Wearable Temperature Sensor with High Resolution for Skin Temperature Monitoring

Square-shaped Cu2MoS4 loaded on three-dimensional flower-like AgBiS2 to form S-scheme heterojunction as a light-driven photoelectrochemical sensor for efficient detection of serotonin in biological samples

Serotonin (5-HT) is a crucial neurotransmitter in the body, with its levels being particularly significant for life safety. Here, we designed the AgBiS2/Cu2MoS4 S-scheme heterojunction by uniformly immobilizing lamellar Cu2MoS4 on the surface of three-dimensional (3D) flower-like AgBiS2 using a simple physical mixing technique. In this case, AgBiS2 and Cu2MoS4 are bonded together by electrostatic attraction to form an active surface with a large specific surface area. Subsequently, the detector 5-HT bound to AgBiS2/Cu2MoS4/GCE undergoes hole oxidation and the photocurrent signal increases significantly. Meanwhile, the reaction mechanism of AgBiS2/Cu2MoS4 composite material was investigated through density functional theory calculations. The AgBiS2/Cu2MoS4/GCE sensor demonstrates a low detection limit of 0.046 nM and a wide linear range (0.0001-8 μM). Furthermore, by comparing UV-Vis spectrophotometry and fluorescence spectroscopy for the detection of 5-HT in human serum, it was proved that the sensor has an impressive recovery rate.

Smart Textiles for Personalized Sports and Healthcare

Advances in wearable electronics and information technology drive sports data collection and analysis toward real-time visualization and precision. The growing pursuit of athleticism and healthy life makes it appealing for individuals to track their real-time health and exercise data seamlessly. While numerous devices enable sports and health monitoring, maintaining comfort over long periods remains a considerable challenge, especially in high-intensity and sweaty sports scenarios. Textiles, with their breathability, deformability, and moisture-wicking abilities, ensure exceptional comfort during prolonged wear, making them ideal for wearable platforms. This review summarized the progress of research on textile-based sports monitoring devices. First, the design principles and fabrication methods of smart textiles were introduced systematically. Textiles undergo a distinctive fiber-yarn-fabric or fiber-fabric manufacturing process that allows for the regulation of performance and the integration of functional elements at every step. Then, the performance requirements for precise sports data collection of smart textiles, including main vital signs, joint movement, and data transmission, were discussed. Lastly, the applications of smart textiles in various sports scenarios are demonstrated. Additionally, the review provides an in-depth analysis of the emerging challenges, strategies, and opportunities for the research and development of sports-oriented smart textiles. Smart textiles not only maintain comfort and accuracy in sports, but also serve as inexpensive and efficient information-gathering terminals. Therefore, developing multifunctional, cost-effective textile-based systems for personalized sports and healthcare is a pressing need for the future of intelligent sports.

A Sensor-Based Classification for Neuromotor Robot-Assisted Rehabilitation

Neurological diseases leading to motor deficits constitute significant challenges to healthcare systems. Despite technological advancements in data acquisition, sensor development, data processing, and virtual reality (VR), a suitable framework for patient-centered neuromotor robot-assisted rehabilitation using collective sensor information does not exist. An extensive literature review was achieved based on 124 scientific publications regarding different types of sensors and the usage of the bio-signals they measure for neuromotor robot-assisted rehabilitation. A comprehensive classification of sensors was proposed, distinguishing between specific and non-specific parameters. The classification criteria address essential factors such as the type of sensors, the data they measure, their usability, ergonomics, and their overall impact on personalized treatment. In addition, a framework designed to collect and utilize relevant data for the optimal rehabilitation process efficiently is proposed. The proposed classifications aim to identify a set of key variables that can be used as a building block for a dynamic framework tailored for personalized treatments, thereby enhancing the effectiveness of patient-centered procedures in rehabilitation.

Humidity- and Temperature-Sensing Properties of 2D-Layered Tungsten Di-Selenide (2H-WSe2) Electroconductive Coatings for Cotton-Based Smart Textiles

Electroconductive textiles (e-Textiles) are vital in developing wearable sensors that preserve the comfort and characteristics of textiles. Among two-dimensional (2D) transition metal dichalcogenides (TMDs), considered a promising option for sensor applications, tungsten di-selenide (WSe2) homostructures have been used as humidity- and temperature-sensing materials for developing e-textiles, as mentioned in a first-of-its-kind report. Exfoliated chemical vapor deposition (CVD)-grown 2H-WSe2 nanosheets were dispersed in hydroalcoholic solutions using an amino-functionalized silane to improve dispersion. Acrylic thickener was added to create 2H-WSe2-based pastes, which were applied onto cotton using the knife-over-roll technique to obtain thin, flexible electroconductive coatings on textiles. Various characterization techniques confirmed the even distribution of 2D-WSe2-based coatings on fabrics and the maintenance of textile comfort and wearability. The conductivity of coated fabrics was measured at room temperature and ranged between 2.9 × 108 and 1.6 × 109 Ω sq-1. The WSe2-based textile sensors functioned well as resistance humidity detectors within 30-90% relative humidity (RH), revealing good repeatability and sensitivity after multiple exposure cycles. To a lesser extent, WSe2-based textile sensors act as temperature detectors within 20-60 °C with limited repeatability. The 2D-based textiles exhibited a quadratic dependence of resistance on temperature and a characteristic thermal hysteresis. This proposed strategy marks a significant milestone in developing scalable and flexible 2D TMD-based detectors with great potential for wearable sensing devices.

