Intelligent Soft Sweat Sensors for the Simultaneous Healthcare Monitoring and Safety Warning

Development of a wearable microfluidic amperometric sensor based on spatial three-electrode system for sweat glucose analysis

Most amperometric glucose sensors utilize nanomaterials to increase the surface area of the working electrode for sensitivity enhancement. However, this approach not only increases the cost and complicates the fabrication process, but also results in functional surfaces with limited durability. We propose a wearable microfluidic amperometric sensor featuring a spatially arranged three-electrode system (TES) for sweat glucose analysis. We optimize sensing electrodes' shape, size, spacing, and spatial arrangement through simulations and electrochemical measurements by comparing cyclic voltammogram behavior. The spatial TES is then designed based on the geometry of the microfluidic chamber, and the sensor is fabricated using a combination of laser cutting, screen printing, and layer-by-layer assembly techniques. The wearable microfluidic amperometric glucose sensor exhibits excellent linearity and specificity in in-vitro characterization. Additionally, it achieves comparable detection sensitivity (approximately 7.2 μA/mM) relative to sensors utilizing nanomaterials. By continuously analyzing glucose variations in sweat samples from the subject's abdomen, we validate the reliability and practicality of this device for real-time monitoring of sweat glucose.

Wearable epidermal sensor patch with biomimetic microfluidic channels for fast and time-sequence monitoring of sweat glucose and lactate

Wearable sweat sensors enable non-invasive tracking and monitoring of human physiological information, which is expected to attract wide interest and rapid development in dietary health management and disease prevention. Unfortunately, sweat sensors are limited by rapid evaporation and low secretion rates of sweat. Herein, a sweat detection patch is proposed, which integrates bionic microchannels and multiparameter electrochemical sensors. The microfluidic channel (5°), which mimics ginkgo biloba veins, provided a 40 % higher flow rate compared to the normal channel (0°). Combined with burst pressure, the bionic channel enabled unidirectional transport of 6 μL sweat, effectively avoiding the mixing of old and new sweat. The electrochemical sensors possessed excellent specificity recognition, stability and durability, and have been used to detect substances in sweat, in particular to analyze changes in glucose concentration at different dietary intakes and changes in lactate metabolism after exercise. The rapid collection effect of the microchannels on trace sweat and the fast response of sensors have broad application prospects in real-time human health monitoring.

An integrated wearable microfluidic biosensor for simultaneous detection of multiple biomarkers in sweat

Simultaneous detection of biomarkers in sweat is crucial for comprehensive health assessment and personalized monitoring. However, the low sweat secretion rate and low metabolite concentrations present challenges for developing non-invasive wearable sensors. This study aims to develop a flexible wearable biosensor for simultaneous detection of low-concentration biomarkers in sweat, enabling comprehensive health assessment. This study synthesized an innovative bimetallic tungstate Ag@Ag2WO4 and evaluated its performance for detecting uric acid (UA, 10-1000 μM), dopamine (DA, 3-500 μM), and tyrosine (Tyr, 5-1000 μM). The detection limits (LODs) for DA, UA, and Tyr sensors were 3.10 μM, 8.47 μM, and 4.17 μM, respectively, with relative standard deviations (RSDs) of 4.76 %, 2.66 %, and 3.51 %, respectively. Additionally, this study designed a hydrophilic microfluidic collection system inspired by bamboo leaf structures to enhance sweat collection efficiency. Validation studies demonstrated that the wearable biosensor effectively detects UA and TA in the sweat of volunteers. We believe this research could contribute to advancing personalized healthcare by improving the convenience and effectiveness of health monitoring technologies.

