Monitoring Of Human Physiological Signals Research Articles

Flexible and wearable multilayer structure fiber sensor for motion and human physiological signal monitoring

AbstractThe development of flexible piezoresistive sensors has increasingly attracted widespread attention due to their various potential applications in wearable devices, human–machine interfaces, and health monitoring systems. Developing high‐performance sensors that can accurately monitor movement and human health monitoring is very necessary. This study uses silver nanoparticles, MXene, and polypyrrole to prepare conductive fabrics based on various fabrics through layer‐by‐layer encapsulation. Finally, conductive fabrics with different layers were encapsulated to prepare a multilayer fiber sensor. Next, the series piezoresistive performance of sensors made of different fabric materials and sensors with different layers were tested. The experimental results show that the sensor prepared has the best performance when the selected fabric material is mulberry silk and the number of layers of the fabric is five. After testing, the sensitivity of the sensor is 4.9029 at low strain and 0.7901 at high strain. Moreover, it exhibits good stability during 1600 compression‐release cycles and temperatures range from −20 to 60°C. The designed sensor performs well in motion and human physiological signal monitoring. This study provides new ideas and references for the design and research of multilayer fiber sensors.

A flexible sensor based on ionogel/knitted coil prepared by a simple method for accurate monitoring of human physiological signals

Flexible sensors have received increasing attention due to their various applications in health monitoring, artificial intelligence, and other fields. The simple fabrication of flexible sensing devices with high performances has been a research hotpot. In this work, an ionogel composite sensor combined with elastic knitted coil (EIC) is proposed as a wearable device to monitor human movement and related feature information. This sensor can be fabricated in a simple and easy protocol, which can work as a clothing accessary to track the wellness status parameters in daily life. After washing, the redundant gel originally embedded between the fibers was removed, improving the sensitivity of the sensor, which can provide accurate information about human joint movements and other physiological activities. The EIC sensor is in high sensitivity with superior working durability, which can provide continuous piezoresistive signals in detection mode. Other than the common joint bending movements (wrist, knee, elbow and finger) of human body, this sensor can also accurately output monitoring data on periocular, oral, and pharyngeal movements, providing information about human health status. Besides, a Morse codes transmission system can be constructed based on the piezoresistive outputs of this EIC sensor under different tapping modes, providing a new working platform in other related applications.

Waterproof strain sensor based on silver/graphene composite film for fine and large strain detection

The development of waterproof sensors with fine and large strain detection capabilities can be better applied to the monitoring of human physiological signals, such as fine physiological signals and joint activities with large amplitude. In this paper, we studied a waterproof sensor by using microstructures to improve the sensitivity of the sensor, and using graphene to bridge microcracks in the silver film, which makes the sensor has low detection limit (as low as 0.2 % strain) and large strain stability detection(up to 50 % strain) with high sensitivity (GF=1814.25, 44 %<ε < 50 %), excellent durability (1,400 dynamic responses), and water resistance(48 h). This makes it suitable for fine and large strain detection, including arterial pulse signals, vibration, and large movements of joint flexion.

Highly-sensitive ultrathin flexible pressure sensor based on quasi-2D conductive network for human physiological signal monitoring

Ultrathin flexible pressure sensors are highly desirable for human physiological signal monitoring due to their portability and ability to conform to the body. However, existing ultrathin pressure sensors face challenges in balancing the sensitivity and their range. A spatial-dimensionally constrained strategy was proposed to construct an ultrathin active layer. In detail, multi-walled carbon nanotubes (MWCNTs) with an average length of ∼1.3 μm were intentionally spin-coated into a thin thermoplastic polyurethane (TPU) film with a thickness of 1.5 μm. By doing so, a quasi-2D MWCNTs conductive network is constructed, which enabled the sensor to have ultrahigh sensitivity of 27.04 kPa−1, a wide liner detection range of 0.2–24 kPa, ultrafast response time of 40 ms and a recovery time of 10 ms, and high durability in 1500 cycles under 0.2 kPa with loading/unloading frequency of 2 Hz. Thanks to this superior performance, the ultrathin pressure sensor can be used to monitor human movement and physiological signals, including finger touch, finger bending, wrist bending, and deep breathing. Moreover, the sensor can be attached to the side wall of the tip of the renal ureteroscope, allowing for the monitoring of renal pelvic pressure. Therefore, this spatial-dimensionally constrained strategy will open up a new way to fabricate highly sensitive ultrathin pressure sensors and have great application prospects in health monitoring.

