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

Abstract:
The shape and size of graphene crucially influence the performances of graphene devices, thus an important research direction emerges, of fabricating high-quality graphene with sound patterns. However, the existing methods are time-consuming and costly with several transfer steps, and there are even no adequate researches of direct fabricating graphene patterns on insulated substrates, especially flexible substrates. This research presents a method for rapid fabricating and patterning graphene in one step on insulated flexible substrates. Nanosecond ultraviolet laser is used to direct write and reduce graphene oxide to graphene in one step under ambient conditions. The effect of processing parameters (including laser power, scan speed, defocus and scan times) on the resolution and reduction degree of fabricated graphene patterns was systematically studied. Various graphene patterns, including line arrays, spirals and texts were fabricated. A simple and cost-effective method to rapid fabricate arbitrary graphene patterns was proposed in the research, boasting huge prospect for fabricating flexible graphene functional devices.

Authors:Jianing An, Young-Jin Kim

Abstract:
Artificial electronic devices with skin-like properties hold great promises in healthcare monitoring, soft robotics, and human-machine interfaces [1]. Conferring flexibility and stretchability to biomimetic sensing electronics thus allowing for their intimate contact with curved surfaces can drastically enhance their functions such as capturing high-quality signals [1]. However, it is still challenging to achieve stretchable devices that can maintain high performance under severe deformation. Here we report an all-laser-patterning strategy to design a stretchable electronic skin where the femtosecond laser direct writing (FsLDW) was employed to respectively fabricate a graphene-based temperature sensor on a low-melting polymer film and create regular patterns on an elastomer substrate. Ordered buckling structures were formed by transferring the graphene- based temperature sensor onto the pre-strained elastomer substrate, which enables the active sensor area to endure stretching and exhibit stable sensing properties until the buckling profile was converted to a flat configuration [2].
As shown in Figure 1a, a temperature sensor was fabricated by FsLDW on a graphene oxide (GO) film coated on a polyester (PE) film (thickness of 10 μm), where the pristine GO functions as active material and the interdigitated reduced graphene oxide (rGO) patterns serve as the electrodes. The temperature sensing properties was examined by monitoring the impedance change against temperature in the range of 20 to 70 °C in an open-air environment (relative humidity, RH = 57%). As shown in Figure 1b, the impedance increases monotonically with the temperature, which can be attributed to the desorption of water molecules at elevated temperature leading to a decreased ionic conductivity (Figure 1c) [3].

Authors:Waqas Asghar *#†, Yiwei Liu*#, Runwei Li*#

Abstract:
Highly sensitive flexible tactile sensors fabricated in a low cost and efficient way are crucial for future electronic skins (e-skins). Generally, high performance capacitive tactile sensors are obtained by micropatterning their dielectric layers, using expensive photolithography and natural molds based conventional techniques. Herein, we report a novel strategy for the microstructuration of dielectric layer based on magnetic field induced dielectric interface. Microneedles based sensor’s dielectric interface is obtained by varying nanoparticles concentration (mixed in PDMS) and magnitude of vertical magnetic field, applied during curing. Sensor containing dielectric layer prepared at 1:1 (PDMS : nanoparticles) and 170 mT curing magnetic field has shown high sensitivity of 0.15 kPa-1 , fast response time of 41 ms. Young’s Modulus tests and SEM analysis confirms that sparse and high-aspect-ratio microneedles having lowest nanoparticles concentration are critical to achieve high sensitivity, low limit of detection, and fast response to external stimulus. Moreover, placing sensor in external magnetic field, affects its sensitivity which make this sensor unique from other sensors. More importantly, the currently developed flexible tactile sensors are potentially useful in intelligent soft robots, health monitoring, and motion detection.

