A Wearable and Highly Sensitive Graphene Strain Sensor for Precise Home-Based Pulse Wave Monitoring

Multispecies-coadsorption-induced rapid preparation of graphene glass fiber fabric and applications in flexible pressure sensor

Direct chemical vapor deposition (CVD) growth of graphene on dielectric/insulating materials is a promising strategy for subsequent transfer-free applications of graphene. However, graphene growth on noncatalytic substrates is faced with thorny issues, especially the limited growth rate, which severely hinders mass production and practical applications. Herein, graphene glass fiber fabric (GGFF) is developed by graphene CVD growth on glass fiber fabric. Dichloromethane is applied as a carbon precursor to accelerate graphene growth, which has a low decomposition energy barrier, and more importantly, the produced high-electronegativity Cl radical can enhance adsorption of active carbon species by Cl-CH2 coadsorption and facilitate H detachment from graphene edges. Consequently, the growth rate is increased by ~3 orders of magnitude and carbon utilization by ~960-fold, compared with conventional methane precursor. The advantageous hierarchical conductive configuration of lightweight, flexible GGFF makes it an ultrasensitive pressure sensor for human motion and physiological monitoring, such as pulse and vocal signals.

Fabrication of a Capacitive 3D Spacer Fabric Pressure Sensor with a Dielectric Constant Change for High Sensitivity

Smart wearable sensors are increasingly integrated into everyday life, interfacing with the human body to enable real-time monitoring of biological signals. This study focuses on creating high-sensitivity capacitive-type sensors by impregnating polyester-based 3D spacer fabric with a Carbon Nanotube (CNT) dispersion. The unique properties of conductive particles lead to nonlinear variations in the dielectric constant when pressure is applied, consequently affecting the gauge factor. The results reveal that while the fabric without CNT particles had a gauge factor of 1.967, the inclusion of 0.04 wt% CNT increased it significantly to 5.210. As sensor sensitivity requirements vary according to the application, identifying the necessary CNT wt% is crucial. Artificial intelligence, particularly the Multilayer Perception (MLP) model, enables nonlinear regression analysis for this purpose. The MLP model created and validated in this research showed a high correlation coefficient of 0.99564 between the model predictions and actual target values, indicating its effectiveness and reliability.

Electronic Skin for Health Monitoring Systems: Properties, Functions, and Applications

Electronic skin (e-skin), a skin-like wearable electronic device, holds great promise in the fields of telemedicine and personalized healthcare because of its good flexibility, biocompatibility, skin conformability, and sensing performance. E-skin can monitor various health indicators of the human body in real time and over the long term, including physical indicators (exercise, respiration, blood pressure, etc.) and chemical indicators (saliva, sweat, urine, etc.). In recent years, the development of various materials, analysis, and manufacturing technologies has promoted significant development of e-skin, laying the foundation for the application of next-generation wearable medical technologies and devices. Herein, the properties required for e-skin health monitoring devices to achieve long-term and precise monitoring and summarize several detectable indicators in the health monitoring field are discussed. Subsequently, the applications of integrated e-skin health monitoring systems are reviewed. Finally, current challenges and future development directions in this field are discussed. This review is expected to generate great interest and inspiration for the development and improvement of e-skin and health monitoring systems.

Materials-Driven Soft Wearable Bioelectronics for Connected Healthcare

In the era of Internet-of-things, many things can stay connected; however, biological systems, including those necessary for human health, remain unable to stay connected to the global Internet due to the lack of soft conformal biosensors. The fundamental challenge lies in the fact that electronics and biology are distinct and incompatible, as they are based on different materials via different functioning principles. In particular, the human body is soft and curvilinear, yet electronics are typically rigid and planar. Recent advances in materials and materials design have generated tremendous opportunities to design soft wearable bioelectronics, which may bridge the gap, enabling the ultimate dream of connected healthcare for anyone, anytime, and anywhere. We begin with a review of the historical development of healthcare, indicating the significant trend of connected healthcare. This is followed by the focal point of discussion about new materials and materials design, particularly low-dimensional nanomaterials. We summarize material types and their attributes for designing soft bioelectronic sensors; we also cover their synthesis and fabrication methods, including top-down, bottom-up, and their combined approaches. Next, we discuss the wearable energy challenges and progress made to date. In addition to front-end wearable devices, we also describe back-end machine learning algorithms, artificial intelligence, telecommunication, and software. Afterward, we describe the integration of soft wearable bioelectronic systems which have been applied in various testbeds in real-world settings, including laboratories that are preclinical and clinical environments. Finally, we narrate the remaining challenges and opportunities in conjunction with our perspectives.

Welded Carbon Nanotube-Graphene Hybrids with Tunable Strain Sensing Behavior for Wide-Range Bio-Signal Monitoring

Carbon nanotubes (CNTs) and graphene have commonly been applied as the sensitive layer of strain sensors. However, the buckling deformation of CNTs and the crack generation of graphene usually leads to an unsatisfactory strain sensing performance. In this work, we developed a universal strategy to prepare welded CNT-graphene hybrids with tunable compositions and a tunable bonding strength between components by the in situ reduction of CNT-graphene oxide (GO) hybrid by thermal annealing. The stiffness of the hybrid film could be tailored by both initial CNT/GO dosage and annealing temperature, through which its electromechanical behaviors could also be defined. The strain sensor based on the CNT-graphene hybrid could be applied to collect epidermal bio-signals by both capturing the faint skin deformation from wrist pulse and recording the large deformations from joint bending, which has great potential in health monitoring, motion sensing and human-machine interfacing.

