Human Body Monitoring Research Articles

PEDOT:PSS-Based Wearable Flexible Temperature Sensor and Integrated Sensing Matrix for Human Body Monitoring.

Flexible temperature sensors have been widely used in electronic skins and health monitoring. Body temperature as one of the key physiological signals is crucial for detecting human body's abnormalities, which necessitates high sensitivity, quick responsiveness, and stable monitoring. In this paper, we reported a resistive temperature sensor designed as an ultrathin laminated structure with a serpentine pattern and a bioinspired adhesive layer, which was fabricated with a composite of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/single-wall carbon nanotubes/reduced graphene oxide (PEDOT:PSS/SWCNTs/rGO) and polydimethylsiloxane (PDMS). The temperature sensor exhibited a high temperature sensitivity of 0.63% °C-1, coupled with outstanding linearity of 0.98 within 25-45 °C. Furthermore, it showed fast response and recovery speeds of 4.8 and 5.8 s, respectively, between 25 and 36 °C. It also demonstrated exceptional stability when subjected to stress and bending disturbances with the maximum bending interference deviation of 0.03%. Additionally, it displayed good cyclic stability over a broad temperature range from 25 to 85 °C, and the standard deviation at 25 °C is 0.14%. A series of experiments including blowing detection, respiratory monitoring with or without a mask, and during rest or sleep were conducted to show the potential of the flexible temperature sensors in human body monitoring. Furthermore, a 4 × 4 flexible temperature sensor matrix was integrated to detect and map objects such as wrenches and blood vessels through human hand skin. The results were consistent with those of infrared measurements. The flexible temperature sensor is capable of real-time temperature monitoring and has the potential in tracking human respiration, assessing sleep quality, and mapping the temperature of various objects.

Self-powered strain sensing devices with wireless transmission: DIW-printed conductive hydrogel electrodes featuring stretchable and self-healing properties

With rapid advancements in health and human–computer interaction, wearable electronic skins (e-skins) designed for application on the human body provide a platform for real-time detection of physiological signals. Wearable strain sensors, integral functional units within e-skins, can be integrated with Internet of Things (IoT) technology to broaden the applications for human body monitoring. A significant challenge lies in the reliance of most existing wearable strain sensors on rigid external power supplies, limiting their practical flexibility. In this study, we present an innovative strategy to fabricate glutaraldehyde (GA)-poly(vinyl alcohol) (PVA)/cellulose nanocrystals (CNC)/Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) conductive hydrogels through multiple hydrogen bonding systems. Combining the advantageous rheological properties of the precursor solution and the high specific surface area after freeze–thaw cycling, we have created a self-powered sensing system prepared by large-area printing using direct ink writing (DIW) printing. The resulting conductive hydrogel exhibits commendable mechanical properties (411 KPa), impressive stretchability (580 %), and robust self-healing capabilities (>98.3 %). The strain sensor, derived from the conductive hydrogel, demonstrates a gauge factor (GF) of 2.5 within a stretching range of 0–580 %. Additionally, the resultant supercapacitor displays a peak energy density of 0.131 mWh/cm3 at a power density of 3.6 mW/cm3. Benefiting from its elevated strain response and remarkable power density features, this self-powered strain sensing system enables the real-time monitoring of human joint motion. The incorporation of a 5G transmission module enhances its capabilities for remote data monitoring, thereby contributing to the progress of wireless tracking technologies for self-powered electronic skin.

High-energy fiber-shaped calcium-ion batteries enable integrated wearable electronics for human body monitoring

Electronic textiles hold the merits of high conformability with the human body and natural surrounding, possessing large market demand and wide application foreground in smart wearable and portable devices. However, their further application is largely hindered by the shortage of flexible and stable power sources with multifunctional designability. Herein, a free-standing ZnHCF@CF electrode (ZnHCF grown on carbon nanotube fiber) with good mechanical deformability and high electrochemical performance for aqueous fiber-shaped calcium ion battery (FCIB) is reported. Benefiting from the unique Ca2+/H+ co-insertion mechanism, the ZnHCF@CF cathode can exhibit great ion storage capability within a broadened voltage window. By pairing with a polyaniline (PANI)@CF anode, a ZnHCF@CF//PANI@CF FCIB is successfully fabricated, which exhibits a desirable volumetric energy density of 43.2 mWh cm−3 and maintains superior electrochemical properties under different deformations. Moreover, the high-energy FCIB can be harmoniously integrated with a fiber-shaped strain sensor (FSS) to achieve real-time physiological monitoring on knees during long-running, exhibiting great promise for the practical application of electronic textiles.