Sulfur-Functionalized Carbon Nanotubes with Inlaid Nanographene for 3D-Printing Micro-Supercapacitors and a Flexible Self-Powered Sensing System.

Digital fabrication of miniaturized micro-supercapacitors (MSCs) holds immense promise for advancing customized, integrated microelectronic systems. As potential electrode materials, carbonaceous nanomaterials, such as carbon nanotubes (CNTs), stand out due to their excellent conductivity and mechanical robustness yet suffer from low ionic storage sites, which restrict further applications. Herein, we introduce a sulfur-assisted in situ activating strategy for obtaining sulfur-functionalized carbon nanotube frameworks integrated with inlaid graphene nanosheets (S-CNT/GNS). Specifically, sulfur functionality enriches the surface charge density with improved interfacial hydrophilicity, while the inlaid nanographene sheets provide abundant ionic adsorption sites. By direct 3D printing of the S-CNT/GNS ink, planar MSCs were fabricated with desirable functionality and outstanding electrochemical performance. Notably, the developed MSCs exhibit a high areal capacitance of 0.47 F cm-2, an exceptional energy density of 64.6 μWh cm-2, and a high-power density of 34.2 mW cm-2. Furthermore, an all-flexible self-powered sensing system with photovoltaic cells and a stretchable sensor was built upon the customized S-CNT/GNS MSCs, demonstrating a highly effective capability for real-time monitoring of human physiological signals and body movements. This work not only presents a promising approach for the development of high-performance MSCs but also lays the groundwork for the creation of advanced wearable/flexible microelectronics systems.

Deep learning-assisted flexible piezoresistive sensor with liquid-phase reduced metal electrodes for fitness movement recognition and correction

Flexibility and wearability in electronic devices gain prominence with the rise of national fitness campaigns. Among them, piezoresistive sensors stand out for their ability to accurately monitor health signals due to their high sensitivity. However, conventional metal nanoparticle ink electrodes face issues like peeling, chemical instability, and substrate limitations. This study introduces a novel method for fabricating high-performance flexible piezoresistive sensors using liquid-phase reduced metal electrodes. Integration of porous polydimethylsiloxane (PDMS) substrates with highly conductive interdigital silver electrodes (1.6 × 10−6 Ω·m) addresses conventional electrode shortcomings, offering permeability, flexibility, and outstanding conductivity. Incorporation of a graphene (GR)/carbon nanotube (CNT)/Ecoflex composite enhances sensor piezoresistive sensing capabilities, with features including high sensitivity (3.57 KPa−1), rapid response time (58 ms/72 ms), and excellent cycle stability (>10000 cycles). The sensor finds utility in various applications, including human physiological signal monitoring, pressure array recognition, and handwriting recognition. Additionally, with deep learning techniques, the system achieves accurate recognition (99.25 %) and correction (98.75 %) of diverse fitness movements, aiming to promote safer exercise practices, enhance training efficiency, and advance intelligent wearable fitness devices.

Design and signal processing of plastic optical fiber respiratory sensors based on smartphones

A respiratory signal sensing scheme based on plastic optical fiber and smartphone is proposed. Respiratory signals are achieved by detecting the changes in abdominal circumference caused by the inhalation and exhalation of air from the lungs during breathing. A flexible clamp is prepared based on the 3D printing technology and the changes in abdominal circumference are leading to the lateral distance variation between the end face of the two plastic optical fibers in the clamp. The experiment demonstrates the scheme’s capability to detect a broad range of stable respiratory frequencies and weak signals. Finally, an automatic multi-scale peak detection algorithm is utilized to achieve real-time display of transient respiratory rate, which enables the timely feedback of apnea and abnormal signals. The proposed respiratory sensing system provides an efficient, accurate, convenient and low-cost solution for human physiological signal monitoring.

