Authors:Bingjie Dang *, Hong Wang*, Yue Hao*

Abstract:
Here we demonstrate a novel physically transient true random number generator based on magnesium oxide volatile threshold switches, using the intrinsic variation in resistive switching as a natural source of randomness. Taking advantage of the volatile nature in switching, a reset operation is not required in each cycle and the operation is largely simplified. It is demonstrated that such random number generators can be applied for complex numerical calculations, and the value of π was successfully calculated in Monte Carlo method based on the random number generators. Such random number generators based on physically transient threshold switches can have a great prospect in Monte Carlo computing and secure electronics.

Authors:He Ding* , Xing Sheng#

Abstract:
Optical upconversion that converts infrared light into visible light is of significant interest for broad applications in biomedicine, imaging, and displays[1]. Conventional upconversion materials, e.g., rare-earth, organic dyes and quantum dots, rely on non-linear light-matter interactions, exhibit incidence dependent efficiencies and require high power excitation. By taking advantage of a fully integrated heterostructures based on III – V materials with photon – “free electron” – photon processes, we report a near-infrared (∼810 nm) to visible [630 nm (red) or 590 nm (yellow)] upconversion that is linearly dependent on incoherent, low-power excitation, with a quantum yield of ∼1.5%. By means of the new upconversion strategy based on devices design, a linearly dependent on incoherent, low-power excitation, fast transient decay of infrared- to-visible light process can be realized [2]. By exploiting the advanced manufacturing method, encapsulated, freestanding devices are transferred onto heterogeneous substrates and show desirable biocompatibilities within biological fluids and tissues. These microscale devices are implanted in behaving animals, with in vitro and in vivo experiments demonstrating their utility for optogenetic neuromodulation[3].
To summarize, the concepts presented here demonstrate materials and device strategies for highly efficient IR-to-visible upconversion that bypass many limitations of previously explored techniques. Furthermore, other approaches like wafer bonding and transfer printing instead of direct epi-growth can be explored to realize highly compact, heterogeneously integrated structures. By combining with light-sensitive receptors or drugs, these miniaturized devices can be applied to deep-tissue light stimulation or therapy. These results provide routes for high- performance upconversion materials and devices and their unprecedented potential as optical biointerfaces.

Authors:Yichun Ding*,†, Wenhui Xu,# Zhengtao Zhu†

Abstract:
The past few years have witnessed the ever-increasing development of flexible and wearable electronics, which have great potentials for human health monitoring, artificial intelligence, and Internet of Things (IoT) [1]. The flexible and wearable healthcare monitoring system can provide real-time monitoring of human body activities/conditions thus gathering timely information about human health status. A fully functional wearable sensing system not only requires active sensors but also needs other components including power supply, conductor, data acquisition, and signal processing modules, etc. While substantial achievements have been progressively made due to the continued innovation of materials and fabrication technologies, advanced materials and high-performance devices are still eagerly desired for paving the way of flexible electronics to practical applications.
In recent years, we have been exploring electrospun nanofibers as a key component in flexible and wearable electronic devices such as flexible sensors, conductors, and power supply devices (Figure 1). Electrospun nanofibers, produced by electrospinning technique, represents a class of promising nanomaterials for various applications in biomedical engineering, microelectronics, energy storage and conversion devices, and environmental remediation, owing to their advantageous properties of ultrasmall diameter, large surface area, scalable fabrication, and facile functionalization [2]. Using electrospun carbon nanofiber as a piezoresistive element, we have demonstrated highly stretchable strain sensors by embedding freestanding electrospun carbon nanofibrous mat in an elastomer for human motion monitoring [3]. We also prepared a three-dimensional (3D) conductive sponge by freeze-drying of the building blocks of shortened electrospun nanofibers, which was then used for assembling a highly compressible tactile sensor for electronic skin application [4]. To develop a stretchable and wearable conductive textile on a large scale, we combined electrospinning of an elastomer (e.g., polyurethane) with dip coating technique. The fabricated conductive fibrous nonwoven (PEDOT:PSS@PU) could be used directly or integrated into cloth for wearable conductor applications [5]. We are currently developing flexible power supply devices (e.g., battery, nanogenerator) by adopting electrospun nanofibers as an active material or substrate. Herein, we present our results as well as on-going projects regarding electrospun nanofibers for flexible devices. We anticipate that the powerful tool of electrospinning technique will stimulate development of flexible and wearable electronics and potentially a fully funcational wearable electronic system can be achieved using all-electrospun nanofibers-based devices.

