Monitoring Of Physiological Activity Research Articles

Regulating Water Activity and Solvation Structure via Zwitterion‐Enhanced Polymer Electrolyte for Long‐Life Zn‐Ion Hybrid Capacitors with Low‐Temperature Applicability

AbstractThe development of aqueous Zn‐based energy storage systems is plagued by poor cyclability and limited operating temperatures caused by Zn anode issues and highly active water. Herein, a frost‐tolerant hydrogel electrolyte (PABCHE) promoted by hydroxyl‐rich β‐cyclodextrin (β‐CD) and zwitterionic betaine (BA) additives is fabricated in situ to protect Zn anodes and enhance low‐temperature adaptability. Both additives synergistically disrupt the hydrogen‐bonding network between water molecules to remarkably reduce the freezing point of PABCHE and alleviate water‐associated side effects. Zwitterionic BA constructs ion‐migration channels and regulate Zn2+ solvation structure, promoting uniform and rapid transport of Zn2+. Additionally, PABCHE renders the Zn2+ homoepitaxially depositing along the (002) plane to achieve dendrite‐free Zn anodes. As a result, versatile PABCHE enables Zn//Zn cells to cycle stably for 1100 and 3600 h at 20 and −20 °C, respectively. Furthermore, the Zn‐ion hybrid capacitors optimized by PABCHE deliver favorable cyclability over 30000 cycles at 20 °C (with a capacity retention of 81.8%) and −20 °C (with a capacity retention of 84.2%). Additionally, PABCHE can be applied as a flexible strain sensor for real‐time monitoring of physiological activities. This work offers valuable insights for developing antifreeze hydrogel electrolytes toward applications of dendrite‐free low‐temperature Zn‐based devices and strain sensors.

Bioinspired High-Linearity, Wide-Sensing-Range Flexible Stretchable Bioelectronics Based on MWCNTs/GR/Nd2Fe14B/PDMS Nanocomposites for Human-Computer Interaction and Biomechanics Detection.

In recent years, flexible and stretchable strain sensors have emerged as a prominent area of research, primarily due to their remarkable stretchability and extremely low strain detection threshold. Nevertheless, the advancement of sensors is currently constrained by issues such as complexity, high costs, and limited durability. To tackle the aforementioned issues, this study introduces a lepidophyte-inspired flexible, stretchable strain sensor (LIFSSS). The stretchable bioelectronics composites were composed of multiwalled carbon nanotubes, graphene, neodymium iron boron, and polydimethylsiloxane. Unique biolepidophyted microstructures and magnetic conductive nanocomposites interact with each other through synergistic interactions, resulting in the effective detection of tensile strain and magnetic excitation. The LIFSSS exhibits a 170% tensile range, a linearity of 0.99 in 50-170% strain (0.96 for full-scale range), and a fine durability of 7000 cycles at 110% tensile range. The sensor accurately detects variations in linear tensile force, human movement, and microexpressions. Moreover, LIFSSS demonstrates enhanced efficacy in sign language recognition for individuals with hearing impairments and magnetic grasping for robotic manipulators. Hence, the LIFSSS proposed in this study shows potential applications in various fields, including bioelectronics, electronic skin, and physiological activity monitoring.

Wireless Sensor System Based on Organohydrogel Ionic Skin for Physiological Activity Monitoring.

Supermolecular hydrogel ionic skin (i-skin) linked with smartphones has attracted widespread attention in physiological activity detection due to its good stability in complex scenarios. However, the low ionic conductivity, inferior mechanical properties, poor contact adhesion, and insufficient freeze resistance of most used hydrogels limit their practical application in flexible electronics. Herein, a novel multifunctional poly(vinyl alcohol)-based conductive organohydrogel (PCEL5.0%) with a supermolecular structure was constructed by innovatively employing sodium carboxymethyl cellulose (CMC-Na) as reinforcement material, ethylene glycol as antifreeze, and lithium chloride as a water retaining agent. Thanks to the synergistic effect of these components, the PCEL5.0% organohydrogel shows excellent performance in terms of ionic conductivity (1.61 S m-1), mechanical properties (tensile strength of 70.38 kPa and elongation at break of 537.84%), interfacial adhesion (1.06 kPa to pig skin), frost resistance (-50.4 °C), water retention (67.1% at 22% relative humidity), and remoldability. The resultant PCEL5.0%-based i-skin delivers satisfactory sensitivity (GF = 1.38) with fast response (348 ms) and high precision under different deformations and low temperature (-25 °C). Significantly, the wireless sensor system based on the PCEL5.0% organohydrogel i-skin can transmit signals from physiological activities and sign language to a smartphone by Bluetooth technology and dynamically displays the status of these movements. The organohydrogel i-skin shows great potential in diverse fields of physiological activity detection, human-computer interaction, and rehabilitation medicine.

