Materials with Tunable Optical Properties for Wearable Epidermal Sensing in Health Monitoring

Tuning the Photochromism of Spiropyran in Functionalized Nanoporous Silica Nanoparticles for Dynamic Anticounterfeiting Applications

Here, we report a novel invisible ink with different decay times based on thin films with different molar ratios of spiropyran (SP)/Si, which allows the encryption of messages over time. Nanoporous silica has been found to be an excellent substrate to improve the solid photochromism of spiropyran, but the hydroxyl groups of silica have a serious effect on fade speeds. The density of silanol groups in silica has an influence on the switching behavior of spiropyran molecules, as they stabilize the amphiphilic merocyanine isomers and thus slow down the fading process from the open to the closed form. Here, we investigate the solid photochromic behavior of spiropyran by sol-gel modification of the silanol groups and explore its potential application in UV printing and dynamic anticounterfeiting. To extend its applications, spiropyran is embedded in organically modified thin films prepared by the sol-gel method. Notably, by using the different decay times of thin films with different SP/Si molar ratios, time-dependent information encryption can be realized. It provides an initial "false" code, which does not display the required information, and only after a given time will the encrypted data appear.

High-Fidelity sEMG Signals Recorded by an on-Skin Electrode Based on AgNWs for Hand Gesture Classification Using Machine Learning

The human forearm is one of the most densely distributed parts of the human body, with the most irregular spatial distribution of muscles. A number of specific forearm muscles control hand motions. Acquiring high-fidelity sEMG signals from human forearm muscles is vital for human-machine interface (HMI) applications based on gesture recognition. Currently, the most commonly used commercial electrodes for detecting sEMG or other electrophysiological signals have a rigid nature without stretchability and cannot maintain conformal contact with the human skin during deformation, and the adhesive hydrogel used in them to reduce skin-electrode impedance may shrink and cause skin inflammation after long-term use. Therefore, developing elastic electrodes with stretchability and biocompatibility for sEMG signal recording is essential for developing HMI. Here, we fabricated a nanocomposite hybrid on-skin electrode by infiltrating silver nanowires (AgNWs), a one-dimensional (1D) nano metal material with conductivity, into polydimethylsiloxane (PDMS), a silicone elastomer with a similar Young's modulus to that of the human skin. The AgNW on-skin electrode has a thickness of 300 μm and low sheet resistance of 0.481 ± 0.014 Ω/sq and can withstand the mechanical strain of up to 54% and maintain a sheet resistance lower than 1 Ω/sq after 1000 dynamic strain cycles. The AgNW on-skin electrode can record high signal-to-noise ratio (SNR) sEMG signals from forearm muscles and can reflect various force levels of muscles by sEMG signals. Besides, four typical hand gestures were recognized by the multichannel AgNW on-skin electrodes with a recognition accuracy of 92.3% using machine learning method. The AgNW on-skin electrode proposed in this study has great potential and promise in various HMI applications that employ sEMG signals as control signals.

Engineering Smart Composite Hydrogels for Wearable Disease Monitoring

Growing health awareness triggers the public's concern about health problems. People want a timely and comprehensive picture of their condition without frequent trips to the hospital for costly and cumbersome general check-ups. The wearable technique provides a continuous measurement method for health monitoring by tracking a person's physiological data and analyzing it locally or remotely. During the health monitoring process, different kinds of sensors convert physiological signals into electrical or optical signals that can be recorded and transmitted, consequently playing a crucial role in wearable techniques. Wearable application scenarios usually require sensors to possess excellent flexibility and stretchability. Thus, designing flexible and stretchable sensors with reliable performance is the key to wearable technology. Smart composite hydrogels, which have tunable electrical properties, mechanical properties, biocompatibility, and multi-stimulus sensitivity, are one of the best sensitive materials for wearable health monitoring. This review summarizes the common synthetic and performance optimization strategies of smart composite hydrogels and focuses on the current application of smart composite hydrogels in the field of wearable health monitoring.