Authors:Qifeng Du†, Jun Ai†, Ying Chen†, Xue Feng#,*

Abstract:
Flexible pressure sensors have attracted wide attention for applications in health monitoring and human-machine interface. However, the conflict between their high sensitivity and wide linearity pressure range restricts their practical applications. Herein, a simple and large-scale manufacturing method for the fabrication of a flexible capacitive pressure sensor with multilevel microstructured polydimethylsiloxane (PDMS) is presented. The multilevel microstructures consist of arrays of microscale bulge and multiholes produced by replicating the laser-ablated template and salt leaching method, respectively. Under different pressures, sharp increases in the contact area and additional dielectric constant changes caused by the multilevel microstructures contribute to the high sensitivity and the wide linearity pressure range. The flexible pressure sensor shows potential applications in the detection of human physiological signals, such as wrist pulse, heart rate, breathing rate and foot plantar pressure.

Authors:Shengshun Duan*, Jun Wu*

Abstract:
The combination of the Internet of Things and the flexible wearable electronics is considered as an effective way to realize data acquisition, processing and feedback and has drawn increasing attention in recent years. Therefore, A flexible bionic wearable angle sensor with linear sensing ability based on PVA-Microstructured PU sponge-PVA sandwich structure was fabricated by a simple two-step method including laser-engraving and dip-coating, which was inspired by the crack-shaped slit sensilla of the heterometrus petersii. The sensor took advantage of microstructured PU sponge as sensing functional layer and PVA thin film as supporting layer and strain transmitted layer.

Authors:Wen-Ting Fan, Jing Yan, Yan-Ling Liu, Yu Qin, Wei-Hua Huang*

Abstract:
The vasculature is always exposed to complex biomechanical stress, abnormal stress would disequilibrate its homeostasis and ultimately trigger a series of vascular diseases, such as atherosclersis[1]. Accumulating evidence suggests that reactive oxygen species (ROS) are intimately involved in the occurrence and development of these diseases induced by stress[2]. Therefore, it is of great significance to obtain the dynamic information of ROS production and metabolism under the pathophysiological conditions. However, its high reactivity and short half-time make it quite diffcult to detect ROS from complicated biological system in real-time, especially released from the cell or tissue in dynamic stretching state. Hence, the development of ROS sensors equipped with both sensitive response and mechanical compliance are rather urgent and challenging.
Flexible electrochemical sensor, as an emerging but attractive technique, possesses many prominent merits in monitoring signalling molecules from deformed cells and curvilinear tissues in real-time and continuously[3]. In this work, we fabricate a flexible electrochemical sensor based on ultra-small Pt NPs inlaid Au NTs networks onto PDMS film (Pt NPs/Au NTs/PDMS) with excellent electrocatalytic performance toward the oxidation of H2O2. Furthermore, the asprepared device remains desirable electrochemical activity even under 50% tensile deformation. These results demonstrate that this sensor can be potentially used to induce and monitor simultaneously H2O2 release from vascular cells, thereby providing a better understanding of the role of ROS during various pathophysiological processes.