Effect of Ambient Temperature on Impedance-Based Physiological Activity Evaluation of Zelkova Tree

A system has been developed to remotely, continuously, and quantitatively measure the physiological activity of trees. The developed tree physiological activity monitoring (TPAM) system is equipped with electrical impedance, temperature, and light intensity measurement functions. In the two-contact impedance measurement method used in the previous plant impedance measurement, errors due to the polarization impedance of the electrodes could not be avoided. The developed TPAM system adopted a four-contact measurement method that could avoid polarization impedance errors, and, with it, the long-term monitoring of zelkova trees was performed. The monitoring of seasonal changes was conducted from July to November, and an impedance change pattern that repeated on a daily basis was observed in the short term, and an overall increase in the impedance was observed in the long term. Impedance changes related to daily temperature changes were observed even after all the tree leaves had fallen, meaning that this effect should be excluded when using impedance to evaluate tree vitality. For this reason, the influence of temperature fluctuations was excluded by using only the impedance values at the same daily temperature of 25 degrees from July to November. The analysis results at 25 degrees showed that the tree impedance value increased linearly by 8.7 Ω per day. The results of this series of long-term monitoring and analysis revealed that the ambient temperature must be taken into account in the evaluation of tree physiological activity based on electrical impedance.

Performance Optimization of Ionic Polymer Sensors through Characteristic Regulation of Chemically Prepared Interfacial Electrodes.

Ionic polymer sensors (IPSs) have broad application prospects in health monitoring, environmental perception, and human-computer interaction. The performance of IPSs with chemically prepared electrodes is generally superior to that with physically prepared electrodes due to the area difference of the electric double layer (EDL), but the effects of the electrode characteristics prepared by chemical methods on the performance of IPSs have not been revealed. Therefore, in this paper, we studied the impact of the characteristics of chemically prepared electrodes on the performance of IPSs and realized the performance optimization of IPSs through electrode characteristic regulation. By controlling the matrix surface roughening, immersion reduction plating (IRP) cycles, and electroplating (EP) time, the sensing performances of IPS samples with different electrode interface roughnesses, electrode penetration depths, and surface resistances were investigated, respectively. The experimental results indicated that the response voltage of the IPS can be improved by increasing the electrode interface roughness and the electrode penetration depth and reducing the surface resistance. In addition, we have proven that the sensing performance of the IPS is determined by its intrinsic capacitance characteristics. Through coupling electrode characteristic regulations such as roughening and increasing IRP cycles and EP time, a high-performance IPS was obtained, and its response amplitude was improved by 237.8%. The obtained high-performance sensor has been applied in human motion detection, which has good potential to develop wearable devices with high stability for physiological activity monitoring.

Skin‐customized wearable device adhesive without skin damage

AbstractWearable medical devices are gaining popularity owing to their potential for seamless integration with the human body and long‐term monitoring of physiological activity. However, conventional adhesives were developed based on the assumption of healthy adult skin and may not account for variations in skin characteristics across different species, environments, and body parts. Consequently, the adhesive strength of wearable devices may significantly differ depending on the skin surface to which they are attached, potentially causing skin damage. In this study, we developed a customized wearable‐device adhesive without skin damage by analyzing the characteristics of the skin surface based on oil and water content and roughness according to different species and parts. Our findings demonstrated that increased root‐mean‐square roughness of the skin surface led to reduced contact area and decreased adhesion force between the polydimethylsiloxane (PDMS) pad and skin surface. Surprisingly, hairless skin exhibited 1.5 times higher adhesion strength than hairy skin due to stronger molecular forces resulting from the higher surface energy of the skin. Additionally, the hole‐patterned PDMS pad on sweaty skin displayed improved adhesion properties compared to the cylinder‐patterned PDMS pad. Therefore, customized wearable adhesives provide an effective strategy for developing skin‐damage‐free wearable devices.