Fast Response and Visual Transparency Switching Hydrochromic Film Based on the Rational Structure of Cellulose/Poloxamer Copolymers Design for Smart Window

The authors are motivated to develop a series of hydrochromic copolymers with fast response, reversibility, repeatability, and visual transparency transition. The hydrochromic block copolymers are based on the rational ratio of hydrophilic segments of poloxamer block and hydrophobic segments of ethyl cellulose according to the preparation method of polyurethane. By tuning the ratio of hydrophilic segments or adding hygroscopic salts, the hydrochromic polymer is endowed with the ability to visualize the transparency in response to the relative humidity. Especially, the response time of the polymer is extremely shortened, up to 1 s for the optimized sample. Within the moisture stimulation, the hygroscopic swelling increases the film thickness, leading to a reversible transparency switching from a highly transparent state (82%) to an opaque white state (20.5%).

Pruney Finger-Inspired Switchable Surface with Water-Actuated Dynamic Textures

Switchable surfaces play an important role in the development of functional materials. However, the construction of dynamic surface textures remains challenging due to the complicated structural design and surface patterning. Herein, a pruney finger-inspired switchable surface (PFISS) is developed by constructing water-sensitive surface textures on a polydimethylsiloxane substrate by taking advantage of the hygroscopicity of the inorganic salt filler and the 3D printing technology. Like human fingertips, the PFISS shows high water sensitivity with obvious surface variation in wet and dry states, which is actuated by water absorption-desorption of the hydrotropic inorganic salt filler. Besides, when the fluorescent dye is optionally added into the matrix of the surface texture, water-responsive fluorescent emitting is observed, providing a feasible surface-tracing strategy. The PFISS shows effective regulation of the surface friction and performs a good antislip effect. The reported synthetic strategy for the PFISS offers a facile way for building a wide range of switchable surfaces.

Construction of Wash-Resistant Photonic Crystal-Coated Fabrics based on Hydrogen Bonds and a Dynamically Cross-Linking Double-Network Structure

Structural coloration as the most possible way to realize the ecofriendly dying process for textiles or fabrics has attracted significant attention in the past decades. However, photonic crystals (PCs) are a typical example of materials with structural color usually located on the surface of the fabrics or textiles, which make them not stable when rubbed, bent, or washed due to the weak interaction between the PC coatings and fabrics. Here, double networks were constructed between the PC coatings and the fabrics for the first time via a hydrogen bond by introducing tannic acid (TA) and dynamic cross-linking with 2-formylphenylboronic acid to increase the wash resistance of the structural colored fabrics. On modifying the monodispersed SiO₂ nanoparticles, poly(dimethylsiloxane), and the fabrics, the interaction between the PC coatings and the fabrics increased by the formation of double networks. The structural color, wash, and rub resistance of the PC-coated fabrics were systematically studied. The obtained fabrics with the TA content at 0.030% (SiDT30) showed the best wash and rub resistance. The construction of double networks not only improved the wash and rub resistance of PCs but also retained the bright structural color of the PC coatings, facilitating the practical application of structural coloration in the textile industry.

Carbon Quantum Dot/Chitosan-Derived Hydrogels with Photo-stress-pH Multiresponsiveness for Wearable Sensors

In recent years, hydrogels have attracted extensive attention in smart sensing owing to their biocompatibility and high elasticity. However, it is still a challenge to develop hydrogels with excellent multiple responsiveness for smart wearable sensors. In this paper, a facile synthesis of carbon quantum dots (CQDs)-doped cross-linked chitosan quaternary/carboxymethylcellulose hydrogels (CCCDs) is presented. Designing of dual network hydrogels decorated with CQDs provides abundant crosslinking and improves the mechanical properties of the hydrogels. The hydrogel-based strain sensor exhibits excellent sensitivity (gauge factor: 9.88), linearity (R² : 0.97), stretchable ability (stress: 0.67 MPa; strain: 404%), good cyclicity, and durability. The luminescent properties are endowed by the CQDs further broaden the application of hydrogels for realizing flexible electronics. More interestingly, the strain sensor based on CCCDs hydrogel demonstrates photo responsiveness (ΔR/R₀ ≈20%) and pH responsiveness (pH range ≈4-7) performance. CCCDs hydrogels can be used for gesture recognition and light sensing switch. As a proof-of-concept, a smart wearable sensor is designed for monitoring human activities and detecting pH variation in human sweat during exercise. This study reveals new possibilities for further applications in wearable health monitoring.

