Authors:Jianliang Xiao

Abstract:
Sweat is an attractive biofluid for non-invasive diagnose due to its abundance of biochemical information. Wearable sweat biosensor holds promising potential in real-time monitoring the wearer’s physiological state. However, the easy collection and directional transport of sweat sample and the synchronous detection of multi-analyte in sweat still remain challenges. Herein, we present a wearable sweat biosensing device composed of Janus membrane and multiplexed sensor array which can simultaneously detect diverse metabolites (such as glucose and lactate) and electrolytes (such as sodium and potassium ions) in sweat, as shown in Figure 1 . The Janus porous membrane endows the device with fantastic sweat harvesting and directional transporting capability. The sweat generated on skin can be collected and drawn through the Janus membrane form the hydrophobic side to the hydrophilic side due to the wettablity gradient. The sensor array sandwiched between two porous layers continuously detects the analytes in sweat passing by, overcoming the defect that old sweat can mix with and contaminate new sweat. Skin temperature and pH of sweat are also monitored to calibrate the response of the sensors. This wearable device can make a real-time assessment of the physiological state of the human subjects during physical activities, and enable a wide range of personalized diagnostic and physiological monitoring applications.

Authors:Borui Xu*, Gongjin Li*, Zhe Ma#, Chunyu You*, Zengfeng Di#, Yongfeng Mei*

Abstract:
Flexible integrated smart electronics presents great potential in wearable and portable systems ranging from health care to environmental monitoring. Sensing module which could detect and sense surrounding stimuli and output with digital signals is of great importance in these applications. Benifiting from the reliable and ultra-high on-off ratio (~106) of our flexible silicon nanomembrane phototransistor, we proposed a strategy to construct a platform with on- demand sensing functions combined with smart materials. Highly sensitive response to illumination of the silicon nanomembrane provides an ideal device to detect the variation of optical property change in above smart materials. This platform is capable in all kinds of sensing situations, as hydrogen and humidity, with the integration of corresponding smart materials and suggests a promising future for next-generation smart systems.

Authors:Chengtao Xu , Biao Ma, Hong Liu†

Abstract:
Soft, wet and biocompatible hydrogels have emerged as a promising material candidate for flexible and stretchable electronics[1]. However, most existing conductors designed for hydrogel suffer from poor biocompatibility, low conductivity, or mechanical mismatch with hydrogel. In this work, we show direct patterning of intrinsically stretchable and highly conductive liquid metal (LM) on hydrogel substrate for completely soft and stretchable hydrogel electronics without mechanical mismatch[2]. This was achieved by patterning of liquid metal dispersed with magnetic microparticles on the wet hydrogel using magnetic field. High resolution and uniform LM patterns were obtained with an assistance of a laser cutting mask. In addition, the encapsulated liquid metal in the hydrogel matrix can also enhance the mechanical strength of the hydrogel. Moreover, mechanical and electrical self-healing can be achieved simultaneously at the damaged region, by taking advantages of the hydrogen bonds in the PVA hydrogel network and the merging of the liquid metal, respectively. We also demonstrated a few applications of the LM enabled hydrogel bioelectronics for wearable sensors, soft wireless communication device and self-healing electronics.

Authors:Gang Xu, Zhaoyang Liu, Chen Cheng, Jinglong Liu, Xin Li, Yanli Lu, Qingjun Liu