A Review on Knitted Flexible Strain Sensors for Human Activity Monitoring

AbstractThe recent surge in using wearable personalized devices has made it increasingly important to flexible textile‐based sensors that can be worn comfortably and can sense various body strains. Among them, the knit‐based flexible strain sensors (KFSS) show growing promise for human activity monitoring applications due to its processing flexibility, low cost, wearing comfortability, large strain performance, and high elastic recovery rate. Herein, five sensing mechanisms of knitted flexible strain sensors containing contact resistance, length resistance, tunneling effect, micro‐crack propagation, and disconnection mechanism are summarized, which can be used on different human activity strain conditions, e.g., physiological activities and limb activities. The main fabrication approaches, including knitting techniques, post‐processing techniques, embroidery, and sewing techniques are discussed. Six crucial parameters with corresponding calculation formulas for evaluating sensing performance and review specific applications of KFSS for human limb activity and physiological activity monitoring in healthcare, motion tracking, safety protection, and human–machine interaction are also described. Finally, the tough challenges and prospects of KFSS with the aim of providing meaningful guidance and direction for future research are critically analyzed.

Synthesis and characteristics of BaYF5:Yb3+, Er3+@BaYF5 nanoparticles as a new near-infrared fluorescence bioimaging probe

Fluorescent bioimaging technology has been widely used in clinic because of its high sensitivity, quick feedback, and no radiation. Among them, NIR-II imaging has lower absorption, tissue scattering, self-fluorescence, and higher signal-to-noise ratio. As a precursor of nanoprobe, BaYF5 is an excellent material due to its low phonon energy, which makes it easy to achieve rare earth ion energy level transition and obtain strong upconversion luminescence. A near-infrared II (NIR-II) rare earth fluoride nanoparticle (NP) BaYF5 : Yb3 + , Er3 + @ BaYF5 has been constructed. The luminescence principle of the material was deeply analyzed, and the influence of different doping ion ratio on fluorescence intensity was explored. Finally, the optimal doping ratio for this matrix material was obtained. In addition, according to the surface properties of the materials, the water solubility and biocompatibility of the NPs were significantly improved by the modification. Our work also systematically tested and analyzed the cytotoxicity, hematotoxicity, and tissue toxicity of the NPs and finally realized the high-resolution fluorescence imaging in living mice. This NP can be used as an effective and safe NIR-II contrastive agent, which provides the possibility for the detection and monitoring of physiological activity under deep tissue in vivo.

Self-powered biocompatible humidity sensor based on an electrospun anisotropic triboelectric nanogenerator for non-invasive diagnostic applications

The development of innovative devices that enables real-time monitoring of physiological activities and environmental conditions for healthcare applications has gained momentum in recent years. However, it is still a challenge to fabricate a self-sustainable wearable device with inherent comfort, long-time wearing and electrostatic discharge (EDS) safety for the monitoring of human-status. Herein, we developed a self-powered humidity sensor using an electrospun anisotropic triboelectric nanogenerator (A-TENG) composed of aligned MXene nanofibers (NFs) and cellulose acetate (CA) NFs. Importantly, such developed anisotropic structure of TENG exhibits its potential in sensitive moisture detection upon fast adsorption/desorption of water molecules due to increased pore length of prepared NFs. Moreover, it also benefits the device in reducing the EDS risks based on the working orientation of A-TENG. The practical application of detecting the skin moisture using finger-tapping is also demonstrated. Furthermore, CA NFs render superior antibacterial performance due to the high release of loaded copper nanoparticles at targeted skin surfaces, enabling long-time wearability of A-TENG. The above findings suggest that the highly ordered alignment of collected NFs is found to be favorable for the development of future-generation wearable devices.