Structurally colored aramid fabric construction and its application as a recyclable photonic catalyst

Structural colors can be used in fabric coloring due to their bright color and non-fading properties. However, it is still a challenge to construct structural color on high crystallinity, smooth surfaced and yellow colored aramid fabrics. Herein, for the first time, photonic crystals (PCs) with structural color were constructed on aramid fabrics by introducing dopamine to modify aramid fabrics and synthesizing monodisperse high refractive index zinc sulfide nanoparticles (ZnS). The influence of the PC coatings on the structural color, mechanical properties, and thermal stability of the structurally colored aramid fabrics or fibers was further investigated. Moreover, due to the excellent catalytic properties of ZnS and the slow photon effects of PCs, the structurally colored fabrics showed good photocatalytic properties, which will be beneficial in reusing the catalysts, which is crucial to their application in the coloring of fabrics but also facilitates the recycling of waste PC coated aramid fabrics.

Wearable Hydrogel-Based Epidermal Sensor with Thermal Compatibility and Long Term Stability for Smart Colorimetric Multi-Signals Monitoring

Hydrogel-based wearable epidermal sensors (HWESs) have attracted widespread attention in health monitoring, especially considering their colorimetric readout capability. However, it remains challenging for HWESs to work at extreme temperatures with long term stability due to the existence of water. Herein, a wearable transparent epidermal sensor with thermal compatibility and long term stability for smart colorimetric multi-signals monitoring is developed, based on an anti-freezing and anti-drying hydrogel with high transparency (over 90% transmittance), high stretchability (up to 1500%) and desirable adhesiveness to various kinds of substrates. The hydrogel consists of polyacrylic acid, polyacrylamide, and tannic acid-coated cellulose nanocrystals in glycerin/water binary solvents. When glycerin readily forms strong hydrogen bonds with water, the hydrogel exhibits outstanding thermal compatibility. Furthermore, the hydrogel maintains excellent adhesion, stretchability, and transparency after long term storage (45 days) or at subzero temperatures (-20 °C). For smart colorimetric multi-signals monitoring, the freestanding smart colorimetric HWESs are utilized for simultaneously monitoring the pH, T and light, where colorimetric signals can be read and stored by artificial intelligence strategies in a real time manner. In summary, the developed wearable transparent epidermal sensor holds great potential for monitoring multi-signals with visible readouts in long term health monitoring.

Portable, Automated and Deep-Learning-Enabled Microscopy for Smartphone-Tethered Optical Platform Towards Remote Homecare Diagnostics: A Review

Globally new pandemic diseases induce urgent demands for portable diagnostic systems to prevent and control infectious diseases. Smartphone-based portable diagnostic devices are significantly efficient tools to user-friendly connect personalized health conditions and collect valuable optical information for rapid diagnosis and biomedical research through at-home screening. Deep learning algorithms for portable microscopes also help to enhance diagnostic accuracy by reducing the imaging resolution gap between benchtop and portable microscopes. This review highlighted recent progress and continued efforts in a smartphone-tethered optical platform through portable, automated, and deep-learning-enabled microscopy for personalized diagnostics and remote monitoring. In detail, the optical platforms through smartphone-based microscopes and lens-free holographic microscopy are introduced, and deep learning-based portable microscopic imaging is explained to improve the image resolution and accuracy of diagnostics. The challenges and prospects of portable optical systems with microfluidic channels and a compact microscope to screen COVID-19 in the current pandemic are also discussed. It has been believed that this review offers a novel guide for rapid diagnosis, biomedical imaging, and digital healthcare with low cost and portability.