Directionally Exfoliated Ni/Co Hydroxide-Organic Framework Nanosheets for Enhanced Wearable Glucose Sensing.

We report two-dimensional (2D) Ni/Co-based metal hydroxide-organic framework nanosheets (Ni/Co-MHOF NSs) for the construction of an efficient electrochemical nonenzymatic glucose sensor. The nanosheet architecture maximizes the exposure of coordinatively unsaturated metal sites, which enables a largely improved electrocatalytic performance toward the glucose oxidation reaction. The as-designed nonenzymatic sensor exhibits a high sensitivity of 235.71 μA·mM-1·cm-2 and a wide linear range of 1-3000 μM. The sensor presents excellent selectivity against several potential interferences and a short response time of 3.0 s. Of interest, a high-performance flexible sensor is developed by depositing the Ni/Co-MHOF NSs on screen-printed electrodes, which reveal decent bending stability. The designed glucose sensor patch can attach to the human body and realize noninvasive glucose monitoring in human sweat. This work may shed light on the application of novel MHOFs in the field of wearable electrochemical sensing.

Ultrafast response humidity sensor based on titanium dioxide quantum dots/silica and its multifunctional applications

Humidity sensors with ultrafast response and recovery speed are very popular for humidity monitoring in dynamic environments such as complex operating conditions and human body monitoring. In this work, we prepared titanium dioxide quantum dots by hydrothermal synthesis and silica microspheres by Stober method. In addition, the electrostatic self-assembly method was used to prepare the two films with ultrafast response for moisture sensitivity. Due to the superhydrophilic properties of TiO2 QDs, water molecules can be adsorbed and resolved quickly on their surface. While the addition of SiO2 microspheres further increases the specific surface area of moisture-sensitive films and improves the moisture-sensitive properties of TiO2 QDs. The TiO2 QDs/SiO2 resistive humidity sensors not only exhibit excellent stability and repeatability, but also have fast water adsorption/desorption capacity. Between 11 % and 97 % relative humidity, the resistance change of the sensor reaches 6 orders of magnitude. In order to simulate the actual application environment, an experimental platform was built to verify the ultrafast response of the humidity sensor, and the response/recovery time of the sensor was as short as 22.4 ms/40.8 ms, which can quickly detect the change of humidity. The TiO2 QDs/SiO2 ultrafast humidity sensors proposed in this paper have great application potential in rapidly changing humidity environments such as complex working conditions, human body detection, humidity alarm and voice recognition.

An integrative warning-protection shear thickened composite sponge towards sensing performance and impact resistance with excellent flame retardant

The mechanical shock and thermal damage generally exist together in hazardous environment, whereas traditional single protective materials are difficult to achieve all-round protection under extreme environment. Herein, to realize the integration of multifunctional abilities about impact resistance, flame-retardant and sensing performance, a “solid-liquid host-guest” structural shear thickened composite sponge is proposed, which flame-retardant shear thickening fluids with an extraordinary thickening ratio of 2183.95 % continuously disperse in 3D sponge matrix. The resulting composite sponge effectively attenuates the impact force by nearly 80 % with the thickness of only 4 mm via a cooperation between the effect of shear hardening and structure densification. Meanwhile, after burning on the alcohol flame for 12 s, the composite sponge with 7 wt.% fire-retardant additive maintains a complete morphology and realizes self-extinguishing with a reliable flame-retardant ability. Attributed to the good electrical conductivity of shear thickening fluid, the composite sponge serves favorably in human body monitoring, impact sensing and fire warning. In a word, this multifunctional lightweight composite sponge is expected to realize the integration of early warning and protection, which is a competitive candidate material for the intelligent protection in complex environments.