An ultra-thin transparent multi-functional sensor based on silk hydrogel for health monitoring

With the gradual improvement of people’s health awareness, wearable devices occupy an important position in daily health care and human physiological activity monitoring. As traditional silicon-based electronic products face problems such as interface mismatch, silk fibroin has gradually become an alternative choice for next-generation wearable electronic devices due to its excellent performance. Herein, an ultra-thin transparent and flexible multi-functional sensor based on silk hydrogel with self-patterned microstructure is proposed. The silk hydrogel exhibits superior transparency (>82%) and thin thickness (∼100 μm). Furthermore, the self-patterned microstructure on the silk hydrogel surface is beneficial for the high sensitivity of pressure sensing response (1.6 kPa−1). This device exhibits advantageous performance on temperature (top sensitivity of 6.25% °C−1) and humidity (top sensitivity of 0.16% RH−1) sensing response. It also shows fast response (0.16 s) and durable stability (over 2000 dynamic cycles). Moreover, this device can be applied to monitor human facial expression, joint movements, temperature change, breathing and other health indicators. It is worth mentioning that this multi-functional sensor can monitor the signal of breathing and throat, so it can be applied to the clinical physiological activity monitoring of patients with upper respiratory tract infection. In addition, we also demonstrate a grasping and relaxing experiment of intelligent manipulator to verify the pressure and temperature sensing performance, providing a possibility for its application in the field of prosthetics. According to these advantages, the reported ultra-thin transparent multi-functional sensor based on silk hydrogel has broad prospects in the fields of health monitoring, intelligent prosthetics, and electronic skin, etc.

Recent advances in flexible and soft gel-based pressure sensors

Gels, as typical flexible and soft materials, possess the intrinsic merits of transparent bionic structures, superior mechanical properties and excellent elasticity and viscosity. Recently, gel-based materials have attracted significant attention as a result of their broad and promising applications in biomedical, energy storage, light emission, actuator, military and aerospace devices, especially the intelligent sensing for human-related applications. Among the various flexible and soft pressure sensors, gel-based ones have been gradually studied as an emerging hot research topic. This review focuses on the latest findings in the rapidly developing field of gel-based pressure sensors. Firstly, the classification and properties of the three types of gels and their corresponding fabrication methods are introduced. Secondly, the four basic working principles of pressure sensors are summarized with a comparison of their advantages and disadvantages, followed by an introduction to the construction of pressure sensors based on gel structures. Thirdly, the latest representative research on the three types of gel-based materials towards various wearable sensing applications, including electronic skin, human motion capture, healthcare and rehabilitation, physiological activity monitoring and human-machine interactions, is comprehensively reviewed. Finally, a summary of the remaining challenges and an outline of the development trend for this field are presented.

Highly Responsive Asymmetric Pressure Sensor Based on MXene/Reduced Graphene Oxide Nanocomposite Fabricated by Laser Scribing Technique

Flexible pressure sensors play a vital role in wearable devices, human physiological activity monitoring, smart robots and other fields. However, current flexible piezoresistive sensors typically have the disadvantages of complex preparation processes, inability to take into account sensitivity and pressure response range, and poor cycle stability. Herein, a novel flexible asymmetric pressure sensor has been proposed by adjusting sensing material and optimizing the structure of electrode. As a crucial piezoresistive material, MXene/reduced graphene oxide (MXene/rGO) nanocomposite with a layer by layer stacked structure is developed by an efficient and precise one-step laser scribing technology. Benefit from this designed layer by layer crosslinked structure, the proposed flexible MXene/rGO asymmetric pressure sensor exhibits excellent pressure-sensing performances, such as high sensitivity of 2.25 kPa^&#x2212;1 (0 &#x2013; 200 Pa), low detection limit of about 2.5 Pa, fast responsive recovery, and long cycle durability. So that our flexible MXene/rGO asymmetric pressure sensor can detect subtle body physiological motions in real time, such as wrist pulse, vocal vibration, finger movement, and breath. Additionally, the as-prepared sensor array integrated by <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> identical MXene/rGO asymmetric pressure sensors exhibits good multi-touch function. Therefore, such conspicuous sensing performances endow our MXene/rGO asymmetric pressure sensor for widespread practical applications in future flexible wearable electronics.

All-Fabric Ultrathin Capacitive Sensor with High Pressure Sensitivity and Broad Detection Range for Electronic Skin.