Continuous Core Body Temperature Monitoring for Heatstroke Alert via a Wearable In-Ear Thermometer

Heatstroke, a global concern exacerbated by climate change, poses significant health risks, potentially leading to multiorgan damage and fatalities. Core body temperature (CBT) is a critical and precise indicator of heatstroke, and its continuous monitoring could serve as a pivotal tool for early detection. Traditional CBT measurements, often invasive (e.g., surgical intubation, rectal or oral placement), and disrupt daily activities, whereas existing wearable devices predominantly measure skin temperatures which is susceptible to ambient environment, thus unreliable for heatstroke alert. To overcome these limitations, this study introduces an innovative in-ear wearable device to measure CBT via the cochlea, which allows for accurate CBT monitoring and timely heatstroke alerts during activities in high-temperature and high-humidity environments. The device comprises a negative temperature coefficient (NTC) thermometer integrated into a flexible precision circuit (FPC), a compact Bluetooth module, an 8 mA h micro battery, and a biocompatible, low-stimulus silica gel casing. With dimensions of 27 mm × 18 mm and a maximum in-ear diameter of 5 mm, weighing just 1.3 g, the device offers high portability and comfort, with a continuous operational lifespan of at least 24 h postcharging. A complementary software system facilitates continuous CBT monitoring, heatstroke alerts, and device management. Preliminary human trials demonstrate the device's accuracy in CBT measurement, rivaling that of rectal thermometry, and superior to the performance of surface body temperature measurement at different body parts. Long-term experiments affirm the device's efficacy in detecting rapid CBT escalations, enabling timely preventive measures against heatstroke.

Polymer-Layered Optical Wearable (PLOW) for Healthcare Applications: Temperature and Stretching Monitoring

Thermal and stretching characteristics are crucial variables in healthcare, robotics, and human-machine interaction applications. Here, we present a single-mode fiber-based, balloon-shaped, single- and dual polymer-layered optical wearable (PLOW) system that can sense both temperature and stretching. These two types of PLOWs are compared in terms of their detection performance across all criteria. Dual polymer-based systems have a substantial temperature sensitivity of -1.39 nm/°C, while single polymer ones show a sensitivity of -0.18 nm/°C. The increased sensitivity is attributed to the higher thermo-optic coefficient of the bipolymer (polymer jacket and PDMS) encasing. In terms of stretching sensing, single PLOWs beat dual ones for both longitudinal and lateral stretching due to the large change in shape variable at the same extrusion pressure in single PLOWs. The fast temporal response, high-temperature tolerance, long-term stability, and stretching sensitivity of both PLOWs make them ideal for real-time monitoring of skin temperature, wrist pulse, voice recognition, and different mechanical stimuli. These measures are critical for correctly assessing invasive human health parameters. We believe that these technologies will hold tremendous promise in wearable optical systems, with applications ranging from healthcare to humanoid robotics.

Emerging Wearable Acoustic Sensing Technologies

Sound signals not only serve as the primary communication medium but also find application in fields such as medical diagnosis and fault detection. With public healthcare resources increasingly under pressure, and challenges faced by disabled individuals on a daily basis, solutions that facilitate low-cost private healthcare hold considerable promise. Acoustic methods have been widely studied because of their lower technical complexity compared to other medical solutions, as well as the high safety threshold of the human body to acoustic energy. Furthermore, with the recent development of artificial intelligence technology applied to speech recognition, speech recognition devices, and systems capable of assisting disabled individuals in interacting with scenes are constantly being updated. This review meticulously summarizes the sensing mechanisms, materials, structural design, and multidisciplinary applications of wearable acoustic devices applied to human health and human-computer interaction. Further, the advantages and disadvantages of the different approaches used in flexible acoustic devices in various fields are examined. Finally, the current challenges and a roadmap for future research are analyzed based on existing research progress to achieve more comprehensive and personalized healthcare.

Revolutionizing human healthcare with wearable sensors for monitoring human strain

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

Validation of a Wearable Sensor Prototype for Measuring Heart Rate to Prescribe Physical Activity: Cross-Sectional Exploratory Study

BACKGROUND

Wearable sensors are rapidly evolving, particularly in health care, due to their ability to facilitate continuous or on-demand physiological monitoring.

OBJECTIVE

This study aimed to design and validate a wearable sensor prototype incorporating photoplethysmography (PPG) and long-range wide area network technology for heart rate (HR) measurement during a functional test.