Flexible piezo-resistive strain sensors using all-polydimethylsiloxane based hybrid nanocomposites for wearable electronics

We report flexible piezo-resistive strain sensors composed of silver nanoparticle (Ag NP), graphene nanoplatelet (GNP), and multi walled carbon nanotube (MWCNT)-based ternary conductive hybrid nanocomposites as an active sensing layer fabricated using a simple solution processing method on flexible polydimethylsiloxane (PDMS) substrates. The electrical characteristics have been studied in PDMS-based flexible devices having three different kinds of structures, namely Ag NPs/MWCNT/PDMS, GNP/PDMS and Ag NPs/GNP/PDMS. The microscopic analysis of the hybrid nanocomposites is undertaken using field emission scanning electron microscopy. The diameter of the CNTs is found to be in the range of 20-40 nm, whereas the length is determined to be 100-800 nm. The average diameter and length of the GNPs are observed to be 30-50 nm and 100-500 nm, respectively. The crystallite size of the silver nanoparticles in the Ag NPs/MWCNT/PDMS and Ag NPs/GNP/PDMS-based nanocomposites is determined to be 22.8 nm and 29.1 nm, respectively. The prepared sample of Ag NPs shows four distinct peaks in the X-ray diffraction pattern, which correspond to the (111), (200), (220), and (311) face-centered cubic (FCC) crystalline planes. Raman spectroscopy is undertaken to study the fundamental physical properties and chemical analysis of the nanocomposites. Ag NPs/GNP/PDMS-based sensors exhibit superior performance in terms of sensitivity, response and recovery time during breathing/unbreathing analysis. The large surface area of the Ag NPs and GNPs promotes uniform distribution of Ag NPs to fill into the porous GNP surface, thereby facilitating high contact area along with better electron transport in the Ag NPs/GNP/PDMS hybrid nanocomposite-based sensors. The gauge factor (GF), response and recovery time of the Ag NPs/GNP/PDMS hybrid nanocomposite-based sensors are determined to be 221, 130 ms and 119 ms, respectively. The ternary conductive nanocomposite-based sensors are free from the drawbacks of binary nanocomposite-based sensors where the high percolation threshold and poor mechanical behaviour lead to the degradation of the device performance.

Paper-Based Supercapacitive Pressure Sensor for Wrist Arterial Pulse Waveform Monitoring

Recent developments in wearable pressure sensors have led to the need for high sensitivity and a broad sensing range to accurately detect various physiological states. However, high sensitivity does not always translate to a wide sensing range, and manufacturing sensors with such high sensitivity is a complex and expensive process. In this study, we present a capacitive pressure sensor based on tissue paper that is simple to produce and cost-effective yet still exhibits high linear sensitivity of 2.9 kPa-1 in the 0-16 kPa range. The linear sensitivity of 1.5 kPa-1 was achieved from 16 to 90 kPa. The sensor also demonstrated a fast response time of 0.2 s, excellent pressure resolution at both low and high pressures, and a sufficient signal-to-noise ratio, making it ideal for detecting wrist arterial pulse waveforms. We were also able to demonstrate the sensor's practicality in real-world applications by cycling it 5000 times and showing its capability to capture pulse waveforms from different arterial locations. These low-cost sensors possess all the intrinsic features necessary for efficient measurement of pulse waveforms, which may facilitate the diagnosis of cardiovascular diseases.

Flexible Transparent Conductive Electrodes: Unveiling Growth Mechanisms, Material Dimensions, Fabrication Methods, and Design Strategies

Flexible transparent conductive electrodes (FTCEs) constitute an indispensable component in state-of-the-art electronic devices, such as wearable flexible sensors, flexible displays, artificial skin, and biomedical devices, etc. This review paper offers a comprehensive overview of the fabrication techniques, growth modes, material dimensions, design, and their impacts on FTCEs fabrication. The growth modes, such as the "Stranski-Krastanov growth," "Frank-van der Merwe growth," and "Volmer-Weber growth" modes provide flexibility in fabricating FTCEs. Application of different materials including 0D, 1D, 2D, polymer composites, conductive oxides, and hybrid materials in FTCE fabrication, emphasizing their suitability in flexible devices are discussed. This review also delves into the design strategies of FTCEs, including microgrids, nanotroughs, nanomesh, nanowires network, and "kirigami"-inspired patterns, etc. The pros and cons associated with these materials and designs are also addressed appropriately. Considerations such as trade-offs between electrical conductivity and optical transparency or "figure of merit (FoM)," "strain engineering," "work function," and "haze" are also discussed briefly. Finally, this review outlines the challenges and opportunities in the current and future development of FTCEs for flexible electronics, including the improved trade-offs between optoelectronic parameters, novel materials development, mechanical stability, reproducibility, scalability, and durability enhancement, safety, biocompatibility, etc.

Recent development of piezoelectric biosensors for physiological signal detection and machine learning assisted cardiovascular disease diagnosis

As cardiovascular disease stands as a global primary cause of mortality, there has been an urgent need for continuous and real-time heart monitoring to effectively identify irregular heart rhythms and to offer timely patient alerts. However, conventional cardiac monitoring systems encounter challenges due to inflexible interfaces and discomfort during prolonged monitoring. In this review article, we address these issues by emphasizing the recent development of the flexible, wearable, and comfortable piezoelectric passive sensor assisted by machine learning technology for diagnosis. This innovative device not only harmonizes with the dynamic mechanical properties of human skin but also facilitates continuous and real-time collection of physiological signals. Addressing identified challenges and constraints, this review provides insights into recent advances in piezoelectric cardiac sensors, from devices to circuit systems. Furthermore, this review delves into the integration of machine learning technologies, showcasing their pivotal role in facilitating continuous and real-time assessment of cardiac status. The synergistic combination of flexible piezoelectric sensor design and machine learning holds substantial potential in automating the detection of cardiac irregularities with minimal human intervention. This transformative approach has the power to revolutionize patient care paradigms.

Construction of Wearable Touch Sensors by Mimicking the Properties of Materials and Structures in Nature

Wearable touch sensors, which can convert force or pressure signals into quantitative electronic signals, have emerged as essential smart sensing devices and play an important role in various cutting-edge fields, including wearable health monitoring, soft robots, electronic skin, artificial prosthetics, AR/VR, and the Internet of Things. Flexible touch sensors have made significant advancements, while the construction of novel touch sensors by mimicking the unique properties of biological materials and biogenetic structures always remains a hot research topic and significant technological pathway. This review provides a comprehensive summary of the research status of wearable touch sensors constructed by imitating the material and structural characteristics in nature and summarizes the scientific challenges and development tendencies of this aspect. First, the research status for constructing flexible touch sensors based on biomimetic materials is summarized, including hydrogel materials, self-healing materials, and other bio-inspired or biomimetic materials with extraordinary properties. Then, the design and fabrication of flexible touch sensors based on bionic structures for performance enhancement are fully discussed. These bionic structures include special structures in plants, special structures in insects/animals, and special structures in the human body. Moreover, a summary of the current issues and future prospects for developing wearable sensors based on bio-inspired materials and structures is discussed.