Flexible pressure sensors have emerged as an indispensable part of wearable devices due to their application in physiological activity monitoring. To realize long-term on-body service, they are increasingly required for properties of conformability, air permeability, and durability. However, the enhancement of sensitivity remains a challenge for ultrathin capacitive sensors, particularly in the low-pressure region. Here, we introduced a highly sensitive and ultrathin capacitive pressure sensor based on a breathable all-fabric network with a micropatterned nanofiber dielectric layer, an all-fabric capacitive sensor (AFCS). This all-fabric network endows a series of exceptional performances, such as high sensitivity (8.31 kPa-1 under 1 kPa), ultralow detection limit (0.5 Pa), wide detection range (0.5 Pa to 80 kPa), and excellent robustness (10 000 dynamic cycles). Besides, the all-fabric structure provides other properties for the AFCS, e.g., high skin conformability, super thinness (dozens of micrometers), and exceptional air permeability. Our AFCS shows promising potential in breathing track, muscle activity detection, fingertip pressure monitoring, and spatial pressure distribution, paving way for comfortable skinlike epidermal electronics.

Novel multi-walled carbon nanotubes-embedded laser-induced graphene in crosslinked architecture for highly responsive asymmetric pressure sensor

Flexible and wearable pressure sensors are attracting a considerable interest for the essential requirements of personalized health monitoring and electronic skin in next-generation electronics. However, reliable and cost-effective preparation of high-performance pressure sensors remains a challenge. Herein, a novel flexible asymmetric pressure sensor composed of multi-walled carbon nanotubes (MWCNTs) and laser-induced graphene (LIG) has been developed. The key resistance sensitive material of MWCNTs-embedded LIG (MWCNTs/LIG) with an interconnected hierarchical microstructure is fabricated by a simple, convenient and efficient laser direct writing (LDW) technique. By virtue of this designed three-dimensional crosslinked structure, MWCNTs/LIG hybrid endows the asymmetric pressure sensor with combined excellent characteristics of a high sensitivity (2.41 kPa−1), prominent detectable limit (about 1.2 Pa), very responsive recovery (2 ms), and remarkable durability (>2 000 cycles). This high-performance MWCNTs/LIG asymmetric pressure sensor can clearly detect various subtle human motions (such as breath, vocal vibration, finger movement, and wrist pulse) in real time. Moreover, the integrated MWCNTs/LIG sensory array has a very good multi-point recognition capability. Benefit from its outstanding sensing performances, the as-fabricated pressure sensor has vital inspiration for widespread practical applications in human monitoring of physiological activities, electronic skin, and other wearable fields.

A Flexible Strain Sensor Based on the Porous Structure of a Carbon Black/Carbon Nanotube Conducting Network for Human Motion Detection.

High-performance flexible strain sensors are playing an increasingly important role in wearable electronics, such as human motion detection and health monitoring, with broad application prospects. This study developed a flexible resistance strain sensor with a porous structure composed of carbon black and multi-walled carbon nanotubes. A simple and low-cost spraying method for the surface of a porous polydimethylsiloxane substrate was used to form a layer of synergized conductive networks built by carbon black and multi-walled carbon nanotubes. By combining the advantages of the synergetic effects of mixed carbon black and carbon nanotubes and their porous polydimethylsiloxane structure, the performance of the sensor was improved. The results show that the sensor has a high sensitivity (GF) (up to 61.82), a wide strain range (0%–130%), a good linearity, and a high stability. Based on the excellent performance of the sensor, the flexible strain designed sensor was installed successfully on different joints of the human body, allowing for the monitoring of human movement and human respiratory changes. These results indicate that the sensor has promising potential for applications in human motion monitoring and physiological activity monitoring.