METHODS

We conducted a transversal exploratory study involving 20 healthy participants aged between 20 and 30 years without contraindications for physical exercise. Initially, our laboratory developed a pulse wearable sensor prototype for HR monitoring. Following this, the participants were instructed to perform the Incremental Shuttle Walk Test while wearing the Polar H10 HR chest strap sensor (the reference for HR measurement) and the wearable sensor. This test allowed for real-time comparison of HR responses between the 2 devices. Agreement between these measurements was determined using the intraclass correlation coefficient (ICC3.1) and Lin concordance correlation coefficient. The mean absolute percentage error was calculated to evaluate reliability or validity. Cohen d was used to calculate the agreement's effect size.

RESULTS

The mean differences between the Polar H10 and the wearable sensor during the test were -2.6 (95% CI -3.5 to -1.8) for rest HR, -4.1 (95% CI -5.3 to -3) for maximum HR, -2.4 (95% CI -3.5 to -1.4) for mean test HR, and -2.5 (95% CI -3.6 to -1.5) for mean recovery HR. The mean absolute percentage errors were -3% for rest HR, -2.2% for maximum HR, -1.8% for mean test HR, and -1.6% for recovery HR. Excellent agreement was observed between the Polar H10 and the wearable sensor for rest HR (ICC3.1=0.96), mean test HR (ICC3.1=0.92), and mean recovery HR (ICC3.1=0.96). The agreement for maximum HR (ICC3.1=0.78) was considered good. By the Lin concordance correlation coefficient, the agreement was found to be substantial for rest HR (rc=0.96) and recovery HR (rc=0.96), moderate for mean test HR (rc=0.92), and poor for maximum HR (rc=0.78). The power of agreement between the Polar H10 and the wearable sensor prototype was large for baseline HR (Cohen d=0.97), maximum HR (Cohen d=1.18), and mean recovery HR (Cohen d=0.8) and medium for mean test HR (Cohen d= 0.76).

CONCLUSIONS

The pulse-wearable sensor prototype tested in this study proves to be a valid tool for monitoring HR at rest, during functional tests, and during recovery compared with the Polar H10 reference device used in the laboratory setting.

Wearable Aptasensors

This Perspective explores the revolutionary advances in wearable aptasensor (WA) technology, which combines wearable devices and aptamer-based detection systems for personalized, real-time health monitoring. The devices leverage the specificity and sensitivity of aptamers to target specific molecules, offering broad applications from continuous glucose tracking to early diagnosis of diseases. The integration of data analytics and artificial intelligence (AI) allows early risk prediction and guides preventive health measures. While challenges in miniaturization, power efficiency, and data security persist, these devices hold significant potential to democratize healthcare and reshape patient-doctor interactions.

Capturing forceful interaction with deformable objects using a deep learning-powered stretchable tactile array

Capturing forceful interaction with deformable objects during manipulation benefits applications like virtual reality, telemedicine, and robotics. Replicating full hand-object states with complete geometry is challenging because of the occluded object deformations. Here, we report a visual-tactile recording and tracking system for manipulation featuring a stretchable tactile glove with 1152 force-sensing channels and a visual-tactile joint learning framework to estimate dynamic hand-object states during manipulation. To overcome the strain interference caused by contact with deformable objects, an active suppression method based on symmetric response detection and adaptive calibration is proposed and achieves 97.6% accuracy in force measurement, contributing to an improvement of 45.3%. The learning framework processes the visual-tactile sequence and reconstructs hand-object states. We experiment on 24 objects from 6 categories including both deformable and rigid ones with an average reconstruction error of 1.8 cm for all sequences, demonstrating a universal ability to replicate human knowledge in manipulating objects with varying degrees of deformability.

One-Dimensional Flexible Capacitive Sensor with Large Strain and High Stability for Human Motion Monitoring

Flexible capacitive sensors have attracted the attention of researchers owing to their simple structure, ease of realization, and wearability. Currently, flexible capacitive sensors mainly have three-dimensional and two-dimensional structures, which are subject to several limitations in their applications. A low-cost, high-efficiency, and continuously processable process was used to wrap nylon DTY (PA) filaments on the surface of silver-coated nylon (SCN) core yarns and impregnate them with waterborne polyurethane (WPU) to obtain SCN/PA/WPU composite yarns, which were then utilized in the design of SCN/PA/WPU for the preparation of one-dimensionally structured flexible capacitive sensors. The morphology and mechanical properties of the SCN core yarn, SCN/PA wrapped yarn, and SCN/PA/WPU composite yarn were characterized. The strain-sensing performance of the sensor was analyzed, and the sensor was used to monitor human physiological activities. The sensor exhibited excellent strain capacitance sensing performance with a strain range of up to 140%. With a gauge factor of 0.66 at 10% tensile strain, it can detect strains as low as 1% and has good repeatability, withstanding more than 3200 tensile-unload cycles at 80% strain. The one-dimensional structure sensor can be used to monitor the large-scale movements of joints and muscles in various parts of the human body and the physiological signals of tiny human movements, such as breathing, coughing, and facial expressions, which have potential applications in the fields of sports monitoring and smart wearable.