Simultaneously enhancing sensitivity and operation range of flexible pressure sensor by constructing a magnetic-guided microstructure in laser-induced graphene composite

Flexible pressure sensors play an essential role in the development of flexible electronic systems, which have been widely used in recent times for human activity monitoring and personal healthcare. However, possessing both high sensitivity and a wide operation range for pressure sensor remains challenging, as these requirements are commonly incompatible with each other. Herein, a magnetic induced graphene composite-based pressure sensor (MIPS) is demonstrated by integrating laser induced graphene (LIG) with a patterned valley-peak microstructure and a graphene film doped with magnetic microspheres. Owing to the synergistic effect of the 3D valley-peak microstructures and intercalation-like microstructures within the LIG composite film, the MIPS demonstrates excellent sensing performance in both sensitivity and operation range. The conductive network formed by graphene flakes improves electromechanical response capability, while the incorporation of magnetic microspheres (MMs) promotes the proliferation of conductive pathways in a small applied pressure range, and the valley-peak structure further enhances compressive strength over a large operation range. Accordingly, the MIPS exhibit excellent sensing capability over a range of 0–830 kPa, with an exceptionally high sensitivity of 4426.12 kPa−1 and excellent mechanical stability and durability (2000 cycles at a pressure of 800 kPa). Additionally, we have developed a novel pressure mapping system utilizing the MIPS array, enabling real-time monitoring of pressure spatial distribution and intensity. Notably, the MIPS array exhibits remarkable potential in diverse applications, including the monitoring of human physiological signals and movement. This pressure sensor with a hierarchically composite microstructure presents a promising candidate for the rapid advancement of next-generation wearable bioelectronics.

Self-powered motion state monitoring system based on combined triboelectric nanogenerators for human physiological signal monitoring and energy collection

The study of self-powered motion state monitoring systems based on triboelectric nanogenerators has recently received increasing attention. In this paper, we propose a self-powered system consisting of two low-cost and simply manufactured triboelectric nanogenerators for human physiological signal monitoring and energy collection. This system can monitor the trunk information and gait information during human activities, and measure human motion status in a holistic manner. The triboelectric nanogenerator, which monitors body torso information (B-TENG), we optimize its triboelectric layer through the microstructure of sandpaper to increase its contact area with the skin. In addition, by adding iron powder into the B-TENG electrode layer, the magnetic permeability of the induction electrode is increased to improve its output performance, and its maximum open-circuit voltage can reach 44.3 V. The triboelectric nanogenerator, which is installed on the foot to monitor gait information (F-TENG), can reach an average open-circuit voltage of 205.6 V by adding a rectangular protrusion structure to the triboelectric layer. In addition, due to its high output performance (∼4700 μw), the F-TENG can collect mechanical energy generated from the soles of the feet during daily human activities and charge a 100 μF capacitor to 1.4 V within 60 s, subsequently powering the miniature electronics. During foot walking, F-TENG is able to light up more than 60 light-emitting diodes. By having the experimenters wear these two triboelectric nanogenerators, we can record the frequency and amplitude signals of the experimenter's elbow, knee, breath, and gait in real time. We also monitored three running states of the human body through these two triboelectric nanogenerators, including normal state, insufficient exercise capacity, and dyspnea. We believe that this work provides a new direction for the development of big data motion analysis and self-powered smart exercise devices.

Single-point curved fiber optic pulse sensor for physiological signal prediction based on the genetic algorithm-support vector regression model

For hypertensive patients, a real-time human physiological signal monitoring system helps to track blood pressure status and provides valuable data to clinicians for early diagnosis and timely intervention. Optical fiber pulse sensing has superior conditions such as resistance to electromagnetic interference and richness of measured pulse characteristics. In this study, a monitoring system based on a single-point curved fiber pulse sensor (CFPS) was used to collect the pulse wave signal of a human radial artery. The features of the pulse wave signal were used to estimate the pulse wave transit time (PTT) and Blood Pressure—systolic blood pressure (SBP) and diastolic blood pressure (DBP)—based on support vector regression (SVR) optimized by a genetic algorithm (GA) (GA-SVR model). The results show that the root mean square error (RMSE) of SBP, DBP and PTT were 1.571 mmHg, 3.250 mmHg and 5.719 ms, respectively, and the results met the Advancement of Medical Instrumentation (AAMI) criteria. Therefore, a real-time pulse wave monitoring system based on a single-point CFPS can well predict human physiological signals such as PTT, SBP and DBP.