Authors:Hongzhen Bi1*, Han Zhang2#, Tianyu Zhang1†

Abstract:
Acoustic vortex beams with spiral phase dislocations have attracted great attention in recent years, whose energy and phase distributions make them show great potential for application. Non-contact transfer of the angular momentum enables acoustic vortex beams to be used as acoustic wrenches. The circular distribution of acoustic power enables them to be used as acoustic tweezers. And the multi-order in the topological dimension indicates a great potential of channel multiplexing in acoustic communication. However, the generation of acoustic vortex beams is involved with the complexity of the overall circuit of the system substantially causing difficulty in integration and bringing high costs.
Aimed to obtain the acoustic vortex beans with high power, we employed an interdigital transducer array coated with paired spiral electrodes in this paper. An focused acoustic vortex beam can be generated by applying its beam synthesis principle. With the design of the electrode, the phases of the beams are controlled.
Using COMSOL finite element simulation software, the acoustic field excitation characteristics of the active acoustical vortex beam generation transducer are studied and analyzed. The results show the advantages compared with the traditional approaches based on passive and active methods, such as higher acoustic power, simpler operation and lower cost.
Hence, this kind of structure makes the compactness, integration and flexibility of the active vortex beam generation transducer greatly improved. And it provides a theoretical basis for promoting the practical application of acoustic vortex beams in acoustic communication and manipulation of particles, microorganisms, and cells in the future.

Authors:Catherine Cai, Po-Yen Chen, HongLiang Ren

Abstract:
The use of surgical robots in the field of minimally invasive neurosurgical procedures can offer several benefits and advantages. However, the lack of haptic interfaces hinders and limits the use of surgical robots in such procedures. One of the reasons for the lack of available haptic interfaces is the absence of force sensors that are able to meet the necessary design requirements for neurosurgical procedures. In this project, we have explored two transduction principles that force sensors can employ to measure and detect forces: capacitive and piezoresistive. While capacitive sensors appear more promising, we have found greater potential in the use of piezoresistive sensors in real life medical applications.

Authors:Min Cai, Shuang Nie, Yipu Du, Chengjun Wang, Jizhou Song

Abstract:
Stretchable electronics are of rapidly increasing interests due to their unique ability to function under complex deformations. Strain isolation of stiff functional components from the substrate represents a key challenge in the development of stretchable electronics since their mechanical mismatch may yield undesirable strains to degrade the device performance. The results presented here report an approach to develop a soft strain-isolating polymer substrate with programmable stiffness by spatio-selective ultraviolet (UV) exposure for stretchable electronics. The approach compatible with the well-established lithographic process reduces the fabrication complexity significantly and offers a simple yet robust strain isolation mechanism to ensure the system stretchability of over 100%. Combined experimental and numerical studies reveal the fundamental aspects of the design, fabrication, and operation of the strain-isolating substrate. Demonstration of this concept in a stretchable inorganic metal-based resistive temperature sensor and a stretchable organic photodiode array with unusually high performance shows the simplicity of the approach and the robustness in strain isolation in both component and device levels. This type of strain isolation design not only creates promising routes for potential scalable manufacturing of stretchable electronics but also engineering opportunities for stretchable electronics involving the integration of various functional components, which require the quantitative control of the strain levels to achieve optimal performance.

Authors:Shisheng Cai*#, Xue Feng*#

Abstract:
Manufacture of the next generation of wearable electronic devices and flexible electronics demand ultrathin silicon wafers.1,2 For example, the currently available IC (integrated circuit) chips used in wearable electronic system are built on silicon wafers of thickness less than 100μm. And the inorganic chips used in flexible electronic system3 should be thinned to micro- membranes of thickness about 15μm to improve the mechanical flexibility of devices to adapt to arbitrary curved objects4. Commercially available wafers have thickness of several hundreds of micrometers, so the wafers thus need to be thinned for new applications. Diamond grinding has been recognized as an irreplaceable thinning technique to obtain thinned wafers with good performance for applications in optics, electronics, bio-technology, medicine and flexible electronics. Studies on micro-diamond grinding technique, diamond wheels, and machine tools in silicon grinding process have been extensively reported. However, few articles have reported physical nano-diamond grinding process without any chemistry in silicon grinding technique.
In this paper, we report a strategy to thin silicon wafers and devices used for integrated circuit system (i.e. wearable electronics) and flexible electronics. The grinding technology only uses nano-diamond particles without any chemistry, which is different from previous strategy (i.e. Chemical Mechanical Polishing) and protects chips from chemical corrosion. Then we demonstrate the intrinsic mechanism of nano-diamond grinding to nano-cut and penetrate the substrate surface to obtain ultrathin devices. We also experimentally investigate the behavior of ultra-thin and flexible devices after nano-diamond grinding and compare it to the behavior of devices before-grinding. Finally, we integrate ultra-thin devices onto flexible substrate and package devices in the system.