Graphene-Based Wearable Temperature Sensors: A Review

Flexible sensing electronics have received extensive attention for their potential applications in wearable human health monitoring and care systems. Given that the normal physiological activities of the human body are primarily based on a relatively constant body temperature, real-time monitoring of body surface temperature using temperature sensors is one of the most intuitive and effective methods to understand physical conditions. With its outstanding electrical, mechanical, and thermal properties, graphene emerges as a promising candidate for the development of flexible and wearable temperature sensors. In this review, the recent progress of graphene-based wearable temperature sensors is summarized, including material preparation, working principle, performance index, classification, and related applications. Finally, the challenges and future research emphasis in this field are put forward. This review provides important guidance for designing novel and intelligent wearable temperature-sensing systems.

Crack-Based Sensor with Microstructures for Strain and Pressure Sensing

Recent extensive research on flexible electronics has led to the development of various flexible sensors. In particular, sensors inspired by the slit organs of a spider, which utilize cracks in a metal film to measure strain, have garnered considerable interest. This method exhibited significantly high sensitivity, repeatability, and durability in measuring strain. In this study, a thin-film crack sensor was developed using a microstructure. The results exhibited its ability to simultaneously measure the tensile force and pressure in a thin film, further expanding its applications. Furthermore, the strain and pressure characteristics of the sensor were measured and analyzed using an FEM simulation. The proposed method is expected to contribute to the future development of wearable sensors and artificial electronic skin research.

Graphene-based cardiac sensors and actuators

Graphene, a 2D carbon allotrope, is revolutionizing many biomedical applications due to its unique mechanical, electrical, thermal, and optical properties. When bioengineers realized that these properties could dramatically enhance the performance of cardiac sensors and actuators and may offer fundamentally novel technological capabilities, the field exploded with numerous studies developing new graphene-based systems and testing their limits. Here we will review the link between specific properties of graphene and mechanisms of action of cardiac sensors and actuators, analyze the performance of these systems from inaugural studies to the present, and offer future perspectives.

Cross-Talk Signal Free Recyclable Thermoplastic Polyurethane/Graphene-Based Strain and Pressure Sensor for Monitoring Human Motions

Developing a sensor that can read out cross-talk free signals while determining various active physiological parameters is demanding in the field of point-of-care applications. While there are a few examples of non-flexible sensors available, the management of electronic waste generated from such sensors is critical. Most of such available sensors are rigid in form factor and hence limit their usability in healthcare monitoring due to their poor conformity to human skin. Combining these facets, studies on the development of a recyclable cross-talk free flexible sensor for monitoring human motions and active parameters are far and few. In this work, we report on the development of a recyclable flexible sensor that can provide accurate data for detecting small changes in strain as well as pressure. The developed sensor could decipher the signals individually responsible due to strain as well as pressure. Hence, it can deliver a cross-talk free output. Thermoplastic polyurethane and graphene were selected as the model system. The thermoplastic polyurethane/graphene sensor exhibited a tensile strain sensitivity of GF ≃ 3.375 for 0-100% strain and 10.551 for 100-150% strain and a pressure sensitivity of ∼-0.25 kPa-1. We demonstrate the applicability of the strain sensor for monitoring a variety of human motions ranging from a very small strain of eye blinking to a large strain of elbow bending with unambiguous peaks and a very fast response and recovery time of 165 ms. The signals received are mostly electrical hysteresis free. To confirm the recyclability, the developed sensor was recycled up to three times. Marginal decrement in the sensitivity was noted with recycling without compromising the sensing capabilities. These findings promise to open up a new avenue for developing flexible sensors with lesser carbon footprints.

Recent advances in inkjet-printing technologies for flexible/wearable electronics

The rapid development of flexible/wearable electronics requires novel fabricating strategies. Among the state-of-the-art techniques, inkjet printing has aroused considerable interest due to the possibility of large-scale fabricating flexible electronic devices with good reliability, high time efficiency, a low manufacturing cost, and so on. In this review, based on the working principle, recent advances in the inkjet printing technology in the field of flexible/wearable electronics are summarized, including flexible supercapacitors, transistors, sensors, thermoelectric generators, wearable fabric, and for radio frequency identification. In addition, some current challenges and future opportunities in this area are also addressed. We hope this review article can give positive suggestions to the researchers in the area of flexible electronics.

Biocompatible and Long-Term Monitoring Strategies of Wearable, Ingestible and Implantable Biosensors: Reform the Next Generation Healthcare

Sensors enable the detection of physiological indicators and pathological markers to assist in the diagnosis, treatment, and long-term monitoring of diseases, in addition to playing an essential role in the observation and evaluation of physiological activities. The development of modern medical activities cannot be separated from the precise detection, reliable acquisition, and intelligent analysis of human body information. Therefore, sensors have become the core of new-generation health technologies along with the Internet of Things (IoTs) and artificial intelligence (AI). Previous research on the sensing of human information has conferred many superior properties on sensors, of which biocompatibility is one of the most important. Recently, biocompatible biosensors have developed rapidly to provide the possibility for the long-term and in-situ monitoring of physiological information. In this review, we summarize the ideal features and engineering realization strategies of three different types of biocompatible biosensors, including wearable, ingestible, and implantable sensors from the level of sensor designing and application. Additionally, the detection targets of the biosensors are further divided into vital life parameters (e.g., body temperature, heart rate, blood pressure, and respiratory rate), biochemical indicators, as well as physical and physiological parameters based on the clinical needs. In this review, starting from the emerging concept of next-generation diagnostics and healthcare technologies, we discuss how biocompatible sensors revolutionize the state-of-art healthcare system unprecedentedly, as well as the challenges and opportunities faced in the future development of biocompatible health sensors.

Graphene e-tattoos for unobstructive ambulatory electrodermal activity sensing on the palm enabled by heterogeneous serpentine ribbons

Electrodermal activity (EDA) is a popular index of mental stress. State-of-the-art EDA sensors suffer from obstructiveness on the palm or low signal fidelity off the palm. Our previous invention of sub-micron-thin imperceptible graphene e-tattoos (GET) is ideal for unobstructive EDA sensing on the palm. However, robust electrical connection between ultrathin devices and rigid circuit boards is a long missing component for ambulatory use. To minimize the well-known strain concentration at their interfaces, we propose heterogeneous serpentine ribbons (HSPR), which refer to a GET serpentine partially overlapping with a gold serpentine without added adhesive. A fifty-fold strain reduction in HSPR vs. heterogeneous straight ribbons (HSTR) has been discovered and understood. The combination of HSPR and a soft interlayer between the GET and an EDA wristband enabled ambulatory EDA monitoring on the palm in free-living conditions. A newly developed EDA event selection policy leveraging unbiased selection of phasic events validated our GET EDA sensor against gold standards.

