, interstitial fluid, blood, saliva, and tear. Electrochemical sensors are attractive to integrate with such microfluidics due to the possibility to be miniaturized. Moreover, on-body microfluidics coupled with bioelectronics enable smart integration with modern information and communication technology. This chapter discusses requirements and several challenges when developing on-body microfluidics such as difficulties in manipulating small sample volumes while maintaining mechanical flexibility, power-consumption efficiency, and simplicity of total automated systems. We describe key components, e.g., microchannels, microvalves, and electrochemical detectors, used in microfluidics. We also introduce representatives of advanced lab-on-a-body microfluidics combined with electrochemical sensors for biomedical applications. The chapter ends with a discussion of the potential trends of research in this field and opportunities. On-body microfluidics as modern total analysis devices will continue to bring several fascinating opportunities to the field of biomedical and translational research applications.

Recent advancement in noninvasive glucose monitoring and closed-loop management system for diabetes

Diabetes can cause many complications, which has become one of the most common diseases that may lead to death. Currently, the number of diabetics continues increasing year by year. Thus,...

Integrated Wearable Sensors for Sensing Physiological Pressure Signals and β-Hydroxybutyrate in Physiological Fluids

Flexible and wearable sensors have attracted much attention for their applications in health monitoring and the human-machine interaction. The most studied wearable sensors have been demonstrated for sensing a limited range of metabolites such as ions, glucose, uric acid, lactate, etc. Both sweat and urine contain numerous other physiologically relevant metabolites indicative of health and wellness. This work demonstrates the use of the wearable sensor for the detection of β-hydroxybutyrate (HB) in sweat. HB is an important biomarker for diabetic ketoacidosis, a condition caused by the accumulation of ketone bodies in hyperglycemia or metabolic acidosis patients. Herein, we fabricated an integrated sensing system coupling an HB detection chamber with a serpentine electrode for sensing physiological signals such as pulse beat, vocal cord vibration, etc. The real-time HB detection was based on a β-hydroxybutyrate dehydrogenase enzymatic reaction. The stability of the enzyme and the cofactor couple was achieved by cross-linking networks and a redox mediator, thereby achieving high selectivity and low detection limits to HB in urine and sweat. The dual-functional sensor was integrated with a signal processing circuitry for signal transduction, conditioning, processing, wireless transmission, and real-time convenient health monitoring display to a smartphone via home-developed software.