Authors:Y. Cao*, G. Zhang#, Y.Zhang*, M. Yue*, Y. Chen†, S. Cai*, T. Xie#, X. Feng*

Abstract:
Despite the increasingly important role of stretchable electronics for use as the human– machine interface, their manufacturing in a commercially realistic manner remains an unresolved challenge. The bottleneck lies in the efficiency and scalability of transfer printing that is typically employed in the fabrication process to enable device stretchability via strain isolation. Here, the use of a polymer substrate with programmable rigidity for direct manufacturing of stretchable electronics is reported, forgoing the need for transfer printing while significantly enhancing strain isolation. The process starts with a stretchable elastomeric substrate synthesized via the thiol-acrylate click chemistry. Designable rigid islands can be introduced via spatially confined oxidation of the elastomer. Strain-sensitive microdevices can then be directly fabricated onto the rigid islands without transfer printing. Following this manufacturing scheme, a fast-responding stretchable temperature sensor is demonstrated, with unusual accuracy and real-time temperature monitoring capability suitable for use in a highly dynamic environment. Importantly, the critical fabrication step that introduces the programmable substrate rigidity is fully integrated into a well-established lithographic process. Therefore, the methodology not only reduces greatly the complexity in fabricating prototype devices but also points to a highly effective way for potential manufacturing in a commercial setting.

Authors:Geng Chen, Yajing Cui, Zhuyun Li, Xiaodong Chen*

Abstract:
Soft and stretchable electronic devices are important in wearable and implantable applications because of the high skin conformability. Due to the natural biocompatibility and biodegradability, silk protein is one of the ideal platforms for wearable electronic devices. However, the realization of skin-conformable electronic devices based on silk has been limited by the mechanical mismatch with skin, and the difficulty to integrate stretchable electronics. Here we demonstrate silk protein as the substrates for soft and stretchable on-skin electronics. The original high Young’s modulus (10 GPa) and low stretchability (<10%) are tuned into 0.1~2 MPa, and >400%, respectively. This plasticization is realized by the addition of CaCl2 and ambient hydration, whose mechanism is further investigated by molecular dynamics simulations. Moreover, highly stretchable (>100%) electrodes are obtained by the thin-film metallization and the formation of wrinkled structures after ambient hydration. Finally, our plasticized silk electrodes, with the high electrical performance and skin conformability, achieved on-skin electrophysiological recording comparable to that by commercial gel electrodes. Here proposed skin-conformable electronics based on biomaterials will pave the way towards the harmonized integration of electronics into human.

Authors:Wei-hsiang Chena,b, Linlin Qiub, Zhishan Zhuangb, Lixin Songb, Pingfan Du*b, Jie Xiong*a,b, Frank Koc

Abstract:
In order to increase the applicability and commercialize of perovskite solar cells (PSCs), simple fabrication of high-photovoltaic-performance flexible PSCs with excellent moisture stabilities without the use of a glove-box and an antisolvent is required. In this paper, we present a simple fabrication strategy involving introduction of 4-tert-butylpyridine (tBP) into CH3NH3PbI3 and significantly enhancing tBP morphology-modification effect via a reduction-active flexible poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) interlayer. Owing to the specific oxidation facilitation by the PEDOT:PSS polymer, a perovskite film with large (~1 μm) and quasi-all-in-one-structured grains can be obtained, which significantly enhance the efficiency and the stability of the PSC. Furthermore, the high-efficiency flexible PSC fabricated by the simple strategy exhibit an excellent moisture resistance owing to the stronger coordination and the outside-covering effect of the hydrophobic tBP. The fabrication can be carried out under ambient air (without glovebox, relative humidity > 40%), which paves the way for wearable device application and commercialization.