A highly-sensitive wearable capacitance pressure sensor based on calcium copper titanate/polydimethysiloxane/graphene oxide and polydimethysiloxane/silver nanowires sanwich strustures combination for human body monitoring

In recent years, flexible pressure sensors, with their high sensitivity, low detection limit, wide working pressure range and fast response speed, have been playing an important role in the development of wearable artificial devices, human-computer interaction and healthcare systems, and have attracted wide attention. However, the pressure sensors face challenges related to the weak tightness of bipolar materials, low charge density, and limitation in dielectric layers. In this paper, we present a novel configuration of flexible capacitive pressure sensors, utilizing a polydimethysiloxane (PDMS) thin film covered by silver nanowires (PDMS/SN, PSN) as the electrode materials and a porous material composed of calcium copper titanate (@CCTO), PDMS and graphene oxide (GO)(@CCTO/PDMS/GO, @CPG) as the positive electrode material. The sacrificial material, sugar, is employed to create dense internal pores within the substrate material, @CPG, leading to the formation of a profoundly porous substrate. The integration of the flexible capacitive pressure sensor using @CPG/PSN results in enhanced output performance. The modified sensors achieves a sensitivity of 0.22 kPa−1, which is 7 times higher than that of a pure PDMS dielectric layer sensor. Moreover, the sensors has a response time of 87 ms, a low detection pressure of 5 Pa with an extensive detection range from 0 to 150 kPa, and are capable of enduring 7200 cycles without sustaining damage. To validate the practical performance of the @CPG/PSN sensor, various human body activities are detected, including swallowing, coughing, neck bending, wrist bending, elbow bending, finger flexing, and holding objects like cups using a digitally designed glove capable of accommodating different materials. The pressure sensor based on @CPG/PSN demonstrates significant promise in detecting both low and high pressures, thus expanding the potential applications of capacitive pressure sensors.

Development of a Three-Wavelength Brain Tissue Oxygen Monitoring System Based on Near Infrared Spectrum

In the past 20 years, near infrared spectrum technology has been widely used in human body monitoring due to its non-invasive and real-time characteristics. Oxygen, as the main metabolic substance of the human body, is consumed the most in brain tissue. In order to prevent complications caused by a decrease in brain tissue oxygen during treatment, the patient's brain tissue blood oxygen saturation needs to be monitored in real time. Currently, most of the clinically used non-invasive cerebral blood oxygen detection equipments use dual wavelengths. Other substances on the detection path will cause errors in the measurement results. Therefore, this article proposes a three-wavelength method based on the basic principle of non-invasive monitoring of cerebral blood oxygen using near-infrared spectrum. The brain tissue oxygen saturation monitoring method of detecting light sources was initially verified through the built system, laying the foundation for subsequent system engineering.

A multi-functional flexible piezoresistive sensor based on sericin-functionalized CNTs decorated carbon foams for wearable thermal-therapy devices

With the rapid development of science and technology, multifunctional wearable devices have become a major trend in medical field. There is an urgent need to fabricate multifunctional materials with thermal insulation, mechanical flexibility, piezoresistance, and adjustable heating behavior to cope with the thermal management and health monitoring of human body in the harsh environment. To address this issue, three-dimensional melamine-based carbon foams (CMF) have been developed, with sericin-functionalized carbon nanotubes (CNTs) and in situ-grown carbon nanofibers (CNFs) in the CMF skeleton. The strategy of hierarchical porous micro-nanostructure enhanced the synergistic effect between CNTs and CNFs, resulting in exceptional resilience at 0–80 % compressive strain and cyclic stability at 20 % strain. Such carbon foam composites demonstrated excellent piezoresistive sensing performance, wide pressure range (0–20 kPa), high sensitivity (S = 0.11 kPa−1), and quick response (response/recovery time of 150/120 ms). They also showed good thermal insulation and Joule heating properties, particularly in presenting strain-dependent Joule heating mode at low voltage. Such amazing characteristics provide inspiration for temperature regulation of flexible, energy-efficient heating devices, and make them promising for smart sportswear, human-machine interfaces, and wearable medical devices.