Abstract:
Chronic wound is a major health concern which causes patients physical and mental sufferings worldwide. They are often susceptible to infections and result in changes of biological, chemical, and physiological parameters [1]. Monitoring these parameters and providing timely feedback therapies can help us know the wound condition and accelerate wound healing [2, 3]. Flexible devices are suitable for in situ wound monitoring and drug delivery as they can conform to the unique profile of the wound area with minimum damages [4]. However, most flexible platforms can detect only one or two kind of parameters, which could not comprehensively report the wound conditions[2]. Also, the high power consumption of drug delivery solutions, such as thermal activation, limit the miniaturization of the platform[1, 5, 6]. Here, we developed a battery-free and flexible smart patch, which can simultaneously detect biological, chemical, physiological parameters of the wound, and provide on-demand drug delivery. The top layer of the patch is an NFC-enabled flexible circuit board which enables wireless power harvesting, on site signal processing, drug delivery controlling, and wireless data transmission with widely-used smartphones (Figure 1A). Without the restrictions of on-board batteries, the circuit board is ultrathin and could bend to a great extent. The bottom layer of the patch is a flexible electrode array based on polyethylene terephthalate (PET) substrate, including uric acid sensor, pH sensor, temperature sensor, and a drug electrode with cefazolin sodium coated in the membrane of polypyrrole (Figure 1B). In the application (Figure 1C), the two layers are adhered together with silica gel and electrically connected with conductive pads. The temperature sensor on the reverse side of the circuit board will then embed into the corresponding hole of the electrode array. Figure 1D illustrates the schematic block diagram of the system. While the wound area is infected with bacteria, the changes of uric acid, pH value and temperature will be recorded by the platform and transmitted to the smartphone (Figure 1E to 1G). If necessary, the command will be sent by the phone and the polypyrrole electrode will be activated to release on-demand antibacterial agents to the wound area (Figure 1H). The smart patch provides a powerful sensing platform, which cover three main types of biomedical parameters, including biological, chemical, and physiological signals. With the low-power electrically activated drug delivery module, the feedback therapy was firstly achieved on the battery-free and flexible platform. It can be widely applied in dynamic wound monitoring and therapies.

Authors:Guangyuan Xu*, #, †, Paul A. Kilmartin#, Jadranka Travas-Sejdic#, †, Xue Feng*

Abstract:
A range of novel carbon nanomaterials, including 0D fullerene, 1D carbon nanotubes, 1D carbon nanofibers, 2D graphene and graphene oxide, and 3D carbon aerogels, has attracted considerable interest and investments from across the scientific society 1. Due to their excellent performance, the carbon nanomaterials have contributed significantly towards the development of miniaturized integrated point-of-care biological and chemical sensors. Graphene, as a sensing and signal transducing material is well established, and the recently developed method of “laser scribing” has already been demonstrated as a facile approach for manufacturing graphene electronics for highly selective, sensitive biological sensing devices 2-3. Inspired by the different morphologies and derivatives of the carbon nanomaterials that have been fabricated, including carbon nanowalls, graphene nanoribbons, vertically aligned CNTs and laser induced graphene fibers, we first fabricated laser scribed graphene grass (LSG grass) with a novel 3D vertical aligned tree-like morphology 4. We have then used the LSG grass in the application of dopamine detection by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The electrochemical anodic peaks of dopamine (DA), ascorbic acid (AA) and uric acid (UA) using LSG grass electrode were investigated, where UA and AA were considered as common interferences. The sensitivity of LSG grass for DA sensing was highly improved compared to normal LSG. The fabricated LSG grass sensor exhibits a sensitivity of 0.299 μA/μΜ and detection limit of 1 μΜ. The outstanding performance for dopamine detection using LSG grass is a reflection of the promising future of carbon nanomaterials with interesting high surface area morphologies.

Authors:Yang Xu*

Abstract:
Low light absorption and inefficient carrier extraction in Gr are the major bottlenecks which have hindered the development of high-performance Gr-based optoelectronics. Gr hybrid photodetectors where Gr serve as either photoabsorbing or transparent conducting layer have proved and important alternate to improve the efficiency of Gr based photodetectors. Through the integration of Gr with a large family of materials and structures (optical and device), the detection spectrum is expanded from UV to THz with much improved R performance at high speed. Availability of a broad family of photosensitive materials integratable with Gr not only offers the possibility to enhance the photodetection efficiency of these structures but also gives the freedom to design the on-demand photodetectors in a specific wavelength regime. Thanks to the flexibility, extraordinary mechanical properties, and integration of Gr with various substrates and photosensitive materials, hybrid Gr optoelectronics devices have also found applications in flexible and wearable electronics. I will review the recent progress on materials, photoresponse enhancement methods, and the integration of the Gr hybrid structures with Si and other flexible platforms. I will also summarize the challenges and future opportunities of Gr hybrids structures for the optoelectronics applications.