Heat source recognition sensor mimicking the thermosensation function of human skin

The human skin maintains a comfortable and healthy somatosensory state by sensing different aspects of the thermal environment, including temperature value, heat source, energy level, and duration. However, state-of-the-art thermosensors only measure basic temperature values, not the full range of the thermosensation function of human skin. Here, we propose a heat source recognition (hsr) sensor of poly(butyl acrylate)-lithium bis(n-fluoroalkylsulfonyl)imide (PBA-Li:nFSI; n = 1, 3, 5), which enables response to temperature, pressure, and proximity stimulus signals based on the relaxation behavior of the ionic gel and distinguished between different types of heat sources (i.e., radiation, convection, and conduction). The hsr sensor was integrated into a prosthetic limb covered by an e-skin with isothermal regulation, and experiments with a robot showed that it could achieve human-like thermosensation function, recognizing multidimensional information about thermal environments, such as temperature value, comfort level, and heat source signal. This work deeply mimics the human body's thermosensation function and provides a reliable solution for the development of bionic e-skin for intelligent robots and prosthetics.

Infrared Thermometry and Thermography in Detecting Skin Temperature Variations to Predict Venous Leg Ulcer Reulceration: A Case Report

BACKGROUND

We aimed to determine whether monitoring skin temperature (Tsk) over recently healed venous leg ulcers (VLUs) can provide an objective approach to predicting reulceration. The cases presented in this article were part of a larger, multisite, 6-month randomized clinical trial of a cooling intervention to prevent ulcer recurrence among patients with chronic venous disease (CVD) and with recently healed VLUs.

CASES

We report a series of four patients with CVD, three experienced VLU reulceration, and one case remained free of recurrence. Assessments of recurrence likelihood is based on daily patient Tsk self-reports using a handheld infrared (IR) thermometer and clinic visits using a combination digital and long-wave IR camera. All three cases with reulceration demonstrate a persistent 2°C above baseline average Tsk increase and a "dip-and-spike" pattern from -3°C to +5°C for several days prior to reulceration. In contrast, the patient who remained free of VLU recurrence showed a stable pattern of Tsk with minimal daily fluctuations. Thermal images showed Tsk of the affected extremity is warmer compared with the contralateral limb and increased between visits when ulcers recurred.

CONCLUSION

Using IR devices to monitor Tsk among patients with CVD at risk of reulceration is an objective and reliable approach to detect changes over time. Consistent Tsk elevation over the affected area as compared to the contralateral limb and a "dip-and-spike" pattern may predict reulceration. Infrared devices showed effectiveness in detecting changes indicative of Tsk changes in recently healed leg skin over scar tissue after VLU healing.

Recent Advances in Flexible Temperature Sensors: Materials, Mechanism, Fabrication, and Applications

Flexible electronics is an emerging and cutting-edge technology which is considered as the building blocks of the next generation micro-nano electronics. Flexible electronics integrate both active and passive functions in devices, driving rapid developments in healthcare, the Internet of Things (IoT), and industrial fields. Among them, flexible temperature sensors, which can be directly attached to human skin or curved surfaces of objects for continuous and stable temperature measurement, have attracted much attention for applications in disease prediction, health monitoring, robotic signal sensing, and curved surface temperature measurement. Preparing flexible temperature sensors with high sensitivity, fast response, wide temperature measurement interval, high flexibility, stretchability, low cost, high reliability, and stability has become a research target. This article reviewed the latest development of flexible temperature sensors and mainly discusses the sensitive materials, working mechanism, preparation process, and the applications of flexible temperature sensors. Finally, conclusions based on the latest developments, and the challenges and prospects for research in this field are presented.

Ambient energy harvesters in wearable electronics: fundamentals, methodologies, and applications

In recent years, wearable sensor devices with exceptional portability and the ability to continuously monitor physiological signals in real time have played increasingly prominent roles in the fields of disease diagnosis and health management. This transformation has been largely facilitated by materials science and micro/nano-processing technologies. However, as this technology continues to evolve, the demand for multifunctionality and flexibility in wearable devices has become increasingly urgent, thereby highlighting the problem of stable and sustainable miniaturized power supplies. Here, we comprehensively review the current mainstream energy technologies for powering wearable sensors, including batteries, supercapacitors, solar cells, biofuel cells, thermoelectric generators, radio frequency energy harvesters, and kinetic energy harvesters, as well as hybrid power systems that integrate multiple energy conversion modes. In addition, we consider the energy conversion mechanisms, fundamental characteristics, and typical application cases of these energy sources across various fields. In particular, we focus on the crucial roles of different materials, such as nanomaterials and nano-processing techniques, for enhancing the performance of devices. Finally, the challenges that affect power supplies for wearable electronic products and their future developmental trends are discussed in order to provide valuable references and insights for researchers in related fields.