Entropy Information of Pulse Dynamics in Three Stages of Pregnancy

The aim of the present study is to use entropy to explore the change of pulse generated by normal pregnant women with gestational. Firstly, the subjects were divided into early (E), middle (M), and late (L) three stages according to gestational age. Then, pulse signals of the Chi position of 90 pregnant women at different gestational ages were collected. Secondly, the four entropies, namely fuzzy entropy (FuEn), approximate entropy (ApEn), sample entropy (SamEn), and permutation entropy (PerEn), were applied to the analysis of the long-term pulse changes of the pregnancy. Finally, the related information about pulse in different stages of pregnancy is given by the analysis of four kinds of entropy. Furthermore, the statistical tests are conducted for further comparison, and the descriptive statistics and the results are presented. In addition, boxplots are employed to show the distribution of four entropies of pregnancy. This work has studied the changes in pulse during pregnancy from quantitative and qualitative aspects. Our results show that entropy improves the diagnostic value of pulse analysis during pregnancy and could be applied to facilitate noninvasive diagnosis of pregnant women's physiological signals in the future.

Graphene-based strain sensor with sandwich structure and its application in bowel sounds monitoring

Surgery is one of the primary treatment modalities for gastrointestinal tumors but can lead to postoperative ileus (POI), which can aggravate pain and increase costs. The incidence of POI can be effectively reduced by monitoring bowel sounds to assist doctors in deciding the timing of transoral feeding. In this study, we prepared a flexible strain sensor based on a graphene composite material and tested the feasibility of sensor monitoring of bowel sounds using simultaneous stethoscope and sensor monitoring. We found that the time of hearing the bowel sounds (12.0–12.1 s) corresponded to the time of waveform change monitored by the sensor (12.036 s), and the sound tone magnitude corresponded to the waveform amplitude. This proves that the application of sensors to monitor bowel sounds is feasible, which opens up a new field for the application of graphene sensors and provides a new way for clinicians to judge the condition of the intestine.

Combining medicine and materials science. First application of graphene strain sensors for monitoring bowel sounds

High-Performance Strain Sensors Based on Au/Graphene Composite Films with Hierarchical Cracks for Wide Linear-Range Motion Monitoring

Stretchable strain sensors based on nanomaterial thin films have aroused extensive interest for the strain perception of smart skins. However, it still remains challenging to have them achieve high sensitivity over wide linear working ranges. Herein, we propose a facile strategy to fabricate stretchable strain sensors based on Au/graphene composite films (AGCFs) with hierarchical cracks and demonstrate their superior sensing performances. The polydimethylsiloxane substrates were covered with self-assembled graphene films (SAGFs) and sputtered with Au, and then prestretching was applied to introduce hierarchical cracks. The AGCF strain sensors exhibited high sensitivity (gauge factor (GF) ≈ 153) and favorable linearity (R² ≈ 0.9975) in the wide working range (0-20%) with ultralow overshooting (∼1.7% at 20%), fast response (<42.5 ms), and also excellent cycling stability (1500 cycles). Besides, these patternable sensors could further achieve higher GF (∼320) via pattern designing. The dominant effect of the intermediate wrinkled SAGFs in forming hierarchical cracks was studied, and the linear sensing mechanism of the as-formed fractal microstructures was also revealed in detail. Moreover, the AGCF strain sensors were tested for motion monitoring of the human body and electronic bird. Due to the remarkable versatility, scalable fabrication, and integration capability, these sensors demonstrate great potential to construct smart skins.

Minimizing the wiring in distributed strain sensing using a capacitive sensor sheet with variable-resistance electrodes

Strain mapping over a large area usually requires an array of sensors, necessitating extensive and complex wiring. Our solution is based on creating multiple sensing regions within the area of a single capacitive sensor body by considering the sensor as an analogical transmission line, reducing the connections to only two wires and simplifying the electronic interface. We demonstrate the technology by using piezoresistive electrodes in a parallel plate capacitor that create varying proportions of electromagnetic wave dissipation through the sensor length according to the interrogation frequency. We demonstrate, by a sensor divided into four virtual zones, that our cracked capacitive sensor can simultaneously record strain in each separated zone by measuring the sensor capacitance at a high frequency. Moreover, we confirm that by changing the frequency from high to low, our sensor is able to measure the local strain amplitudes. This sensor is unique in its ability to monitor strain continuously over a large area with promoted spatial resolution. This sensing technology with a reduced number of wires and a simple electronic interface will increase the reliability of sensing while reducing its cost and complexity.

Wearable Sensors for Healthcare: Fabrication to Application

This paper presents a substantial review of the deployment of wearable sensors for healthcare applications. Wearable sensors hold a pivotal position in the microelectronics industry due to their role in monitoring physiological movements and signals. Sensors designed and developed using a wide range of fabrication techniques have been integrated with communication modules for transceiving signals. This paper highlights the entire chronology of wearable sensors in the biomedical sector, starting from their fabrication in a controlled environment to their integration with signal-conditioning circuits for application purposes. It also highlights sensing products that are currently available on the market for a comparative study of their performances. The conjugation of the sensing prototypes with the Internet of Things (IoT) for forming fully functioning sensorized systems is also shown here. Finally, some of the challenges existing within the current wearable systems are shown, along with possible remedies.

High-Performance Flexible Pressure Sensor with a Self-Healing Function for Tactile Feedback

High-performance flexible pressure sensors have attracted a great deal of attention, owing to its potential applications such as human activity monitoring, man-machine interaction, and robotics. However, most high-performance flexible pressure sensors are complex and costly to manufacture. These sensors cannot be repaired after external mechanical damage and lack of tactile feedback applications. Herein, a high-performance flexible pressure sensor based on MXene/polyurethane (PU)/interdigital electrodes is fabricated by using a low-cost and universal spray method. The sprayed MXene on the spinosum structure PU and other arbitrary flexible substrates (represented by polyimide and membrane filter) act as the sensitive layer and the interdigital electrodes, respectively. The sensor shows an ultrahigh sensitivity (up to 509.8 kPa^-1 ), extremely fast response speed (67.3 ms), recovery speed (44.8 ms), and good stability (10 000 cycles) due to the interaction between the sensitive layer and the interdigital electrodes. In addition, the hydrogen bond of PU endows the device with the self-healing function. The sensor can also be integrated with a circuit, which can realize tactile feedback function. This MXene-based high-performance pressure sensor, along with its designing/fabrication, is expected to be widely used in human activity detection, electronic skin, intelligent robots, and many other aspects.