Artificial Neural Network-Assisted Wearable Flexible Sweat Patch for Drug Management in Parkinson's Patients Based on Vacancy-Engineered Processing of g-C3N4

Herein, we developed a flexible, low-cost non-enzymatic sweat sensing chip for in situ acquisition of bioinformation in sweat of individuals under exercise conditions to advance personal health monitoring and medication management for patients with Parkinson's disease. This low-cost, flexible, wearable sweat sensor consists of a printed screen electrode modified with g-C₃N₄ material and an external MSME element. The doping strategy and surface activation strategy of the g-C₃N₄-based exhibited efficient glucose oxidase-like activity and electrochemical activity when testing l-dopa and glucose in sweat. The optimized signal was transmitted to a smartphone for processing 12 individuals with simulated dosing, enabling continuous monitoring of l-dopa metabolism in sweat and management of dosing. The generalization ability and robustness of models constructed by methods such as multiple linear regression, artificial neural networks, and convolutional neural networks were compared cross-sectionally. Deep learning models based on artificial neural networks help develop a user-personalized medication administration reminder system, which provides a promising paradigm for reliable medication supervision for Parkinson's patients in the Internet of Things era.

A review on advances in the development of electrochemical sensors for the detection of anesthetic drugs

Surgeries are a crucial medical intervention that has saved countless lives from time immemorial. To reduce pain during surgeries patients are administered with anesthetic drugs, which cause loss of sensation and thus reduce the pain involved. However, anesthetists control the effects of the drug by depending on pharmacokinetic calculations, which may vary from patient to patient, thus leading to a reduction in the quality of anesthetic care and adverse effects. To avoid these adverse effects, it is highly necessary to implement a real time monitoring of plasma drug concentration, which will adjust the drug infusion and maintain the levels of drug within therapeutic levels. To implement such a system, it is highly essential to analyze current advances in electrochemical sensor systems for different types of anesthetic drugs like opioids, intravenous anesthetics, and neuromuscular blockers. This review focuses on the present strategy of electrochemical sensors implemented for the detection of anesthetic drugs and it helps towards developing a real time drug dispensing system with respect to the plasma concentration of the drug. This analysis will contribute towards establishing highly effective real time drug dispensing systems like the total intravenous anesthesia technique and patient-controlled analgesia. Such systems will lead to better usage of anesthetic drugs and improve the quality of anesthetic care thus making surgeries safer and more painless.

Electrospinning Silk Fibroin/Graphene Nanofiber Membrane Used for 3D Wearable Pressure Sensor

With the improvement of science and technology, flexible sensors have become a hot research topic. Flexible sensors have broad application in human health detection and motion detection and other fields. In this paper, the silk fibroin/graphene nanofiber membranes were prepared by double needle electrospinning. In addition, the high sensitivity of the three-dimensional composite hierarchy was obtained by superimposing a monolayer silk fibroin/graphene nanofiber membrane, which was prepared via double needle electrospinning. In addition, the three-dimensional hierarchy was encapsulated by polydimethylsiloxane to prepare a pressure sensor. The sensitivity of the pressure sensor can achieve 7.7 Pa−1. In addition, this pressure sensor has excellent durability (>2000 cycles) and shorter response times (490 ms), which has broad research prospects in human health detection and motion detection.

Wireless Stand-Alone Trimodal Interactive Display Enabled by Direct Capacitive Coupling

With recent advances in interactive displays, the development of a stand-alone interactive display with no electrical interconnection is of great interest. Here, a wireless stand-alone interactive display (WiSID), enabled by direct capacitive coupling, consisting of three layers: two in-plane metal electrodes separated by a gap, a composite layer for field-induced electroluminescence (EL) and inverse piezoelectric sound, and a stimuli-responsive layer, from bottom to top, is presented. Alternating current power necessary for field-induced EL and inverse piezoelectric sound is wirelessly transferred from a power unit, with two in-plane electrodes remotely separated from the WiSID. The unique in-plane power transfer through the stimuli-sensitive polar bridge allows stand-alone operation of the WiSID, making it suitable for the wireless dynamic monitoring of medical fluids. Moreover, a haptic wireless stand-alone trimodal interactive display mounted on a human finger is demonstrated, whereby touch is wirelessly displayed in various outputs of EL, inverse piezoelectric sound, and tactile vibration, making it suitable for a wireless three-mode smart braille display.