Flexible and Wearable Piezoresistive Sensors Based on Double Wrinkled Layers for Motion Monitoring and Human Physiological Signal Monitoring

Flexible and Wearable Piezoresistive Sensors Based on Double Wrinkled Layers for Motion Monitoring and Human Physiological Signal Monitoring

Omnidirectional Configuration of Stretchable Strain Sensor Enabled by the Strain Engineering with Chiral Auxetic Metamaterial.

An electromechanical interface plays a pivotal role in determining the performance of a stretchable strain sensor. The intrinsic mechanical property of the elastomer substrate prevents the efficient modulation of the electromechanical interface, which limits the further evolution of a stretchable strain sensor. In this study, a chiral auxetic metamaterial (CAM) is incorporated into the elastomer substrate of a stretchable strain sensor to override the deformation behavior of the pristine device and regulate the device performance. The tunable isotropic Poisson's ratio (from 0.37 to -0.25) achieved by the combination of CAM and elastomer substrate endows the stretchable strain sensor with significantly enhanced sensitivity (53-fold improvement) and excellent omnidirectional sensing ability. The regulation mechanism associated with crack propagation on the deformed substrate is also revealed with finite element simulations and experiments. The demonstration of on-body monitoring of human physiological signals and a smart training assistant for trampoline gymnastics with the CAM-incorporated strain sensor further illustrates the benefits of omnidirectionally enhanced performance.

Smart battery-free and wireless bioelectronic platform based on a nature-skin-derived organohydrogel for chronic wound diagnosis, assessment, and accelerated healing

Using smart electroactive hydrogels with emerging bioelectronics to monitor wound status wirelessly in real-time is a promising approach as an unremitting therapy for refractory chronic wounds. Based on a natural skin-derived organohydrogel (SGC@MA-Gel) triboelectric nanogenerator, a bioresorbable, battery-free, and wireless smart wound treatment bioelectronic system for pharmacological treatment, nanogenerator-driven electrostimulation, and visual wound condition assessment was engineered in this study. The inherent hierarchical architecture and origins of natural skin, in tandem with the substantial loading capabilities of collagen-based biomaterials, endowed SGC@MA-Gel with favorable characteristics. These included mechanical and adhesive robustness, electrical conductivity, antibacterial properties, controlled on-demand drug release capabilities, and human physiological signal monitoring performance. The customizable bioelectronic system, developed in-house, employs a single-electrode triboelectric nanogenerator, which facilitates skin wound healing via electrostimulation. Consequently, the system's biosensors can simultaneously measure glucose, uric acid, and pH at wound sites, thereby enabling accurate wound diagnosis and real-time assessment. This system accelerates cell proliferation and wound healing in vitro and in vivo, which validates its effectiveness in chronic wound treatment. The results demonstrated that the smart wound treatment bioelectronic system could provide a facile therapeutic strategy to assist with integrated wound monitoring, diagnosis, and therapy for hospitalized patients and those recovering at home.

Dual-Layer All-Textile Flexible Pressure Sensor Coupled by Silver Nanowires with Ti3C2-Mxene for Monitoring Athletic Motion during Sports and Transmitting Information.

At present, wearable flexible pressure sensors have broad application prospects in fields such as motion monitoring and information transmission. However, it is still a challenge to design flexible pressure sensors with high sensitivity over a large sensing range and simple fabrication. Here, we use a simple "dipping-drying" method to fabricate a fabric-based flexible pressure sensor by coupling silver nanowires (AgNWs) with Ti3C2-MXene. The interaction between MXene and AgNWs helps realize a dual-layer sensing network, achieving good synergistic effects between pressure sensitivity and sensing range. The effects of the material combination and dip-coating sequence on the sensor's performance are systematically studied. The results show that the sensor was impregnated sequentially with AgNWs solution, and the MXene solution has the highest sensitivity (0.168 kPa-1) over a wide range (190 kPa). Meanwhile, it has the advantages of low response hysteresis and detection limit, as well as good linearity and durability. We further demonstrate the application of this sensor in human physiological signal monitoring and motion pattern recognition. It can also encrypt and transmit information according to different pressing states. In addition, the proposed pressure sensor array exhibits spatial resolution detection capabilities, laying the foundation for applications in the fields of motion monitoring and human-computer interaction.