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

Abstract:
Stretchable electrochemical sensor has great advantages in real-time monitoring of cell mechanotransduction[1,2], however, it is still a great challenge for existing materials to be used for the fabrication of sensors with both high electrochemical activity and excellent mechanical stretchability. As a conductive polymer, PEDOT has good electrochemical performance, but the low fracture strain (~ 5%) prevents its direct application in the field of stretchable devices[3]. Herein, we report a PEDOT-based stretchable electrochemical sensor by co-doping ionic compound (bis(trifluoromethane) sulfonimide lithium salt, LiTFSI) and phthalocyanine cobalt (CoPc). LiTFSI could significantly improve the stretchability of PEDOT film with stable electrochemical response even in 50% strain (Figure 1A). CoPc endowed the sensor with excellent electrocatalytic activity to the oxidation of H2O2 (Figure 1B). Together, this proposed sensor is expected to be as a powerful platform for the real-time monitoring of ROS released during cell mechanotransduction.

Authors:Yu Yan1*, Yanlong Tai1, Ying Chen1

Abstract:
Organic-inorganic hybrid perovskite materials (OIHPs) perform outstanding optoelectronic properties, extending their extraordinary usage in photovoltaics, photodetectors and light- emitting diodes. However, the mechanical behavior, which is of great importance to the stability of perovskite-based devices, have rarely been explored. Here, based on the methylammonium lead triiodide (MAPbI3) and graphene oxide (GO) composite bilayer film, a flexible actuator was designed with remarkable light-induced actuation performances including ultralarge deformation (rotation angel change >400°) and fast response (<1 s). From in situ variable temperature X-ray diffraction, fluorescence spectrum, numerical simulations and a series of control experiments, the actuating mechanism for macroscopic deformation was elucidated as reversed lattice expansion/contraction of perovskite and GO films triggered by light irradiation. Additionally, logical transistor array could be easily integrated onto this micro-mechanical systems considering the exclusive optoelectronic properties of perovskite. A new way is ushered through this functional flexible actuator with logical transistor array to realize programmable actuation, which is expected to be of paramount importance for soft robots and devices toward practical applications.

Authors:Hui Yang1, Xiaodong Chen2,*

Abstract:
The conformal fabrication of on-skin electrodes enhances the perception and interaction of ambulatory electrophysiological signals for early diagnosis of heart disease and neural dynamics. However, current on-skin electrodes have a poor conformal property under sweaty condition, which gives rise to unreliable ambulatory electrophysiological signals upon sweating. Herein, we fabricated highly conformal all-polymer (CAP) electrodes, made of an ionically crosslinked silk fibroin (SF) gel and stretchable conducting polypyrrole (PPy), which accommodate the large deformation of wet skin for ambulatory electrophysiological sensing upon sweating. The interlocking structure between PPy and SF layer endows on-skin electrode with highly conformal property through making rigid PPy film to be stretchable. SF gel provides a relatively low dynamic modulus on wet surface, leading to the highly conformal property of on-skin electrodes under sweaty condition. Our strategy will provide potential opportunities and applications for continuous health-monitoring, intelligent self-diagnostics system of diseases, and smart human-machine interfaces under extreme condition.