Flexible Sensors Based on Conductive Polymer Composites

Elastic polymer-based conductive composites (EPCCs) are of great potential in the field of flexible sensors due to the advantages of designable functionality and thermal and chemical stability. As one of the popular choices for sensor electrodes and sensitive materials, considerable progress in EPCCs used in sensors has been made in recent years. In this review, we introduce the types and the conductive mechanisms of EPCCs. Furthermore, the recent advances in the application of EPCCs to sensors are also summarized. This review will provide guidance for the design and optimization of EPCCs and offer more possibilities for the development and application of flexible sensors.

Age of Flexible Electronics: Emerging Trends in Soft Multifunctional Sensors

With the commercialization of first-generation flexible mobiles and displays in the late 2010s, humanity has stepped into the age of flexible electronics. Inevitably, soft multifunctional sensors, as essential components of next-generation flexible electronics, have attracted tremendous research interest like never before. This review is dedicated to offering an overview of the latest emerging trends in soft multifunctional sensors and their accordant future research and development (R&D) directions for the coming decade. First, key characteristics and the predominant target stimuli for soft multifunctional sensors are highlighted. Second, important selection criteria for soft multifunctional sensors are introduced. Next, emerging materials/structures and trends for soft multifunctional sensors are identified. Specifically, the future R&D directions of these sensors are envisaged based on their emerging trends, namely i) decoupling of multiple stimuli, ii) data processing, iii) skin conformability, and iv) energy sources. Finally, the challenges and potential opportunities for these sensors in future are discussed, offering new insights into prospects in the fast-emerging technology.

Ultrasensitive Flexible Temperature Sensors Based on Thermal-Mediated Ions Migration Dynamics in Asymmetrical Polymer Bilayers

Accurately acquiring crucial data on the ambient surroundings and physiological processes delivered via subtle temperature fluctuation is vital for advancing artificial intelligence and personal healthcare techniques but is still challenging. Here, we introduce an electrically induced cation injection mechanism based on thermal-mediated ion migration dynamics in an asymmetrical polymer bilayer (APB) composed of nonionic polymer and polyelectrolyte layers, enabling the development of ultrasensitive flexible temperature sensors. The resulting optimized sensor achieves ultrahigh sensitivity, with a thermal index surpassing 10,000 K-1, which allows identifying temperature differences as small as 10 mK with a sensitivity that exceeds 1.5 mK. The mechanism also enables APB sensors to possess good insensitivity to various mechanical deformations─features essential for practical applications. As a proof of concept, we demonstrate the potential impact of APB sensors in various conceptual applications, such as mental tension evaluation, biomimetic thermal tactile, and thermal radiation detection.

Ultrasensitive stretchable bimodal sensor based on novel elastomer and ionic liquid for temperature and humidity detection

In this work, we present a novel stretchable bimodal sensor that can simultaneously detect temperature and humidity changes based on poly-hydroxyethyl acrylate (PHEA) elastomer infused with 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) ionic liquid. The sensor exhibits high transparency, stability, and biocompatibility, as well as excellent mechanical and sensing properties. The sensor can achieve a maximum strain of 761%, a sensitivity of 4.5%/°C at room temperature, a detection range from -35 to 120 °C, and a response time of 10 ms. The sensor is able to provide acute response to movement of human hand at close range and can detect temperature changes as small as 0.004 °C in the range of 20-30 °C. The sensor also responds to humidity change, showing a high sensitivity to humidity change of 4.4%/RH% under the temperature of 30 °C. The sensor can be used for various applications in wearable electronics, human-machine interfaces, and soft robotics.

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.

Optimal bilayer composites for temperature-tracking wireless electronics

Modern silicone-based epidermal electronics engineered for body temperature sensing represent a pivotal development in the quest for advancing preventive medicine and enhancing post-surgical monitoring. While these compact and highly flexible electronics empower real-time monitoring in dynamic environments, a noteworthy limitation is the challenge in regulating the infiltration or obstruction of heat from the external environment into the surface layers of these electronics. The study presents a cost-effective temperature sensing solution by embedding wireless electronics in a multi-layered elastomeric composite to meet the dual needs of enhanced thermal insulation for encapsulation in contact with air and improved thermal conductivity for the substrate in contact with the skin. The encapsulating composite benefits from the inclusion of hollow silica microspheres, which reduce the thermal conductivity by 40%, while non-spherical aluminum nitride enhances the thermal conductivity of the substrate by 370%. The addition of particles to the respective composites inevitably leads to an increase in modulus. Two composite elements are engineered to coexist while maintaining a matching low modulus of 3.4 MPa and a stretchability exceeding 30%, all without compromising the optimized thermal properties. Consecutive thermal, electrical, and mechanical characterization confirms the sensor's capacity for precise body temperature monitoring during a single day's lifespan, while also assessing the influence of behavioral factors on body temperature.