Authors:Haoran Fu*, Ruitao Tang*

Abstract:
Flexible/stretchable electronic technologies are of growing interest, oweing to their ability to render rigid and brittle semiconductors systems in forms that allow extremely large strain deformation. This class of technology opens up diverse engineering applications, ranging from wearable optoelectronic devices to epidermal health monitor, to sensitive robotic skins, and to eye-ball like digital camera. Many such stretchable devices utilize island-bridge design, in which active components are distributed in localized, nondeformable platform (i.e., islands), and joined by deformable interconnects. This strategy could offer considerable stretchablity (≤ 80%), but is limited by the large heat generation and low surface filling ratio due to the narrow and long interconnects (i.e., serpentine interconnects[1] or non-coplanar interconnects[2]). An alternative type of interconnects that exploit self-similar geometries can achieve a much higher surface filling ratio[3], however, it demands highly precise planar fabrication equipment, and the problems of heat generation also remains.
Island-bridge strategy incorporated with kirigami membranes (as shown in Fig. 1) can provide large stretchability while ensuring high surface filling ratio and low heat generation[4]. In this design, membranes with precisely engineered cuts are utilized to form the bridge, and can accomodate nearly all of the deformation under stretching condition. Remarkable progresses have been made in application of stretchable kirigami membranes[5], however, the underlying mechanics that governs the postbuckling process remains unclear, due to the complex geometries and nonlinear buckling behavior.
The aim of this study is to present a systematic investigation for the postbuckling behavior of kirigami membranes, through combined analytical modeling, numerical simulations, and experimental measurements (Fig. 2). By formulating a scaling law to the localized strain, this paper established the correlations between the stretchability and various geometric parameters, providing a design guidelines for practical applications. Furthermore, we demonstrate an optimized kirigami membrane as part of a stretchable metal electrode, with high surface filling ratio and large stretchablity, thereby outperforming interconnects design reported previously.

Authors:Qiqi Fu*, Zhao Pan#

Abstract:
The monitoring of blood flow is important to the recovery of patient after reconstructive surgeries.[1] Here, we reported a flexible pressure sensor for the accurately monitoring of blood flow. The pulse sensor consists of two sensitive strain gauge, made of Au resistor, and connected each other with serpentine traces. The sensitive is proved by the monitoring of human pulse via directly attaching the sensor to the artery of the wrist (Figure 1). The accuracy is demonstrated on a test set-up of mimicking pulsatile behavior and typical expansion of blood vessel. This technology may be advantageous in real-time post-operative monitoring of blood flow after reconstructive surgery.

Authors:Gang Ge†, Wei Huang†#, Xiaochen Dong†

Abstract:
Flexible sensory electronics have received extensive interest due to its simple device configuration, high sensitivity and easy signal processing.[1-3] Hydrogels, which are highly biocompatible, nontoxic and environmentally friendly, are promising in tissue engineering, artifcial actuators and soft electronics. However, traditional hydrogel suffers from poor stretchability and is subjected to irreversible mechanical failure. Herein, highly stretchable, piezoresistive and self-healing hydrogel-based flexible sensors are fabricated. Firstly, polyacrylamide-polyvinyl alcohol (PAM-PVA) composite hydrogel with self-patterned morphology was used as building blocks of sensor.[4] The hydrogel exhibited impressive stretchability (> 500% strain) and superior transparency (> 90%), furthermore, the self-patterned micro-architecture on the hydrogel surface was beneficial to achieving high sensitivity (0.05 kPa-1 for 0 - 3.27 kPa). Various dynamic pressures (3.33, 5.02 and 6.67 kPa) monitoring, fast response time (150 ms), durable stability (500 dynamic cycles) and negligible current variation (6%) were also integrated into the hydrogel-based sensor (Figure 1). More importantly, highly stretchable (> 550% strain), self-healing (497% healed strain with 90.4% healing efficiency after 6h) and anti-freezing (502% strain after freezing under -25°C) binary networked hydrogel- based flexible sensors were prepared.[5] The hydrogel-based sensor behaved fast electrical self- healing (125 ms), which was promising for soft circuit. After being crushed into fragments, the hydrogel could be remolded, which was conducive to renewable electronics (Figure 2).