Authors:Nana Yang, Yaojin Wang*

Abstract:
Ever-evolving advances in flexible magnetic sensors are promising to fuel the technological developments in the fields of touchless human-machine interaction elements, navigations modules for next generation consumer electronics, implantable medical diagnosis and bio- inspired magnetic perception for human or artificial intelligence. [1-3]However, the realization of magnetic sensors with simultaneous high-flexibility, ultra-sensitivity, low power consumption and low-cost remains a challenge.
Here, we report a cost-effective, flexible magnetoelelctric (ME) sensor based on ultra-high piezoelectric thick film and Metglas foils. The flexible piezoelectric thick film was fabricated via sol-gel process assisted by two-dimension Mica substrate, which exhibits an ultrahigh piezoelectric coefficient d33>80 pC/N, extending beyond prior art for all-inorganic flexible piezoelectric materials. The ME laminate composite has a strong ME coupling (higher than all flexible ME composite ever reported) due to the exceptionally high piezoelectricity of PZT thick film. The ME sensor is also found to possess a remarkable sensitivity at low frequencies. Moreover, no degradation of the sensor performance was observed after 4000 bending cycles, showing an excellent mechanical and electrical durability. With high sensitivity, excellent flexibility, the ME sensor provides a platform capable of granting us an additional sense of magnetoception and designing various wearable healthcare devices.

Authors:Xingyan. You, Meidan. Ye*.

Abstract:
Flexible pressure sensors have attracted more and more attention with meeting the requirements of wearable electronic devices. And the heterostructured metal sulfide nanostructures showed promising prospects in flexible devices, such as quantum dot- sensitized solar cells, supercapacitors and pressure sensors. [1,2] We developed flexible pressure sensors based on a series of three-dimensional nanostructures (e.g., Co9S8, NiCo2O4 and MoS2, Figure 1), which showed excellent performance in a large pressure range as well as high stability. The flexible sensors have great application prospects in researching physiology functions of human body. It could detect tiny physiological activities such as heartbeat, breathing and large body movements such as bending the elbow and bending the knee.

Authors:Jingxian Yu, Ya Li, Xian Huang

Abstract:
With the development of optogenetics, people gain the ability to control neuronal activity in high spatial and temporal resolutions. A large amount of integrated, biocompatible, mechanically soft devices with light stimulations, electrophysiological recording and many other functions have been developed, offering powerful apporaches to reveal . These powerful research methods provide the possibility to reveal the relationship between specific neural circuits and biological functions of brain. Despite the apperance of high density of optical and electrical stimualtion and monitoring devices, majority of these devices can only work on limited brain areas, lacking the ability to conduct distributed stimulation and sensing.
Here, we developed a new form of multi-channel implantable optoelectronics that has four fleixble optical fibers coupling with four LEDs to conduct deep brain stimulation. The wavelenghts of the four LEDs can be switched to satisfy the demand of different light-sensitive proteins for optogenetics. In addtion, each fiber was transfer-printed with flexible microelectrodes, which can be used to conduct feedback monitoring to evaluate the effectivenss of optical stimulation. Moreover, defects were deliberately introduced on the fibers, allowing leakage of transmitted light not only on the tips of the fibers but also on selective locations. Other parameters such as pulse duration of each LED and frequencies can be controlled by a wireless circuit.
Experimental results have demonstrated that the light intensity that outputed from the optical fibers satisfy the requirement of optogenetics. All 32 electrodes on the distributed optical fibers have exhibited excellent performance in in-vivo experiemnts using mice. These multifunctional flexible fibers allow us to gain systematic information to reflect the connection among different brain zones, and provide excellent tools to correlate animal behaviors with biophysilogical signal.