Fabrication of polydimethylsiloxane/graphene flexible strain sensors by using the scraping and coating method

Production of flexible strain sensors is complex, time-consuming, and expensive. In this study, a novel fabrication method of polydimethylsiloxane/graphene nanocomposite conductive materials was proposed by using the scraping and coating method for manufacturing sandwich-shape flexible strain sensors. A ZQ-60B tensile testing machine was employed to test the mechanical properties of flexible sensors with 1%, 3%, and 5% graphene content. The results revealed that the stress and strain of the flexible strain sensor exhibited a linear relationship, and the linear correlation coefficients were 0.99706, 0.99819, and 0.99826, respectively. The concentration of graphene was 1%, 3%, and 5%, and the gauge factors (GFs) of the sensor were 24, 6, and 3, respectively. With the increase in the graphene content, the GF decreased gradually. This phenomenon could be attributed to tunneling, which increased the number of conductive pathways with an increase in the graphene content. Furthermore, the sensor exhibited excellent stability after 100 cycles of stretching/scaling. The finger joint bending test revealed that the flexible strain sensor is reproducible and exhibits excellent application prospects in monitoring human movement and health.

Tissue Adhesive, Conductive, and Injectable Cellulose Hydrogel Ink for On-Skin Direct Writing of Electronics

Flexible and soft bioelectronics used on skin tissue have attracted attention for the monitoring of human health. In addition to typical metal-based rigid electronics, soft polymeric materials, particularly conductive hydrogels, have been actively developed to fabricate biocompatible electrical circuits with a mechanical modulus similar to biological tissues. Although such conductive hydrogels can be wearable or implantable in vivo without any tissue damage, there are still challenges to directly writing complex circuits on the skin due to its low tissue adhesion and heterogeneous mechanical properties. Herein, we report cellulose-based conductive hydrogel inks exhibiting strong tissue adhesion and injectability for further on-skin direct printing. The hydrogels consisting of carboxymethyl cellulose, tannic acid, and metal ions (e.g., HAuCl4) were crosslinked via multiple hydrogen bonds between the cellulose backbone and tannic acid and metal-phenol coordinate network. Owing to this reversible non-covalent crosslinking, the hydrogels showed self-healing properties and reversible conductivity under cyclic strain from 0 to 400%, as well as printability on the skin tissue. In particular, the on-skin electronic circuit printed using the hydrogel ink maintained a continuous electrical flow under skin deformation, such as bending and twisting, and at high relative humidity of 90%. These printable and conductive hydrogels are promising for implementing structurally complicated bioelectronics and wearable textiles.

Flexible Pressure Sensor Array with Multi-Channel Wireless Readout Chip

Flexible sensor arrays are widely used for wearable physiological signal recording applications. A high density sensor array requires the signal readout to be compatible with multiple channels. This paper presents a highly-integrated remote health monitoring system integrating a flexible pressure sensor array with a multi-channel wireless readout chip. The custom-designed chip features 64 voltage readout channels, a power management unit, and a wireless transceiver. The whole chip fabricated in a 65 nm complementary metal-oxide-semiconductor (CMOS) process occupies 3.7 × 3.7 mm², and the core blocks consume 2.3 mW from a 1 V supply in the wireless recording mode. The proposed multi-channel system is validated by measuring the ballistocardiogram (BCG) and pulse wave, which paves the way for future portable remote human physiological signals monitoring devices.

Graphene-based temperature, humidity, and strain sensor: A review on progress, characterization, and potential applications during Covid-19 pandemic

Graphene's potential as material for wearable, highly sensitive and robust sensor in various fields of technology has been widely investigated until now in order to capitalize on its unique intrinsic physical and chemical properties. In the wake of Covid-19 pandemic, it has been noticed that there are various potentials roles that can be fulfilled by graphene-based temperature, humidity and strain sensor, whose roles has not been widely explored to date. This paper takes the liberty to mainly highlight the progress layout and characterization technique for graphene-based sensor while including a brief discussion on the possible strategy of sensing data analysis that can be employed to minimize and prevent the risk of Covid-19 infection within a living community. While majority of the reported sensor is still in the in-progress status, its highlighted role in this work may provide a brief idea on how the ongoing research in graphene-based sensor may lead to the future implementation of the device for routine healthcare check-up and diagnostic point-care during and post-pandemic era. On the other hand, the sensitivity and response time data against working temperature, humidity and strain range that are provided could serve as a reference for benchmarking purpose, which certainly would help enthusiast in the development of a graphene-based sensor with a better performance for the future.

Wrist pulse signal acquisition and analysis for disease diagnosis: A review

Pulse diagnosis (PD) plays an indispensable role in healthcare in China, India, Korea, and other Orient countries. It requires considerable training and experience to master. The results of pulse diagnosis rely heavily on the practitioner's subjective analysis, which means that the results from different physicians may be inconsistent. To overcome these drawbacks, computational pulse diagnosis (CPD) is used with advanced sensing techniques and analytical methods. Focusing on the main processes of CPD, this paper provides a systematic review of the latest advances in pulse signal acquisition, signal preprocessing, feature extraction, and signal recognition. The most relevant principles and applications are presented along with current progress. Extensive comparisons and analyses are conducted to evaluate the merits of different methods employed in CPD. While much progress has been made, a lack of datasets and benchmarks has limited the development of CPD. To address this gap and facilitate further research, we present a benchmark to evaluate different methods. We conclude with observations of the status and prospects of CPD.

Wearable multichannel pulse condition monitoring system based on flexible pressure sensor arrays

Pulse diagnosis is an irreplaceable part of traditional Chinese medical science. However, application of the traditional pulse monitoring method was restricted in the modernization of Chinese medical science since it was difficult to capture real signals and integrate obscure feelings with a modern data platform. Herein, a novel multichannel pulse monitoring platform based on traditional Chinese medical science pulse theory and wearable electronics was proposed. The pulse sensing platform simultaneously detected pulse conditions at three pulse positions (Chi, Cun, and Guan). These signals were fitted to smooth surfaces to enable 3-dimensional pulse mapping, which vividly revealed the shape of the pulse length and width and compensated for the shortcomings of traditional single-point pulse sensors. Moreover, the pulse sensing system could measure the pulse signals from different individuals with different conditions and distinguish the differences in pulse signals. In addition, this system could provide full information on the temporal and spatial dimensions of a person's pulse waveform, which is similar to the true feelings of doctors' fingertips. This innovative, cost-effective, easily designed pulse monitoring platform based on flexible pressure sensor arrays may provide novel applications in modernization of Chinese medical science or intelligent health care.