Army Ant Nest Inspired Adaptive Textile for Smart Thermal Regulation and Healthcare Monitoring

A textile material that can dynamically adapt to different environments while serving as an immediate alert system for early detection of life-threatening factors in the surroundings, not only enhances the individual's health management but also contributes to a reduction in energy consumption for space cooling and/or heating. In nature, different species have their own adaptation system to ambient temperature. Inspired by the army ant nest, herein a thermal adaptive textile known as Army ant Nest Textile (ANT) for thermal management and health monitoring is reported. This textile can promptly respond to perspiration, rapidly absorb sweat, and then transform its architecture to facilitate heat dissipation. Simultaneously, the colorimetric sensing function of ANT allows it to emulate the "site migration" behavior of the army ant nest, which empowers individuals to expeditiously identify multiple health-related signals such as body temperature, UV radiation, and sweat pH values, and warn them to move to a secure environment, thereby effectively reducing the likelihood of physical harm. Together with its excellent scalability and biocompatibility, the ANT offers a promising direction for the development of next-generation smart e-textiles for personal thermal and healthcare management, while satisfying the growing demand for energy saving.

A flexible, water anchoring, and colorimetric ionogel for sweat monitoring

As water-saturated polymer networks, the easy water loss of hydrogels directly affects their end-use applications. Minimizing the ratio of free water and increasing the ratio of bound water in the gel system has become key to extending the service life. In this work, an ionogel is prepared that effectively regulates the proportion of free water and bound water through the formation of wrinkle angles by the hydrophilic and hydrophobic chains in the gel system and the non-volatile nature of the ionic liquid. Acrylamide and N-acryloyl phenylalanine are used as free radical comonomers, and phenol red is used as an acid-base indicator. The ionic liquid is used as a dispersant to stabilize the whole framework. Due to the hydrogen bonding interactions, electrostatic interactions, and ion-ion interactions, the ionogel exhibits good stretchability, adhesion, pH sensitivity, and stability. The ionogel can be stretched in multiple directions without cracking and can be bent 180° after being left in air for 45 days. Assembling the ionogel into a wearable device can effectively monitor the pH value of sweat during exercise. The detection results are displayed in the form of RGB values, providing a preliminary diagnosis of the health of the human body.

Miniaturized, portable gustation interfaces for VR/AR/MR

Gustation is one of the five innate sensations for humans, distinguishing from vision, auditory, tactile, and olfaction, as which is a close and chemically induced sense. Despite the fact that a handful of gustation display technologies have been developed, the new technologies still pose significant challenges in miniaturization of the overall size for portability, enriching taste options within a limited working area, supporting natural human-device interaction, and achieving precisely controlled taste feedback. To address these issues, here, we report a set of intelligent and portable lollipop-shaped taste interfacing systems covering from 2 to 9 different taste options for establishing an adjustable taste platform in virtual reality (VR), augmented reality (AR), and mixed reality (MR) environments. Tasteful and food-grade chemicals embedded agarose hydrogels serve as taste sources based on iontophoresis operation principle, with an adjustable feedback intensity and independent operation time by tuning the voltage input. To achieve portability and user-friendly operation, the devices are miniaturized into a gustation interface with 9-channel taste generators in the dimension of 8 cm × 3 cm × 1 cm. To realize both gustation and olfaction feedbacks in Metaverse, an olfaction interface based on 7-channel odor generators is also introduced into the gustation interface system. As a result, the demonstrations of our gustation interface systems in intelligent medical gustation assessment, remote shopping, and mixed reality have proven their advances and great progress in various potential application areas, ranging from human-machine interfaces, to biomedical science, and to entertainment.

A wearable non-enzymatic sensor for continuous monitoring of glucose in human sweat

To enhance personalized diabetes management, there is a critical need for non-invasive wearable electrochemical sensors made from flexible materials to enable continuous monitoring of sweat glucose levels. The main challenge lies in developing glucose sensors with superior electrochemical characteristics and high adaptability. Herein, we present a wearable sensor for non-enzymatic electrochemical glucose analysis. The sensor was synthesized using hydrothermal and one-pot preparation methods, incorporating gold nanoparticles (AuNPs) functionalized onto aminated multi-walled carbon nanotubes (AMWCNTs) as an efficient catalyst, and crosslinked with carboxylated styrene butadiene rubber (XSBR) and PEDOT:PSS. The sensors were then integrated onto screen-printed electrodes (SPEs) to create flexible glucose sensors (XSBR-PEDOT:PSS-AMWCNTs/AuNPs/SPE). Operating under neutral conditions, the sensor exhibits a linear range of 50 μmol/L to 600 μmol/L, with a limit of detection limit of 3.2 μmol/L (S/N = 3), enabling the detection of minute glucose concentrations. The flexible glucose sensor maintains functionality after 500 repetitions of bending at a 180° angle, without significant degradation in performance. Furthermore, the sensor exhibits exceptional stability, repeatability, and resistance to interference. Importantly, we successfully monitored changes in sweat glucose levels by applying screen-printed electrodes to human skin, with results consistent with normal physiological blood glucose fluctuations. This study details the fabrication of a wearable sensor characterized by ease of manufacture, remarkable flexibility, high sensitivity, and adaptability for non-invasive blood glucose monitoring through non-enzymatic electrochemical analysis. Thus, this streamlined fabrication process presents a novel approach for non-invasive, real-time blood glucose level monitoring.