Measuring the Salt Content of Sweat inside a Sweat-Absorbing Skin Adhesive

Biofluids contain a wealth of different biomarkers, and their concentrations are indicative of the state of the body. As one of those biofluids, sweat is easily accessible, and its composition can, for example, be related to particular diseases or sports performance. Due to the relatively low sweat flow rates, however, adequate sampling is paramount. Here, we aim to explore the potential use of sweat-absorbing skin adhesives as a sweat sampling system for wearable sensors with a simple construction. Upon absorption of sweat, the electrochemical properties of the skin adhesive are determined by the composition of sweat and the amount of sweat within the skin adhesive (i.e., hydration). Through the incorporation of two polarizable electrodes within the skin adhesive, its electrical properties can be monitored using impedance spectroscopy. Here, the double layer capacitance is used as an indicator of hydration, while the conductance depends on both the ion concentration and hydration (the mobility of ions). By evaluating the conductance as a function of hydration, the ion concentration within an electrolyte solution can be estimated. We demonstrate the concept based on a simple model sensor patch, which is exposed to electrolyte solutions containing various concentrations of NaCl and an artificial sweat solution. Finally, we show that ion concentrations in human sweat can be estimated when the model sensor patch is worn during exercise.

An Antisweat Interference and Highly Sensitive Temperature Sensor Based on Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) Fiber Coated with Polyurethane/Graphene for Real-Time Monitoring of Body Temperature

Body temperature is an important indicator of human health. The traditional mercury and medical electronic thermometers have a slow response (≥1 min) and can not be worn for long to achieve continuous temperature monitoring due to their rigidity. In this work, we prepared a skin-core structure polyurethane (PU)/graphene encapsulated poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) temperature-sensitive fiber in one step by combining wet spinning technology with impregnation technology. The composite fiber has high sensitivity (-1.72%/°C), super-resolution (0.1 °C), fast time response (17 s), antisweat interference, and high linearity (R2 = 0.98) in the temperature sensing range of 30-50 °C. The fiber is strong enough to be braided into the temperature-sensitive fabric with commercial cotton yarns. The fabric with good comfort and durability can be arranged in the armpit position of the cloth to realize real-time body temperature monitoring without interruption during daily activities. Through Bluetooth wireless transmission, body temperature can be monitored in real-time and displayed on mobile phones to the parents or guardians. Overall, the fiber-based temperature sensor will significantly improve the practical applications of wearable temperature sensors in intelligent medical treatment due to its sensing stability, comfort, and durability.

Self-Powered Sensing in Wearable Electronics─A Paradigm Shift Technology

With the advancements in materials science and micro/nanoengineering, the field of wearable electronics has experienced a rapid growth and significantly impacted and transformed various aspects of daily human life. These devices enable individuals to conveniently access health assessments without visiting hospitals and provide continuous, detailed monitoring to create comprehensive health data sets for physicians to analyze and diagnose. Nonetheless, several challenges continue to hinder the practical application of wearable electronics, such as skin compliance, biocompatibility, stability, and power supply. In this review, we address the power supply issue and examine recent innovative self-powered technologies for wearable electronics. Specifically, we explore self-powered sensors and self-powered systems, the two primary strategies employed in this field. The former emphasizes the integration of nanogenerator devices as sensing units, thereby reducing overall system power consumption, while the latter focuses on utilizing nanogenerator devices as power sources to drive the entire sensing system. Finally, we present the future challenges and perspectives for self-powered wearable electronics.

Advanced Textile-Based Wearable Biosensors for Healthcare Monitoring

With the innovation of wearable technology and the rapid development of biosensors, wearable biosensors based on flexible textile materials have become a hot topic. Such textile-based wearable biosensors promote the development of health monitoring, motion detection and medical management, and they have become an important support tool for human healthcare monitoring. Textile-based wearable biosensors not only non-invasively monitor various physiological indicators of the human body in real time, but they also provide accurate feedback of individual health information. This review examines the recent research progress of fabric-based wearable biosensors. Moreover, materials, detection principles and fabrication methods for textile-based wearable biosensors are introduced. In addition, the applications of biosensors in monitoring vital signs and detecting body fluids are also presented. Finally, we also discuss several challenges faced by textile-based wearable biosensors and the direction of future development.

Intrinsically Stretchable Conductive Self-Healable Organogels for Strain, Pressure, Temperature, and Humidity Sensing

Intrinsically stretchable conductive self-healable organogels containing poly(lipoic acid), Al3+ ion, tannic acid, and reduced graphene oxide are produced in this report. These noncovalent networks interlocked through physical (hydrogen and coordination) bonds offered high stretchabilities and mechanical strengths as well as fast self-healing behaviors. The optimum organogel-based sensor showed outstanding pressure sensitivities (0.94 kPa-1 up to 10 and 1.07 kPa-1 for 10-50 kPa) and high strain responses (corresponding gauge factors of 1.1 and 0.4 for 0-50 and 50-100% stretching ratios). This organogel also revealed high stabilities at ambient atmosphere due to the presence of binary solvents of dimethyl sulfoxide and glycerol. Additionally, this stretchable thermistor displayed remarkable two-stage sensitivities of -2.6 and -0.4%/°C ranging over 0-30 and 30-80 °C, respectively. Besides, the signal variations of water droplet addition and removal with different temperatures were recorded by the organogel sensor to elucidate the practical applicabilities as a temperature sensor. Moreover, the organogel was utilized to demonstrate humidity sensing, where individual sensitivities of 0.89 and 0.55 were obtained in the respective relative humidity ranges of 10-30 and 40-90%. In the meanwhile, the sensor device illustrated distinct humidity signals during respiration monitoring of nose and mouth breathing detection. Accordingly, these quad-functional sensor applications in strain, pressure, temperature, and humidity detection enable this gel to act as a promising material for future multifunctional flexible electronics.