Authors:Xuan Chen, Yaojin Wang*

Abstract:
As is well-known, the vibration exists everywhere in our daily life, which brings numerous damage to structure health and physical safety. However, the real-time monitoring of omni-directional vibrations, stress and strain remains a big challenge [1]. Here, we proposed a flexible, cost-effective, passive vibration-visualization sensor based on heterostructural piezo-electrochromic effect [2]. In this work, an all-inorganic, flexible PbZr0.52Ti0.48O3 (PZT) piezoelectric thick film was prepared by sol-gel method based on two-dimensional mica substrates, whose open-circuit voltage and short-circuit current density reached respectively 120V and 150μA cm-2 [3]. The WO3 film deposited using DC magnetron sputtering was assembled as electrochromic device, which exhibited large transmittance modulation up to 60% and prompt coloration response. The integrated vibration-visualization sensor can convert external pressure signal into real-time color change by a rectifier [4]. Such systems are promising for applications in passive wearable/attachable vibration-monitoring devices for collapse-proof systems of bridges, the structure safety of aircraft wing and human physiological health monitoring.

Authors:Y. Chen*, B. Li#

Abstract:
The polymer matrix is vital for enzyme-based glucose sensors due to its immobilization effect on glucose oxidase (GOx), which is important for the structural intactness and stable functionality of this subtle catalyst. Herein, we present a chitosan matrix by a convenient freeze- drying process suitable for GOx immobilization and sensor fabrication. This chitosan matrix endows the enzyme layer with a hierarchically porous structre and thus faster kinetics for glucose penetration and reaction. Moreover, flexibility and conformability of this chitosan matrix is beneficial to the realization of the flexible and wearable glucose sensors. The availability of chitosan matrix has been verified by a skin-like, noninvasive and integrated glucose sensor and other enzyme-based sensors.

Authors:Chen Cheng*, Gang Xu*, Ning Xu#, Yanli Lu*, Sze Shin Low*, Qingjun Liu*

Abstract:
Recently, wearable medical devices is becoming a hot commodity that could be integrated as medical apparatus and instruments due to its highly recognized advantages such as portability, flexibility, accessibility and other distinct features[1]. Among these devices, smartphone-based wearable medical devices are one of the most popular system, providing promising solutions for personalized medical service. This paper presents a wireless patch for the monitoring of cortisol in perspiration as shown in Figure.1A. The wireless patch is connected to an electrochemical immunosensor and controlled by a smartphone. User could easily attach the wireless patch onto any body parts due to the flexibility and stretchability of the patch as demonstrated in Figure. 1B. Sweat is a common kind of biofluids that contains numerous metabolites and are secreted onto the body surface. These metabolites provide extensive physiological information about human health [2, 3]. For instance, the cortisol in human sweat is a crucial metabolite as it is the final product of the HPA axis(the hypothalamic- pituitary-adrenal axis). Its existence could maintain normal stress response process such as immune response process, food digestion process, sexual behavior process and so on.Based on the physiological significance abovementioned, we have developed a near field communication-based system to detect sweat cortisol via differential pulse voltammetry using smartphone. The advantages of near field communication-enabled smartphone like wireless, battery-free, portability, combining with the high sensitivity and specificity of electrochemical immunosensors, together with the ease of stretchability of the flexible printed circuit board are fully exploited to build an integrated detection system for perspiration-based cortisol as shown in Figure. 1C. Consequently, we could provide a solution to detect sweat cortisol in the field of clinical rapid detection.