Authors:Bowen Geng*, Xiaochen Ren*, Wenping Hu*

Abstract:
The electro-hydrodynamic (EHD) jet printing is a promising technology because it increases the printing resolution over two orders of magnitude than traditional piezoelectric ink-jet printing methods, therefore enables the fabrication of high-resolution flexible electronics. For flexible printing devices, the temperature sensors array play an important role for their several key potential applications, such as thermal management of electronic components, human body temperature mapping and smart monitoring for logistics. In this work, we use EHD jet printing to complete the whole fabrication of an 8×8 temperature sensor array on one inch square flexible substrate. The single sensor device, which is shown in Figure 1, is realized by commercial Ag NPs ink and the sensing mechanism is based on measuring the temperature induced resistance change of Ag electrode. Benefited from the high-resolution of EHD jet printing, the length over width of the Ag wire could be larger than 4000, ensuring a strong reading signal even the temperature coefficient resistance (TCR) of Ag is relatively small and at the same time maintaining small sensor size. As part of the sensor array, the via-holes connect the wiring from different layers, the size of via-holes is also critical for high-resolution circuit/array fabrication, we use high-voltage of EHD jetting system to burn the through holes on the flexible substrate with hole diameter down to 5 μm, which is largely improved compared to other non-lithography based technologies. Finally, the word lines and bit lines are finished by EHD jet printing and a 50μm thick Ecoflex layer is used as the encapsulation on top. The heat transfer simulation is also studied to guide the design of temperature sensor array.

Authors:M. Guo†, X. B. Lu†,*

Abstract:
Flexible strain sensor has captured a lot of attention since it was proposed. Many efforts have been focused on adopting new materials or developing novel structures to detect strain, temperature and even to realize multi-function. The reliability of flexible strain sensor in harsh environments such as at low and high temperatures, however, has so far received few attentions because traditional bendable or stretchable substrates, including polyethylene terephthalate (PET), polyimide (PI), polydimethylsiloxane (PDMS), paper, silk, and cotton, cannot withstand high temperature. The poor thermal stability limits their potential applications in harsh conditions such in interstellar prob, polar exploration, petrochemical, and metal smelting.
In this work, we fabricated a flexible strain sensor consists of a La0.7Sr0.3MnO3 (LSMO) film on top of a 4.5 μm thick mica substrate, This cost-effective and environment friendly strain sensor shows excellent mechanical bending properties, high durability (up to 9 hours) and fast response time (0.1 s). Most importantly, it can work in a broad temperature range from extreme low temperature down to 20 K to high temperature up to 773 K. The device structure and the main results are shown in the following Figure 1. The flexible strain sensor based on the flexible LSMO/mica hetero-structure shows great potential applications for flexible electronics using at extreme temperature environment in the future.

Authors:Guo Rui, Yao Siyuan, Sun Xuyang and Liu Jing*

Abstract:
In this paper, we first discovered that the semi-liquid metal (Ni-EGaIn) exhibited poor adhesion on toners, which could be printed on various flexible substrates using laser printer. Based on the adhesion difference of Ni-EGaIn on toners and PU glue, we developed a super-fast fabrication method for flexible electronics: semi-liquid metal based on adhesion-difference for rolling & transfer (SMART) printing. Here, the Ni- EGaIn could be rolling printed on thermal transfer paper in 10s, which is faster than all the other liquid metal printing methods. More importantly, the Ni-EGaIn printed on paper also could be transfer printed on Ecoflex substrate to fabricate stretchable electronics. A series of paper and stretchable electronics, such as LED array, multilayer circuits and strain sensor were fabricated to show their excellent electrical stability and great application potential for flexible electronics. Finally, we found that the printed Ni-EGaIn with advantages of recyclable ability made it possible to further reduce the cost of fabrication and environment pollution.