Development and Application of IoT Monitoring Systems for Typical Large Amusement Facilities

The advent of internet of things (IoT) technology has ushered in a new dawn for the digital realm, offering innovative avenues for real-time surveillance and assessment of the operational conditions of intricate mechanical systems. Nowadays, mechanical system monitoring technologies are extensively utilized in various sectors, such as rotating and reciprocating machinery, expansive bridges, and intricate aircraft. Nevertheless, in comparison to standard mechanical frameworks, large amusement facilities, which constitute the primary manned electromechanical installations in amusement parks and scenic locales, showcase a myriad of structural designs and multiple failure patterns. The predominant method for fault diagnosis still relies on offline manual evaluations and intermittent testing of vital elements. This practice heavily depends on the inspectors' expertise and proficiency for effective detection. Moreover, periodic inspections cannot provide immediate feedback on the safety status of crucial components, they lack preemptive warnings for potential malfunctions, and fail to elevate safety measures during equipment operation. Hence, developing an equipment monitoring system grounded in IoT technology and sensor networks is paramount, especially considering the structural nuances and risk profiles of large amusement facilities. This study aims to develop customized operational status monitoring sensors and an IoT platform for large roller coasters, encompassing the design and fabrication of sensors and IoT platforms and data acquisition and processing. The ultimate objective is to enable timely warnings when monitoring signals deviate from normal ranges or violate relevant standards, thereby facilitating the prompt identification of potential safety hazards and equipment faults.

Wearable Sensors for Physiological Condition and Activity Monitoring

Rapid technological advancements have transformed the healthcare sector from traditional diagnosis and treatment to personalized health management. Biofluids such as teardrops, sweat, interstitial fluids, and exhaled breath condensate offer a rich source of metabolites that can be linked to the physiological status of an individual. More importantly, these biofluids contain biomarkers similar to those in the blood. Therefore, developing sensors for the noninvasive determination of biofluid-based metabolites can overcome traditionally invasive and laborious blood-test-based diagnostics. In this context, wearable devices offer real-time and continuous physiological conditions and activity monitoring. The first-generation wearables included wristwatches capable of tracking heart rate variations, breathing rate, body temperature, stress responses, and sleeping patterns. However, wearable sensors that can accurately measure the metabolites are needed to achieve real-time analysis of biomarkers. In this review, recent progresses in wearable sensors utilized to monitor metabolites in teardrops, breath condensate, sweat, and interstitial fluids are thoroughly analyzed. More importantly, how metabolites can be selectively detected, quantified, and monitored in real-time is discussed. Furthermore, the review includes a discussion on the utility of, multifunctional sensors that combine metabolite sensing, human activity monitoring, and on-demand drug delivery system for theranostic applications.

Soft Sensors and Actuators for Wearable Human-Machine Interfaces

Haptic human-machine interfaces (HHMIs) combine tactile sensation and haptic feedback to allow humans to interact closely with machines and robots, providing immersive experiences and convenient lifestyles. Significant progress has been made in developing wearable sensors that accurately detect physical and electrophysiological stimuli with improved softness, functionality, reliability, and selectivity. In addition, soft actuating systems have been developed to provide high-quality haptic feedback by precisely controlling force, displacement, frequency, and spatial resolution. In this Review, we discuss the latest technological advances of soft sensors and actuators for the demonstration of wearable HHMIs. We particularly focus on highlighting material and structural approaches that enable desired sensing and feedback properties necessary for effective wearable HHMIs. Furthermore, promising practical applications of current HHMI technology in various areas such as the metaverse, robotics, and user-interactive devices are discussed in detail. Finally, this Review further concludes by discussing the outlook for next-generation HHMI technology.