High-Linearity Flexible Pressure Sensor Based on the Gaussian-Curve-Shaped Microstructure for Human Physiological Signal Monitoring.

Flexible pressure sensors with high-performance show broad application prospects in health monitoring, wearable electronic devices, intelligent robot sensing, and other fields. Although flexible pressure sensors have made significant progress in sensitivity and detection range, most of them still exhibit strong nonlinearity, which leads to significant troubles in signal acquisition and thus limits their popularity in practical applications. It remains a serious challenge for the flexible pressure sensor to achieve high linearity while maintaining high sensitivity. Herein, a doped sensing membrane with a uniformly distributed Gaussian-curve-shaped micropattern array was developed using the micro-electromechanical systems (MEMS) process, and a flexible sensor structure with the doped film as the core was designed and constructed. The prototype sensor has a high sensitivity of 1.77 kPa-1 and a linearity of 0.99 in the full detection range of 20 Pa to 30 kPa. In addition, its excellent performance also includes fast response/recovery times (∼25/50 ms) and long-term endurance (>10,000 cycles at 15 kPa). The prototype sensor has been successfully demonstrated in human pulse monitoring, speech recognition, and gesture recognition. The 2 × 6 sensor array can detect the spatial pressure distribution. Thus, such a microstructure shape design will open a new way to fabricate a high-linearity pressure sensor for potential applications in health monitoring, human-machine interaction, etc.

A Flexible and Biodegradable Piezoelectric‐Based Wearable Sensor for Non‐Invasive Monitoring of Dynamic Human Motions and Physiological Signals

AbstractRecent progress in flexible sensors and piezoelectric materials has enabled the development of continuous monitoring systems for human physiological signals as wearable and implantable medical devices. However, their non‐degradable characteristics also lead to the generation of a significant amount of non‐decomposable electronic waste (e‐waste) and necessitate a secondary surgery for implant removal. Herein, a flexible and biodegradable piezoelectric material for wearable and implantable devices that addresses the problem of secondary surgery and e‐waste while providing a high‐performance platform for continuous and seamless monitoring of human physiological signals and tactile stimuli is provided. The novel composition of bioresorbable poly(l‐lactide) and glycine leads to flexible piezoelectric devices for non‐invasive measurement of artery pulse signals in near‐surface arteries and slight movement of the muscle, including the trachea, esophagus, and movements of joints. The complete degradability of piezoelectric film in phosphate‐buffered saline at 37 °C is also shown. The developed pressure sensor exhibits high sensitivity of 13.2 mV kPa−1 with a response time of 10 ms and shows good mechanical stability. This piezoelectric material has comparable performance to commonly used non‐degradable piezoelectric materials for measuring physiological signals. It can also be used in temporary implantable medical devices for monitoring due to its degradable nature.

Nature-Driven Biocompatible Epidermal Electronic Skin for Real-Time Wireless Monitoring of Human Physiological Signals.

Wearable bioelectronic patches are creating a transformative effect in the health care industry for human physiological signal monitoring. However, the use of such patches is restricted due to the unavailability of a proper power source. Ideal biodevices should be thin, soft, robust, energy-efficient, and biocompatible. Here, we report development of a flexible, lightweight, and biocompatible electronic skin-cum-portable power source for wearable bioelectronics by using a processed chicken feather fiber. The device is fabricated with a novel, breathable composite of biowaste chicken feather and organic poly(vinylidene fluoride) (PVDF) polymer, where the chicken feather fiber constitutes the "microbones" of the PVDF, enhancing its piezoelectric phase content, biocompatibility, and crystallinity. Thanks to its outstanding pressure sensitivity, the fabricated electronic skin is used for the monitoring of different human physiological signals such as body motion, finger and joint bending, throat activities, and pulse rate with excellent sensitivity. A wireless system is developed to remotely receive the different physiological signals as captured by the electronic skin. We also explore the capabilities of the device as a power source for other small electronics. The piezoelectric energy harvesting device can harvest a maximum output voltage of ∼28 V and an area power density of 1.4 μW·cm-2 from the human finger imparting. The improved energy harvesting property of the device is related to the induced higher fraction of the electroactive phase in the composite. The easy process ability, natural biocompatibility, superior piezoelectric performance, high pressure sensitivity, and alignment toward wireless transmission of the captured data make the device a promising candidate for wearable bioelectronic patches and power sources.