Authors:Xiaoyang Guo, Ying Lv, Yi Fan, Jie Lin, Xingyuan Liu

Abstract:
Facing the future development trend of flexible and wearable optoelectronic products, transparent electrode, as an important part of optoelectronic devices, has a crucial impact on the future development of optoelectronic industry. As one of the alternative electrodes to traditional ITO electrode, dielectric−metal−dielectric (DMD) multilayer transparent electrodes possess high transmittance, low sheet resistance and excellent bending durability, which have potential applications on flexible organic or perovskite photovoltaic cells.
During the past few years, a series of DMD transparent electrodes have been developed, such as WO3/Ag/WO3(WAW) [1], NiO/Ag/NiO(NAN) [2], SnO2/Ag/SnO2/Bi2O3(SASB) [3], PVK/Ag/PVK(PAP) and PVK/Ag/PEDOT(PAPE) [4], ect.. All these transparent electrodes show excellent photoelectric and bending characteristics. The flexible polymer solar cells based on these DMD electrodes also display competitive device performance and flexiblity.

Authors:Zhiyuan Han, Xue Feng *

Abstract:
Previously, 3D porous materials have achieved great progress in pressure-sensing or other various applications. For instance, Qin and co-workers fabricated a flexible graphene/polyimide nanocomposite foam with a high pressure sensitivity (0.18kPa-1) for stain sensor application.[1] Another research reported a hierarchical assembly strategy for fabricating nanocomposite foams with lightweight, hydrophobicity, and superinsulating properties.[2]. However, it still remains a challenge to prepare ultrahigh pressure-sensing materials simultaneously owning other versatile characteristics. Herein, an easy-fabricated and cost-efficient preparation has been proposed to fabricate versatile carbon nanofiber aerogels (CNFNs) with superior pressure sensitivity based on modified electrospinning and thermal treatment. 3D floc is directly fabricated by electrospinning, which is different from conventional electrospinning into thin film, and then CNFNs was prepared with the floc through thermal carbonization. To the best of our knowledge, the CNFNs exhibited the highest pressure sensitivity of 1.41 kPa-1 compared with similar 3D porous materials. Different from traditional carbonaceous materials with brittle feature [3], the CNFNs preformed robust mechanical properties, excellent flexibility, stable resilience and super compressibility of >95%.
Contributing to the stable mechanical and piezoresistive properties of the CNFNs, a pressure sensor is designed with the CNFNs, which is capable in monitoring human physiological signals, such as phonation, pulse, respiration activities of human joints. The three peaks in a pulse waveform correspond to percussion wave (P-wave), tidal wave (T-wave) and diastolic wave (D- wave), respectively, which is assistant information for medical diagnosis. Meanwhile, an arch- array platform for direction identification of tangential forces and an artificial electronic skin bioinspired by human’s hairy skin have been ingeniously designed. Besides the high pressure sensitivity, the CNFNs demonstrate other versatile properties as well, concluding ultralight density of 3.6 mg/cm3, hydrophobicity, a relatively low thermal conductivity (23 mW·m-1·K- 1) and infrared emissivity (0.62). Therefore the CNFNs show promising potential in a wide range of applications, such as thermal insulation, infrared stealth and electrodes for supercapacitors, etc.

Authors:W. E. He†, X. B. Lu†,*

Abstract:
Nonvolatile memory devices based on organic thin-film transistors (OTFTs) have been widely studied as one of the leading flexible memory technologies. In spite of substantial progress in terms of selecting and optimizing charge-blocking and/or tunneling layers, OTFT devices reported to date still suffer from a series of deficiencies that hinder the extensive use of OTFTs in practical applications. These deficiencies include high operating voltage, low operating speed, poor reliability, etc.
In this study, we fabricated a high quality amorphous La2O3 dielectric film at low temperature via a low-cost solution process and realized a flexible nonvolatile memory made by using pentacene as semiconducting channel, poly(ɑ-methylstyrene) as charge trapping layer, and solution processed amorphous La2O3 film as charge blocking layer, deposited in sequence on Au-coated flexible muscovite substrate, as shown in Figure 1(a). The device with 120°C- annealed La2O3 film shows a very low gate leakage current (1.66 nA at –4 V) during the Ids–Vgs voltage scanning cycle (Figure 1(b)).
A memory window as wide as Vth = 1.0 V is achieved at a low continuous sweeping voltage between  4.5 V under the 365 nm-UV light. When it was applied with pulsed program (+8 V/1 ms)/erase (–7 V/100 s) voltages, the flexible OTFT shows the excellent electrical performance such as operation speed as fast as 100 s, largest memory window as wide as 2.7 V. In summary, flexible OTFT memory device with a solution processable La2O3 is promising for future applications in low power consumption and wearable flexible nonvolatile memory devices.