Intelligent and Multifunctional Graphene Nanomesh Electronic Skin with High Comfort

As the aging population increases in many countries, electronic skin (e-skin) for health monitoring has been attracting much attention. However, to realize the industrialization of e-skin, two factors must be optimized. The first is to achieve high comfort, which can significantly improve the user experience. The second is to make the e-skin intelligent, so it can detect and analyze physiological signals at the same time. In this article, intelligent and multifunctional e-skin consisting of laser-scribed graphene and polyurethane (PU) nanomesh is realized with high comfort. The e-skin can be used as a strain sensor with large measurement range (>60%), good sensitivity (GF≈40), high linearity range (60%), and excellent stability (>1000 cycles). By analyzing the morphology of e-skin, a parallel networks model is proposed to express the mechanism of the strain sensor. In addition, laser scribing is also applied to etch the insulating PU, which greatly decreases the impedance in detecting electrophysiology signals. Finally, the e-skin is applied to monitor the electrocardiogram, electroencephalogram (EEG), and electrooculogram signals. A time- and frequency-domain concatenated convolution neural network is built to analyze the EEG signal detected using the e-skin on the forehead and classify the attention level of testers.

Spatiotemporal Measurement of Arterial Pulse Waves Enabled by Wearable Active-Matrix Pressure Sensor Arrays

Wearable pressure sensors have demonstrated great potential in detecting pulse pressure waves on the skin for the noninvasive and continuous diagnosis of cardiac conditions. However, difficulties lie in positioning conventional single-point sensors on an invisible arterial line, thereby preventing the detection of adequate signal amplitude for accurate pulse wave analysis. Herein, we introduce the spatiotemporal measurements of arterial pulse waves using wearable active-matrix pressure sensors to obtain optimal pulse waveforms. We fabricate thin-film transistor (TFT) arrays with high yield and uniformity using inkjet printing where array sizes can be customizable and integrate them with highly sensitive piezoresistive sheets. We maximize the pressure sensitivity (16.8 kPa^-1) and achieve low power consumption (10¹ nW) simultaneously by strategically modulating the TFT operation voltage. The sensor array creates a spatiotemporal pulse wave map on the wrist. The map presents the positional dependence of pulse amplitudes, which allows the positioning of the arterial line to accurately extract the augmentation index, a parameter for assessing arterial stiffness. The device overcomes the positional inaccuracy of conventional single-point sensors, and therefore, it can be used for medical applications such as arterial catheter injection or the diagnosis of cardiovascular disease in daily life.

A nature-inspired hierarchical branching structure pressure sensor with high sensitivity and wide dynamic range for versatile medical wearables

Pressure-sensing capability is essential for flexible electronic devices, which require high sensitivity and a wide detection range to simplify the system. However, the template-based pressure sensor is powerless to detect high pressure due to the rapid deformation saturation of microstructures. Herein, we demonstrated that a nature-inspired hierarchical branching (HB) structure can effectively address this problem. Finite element analysis demonstrates that the HB structure permits a step-by-step mobilization of microstructure deformation, resulting in a dramatically improved sensitivity (up to 2 orders of magnitude) when compared with the traditional monolayer structure. Experiments show that the HB structure enables pressure sensors to have a lower elastic modulus (1/3 of that of monolayer sensors), a high sensitivity of 13.1 kPa^-1 (almost 14 times higher than the monolayer sensor), and a wide dynamic range (0-800 kPa, the minimum detection pressure is 1.6 Pa). The maximum frequency that the sensor can detect is 250 Hz. The response/recovery time is 0.675/0.55 ms respectively. Given this performance, the HB sensor enables high-resolution detection of the weak radial artery pulse wave characteristics in different states, indicating its potential to noninvasively reveal cardiovascular status and the effectiveness of related interventions, such as exercise and drug intervention. As a proof of concept, we also verified that the HB sensor can serve as a versatile platform to support diverse applications from low to high pressure.

Ultrafast-Response/Recovery Flexible Piezoresistive Sensors with DNA-Like Double Helix Yarns for Epidermal Pulse Monitoring

A key challenge in textile sensors is to adequately solve the hysteresis for more broad and exacting applications. Unlike the conventional strategy in integrating elastic polymers into the textile, the hysteretic issue is critically addressed here through the structural design of yarns to provide a twisting force. The underlying mechanism is fully discussed based on theory and modeling, which are in good agreement with experimental data. Impressively, the pressure sensor outperforms almost all reported textile-based sensors in terms of recovery index, which refers to the ability to overcome the lagged deformation reflected by the hysteresis (5.3%) and relaxation time (2 ms). Besides, the sensor superiority is also demonstrated by way of its ultrafast response time (2 ms). Thanks to these merits, this pressure sensor is demonstrated to be capable of monitoring epidermal pulses and meanwhile shows great potential to advance the standardization and modernization of pulse palpation in traditional Chinese medicine.

Network crack-based high performance stretchable strain sensors for human activity and healthcare monitoring

In this study, high performance wearable and stretchable strain sensors are developed for human activity and healthcare monitoring, and wearable electronics.

Mechanical sensors based on two-dimensional materials: Sensing mechanisms, structural designs and wearable applications

Compared with bulk materials, atomically thin two-dimensional (2D) crystals possess a range of unique mechanical properties, including relatively high in-plane stiffness and large bending flexibility. The atomic 2D building blocks can be reassembled into precisely designed heterogeneous composite structures of various geometries with customized mechanical sensing behaviors. Due to their small specific density, high flexibility, and environmental adaptability, mechanical sensors based on 2D materials can conform to soft and curved surfaces, thus providing suitable solutions for functional applications in future wearable devices. In this review, we summarize the latest developments in mechanical sensors based on 2D materials from the perspective of function-oriented applications. First, typical mechanical sensing mechanisms are introduced. Second, we attempt to establish a correspondence between typical structure designs and the performance/multi-functions of the devices. Afterward, several particularly promising areas for potential applications are discussed, following which we present perspectives on current challenges and future opportunities

The Role of Soft Robotic Micromachines in the Future of Medical Devices and Personalized Medicine

Developments in medical device design result in advances in wearable technologies, minimally invasive surgical techniques, and patient-specific approaches to medicine. In this review, we analyze the trajectory of biomedical and engineering approaches to soft robotics for healthcare applications. We review current literature across spatial scales and biocompatibility, focusing on engineering done at the biotic-abiotic interface. From traditional techniques for robot design to advances in tunable material chemistry, we look broadly at the field for opportunities to advance healthcare solutions in the future. We present an extracellular matrix-based robotic actuator and propose how biomaterials and proteins may influence the future of medical device design.