High performance fully-printed strain-sensing e-textile for human posture recognition

Developing strain-sensing electronic textiles (e-textiles) that combine the functionality of stretchable strain sensors with the wearing comfort of textiles is an important development direction for wearable electronics. However, achieving low-cost and high-volume fabrication of strain-sensing e-textiles with both a wide strain working range and high sensitivity remains a huge challenge. Herein, we report high-performance printed strain-sensing e-textiles by designing the composite conductive ink from the perspective of optimizing polymer binders. The composite conductive inks based on different polymer binders present different rheological properties, volume shrinkage, and mechanical properties, which further affect the sensing performance of printed strain-sensing e-textiles. Compared with other four composite conductive inks, the carbon blacks/high elastic transparent glue-based printed strain-sensing e-textile with microcrack structure exhibits higher sensitivity (120.6 at a strain range of 0–100%) over a wide strain working range (150%), while also exhibiting low detection limits (0.1%) and outstanding dynamic stability (10000 cycles). On this basis, the demonstration of smart clothing integrated with 9 printed strain-sensing elements in human body posture recognition and monitoring proves its application prospects in human–machine interaction and virtual reality. This work opens a new research idea for constructing high-performance strain-sensing e-textiles.

Flexible capacitive and piezoresistive pressure sensors based on screen-printed parylene C/polyurethane composites in low-pressure range

The use of polymers to fabricate flexible pressure sensors as an alternative to conventional pressure sensors has led to the development of physiological monitoring of human body and the electronic skin. In particular, the fabrication of flexible capacitive and piezoresistive sensors using a variety of materials and the investigation of their electromechanical properties are further developments in these fields. Herein, parylene C is synthesized via chemical vapor deposition method. Pressure-sensitive inks are prepared with a composite of parylene C, polyurethane, polymethylmethacrylate, and activated carbon at certain weight ratios. Flexible capacitive and piezoresistive pressure sensors are fabricated by the screen printing method. The sensitivity, detection limit, linearity range, and response/relaxation time, which define the capacitive and piezoresistive properties are investigated and presented in this paper. The sensitivities of the flexible capacitive and piezoresistive pressure sensors are 0.124 kPa−1 and 0.074 kPa−1 in the pressure range of 0.07–1.39 kPa. This study enables parylene C to be used in the composite structure and shows that it can be used not only as a protective layer but also in flexible pressure sensor applications. It also ensures that the design of the flexible capacitance pressure sensor can measure low pressure with high sensitivity compared to the flexible piezoresistive pressure sensor.

Stretchable Sensors: Novel Human Motion Monitoring Wearables.

A human body monitoring system remains a significant focus, and to address the challenges in wearable sensors, a nanotechnology-enhanced strategy is proposed for designing stretchable metal-organic polymer nanocomposites. The nanocomposite comprises reduced graphene oxide (rGO) and in-situ generated silver nanoparticles (AgNPs) within elastic electrospun polystyrene-butadiene-polystyrene (SBS) fibers. The resulting Sandwich Structure Piezoresistive Woven Nanofabric (SSPWN) is a tactile-sensitive wearable sensor with remarkable performance. It exhibits a rapid response time (less than three milliseconds) and high reproducible stability over 5500 cycles. The nanocomposite also demonstrates exceptional thermal stability due to effective connections between rGO and AgNPs, making it suitable for wearable electronic applications. Furthermore, the SSPWN is successfully applied to human motion monitoring, including various areas of the hand and RGB sensing shoes for foot motion monitoring. This nanotechnology-enhanced strategy shows promising potential for intelligent healthcare, health monitoring, gait detection, and analysis, offering exciting prospects for future wearable electronic products.

Tissue-Matchable and Implantable Batteries Toward Biomedical Applications.

Implantable electronic devices can realize real-time and reliable health monitoring, diagnosis, and treatment of human body, which are expected to overcome important bottlenecks in the biomedical field. However, the commonly used energy supply devices for them are implantable batteries based on conventional rigid device design with toxic components, which both mechanically and biologically mismatch soft biological tissues. Therefore, the development of highly soft, safe, and implantable tissue-matchable flexible batteries is of great significance and urgency for implantable bioelectronics. In this work, the recent advances of tissue-matchable and implantable flexible batteries are overviewed, focusing on the design strategies of electrodes/batteries and their biomedical applications. The mechanical flexibility, biocompatibility, and electrochemical performance in vitro and in vivo of these flexible electrodes/batteries are then discussed. Finally, perspectives are provided on the current challenges and possible directions of this field in the future.