Temperature Sensors Integrated with an Electrochromic Readout toward Visual Detection

Temperature sensors have attracted great attention for personal health care and disease diagnosis in recent years. However, it is still a great challenge to fabricate reliable and highly sensitive temperature sensors that can convert physiological signals into easily readable signals in a convenient way. Herein, an integrated smart temperature sensor system based on a traditional temperature sensor and electrochromic display is proposed for real-time visual detection of temperature. Significantly, a voltage-regulated electrochromic device (ECD) based on tungsten oxide (WO3) and polyaniline (PANI) as the real-time visualization window was integrated into the platform to provide feedback on the temperature change. The ECD would change its color from green to blue based on the electrical signal of the temperature sensor, resulting in a visualized readout that can be monitored through our naked eye. Additionally, the smart temperature sensor system possesses an extremely durable property and cycle stability, remaining around 90% of the initial value even after 15,000 s continuous cycle. Thus, the novel design and low power consumption advantages make it a good candidate to pave the way for developing interactive wearable electronics and intelligent robots as real-time temperature feedback systems.

Compact Vernier sensor with an all-fiber reflective scheme for simultaneous measurements of temperature and strain

We propose an all-fiber reflective sensing scheme to simultaneously measure temperature and strain. A length of polarization-maintaining fiber serves as the sensing element, and a piece of hollow-core fiber assists with introducing Vernier effect. Both theoretical deductions and simulative studies have demonstrated the feasibility of the proposed Vernier sensor. Experimental results have shown that the sensor can deliver sensitivities of -88.73 nm/°C and 1.61 nm/με for temperature and strain, respectively. Further, Both theoretical analyses and experimental results have suggested the capability of simultaneous measurement for such a sensor. Significantly, the proposed Vernier sensor not only presents high sensitivities, but also exhibits a simple structure, compact size and light weight, as well as demonstrates ease of fabrication and hence high repeatability, thus holding great promise for widespread applications in daily life and industry world.

A hybrid multifunctional physicochemical sensor suite for continuous monitoring of crop health

This work reports a first-of-its-kind hybrid wearable physicochemical sensor suite that we call PlantFit for simultaneous measurement of two key phytohormones, salicylic acid, and ethylene, along with vapor pressure deficit and radial growth of stem in live plants. The sensors are developed using a low-cost and roll-to-roll screen printing technology. A single integrated flexible patch that contains temperature, humidity, salicylic acid, and ethylene sensors, is installed on the leaves of live plants. The strain sensor with in-built pressure correction capability is wrapped around the plant stem to provide pressure-compensated stem diameter measurements. The sensors provide real-time information on plant health under different amounts of water stress conditions. The sensor suite is installed on bell pepper plants for 40 days and measurements of salicylic acid, ethylene, temperature, humidity, and stem diameter are recorded daily. In addition, sensors are installed on different parts of the same plant to investigate the spatiotemporal dynamics of water transport and phytohormone responses. Subsequent correlation and principal component analyses demonstrate the strong association between hormone levels, vapor pressure deficit, and water transport in the plant. Our findings suggest that the mass deployment of PlantFit in agricultural settings will aid growers in detecting water stress/deficiency early and in implementing early intervention measures to reduce stress-induced yield decline.

Stretchable and Skin-Mountable Temperature Sensor Array Using Reduction-Controlled Graphene Oxide for Dermatological Thermography

Since thermometry of human skin is critical information that provides important aspects of human health and physiology, accurate and continuous temperature measurement is required for the observation of physical abnormalities. However, conventional thermometers are uncomfortable because of their bulky and heavy features. In this work, we fabricated a thin, stretchable array-type temperature sensor using graphene-based materials. Furthermore, we controlled the degree of graphene oxide reduction and enhanced the temperature sensitivity. The sensor exhibited an excellent sensitivity of 2.085% °C^-1. The overall device was designed in a wavy meander shape to provide stretchability for the device so that precise detection of skin temperature could be performed. Furthermore, polyimide film was coated to secure the chemical and mechanical stabilities of the device. The array-type sensor enabled spatial heat mapping with high resolution. Finally, we introduced some practical applications of skin temperature sensing, suggesting the possibility of skin thermography and healthcare monitoring.