Multifunctional Graphene Sensor Ensemble as a Smart Biomonitoring Fashion Accessory

Biomonitoring wearable sensors based on two-dimensional nanomaterials have recently elicited keen research interest and potential for a new range of flexible nanoelectronic devices. Practical nanomaterial-based devices suited for real-world service, which exhibit first-rate performance while being an attractive accessory, are still distant. We report a multifunctional flexible wearable sensor fabricated using an ultrathin percolative layer of graphene nanosheets on laser-patterned gold circular interdigitated electrodes for monitoring vital human physiological parameters. This graphene on laser-patterned electrode (GLE) sensor displays an excellent strain resolution of 245 με (0.024%) and a record high gauge factor of 6.3 × 10⁷, with exceptional stability and repeatability in its operating range. The sensor was tested for human physiological monitoring like measurement of heart rate, breathing rate, body temperature, and hydration level, which are vital health parameters, especially considering the current pandemic scenario. The sensor also served in applications such as a pedometer, limb movement tracker, and control switch for human interaction. The innovative laser-etch process used to pattern gold thin-film electrodes, with the multifunctional incognizable graphene layer, provides a technique for integrating multiple sensors in a wearable band. The reported work marks a giant leap from the conventional banal devices to a highly marketable multifunctional sensor array as a biomonitoring fashion accessory.

Graded Microstructured Flexible Pressure Sensors with High Sensitivity and an Ultrabroad Pressure Range for Epidermal Pulse Monitoring

Precisely detecting epidermal pulse waves with pressure sensors is crucial for pulse-based personalized health-monitoring technologies. However, developing a pressure sensor that simultaneously demonstrates high sensitivity and an ultrabroad pressure range and a convenient fabrication process for large-scale production is a considerable challenge. Herein, by utilizing a commercial conductive fabric (CF) and a silica gel film, we develop a high-performance pressure sensor (HPPS) for the monitoring of human physiological signals. Based on convenient turnover formwork technology, the silica gel film was fabricated by replicating the microstructure of the sandpaper surface. This microstructure and the plain weave structure on the CF surface together provide a sharp increase in the contact-separation area and structural compressibility, which are beneficial for the enhancement of output performance. Made of these two materials, the graded microstructured HPPS holds high sensitivity (4.5 mV/Pa), an ultrabroad pressure range (0-30 kPa), a wide working frequency bandwidth (up to 35 Hz), decent stability (>50,000 cycles), and a simple fabrication process that is suitable for large-scale production. Given these noticeable features, the developed HPPS not only succeeds in precisely detecting subtle pulse waves on various positions of different people but can also objectively capture changes in cardiovascular parameters caused by exercise training at different intensities in real time. These findings exhibit the enormous potential application of HPPS in tracking an individual's health status and comprehensively evaluating exercise intensity.

Pulse taking by a piezoelectric film sensor via mode energy ratio analysis helps identify pregnancy status

In order to solve the problem of non-invasive diagnosis and monitoring of women during pregnancy, a piezoelectric film pulse sensing system combined with the mode energy ratio (MER) analysis is utilized to detect human pulses to reveal pregnant conditions. Inspired by traditional Chinese medicine (TCM), pulse diagnosis has a history of more than 2,500 years. The life energy of the human body helps the diagnosis of the disease through the circulation of blood vessels connected to the organs. A PVDF piezoelectric film sensor is used to emulate the pulse taking process in TCM to record the pulse signals. And the algorithm of MER is proposed based on empirical mode decomposition (EMD). Through the MER analysis of 83 female volunteers with different pregnancy statuses, the identification and warning of pregnancy status and physical health indicators are realized.

High Channel Temperature Mapping Electronics in a Thin, Soft, Wireless Format for Non-Invasive Body Thermal Analysis

Hemodynamic status has been perceived as an important diagnostic value as fundamental physiological health conditions, including decisive signs of fatal diseases like arteriosclerosis, can be diagnosed by monitoring it. Currently, the conventional hemodynamic monitoring methods highly rely on imaging techniques requiring inconveniently large numbers of operation procedures and equipment for mapping and with a high risk of radiation exposure. Herein, an ultra-thin, noninvasive, and flexible electronic skin (e-skin) hemodynamic monitoring system based on the thermal properties of blood vessels underneath the epidermis that can be portably attached to the skin for operation is introduced. Through a series of thermal sensors, the temperatures of each subsection of the arrayed sensors are observed in real-time, and the measurements are transmitted and displayed on the screen of an external device wirelessly through a Bluetooth module using a graphical user interface (GUI). The degrees of the thermal property of subsections are indicated with a spectrum of colors that specify the hemodynamic status of the target vessel. In addition, as the sensors are installed on a soft substrate, they can operate under twisting and bending without any malfunction. These characteristics of e-skin sensors exhibit great potential in wearable and portable diagnostics including point-of-care (POC) devices.

Tensible and flexible high-sensitive spandex fiber strain sensor enhanced by carbon nanotubes/Ag nanoparticles

Although the wearable strain sensors have received extensive research interest in recent years, it remains a huge challenge conforming the requirements in both of ultrahigh stretchability and high strain coefficient (gauge factor). Herein, a stretchable and flexible spandex fiber strain sensor coupled with carbon nanotubes (CNTs)/Ag nanoparticles (Ag NPs) that assembled through an efficient and large-scale layer-by layer self-assembly is presented. To ensure CNTs and Ag NPs can attach well to the spandex fiber without falling off, achieving high sensitivity under large tensile, sodium dodecyl benzene sulfonate, polyvinyl alcohol, and polystyrene sulfonic acid are introduced to improve the adhesion via the molecular entanglement and other interactions between them. Consequently, the strain sensor exhibits remarkable performance, such as an ultrahigh gauge factor of 58.5 in the low-strain range from 0% to 20%, a wide strain range (0%-200%), a fast response time of 42 ms and good working stability (>5000 stretching-releasing cycles). Subsequently, detailed mechanism of the sensor and its use in full range of human motion monitoring are further studied. It is worth noting that with the distinctive mechanism and structure, the special spandex fiber sensor is able to monitor minimum strain as low as 0.053%, showing tremendous prospect for the field of smart fabrics and wearable health care devices.