Authors:Zhe Yu#,†,†, Yiwei Liu#,†, Jie Shang#,†, Run-Wei Li#,†

Abstract:
With the development of stretchable sensors, the flexible pressure sensors are expected to be soft and stretchable as human skin. The intrinsically stretchable composites, composed of conductive particle fillers and elastic polymer matrixes, are ideal pressure-sensitive materials for stretchable pressure sensors. However, the pressure sensors based on pressure-sensitive composites are sensitive to stretching strain and not durable under repeated stretching.[1] Because the random distribution of fillers in matrixes will change by strain, and the polymer chains will creep while repeated stretching.
Here, the magnetic particle with nanostructured spines (Figure 1a) and polyurethane (PU) with non-plane rings are chose as filler and matrix, respectively. To the filler, it will form ordered distribution with vertical aligned columns by applying magnetic field to weaken the effect of strain (Figure 1b), and its spines increase the sensitivity of pressure.[2] To the matrix, PU can store and release strain energy by the isomeric transformation of non-planer rings to ensure the durability of composite (Figure 1c). [3]
Therefore, the stretchable pressure sensor based on our composite exhibits strain- insensitivity and great durability. It remains a high sensitivity (> 10 kPa-1) while stretching to 400% stain (Figure 1d). After repeated stretching for 10,000 cycles, the sensor reproduces the original performance well. We successfully demonstrated the sensor array to detect finger pressure during repeated movement, which shows the potential of our stretchable pressure sensor in human-machine Interfaces.

Authors:Haozhi Yuan, Kai Wu*, Jinyu Zhang, Yaqiang Wang, Gang Liu*, Jun Sun*

Abstract:
Topographical patterns endow the material surfaces with unique and intriguing physical and chemical properties. For the flat hard film/soft substrate system, spontaneously formed wrinkling has been harnessed to generate the surface topography for various functionalities. Despite promising applications in biomedical devices and robot engineering, the friction behavior of wrinkling on curved surfaces remains unclear. Herein, wrinkled surfaces were induced by sputtering metals on PDMS microspheres and three wrinkling patterns are prepared(dimple, labyrinth, herringbone). The wrinkle morphologies and length scales can be controlled precisely by tailoring the microsphere radius (substrate curvature) and film thickness. The wrinkled surfaces exhibit tunable friction property, depending on the wrinkling patterns and length scales. An increase in friction force with increasing surface roughness is generally found for dimple patterns and labyrinth patterns. The dimple patterns show the lowest friction due to strong curvature constraint. The herringbone patterns exhibit apparent friction anisotropy with respect to topographic orientation. The present results will guide future design of wrinkled surfaces for friction by harnessing substrate curvature.

Authors:Xiangjun Zha, Kai Ke, Mingbo Yang, Wei Yang

Abstract:
Conductive hydrogels, as a class of intrinsically stretchable and conductive material, have recently attracted tremendous research interests for potential applications in electronic skin, soft robotics, and wearable devices. However, traditional conductive hydrogel consisting of colored polymer and carbon nanomaterials are unsuitable for practical applications in skin-mountable devices due to their poor biocompatibility, low transparency and unsatisfactory mechanical performance. Herein, biocompatible polyvinyl alcohol (PVA)/glycerol-water organohydrogel with high transparency (80%) and large stress (1.4 MPa) is developed via a one-step physical crosslinkning strategy, enabling sensitive strain sensing ability in a wide temperature range. The PVA organohydrogel shows high linear sensitivity (GF is 1.6 ) for 0~300% strain, fast response and relaxation times (< 270 ms) and good repeatability (50% strain, 900 cycles). Various human motions corresponding to different strain levels are monitored by the strain sensor from −18 to 25 °C. This work sheds light on the fabrication of physically crosslinked biocompatible organohydrogels with stable, high mechanical performance and high linear strain sensitivity for the applications of emerging wearable electronics.