Authors:Jianlong Hong, Jun Wu

Abstract:
Laser scribed graphene(LSG), with programmable patterns and superior electronic properties, has attracted considerable attentions and has been widely applied in various wearable electronics. [1] However, its characteristics such as easy peeling, weak stretchability has prevent it from further industrial applications. Herein, this work reports a durable, ultrathin, skin- conformable laser scribed graphene based sensor by transferring LSG to a commercial make-up accessory (nose film), which has been reported as a pollution-free and skin-friendly flexible substrate. [2] Without any packaging, the sensor exhibits excellent durability, relatively high sensitivity with a gauge factor over 300, large stretch range of more than 50%. Its superior performance and printable preparation process can promote the industrialization of flexible strain sensors.

Authors:Xinghua Hong*#, Ming Hou*#, Yanjun Tang*#, Ziming Jin*#, Aidan Zhang*#

Abstract:
Flexible piezoresistivity-based smart fabric with the ability to sense is valuable for numerous applications and have attracted considerable attention in recent years. Which commonly involve the coating of conventional fabrics with functional materials, the use of multiple types of filament in forming of a yarn, the use of a hybrid fabric and the integration of sensors in the fabric. Their flexibility, durability, functional area, strain sensing range and cost of the sensors are of concern. Piezoresistivity refers to the phenomenon in which the electrical resistivity of a material changes with the strain. Here we report a negative piezoresistivity- based smart fabric distinguishes regular smart fabric from the essential features of the anti- variations of electrical resistivity with the strain. The flexible negative piezoresistivity- based sensing fabrics were fabricated through impregnated treatment of graphene oxide (GO), followed was suffered through the chemical method of reduction in the presence of hydrazine hydrate. The GO was reduced to reduced graphene oxide (RGO) that impacted the fabric electrical conductivity. The electromechanical performance and strain sensing properties of the fabric, which involves the dynamic resistance fluctuation in accordance to the variation of external action pertain to the electrical resistance, displacement and load, were measured simultaneously, continuously and digitally during load increase and the subsequent period of upload by using the four-probe resistence meter and screw-action mechanical testing system. In addition, the composition and structural properties were preformed for the treated fabrics involve the using of the scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy and contact angles. Negative piezoresistivity behavior (relative resistance variation (∆R/R0) up to -65% versus cyclic tensile strain of ~10%) has been discovered in our fabric due to multistage composite structure involve the fibers, yarns and fabric weave. The fabric has considerable attributes of hydrophobicity (contact angle nearby 140o). This aussichtsreich smart textile as flexible strain sensors that are enable to monitor the action of body and has more potential applications in flexible electronics.

Authors:Luhing Hu, Jae Yong Choi, Sumin Hwangbo, Jong-Hyun Ahn*

Abstract:
Gallium Nitride (GaN) based blue light emitting diode (LED) is definitely an emerging technology which already grabbed attention from various fields, including indoor and outdoor lighting systems, displays, and medical devices because of its excellent quality of light illumination. GaN LEDs in micrometer scale can be driven at higher current densities and give promising energy efficiency in light emission. The outstanding performance of micro-LEDs have attracted many researches that study the potential applications of micro-LEDs. [2] In this report, we have studied method to realize full color RGB micro-LED display by patterning quantum dots (QD) on GaN micro-LED, which will convert blue light into either red or green light. We developed QD-PR that can be photolithographically patterned in micro scale using conventional method. By mixing high refractive index nanoparticles, TiO2 as scattering enhancers into the QD-PR, the light output intensity can be improved and standard RGB can be achieved. In addition, in order to realize flexible micro-LED display, we released the devices from Si substrate by wet etching process and then transfer the devices onto ultrathin plastic substrate. Finally, flexible RGB micro-LED display was demonstrated.