Highly sensitive pressure sensor based on structurally modified tissue paper for human physiological activity monitoring

ABSTRACTPressure sensor has become an important part of physiological condition monitoring system because it can respond to small pressure in human activities. Tissue paper has been studied as a carrier of sensitive unit layer for pressure sensors in recent years due to its internal pore structure and wrinkle morphology of surface. In this work, the pore structure of the tissue paper is improved by the principle of hydration and destruction of hydrogen bonds. Based on flexible substrate of NaOH modified tissue paper (NMTP) with enhanced pore structure, combined with dip‐coating composite conductive filler, the pressure sensor is fabricated by sandwiching the sensitive unit between the interdigital electrode and the microdome elastomer through layer‐by‐layer assembly method. Thanks to the excellent interfacial resistance effect of porous NMTP under pressure, the sensitivity of NMTP‐based pressure sensor is as high as 37.5 kPa−1 in a pressure range of 0–2 kPa. Finally, the follow‐up studies on pressure sensors have been proven to be applicable to a variety of physiological activity such as pulse detection, respiration detection and voice recognition. The NMTP‐based sensitive unit provides alternative strategy to improve performance of pressure sensors and extends potential applications in monitoring human physiological activities. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48973.

GPS-based analysis of physical activities using positioning and heart rate cycling data

This paper addresses the use of multichannel signal processing methods in analysis of heart rate changes during cycling using the global positioning system (GPS) to record the route conditions. The main objectives of this work are in monitoring of physiological activities, cycling features extraction, their classification and visualization. Real data were acquired from 41 cycling rides of the same 11.48-km long route divided into 2460 segments of approximately 60 s. The data were recorded with a varying sampling period within the range of 1–22 s depending on the route profile. The pre-processing stage included preparatory analysis, filtering and resampling of the data to a constant sampling rate. The proposed algorithm includes the evaluation of the cross-correlation between the heart rate and the altitude gradient as recorded by a GPS satellite system. A Bayesian approach was then applied to classify the cycling segment features into two classes (specifying cycling up and down) with the classification accuracy better than 93 %. A comparison with other classification methods is presented in the paper as well. The results include the following relationships: (1) the heart rate and altitude gradient, which shared a positive correlation coefficient of 0.62; (2) the heart rate and speed, which shared a negative correlation coefficient of −0.72 over all of the analysed segments; and (3) the mean heart rate change delay (6.8–11.5 s) in relation to the changes in the altitude gradients associated with cycling up and down. The paper forms a contribution to the use of computational intelligence and visualization for data processing both in cycling and fitness physical activities as well.

Non-contact, laser-based monitoring of physiological activity

Non-contact, laser-based monitoring of physiological activity

Low-power CMOS wireless MEMS motion sensor for physiological activity monitoring

In this paper, a short distance wireless sensor node "AccuMicroMotion" for physiological activity monitoring is proposed for detecting motions in six degrees of freedom. System architecture, relevant microstructures, and electronic circuits to implement the sensor node are presented. A three-axis microelectromechanical systems (MEMS) accelerometer and a z-axis gyroscope are designed and fabricated using a new deep-reactive ion-etch CMOS-MEMS process. The interface circuits, an analog-to-digital converter, and a wireless transmitter are designed using Taiwan Semiconductor Manufacturing Company 0.35-/spl mu/m CMOS process, wherein the interface circuits adopt chopper stabilization technique and can resolve a signal (dc to 1 kHz) as low as 200 nV from the microsensors; digitized outputs from the microsensors are transmitted by a 900-MHz amplitude-shift-keying radio-frequency transmitter that delivers a 2.2-mW power to a 50-/spl Omega/ antenna. The system draws an average current of 4.8 mA from a 3-V supply when six sensors are in operation simultaneously and provides an overall 60-dB dynamic range.

An automated computer-controlled gas-exchange system for continual monitoring of physiological activities in plants

A computer-controlled automated gas-exchange system was developed to perform repetitive measurements of physiological activities in intact plants. Shoot and root temperatures, flow rates, gas pressures, rates of leaf CO2 and H2O exchange, and rates of CO2 exchange, H2 evolution, and C2H2 reduction by the roots can be determined for four plants in a single experiment. The controlling computer operates 32 switches that control gas flows, sampling devices, lighting, and irrigation and it records and processes analog data from 15 measuring instruments. Rates of physiological activities are calculated automatically and results are printed and stored on diskettes for later plotting or analysis. A wide variety of experimental protocols are possible with little need for computer programming, because the system is controlled by a master program and an interactively developed file of experimental variables. The values recorded from the measuring instruments are proportional (r2 &gt; 0.999) to either independent determinations or to calibration standards and the rates of physiological processes, measured with the system, are reproducible and within expected ranges.