Authors:Bocheng Zhang, Lanlan Liu, Zujun Peng, Ying Chen, Xue Feng*

Abstract:
The detection of blood in the aorta plays a guiding role in the prevention and treatment of cardiovascular diseases. The detection of local blood in the diseased vessels is a difficult subject in scientific research. This paper introduces a sensor for local blood detection that can be combined with a cardiovascular stent. The sensor uses shape memory polymer (SMP) as a flexible substrate. After the cardiovascular stent enters the lesion site of human body, the device is deformed by external conditions to complete the device deployment and fixation. The sensing unit endows the interdigital electrode with unique stretching and bending characteristics through the design of the serpentine wire. The detection sensitivity and detection limit of the sensor can be adjusted by designing the number and length of the interdigital electrode through electric field simulation. Finally, the blood detection device was fabricated by 3D printing and several key blood parameters were tested, and the accuracy of the device was evaluated.

Authors:Hang Zhang*, Xiaogang Guo, Jun Wu, Daining Fang#, Yihui Zhang†

Abstract:
Soft adaptable materials that change their shapes, volumes and properties in response to changes in ambient conditions have important applications in tissue engineering, soft robotics, biosensing and flexible displays. Upon water absorption, most existing soft materials, such as hydrogels, show a positive volume change, corresponding to a positive swelling. In contrast, the negative swelling represents a relative unusual phenomenon that does not exist in most natural materials. The development of material systems capable of large or anisotropic negative swelling remains a challenge. Here, we combine analytic modeling, finite element analyses (FEA) and experiments to design a type of soft mechanical metamaterials that can achieve large effective negative swelling ratios and tunable stress-strain curves, with desired isotropic/anisotropic features. This material system exploits horseshoe-shaped composite microstructures of hydrogel and passive materials as the building blocks, which extend into a periodic network, following the lattice constructions. The building block structure leverages a sandwiched configuration to convert the hydraulic swelling deformations of hydrogel into bending deformations, thereby resulting in an effective shrinkage (up to around -47% linear strain) of the entire network. By introducing spatially heterogeneous designs, a range of unusual, anisotropic swelling responses were demonstrated, including those with expansion along a direction and simultaneously, shrinkage along the perpendicular direction. The design approach, as validated by experiments, allows the determination of tailored microstructure geometries to yield desired length/area changes. These design concepts expand the capabilities of existing soft materials, and hold promising potentials for applications in a diverse range of areas.

Authors:Huiqing Zhanga,b,c, Rongyan Heb,c, Hao Liub,c, Zedong Lib,c, Xiongwen Zhanga,b, Feng Xub,c

Abstract:
Wearable electronics has recently found widespread applications in biomedical fields, where substrate materials with breathable and washable features are of great importance for the practical applications. In this work, we developed a breathable and washable graphene-cellulose e-paper as substrate material for wearable electronics through a facile and scalable paradigm. We directly mixed hydrophilic graphene oxide with hydrophilic cellulose fibers during papermaking to ensure that graphene nanosheets uniformly spread all over the paper matrix during papermaking, thus providing extraordinary electrical conductivity after thermal reduction of graphene oxide. The unique 3D hierarchical porous structure of the e-paper enables excellent breathability and provides a comfortable implementation on skin surface even for long-term monitoring as demonstrated in rabbit skin in vivo. Besides, this graphene-cellulose e- paper can endure long-time soaking in water and multiple washing-drying cycles with maintained structural property and functional performance. The e-paper has also been demonstrated to be feasible as a human motion detector, even after soaking or washing. The developed graphene-cellulose e-paper holds great promise for versatile applications in advanced wearable electronics for monitoring human healthcare.