Highly Stretchable, Self-Adhesive, Antidrying Ionic Conductive Organohydrogels for Strain Sensors.

As flexible wearable devices, hydrogel sensors have attracted extensive attention in the field of soft electronics. However, the application or long-term stability of conventional hydrogels at extreme temperatures remains a challenge due to the presence of water. Antifreezing and antidrying ionic conductive organohydrogels were prepared using cellulose nanocrystals and gelatin as raw materials, and the hydrogels were prepared in a water/glycerol binary solvent by a one-pot method. The prepared hydrogels were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The mechanical properties, electrical conductivity, and sensing properties of the hydrogels were studied by means of a universal material testing machine and LCR digital bridge. The results show that the ionic conductive hydrogel exhibits high stretchability (elongation at break, 584.35%) and firmness (up to 0.16 MPa). As the binary solvent easily forms strong hydrogen bonds with water molecules, experiments show that the organohydrogels exhibit excellent freezing and drying (7 days). The organohydrogels maintain conductivity and stable sensitivity at a temperature range (-50 °C-50 °C) and after long-term storage (7 days). Moreover, the organohydrogel-based wearable sensors with a gauge factor of 6.47 (strain, 0-400%) could detect human motions. Therefore, multifunctional organohydrogel wearable sensors with antifreezing and antidrying properties have promising potential for human body monitoring under a broad range of environmental conditions.

Sports health monitoring management system based on artificial intelligence algorithm

With the improvement of people's material living standards, more and more people start to pay attention to health issues. This paper takes the health field as the main research object, and discusses the current development and status quo of the health field. Through literature review, it is found that the current health field mainly focuses on the single monitoring of a certain organ or body function, and there are limitations in systematic health monitoring research, and most of the research stays at the stage of human body monitoring. Therefore, this paper intends to design a sports health monitoring and management system based on artificial intelligence. The system is mainly divided into a body temperature monitoring module, a blood pressure monitoring module and an exercise monitoring module, through which the user's health data is monitored. In order to ensure the practicability of the system, this paper selects three common life states in daily life for experimental testing, namely exercise state, rest state and sick state. The experimental test results show that each monitoring module can operate correctly and normally under three different states. The lowest temperature was 36.5° and the highest temperature was 37.1° under the exercise state. The lowest blood pressure is 70 in the resting state, and the highest blood pressure is 80. In the sick state, the maximum value of motor threshold is 0.2, the minimum value is 0.1, and the threshold difference is 0.1. Each module reads and backs up relevant data, and sends it to the platform for intelligent analysis. The platform will analyze and compare the data of different modules at the same time, judge the health status of the user at that time, choose whether to issue a health alert for the user, and finally complete the entire system process of the health monitoring management system. This proves that the sports health monitoring management system based on artificial intelligence algorithm designed in this paper is effective and feasible.

Advances in Humidity Nanosensors and Their Application: Review.

As the technology revolution and industrialization have flourished in the last few decades, the development of humidity nanosensors has become more important for the detection and control of humidity in the industry production line, food preservation, chemistry, agriculture and environmental monitoring. The new nanostructured materials and fabrication in nanosensors are linked to better sensor performance, especially for superior humidity sensing, following the intensive research into the design and synthesis of nanomaterials in the last few years. Various nanomaterials, such as ceramics, polymers, semiconductor and sulfide, carbon-based, triboelectrical nanogenerator (TENG), and MXene, have been studied for their potential ability to sense humidity with structures of nanowires, nanotubes, nanopores, and monolayers. These nanosensors have been synthesized via a wide range of processes, including solution synthesis, anodization, physical vapor deposition (PVD), or chemical vapor deposition (CVD). The sensing mechanism, process improvement and nanostructure modulation of different types of materials are mostly inexhaustible, but they are all inseparable from the goals of the effective response, high sensitivity and low response-recovery time of humidity sensors. In this review, we focus on the sensing mechanism of direct and indirect sensing, various fabrication methods, nanomaterial geometry and recent advances in humidity nanosensors. Various types of capacitive, resistive and optical humidity nanosensors are introduced, alongside illustration of the properties and nanostructures of various materials. The similarities and differences of the humidity-sensitive mechanisms of different types of materials are summarized. Applications such as IoT, and the environmental and human-body monitoring of nanosensors are the development trends for futures advancements.