Tetra-Nuclear Cluster-Based Lanthanide Metal-Organic Frameworks as White Phosphor, Information Encryption, Self-Calibrating Thermometers, and Fe2+ Sensors

The application of one kind of metal-organic framework (MOF) material used in multiple fields is one of the most interesting research topics. In this work, four new tetra-nuclear cluster-based lanthanide metal-organic frameworks (LnMOFs) [Ln₂(BTDB)₃(DMA)(phen)]_n (Ln = Tb TbMOF, Eu EuMOF, Gd GdMOF, Tb_1.830Eu_0.170 Tb,EuMOF, 3,5-bis(trifluoromethyl)-4',4″-dicarboxytriphenylamine = H₂BTDB, 1,10-phenanthroline = phen) are obtained based on the ligand of H₂BTDB that is synthesized in our laboratory, and the precise single-crystal structure of H₂BTDB is obtained for the first time. The white phosphor was obtained by facilely hybridizing two components of the orange-yellow emission phosphor of Tb,EuMOF and the blue luminescence material of triphenylamine according to the trichromatic theory. At the same time, TbMOF, EuMOF, Tb,EuMOF, and the white phosphor can be used for information encryption, demonstrating their potential application in the field of anti-counterfeiting. Tb,EuMOF is also a multi-mode and self-calibrating thermometer within a broad temperature range of 110-300 K. Further studies show that EuMOF is a rapid response sensor for Fe²⁺, with a very low limit of detection of 2.0 nM, which is much lower than the national standards for Fe²⁺ (GB 5749-2005, 5.357 μM). It can achieve strong anti-interference detection of Fe²⁺ in actual samples of tap water and lake water. In addition, EuMOF can also be made into an easy-to-use sensing device of test paper for real-time and visual sensing of Fe²⁺.

A one-pot approach to prepare stretchable and conductive regenerated silk fibroin/CNT films as multifunctional sensors

Silk fibroin (SF)-based materials are characterized by their outstanding biocompatibility and biodegradability and are considered as the most promising candidates for next-generation flexible electronics. In order to generate such devices, SF can be mixed with carbon nanotubes (CNTs) which feature excellent mechanical, electrical, and thermal properties. However, obtaining regenerated SF with homogeneous dispersion of CNTs in a sustainable manner represents a challenging task, mainly due to the difficulty in overcoming van der Waals forces and strong π-π interactions that hold together the CNT structure. In this study, a one-pot strategy for fabricating SF/CNT films is proposed by designing SF as a modifier of CNTs through non-covalent interactions with the assistance of aqueous phosphoric acid solution. Glycerol (GL) was introduced, endowing the SF/GL/CNT composite film with excellent flexibility and stretchability. The sustainable strategy greatly simplifies the preparation process, avoiding dialysis of SF and the use of artificial dispersants. The as-fabricated SF/GL/CNT films showed an excellent mechanical strength of 1.20 MPa and high sensitivity with a gauge factor of up to 13.7 toward tensile deformation. The composite films had a sensitive monitoring capability for small strains with detection limits as low as 1% and can be assembled into versatile sensors to detect human movement. Simultaneously, the composite films showed a superb thermosensitive capacity (1.64% °C^-1), which satisfied the requirement of real-time and continuous skin temperature monitoring. We anticipate that the presented one-pot strategy and the prepared composite films could open a new avenue for forthcoming technologies for electronic skins, personal health monitoring, and wearable electronics.

High-stretchable, self-healing, self-adhesive, self-extinguishing, low-temperature tolerant starch-based gel and its application in stimuli-responsiveness

Starch with active hydroxyl groups is one of the most attractive carbohydrates for the preparation of gels in recent years. However, the mechanical properties, self-healing properties, self-adhesion properties, especially low-temperature resistance are generally unsatisfactory for current starch-based gels. Based on that, a multiple network structure of amylopectin-carboxymethyl cellulose-polyacrylamide (ACP) gel was prepared by a "cooking" method. Tannic acid (TA) was used to construct multiple hydrogen bonds among molecular chains. ACP gel demonstrates high elongation at break (1090 %) and strength, self-healing performance and adhesion behavior, extraordinary low-temperature resistance (-80 °C) and self-extinguishing. As a sensor device, ACP gel can effectively monitor human movements and microscopic expression changes and achieve real-time monitoring under harsh conditions (After multiple cutting-healing steps, under low-temperature conditions, even a month later). Additionally, ACP gel could be served to detect temperature changes with a wide operating range and a high sensitivity of 33 %·°C^-1, which is promising to monitor the changes in temperature. More interestingly, ACP gel can even monitor the cooking process and breathing frequency with fast response, implying applications in food processing, disease diagnosis and medical treatment. This study provides new opportunities for the design and fabrication of carbohydrate-based gels with multiple performance and multifunctional electronic devices.

Electrospinning-Based Biosensors for Health Monitoring

In recent years, many different biosensors are being used to monitor physical health. Electrospun nanofiber materials have the advantages of high specific surface area, large porosity and simple operation. These properties play a vital role in biosensors. However, the mechanical properties of electrospun nanofibers are poor relative to other techniques of nanofiber production. At the same time, the organic solvents used in electrospinning are generally toxic and expensive. Meanwhile, the excellent performance of electrospun nanofibers brings about higher levels of sensitivity and detection range of biosensors. This paper summarizes the principle and application of electrospinning technology in biosensors and its comparison with other technologies.