Authors: Lei Zhang, Qiulin Tan

Abstract:
In recent years, wearable electronics and artificial intelligence (AI) have made great progress. Wearable electronics can collect human physiological information parameters, while AI can analyze the data to monitor human health [1-2]. However, due to limitations of measurement accuracy, response time and other factors, wearable sensors are difficult to analysis of human health real-time currently. As one of the essential components for human body, water molecules play a vital role in human health. In addition, water molecules in the human body contain a large amount of information about the state of human health [3-4]. Therefore, monitoring the water molecules metabolized by the human body and the skin humidity can monitor the state of human health in real time. In this paper, a wireless wearable humidity sensor based on RGO-WS2 heterojunction was proposed.
Figure 1(a) shows the schematic of the wireless humidity sensor, the size of the sensor is 10×10 mm, the substrate is polyimide which is appropriate for the wearable sensor. The humidity sensing material RGO-WS2 was fabricated by supercritical CO2 method [5]. Due to the van der Waals force between the RGO and WS2 [6], they can generate heterojunction naturally. As shown in Figure 1(b) and 1(c), they are SEM images of the RGO-WS2. From Figure 1(b), it can be seen that the morphology is similar to that of a hexagon. Figure 1(c) shows WS2 nanosheet attached on RGO nanosheet. As shown in Figure 1(d) and 1(e), it is the Raman spectroscopy of RGO, WS2 and RGO-WS2, respectively. The peaks of RGO-WS2 for in-plane (E ) and out-of-plane (A ) are 354.1 and 420.3 cm-1, respectively. Compared to the pristine 1g WS , both the peaks of E and A red shift (E from 353.1 cm-1 to 354.1 cm-1 and A from 21g 1g 419.3 cm-1 to 420.3 cm-1) maintaining the same gap 1 cm-1, which means that WS2 in RGO-WS2 has the same layers as the pristine WS2. And it can be also as an evidence of coupling between RGO and WS2. In addition, RGO possess much larger area than WS2 sheet, the peaks of RGO in RGO-WS2 did not show obvious shift compared to the pristine RGO. They indicated van der Waals heterojunction was formation between RGO and WS2 sheet.
As shown in Figure 1(f), it is the sensor performance under humidity ranged from 10% RH to 90% RH. Then extract the resonant frequency of the sensor under different humidity and the result is shown in Figure 1(g). As the increase of humidity, resonant frequency of sensor decrease accordingly. In Figure 1(h), it displays the results of the different distance from 1mm to 10mm between finger and sensor. In addition, human breathing pattern is a non-invasive, simple and repeatable monitoring method that can be widely used in medical fields. As shown in figure 6, it is the result of the sensor under different breathing frequency. The S11 parameter changed with the rate of respiration. It can distinguish the rapid and normal breathing pattern and indicated that the sensor possess ultra-sensitivity property. This indicates that the use of Rgo-WS2 is a viable new and simple strategy to realize a humidity wireless sensor for use in wearable electronics.

Authors:Qi Zhang*#, Bin Peng†, Zi Yao Zhou†, Ming Liu†, Xiao Hui Zhang*#,

Abstract:
Flexible electronics, especially electronic skin, is deemed as a great promising tool that seamlessly connects humans with electrons in order to monitor human health, sharpen human perception of the external environment and even expend human senses1. However, the growing mismatch between traditional materials used in electronic skin and human applications is prompting the development of innovative biocompatible, skin attachable and biodegradable materials to fabricate electronic skin more suitable for the human body. Among all those alternative natural materials, silk fibroin, with its natural abundance, excellent biocompatibility, controllable biodegradability, appropriate mechanical features and comfortable attachment2, is a suitable substrate material electronic skin. Here, we made a silk fibroin based biocompatible biodegradable and ultra-flexible microwave device that exhibits good magnetic properties, sensitive microwave characteristics, and sensitive response to stress and strain. First, due to internal structure of silk fibroin, ultra-thin and flexible films based on B. mori silkworm cocoons was fabricated. In addition, nanoscale CoFeB metal layer was deposited on the silk fibroin film by magnetron sputtering, which shows well-established magnetic properties. Furthermore, we verified the microwave performance of the device by electron paramagnetic resonance (EPR) and broadband ferromagnetic resonance (FMR). Also, a great of FMR frequency shift was obtained during the bent test of flexible microwave device, under external mechanical tensile stress (R=5 mm), which provides sensitive stress-strain detection for microwave devices. This work provides new material possibilities for flexible microwave devices, further narrowing the distance between humans and electronic devices.