Flexible Sweat Sensors: From Films to Textiles.

Flexible sweat sensors have found widespread potential applications for long-term wear and tracking and real-time monitoring of human health. However, the main substrate currently used in common flexible sweat sensors is thin film, which has disadvantages such as poor air permeability and the need for additional wearables. In this Review, the recent progress of sweat sensors has been systematically summarized by the types of monitoring methods of sweat sensors. In addition, this Review introduces and compares the performance of sweat sensors based on thin film and textile substrates such as fiber/yarn. Finally, opportunities and suggestions for the development of flexible sweat sensors are presented by summarizing the integration methods of sensors and human body monitoring sites.

Self-Healing Multimodal Flexible Optoelectronic Fiber Sensors

Fiber-optic sensors are attracting attention because of their high sensitivity, fast response, large capacity-transmission, and anti-electromagnetic interference advantages. Nevertheless, rigid optical fibers are inevitably damaged or even fractured in applications involving large tensile or bending strains (e.g., human body monitoring, soft robotics, and biomedical devices) and the position of the fracture is difficult to locate and repair. Therefore, optically self-healing fiber-optic sensors are highly desirable. Here, we report a design strategy for increasing the polymer segmental mobility and reversible non-covalent bond density of poly(polymerizable deep eutectic solvent) (PDES) to continuously fabricate a core–cladding poly(PDES) optical fiber (CPOF) with significant optical, electrical, and mechanical self-healing abilities. It also possesses low optical propagation attenuation (0.31 dB cm–1), wide temperature tolerance (−77–168 °C), and excellent biocompatibility. Moreover, CPOFs have been validated for gesture recognition, subcutaneous self-healing, and pressure–temperature detection, owing to their ability to transmit dual optical-electrical signals in real time, and are promising for various applications in industrial and technological fields.

Liquid metal @ mxene spring supports ionic gel with excellent mechanical properties for high-sensitivity wearable strain sensor

Conductive ionic gels are considered as potential flexible sensing materials owing to their softness and biocompatibility. Nevertheless, pure ionic gels typically exhibit poor mechanical properties and low sensitivity. In this study, MXene and liquid metal (LM) are introduced for self-assembly to form a spring structure. The enhanced effect of the van der Waals force synergy between the two fillers increases the tensile resistance (925 %, 1091.5 kPa), compression resistance (75 %, 2534.3 kPa) and self-healing (∼90 % recovery) efficiency of the ionic gel. In addition, the conductive paths based on double fillers are greatly destroyed during the straining process, and show a very high gauge factor (15.47) because of their unique spring structure and weak viscous force between them. This study provides a new approach for the preparation of highly sensitive sensing materials for human body monitoring and applications in other domains.

A Flexible Tuned Radio-Frequency Planar Resonant Loop for Noninvasive Hydration Sensing

In this work, a planar radio-frequency sensor based on a flexible polyimide substrate has been developed to monitor the water content changes noninvasively and efficiently in a human body or tissues. The sensor is based on the detection of electromagnetic resonance that is susceptible to dielectric property changes by water content variations. The planar loop resonator tuned with a metal pad features improved resonance, compact size, and flexibility to conform to a curved surface. Designs and experiments to continuously monitor human hydration processes <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> have been demonstrated. The recorded data shows distinct trends when a person becomes hydrated from a dehydrated state. Discrete and continuous measurements are compared with the simulations conducted by using documented, generalized human skin permittivity properties. Discrepancies between the measurements and simulations are investigated and verified with directly measured skin permittivities. Measurements variations are also investigated. With the advantages of being compact, flexible, and planar, the sensor can be integrated into a wearable on the human forearm. Additionally, the sensor has been used to demonstrate its ability to detect water content changes in a phantom made of ground pork. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex vivo</i> results indicate the sensitivity and consequential variations in practical scenarios. The promising results show great potential for human body monitoring and also general applications in agriculture and the food processing industry from the demonstration of the sensing principle in the pork phantom.