Triboelectric Nanogenerator Enabled Sweat Extraction and Power Activation for Sweat Monitoring

Wearable sweat sensors can detect and monitor various substances in sweat, providing valuable information for healthcare monitoring and clinical diagnostics. Recent advances in flexible electronic technologies have enabled the development of wearable sweat sensors that can measure sweat rate and biochemical substances in real time, although several challenges remain, such as power management and sweat extraction issues. Here, a passive sweat extraction strategy as well as a self‐powered monitoring system (SEMS) is reported to be designed for sedentary individuals, i.e., elders. The SEMS system comprises a wearable triboelectric nanogenerator (TENG) for sweat extraction, a sweat‐activated battery (SAB) as the integrated power source, carbachol‐loaded iontophoresis electrodes for sweat extraction, microfluidics with biosensors for detecting physiological information in sweat, and near field communication (NFC)‐based wireless microelectronics for data communication, processing, and collection. By tapping the TENG, sedentary people can passively extract sweat based on the iontophoresis process, allowing the sensors to detect biological information in sweat. The good flexibility of the SEMS device enables real‐time and non‐invasive detection of sweat analytes in a wearable format. This system offers a new strategy of sweat collection and analysis for the elderly group, and therefore can help to understand human physiology and personalize health monitoring deeply.

Skin-Attachable Ink-Dispenser-Printed Paper Fluidic Sensor Patch for Colorimetric Sweat Analysis

In situ analysis of sweat biomarkers potentially provides noninvasive lifestyle monitoring and early diagnosis. Quantitative detection of sweat rate is crucial for thermoregulation and preventing heat injuries. Here, a skin-attachable paper fluidic patch is reported for in situ colorimetric sensing of multiple sweat markers (pH, glucose, lactate, and uric acid) with concurrent sweat rate tracking. Two sets of fluidic patterns-multiplexed detection zones and a longitudinal sweat rate channel-are directly printed by an automated ink dispenser from a specially developed ceramic-based ink. The ceramic ink thermal-cures into an impervious barrier, confining sweat within the channels. The ceramic-ink-printed boundary achieves higher pattern resolution, prevents fluid leakage, attains pattern thermal stability, and resistant to organic solvents. The cellulose matrix of the detection zones is modified with nanoparticles to improve the color homogeneity and sweat sensor sensitivity. The sweat rate channel is made moisture sensitive by incorporating a metal-salt-based dye. The change in saturation/color of the detection zones and/or channels upon sweat addition can be visually detected or quantified by a smartphone camera. A cost-effective way is provided to fabricate paper fluidic sensor patches, successfully demonstrating on-body multiplexed evaluation of sweat analytes. Such skin wearables offer on-site analysis, meaningful to an increasingly health-conscious population.

Biofluid-Activated Biofuel Cells, Batteries, and Supercapacitors: A Comprehensive Review

Recent developments in wearable and implanted devices have resulted in numerous, unprecedented capabilities that generate increasingly detailed information about a user's health or provide targeted therapy. However, options for powering such systems remain limited to conventional batteries which are large and have toxic components and as such are not suitable for close integration with the human body. This work provides an in-depth overview of biofluid-activated electrochemical energy devices, an emerging class of energy sources judiciously designed for biomedical applications. These unconventional energy devices are composed of biocompatible materials that harness the inherent chemistries of various biofluids to produce useable electrical energy. This work covers examples of such biofluid-activated energy devices in the form of biofuel cells, batteries, and supercapacitors. Advances in materials, design engineering, and biotechnology that form the basis for high-performance, biofluid-activated energy devices are discussed. Innovations in hybrid manufacturing and heterogeneous integration of device components to maximize power output are also included. Finally, key challenges and future scopes of this nascent field are provided.