Facile and Controllable Ultrasonic Nebulization Method for Fabricating Ti3C2Tx‐Based Strain Sensor and Monitoring of Human Motion and Sound Wave

AbstractFlexible and wearable electronic devices hold great potential in electronic skins, health monitoring systems and soft robotics. Among them, flexible strain sensors with high performance are key components for wearable health monitoring devices. However, the facile and controllable preparation of highly sensitive sensors still faces significant challenges. By virtue of excellent conductivity of 2D transition metal carbids (MXenes), this work reports a facile and low‐cost fabrication strategy for large‐scale production of strain sensors. The sensitive layer is deposited on flexible interdigital electrodes by ultrasonic nebulization of Ti3C2Tx nanosheets. By controlling the nebulization time, different thicknesses of Ti3C2Tx films has a great influence on the performance of strain sensors. The Ti3C2Tx‐based strain sensor exhibits good sensing performances such as high GF (19.1) in the low strain range (≈0.25%–1.14%), short response time (0.7 s), and stable durability (over 1000 cycles). In practice, the potential applications of the strain sensor in sound frequency detection, human physiological signal monitoring and facial expression recognition are demonstrated. Finally, this work integrates the strain sensor with a miniaturized analyzer to assemble a wearable motion monitoring device for mobile healthcare. This study provides a facile strategy for fabricating flexible strain sensors in the field of wearable electronics.

Advances in Ultrathin Soft Sensors, Integrated Materials, and Manufacturing Technologies for Enhanced Monitoring of Human Physiological Signals

AbstractRecent advances in soft sensors and flexible electronics offer various applications in detecting physical, electrical, and chemical signals. However, there are still technical barriers in current mechanical, electrical, and material properties for enhanced signal sensing. When measuring signals from the human skin, minimizing the skin‐sensor contact impedance is still challenging while maximizing sensitivity through optimized materials and soft electronics. Here, this review summarizes recent advances in materials, manufacturing, and integration technologies to develop ultrathin soft sensors for monitoring various human physiological signals. The enhancements in soft and compliant structures and mechanical properties are critical to making reliable wearable electronic systems. This article shares the details of soft sensors, integration processes, manufacturing methods, and their applications to target physical, electrical, and chemical signals. In addition, the limitations and current trends in developing multifunctional sensors, self‐powered devices, and integration with external stimuli systems are discussed.

Study of flexible piezoresistive sensors based on the hierarchical porous structure CNT /PDMS composite materials

Flexible piezoresistive sensors (FPS) are important components of wearable electronics for human-machine interaction, human physiological signal monitoring and electronic skin. In this work, carbon nanotube (CNT)-polydimethylsiloxane (PDMS) (abbreviated as CP) composite materials with hierarchical porous structures were prepared by a facile solvothermal method. The electrical conductivity and mechanical elasticity of the porous structure CP composite materials can be separately tuned by varying the CNT mass fraction and PDMS composition ratio, respectively. A flexible piezoresistive sensor using porous structure CP composite materials as the sensing material was designed and fabricated. The optimized sensor exhibits a sensitivity of 0.59 kPa −1 in the pressure ranges of 0–260 kPa, a low detection limit of 12 Pa, a fast response time of 25 ms and outstanding cycling stability over 1,700 cycles. Such sensor design can be integrated into flexible wearable electronic devices for physiological signal monitoring in real-time. • The hierarchical porous structure CNT/PDMS composite materials were prepared by solvothermal method. • Mechanical and electrical properties of CNT/PDMS composite materials can be adjusted by changing the process parameters. • Sensing mechanism and sensor performance of FPS based on CNT/PDMS composite materials were studied. •Application of FPS for recording human respiratory volume and rate and human activity were examined.