Authors:Penghao Hu*,#, Lili Yan*, Chaoxian Zhao*, Yangyang Zhang*, Jin Niu*

Abstract:
PVDF-based nanocomposite films are promising in fabrication flexible piezoelectric nanogenerators for self-powered portable devices. In this work, a double-layered heterostructure was designed and the PVDF nanocomposite films contained with barium titanate nanoparticles were prepared by solution spin coating. The nanofillers were concentrated distributed in one layer of half the film, and the remaining half was neat PVDF layer. The double-layered BT/PVDF films were characterized comparatively with their counterpart of single-layer films. Although containing with less content of BT nanoparticles and lower proportion of β-phase in polymer, the piezoelectric nanogenerator (PENG) devices fabricated by double-layered films represent higher piezoelectric outputs in mechanical-to-electric conversion measurement. The charges accumulated at the additional interlayer interface between BT/PVDF layer and PVDF layer contributes much to enhancing electric capacity of the film. Benefited from good interfacial adhesion and better flexibility, the mechanical property and cyclic endurance are also improved. The double-layer film contained with 20 volume fractions (vol%) BTNPs represent excellent comprehensive performance of 6.7 V in output voltage, 2.4 μA in output current, and good stability changed within 3% in more than one thousand circles. The double-layer constructure is promising in nanocomposite films to develop PENGs for self-powered devices.

Authors:Haizhou Huang*, Nan Wu*, Hui Liu*, Shu Wan*, Shi Su*,#, Mao Ye*, Hao Wan*, Zhihong Zhu*, Hengchang Bi*,†, Litao Sun*,#,†

Abstract:
With the development of electronic information technology as well as the arrival of Big Data Era, wearable technology for health monitoring, medical testing and human-machine interaction is also ushering in a new era. Herein, a facile double-transfer technique is applied to fabricate sensors by utilizing nontoxic water-soluble polymer PVA as the substrate and graphene as the active materials, which exhibit conformal contact with skin, stretchable and biodegradable. These sensors have potential in many fields including human vital signals monitoring and human-machine interaction.
The traditional electrode (such as Ag/AgCl electrode) has a couple of disadvantages such as high cost, material waste and heavy metal pollution. Hence, a flexible, biodegradable ECG electrode is designed and fabricated as shown in Figure 1 a,b. The Young's modulus of this flexible sensor is 8.598MPa, and the maximum strain variable is 135%. The resistance fluctuates little when the strain is less than 20%. With the employment of this ECG electrode, the signal processing circuit and a smart phone, the measurement and display of ECG signal in real time is achieved (Figure 1 c,d).
Moreover, these characteristics are also leveraged for monitoring other human vital signals including vocal cords movement, jugular venous pulses (JVPs) and radial artery waves as shown in Figure 1 d,e. Furthermore, this high sensitivity (gauge factor: ≈502) and fast response (≈54 ms) sensor can be implemented in human-machine interaction (Figure 1 f,g). Due to the intrinsic nature of the substrate, this flexible sensor can be disposed by simply spraying deionized (DI) water on the sensors as displayed in a series of photographs in Figure 5 h. The whole sensor disposed completely after 150s. In addition, the dissolution rate can be tailored by changing the water temperature and the thickness of the substrate.
These characteristics including ultra skin-conformal, biodegradable and stretchable make this sensor an effective potential candidate for application in future wearable electronics.