Soft Wearable Healthcare Materials and Devices

In spite of advances in electronics and internet technologies, current healthcare remains hospital-centred. Disruptive technologies are required to translate state-of-art wearable devices into next-generation patient-centered diagnosis and therapy. In this review, recent advances in the emerging field of soft wearable materials and devices are summarized. A prerequisite for such future healthcare devices is the need of novel materials to be mechanically compliant, electrically conductive, and biologically compatible. It is begun with an overview of the two viable design strategies reported in the literatures, which is followed by description of state-of-the-art wearable healthcare devices for monitoring physical, electrophysiological, chemical, and biological signals. Self-powered wearable bioenergy devices are also covered and sensing systems, as well as feedback-controlled wearable closed-loop biodiagnostic and therapy systems. Finally, it is concluded with an overall summary and future perspective.

Nanostructured Gas Sensors: From Air Quality and Environmental Monitoring to Healthcare and Medical Applications

In the last decades, nanomaterials have emerged as multifunctional building blocks for the development of next generation sensing technologies for a wide range of industrial sectors including the food industry, environment monitoring, public security, and agricultural production. The use of advanced nanosensing technologies, particularly nanostructured metal-oxide gas sensors, is a promising technique for monitoring low concentrations of gases in complex gas mixtures. However, their poor conductivity and lack of selectivity at room temperature are key barriers to their practical implementation in real world applications. Here, we provide a review of the fundamental mechanisms that have been successfully implemented for reducing the operating temperature of nanostructured materials for low and room temperature gas sensing. The latest advances in the design of efficient architecture for the fabrication of highly performing nanostructured gas sensing technologies for environmental and health monitoring is reviewed in detail. This review is concluded by summarizing achievements and standing challenges with the aim to provide directions for future research in the design and development of low and room temperature nanostructured gas sensing technologies.

Highly Sensitive Capacitive Flexible Pressure Sensor Based on a High-Permittivity MXene Nanocomposite and 3D Network Electrode for Wearable Electronics

With the fast development of consumer electronic and artificial intelligence equipment, flexible pressure sensors (FPSs) have become a momentous component in the application of wearable electronic, electronic skin, and human-machine interfacing. The capacitive FPS possesses the merits of low energy consumption, high resolution, and fast dynamic response, so it is ideal for mobile and wearable electronics. However, capacitive FPS is vulnerable to electromagnetic interference and parasitic capacitance due to its low sensitivity. Microstructure or porous dielectric materials have been applied to improve the sensitivity of the capacitive FPS, but the high sensitivity is just limited to a narrow region. In this work, we propose a different strategy that incorporates a high-permittivity MXene nanocomposite dielectric with a 3D network electrode (3DNE) to improve the sensing performance of the capacitive FPS. Thanks to the high permittivity of the dielectric layer and hierarchical deformation of the electrode, the fabricated capacitive FPS exhibits a high sensitivity of 10.2 kPa^-1 in the low pressure range (0-8.6 kPa) and still maintains a relatively high sensitivity of 3.65 kPa^-1 with a near-linear response in a wide pressure range (8.6-100 kPa). In addition, the capacitive FPS can withstand over 20,000 times pressure loads without significant signal damping. Furthermore, the working mechanism of the capacitive FPS is illustrated by the finite element analysis (FEA) method and theoretical calculation. The application potential of the sensor in wearable electronics was demonstrated by human pulse wave monitoring and pressure mapping tests with a 4 × 6 sensor microarray.

Triboelectric Nanogenerators for Therapeutic Electrical Stimulation

Current solutions developed for the purpose of in and on body (IOB) electrical stimulation (ES) lack autonomous qualities necessary for comfortable, practical, and self-dependent use. Consequently, recent focus has been placed on developing self-powered IOB therapeutic devices capable of generating therapeutic ES for human use. With the recent invention of the triboelectric nanogenerator (TENG), harnessing passive human biomechanical energy to develop self-powered systems has allowed for the introduction of novel therapeutic ES solutions. TENGs are especially effective at providing ES for IOB therapeutic systems given their bioconformability, low cost, simple manufacturability, and self-powering capabilities. Due to the key role of naturally induced electrical signals in many physiological functions, TENG-induced ES holds promise to provide a novel paradigm in therapeutic interventions. The aim here is to detail research on IOB TENG devices applied for ES-based therapy in the fields of regenerative medicine, neurology, rehabilitation, and pharmaceutical engineering. Furthermore, considering TENG-produced ES can be measured for sensing applications, this technology is paving the way to provide a fully autonomous personalized healthcare system, capable of IOB energy generation, sensing, and therapeutic intervention. Considering these grounds, it seems highly relevant to review TENG-ES research and applications, as they could constitute the foundation and future of personalized healthcare.

A highly sensitive strain sensor with a sandwich structure composed of two silver nanoparticles layers and one silver nanowires layer for human motion detection

The fabrication of strain sensors with high sensitivity, large sensing range and excellent stability is highly desirable because of their promising applications in human motion detection, human-machine interface and electric skin, etc. Herein, by introducing a highly conductive silver nanowire (AgNW) layer between two serried silver nanoparticle (AgNP) layers, forming a sandwich structure, a strain sensor with high sensitivity (a large gauge factor of 2.8 × 10⁵), large sensing range (up to 80% strain) and excellent stability (over 1000 cycles) can be achieved. A combination of experimental and mechanism studies shows that the high performance of the obtained strain sensor is ascribed to the synergy of the highly conductive AgNW layer, astatic AgNP layers and the presence of large cracks in stretching. As a proof-of-concept application, the obtained strain sensor can be used for highly effective human motion detection ranging from large scale motions, i.e. kneel bending and wrist flexion, to subtle scale motions, i.e. pulse and swallowing.

Flexible Hybrid Electronics for Monitoring Hypoxia

Hypoxia refers to insufficient oxygen amounts at the tissue level unable to maintain adequate homeostasis. Severe hypoxia may occur in the absence of subjective breathlessness due to respiratory failure. Precise monitoring of low blood oxygen saturation is crucially desired, catering to the clinical requirements. However, current pulse oximeters cannot function well in monitoring peripheral oxygen saturation limited by the weak peripheral blood circulation at a low oxygen level. In this work, we propose a flexible hybrid electronic (FHE) with a compact structure and high sensitivity for conveniently monitoring hypoxia. This FHE is composed of 10-µm thickness semiconductors with different materials, functionalities, and sizes. Its performance is demonstrated by monitoring arterial blood oxygen saturation (SaO₂) at the body's different arteries. The absolute error is less than 2% within a SaO₂ ranging from 99% to 63%. The efficient techniques presented in this work may bring light to the next-generation flexible hybrid electronics and provide potential widespread use in research and clinical applications, especially for emergency treatment.