Authors:Jiahui Cheng1,2†, Ying Chen3#, Xue Feng1,2*

Abstract:
Similar to living organisms, soft robots have good flexibility and can interact with the environment efficiently and harmoniously. Despite these advantages, soft robots require embedded sensors for perception and response. However, the movements of the soft robots create large deformation, which make it impossible to apply conventional rigid or non-extensible sensors to the soft robot. Flexible electronics have rapidly developed in recent years. Flexible electronic devices have flexibility and extensibility similar to human skin, and can be useful in the sensing of soft robots. This work presents a soft manipulator embedded with stretchable and flexible electronics. As a kind of soft robots, soft manipulator is very suitable for grasping fragile and complicated objects which is composed of several soft actuators. We improve and design the existing soft actuators, increase the degree of freedom of driving, embed flexible electronic devices in the soft actuators, integrate strain, temperature, and pressure sensors to make the manipulator intelligent and dexterous. In this work, three kinds of signals were respectively tested; we collected the data of the pressure and strain sensors when the soft manipulator grasped objects and then processed and analysed the data. The intelligent soft manipulator presented in this work will make a basic contribution in industries such as food, medicine, and logistics sorting, and has fundamental instructionnificance in the sensing of soft robots.

Authors:Ruoran Cheng*, Chunli Zhang*, Weiqiu Chen*, Jiashi Yang#

Abstract:
We study the effect of a uniform temperature change on the extensional deformation of a composite fiber of piezoelectric dielectrics and nonpiezoelectric semiconductors. A one- dimensional model is constructed. Through a theoretical analysis, it is shown that under a temperature change the mobile charges in the semiconductor redistribute under the electric field produced through thermoelastic, pyroelectric and piezoelectric effects. This thermally induced redistribution or motion of charge carriers may be called a thermo-piezotronic effect. It suggests the possibility of sensing or transduction between a temperature change and electric currents. This effect can be applied to design some novel piezotronic devices regulating via temperature.

Authors:Xu Cheng#, Kan Li†, Yihui Zhang# *

Abstract:
Recent progress in stretchable forms of inorganic electronic systems has established a route to new classes of devices, with particularly unique capabilities in functional bio-interfaces, because of their mechanical and geometrical compatibility with human tissues and organs.[1] A reliable approach to physically and chemically protect the electronic components and interconnects is indispensable for practical applications, since a direct exposure to the environment could lead to failure or damage of fragile elements.[2] Although recent reports describe various options in soft, solid encapsulation, the development of approaches that do not significantly reduce the stretchability remains an area of continued focus.[3] Here, we reported a generic, soft encapsulation strategy that is applicable to a wide range of stretchable interconnect designs, including those based on two-dimensional (2D) serpentine configurations, 2D fractal- inspired patterns, and 3D helical configurations. This strategy forms the encapsulation while the system is in a pre-strained state, in contrast to the traditional approach that involves the strain-free configuration, followed by release of the pre-strain to complete the process. Combined theoretical modeling and experimental measurements highlight the deformation mechanisms of the interconnects encapsulated using both the proposed and the traditional strategy. A systematic comparison reveals that substantial enhancements (e.g., ~ 6.0 times for 2D serpentine, ~ 4.0 times for 2D fractal and ~ 2.6 times for 3D helical) in the stretchability can be achieved through use of the proposed strategy. Demonstrated applications in highly- stretchable light-emitting diodes (LEDs) systems that can be mounted onto complex curvilinear surfaces illustrate the general capabilities in functional device systems.

Authors:Yuhua Cheng*#, Chenxi Wang*, Gaofeng Wang*, and Wenjun, Li*#

Abstract:
Magnetically mediated hyperthermia (MMH) [1] is a promising technique to cure tumor by increasing the temperature of the targeted tissue region to a desired temperature range (typically from 41 °C to 46 °C) while keeping the tissue out of the targeted region almost constant. Because the biological tissue is almost non-magnetic and low-conductance, magnetic fields can be applied to heat up the implanted magnetic mediators in the tumor region. Magnetic nanoparticles (MNPs) are the most commonly used mediators through injection due to the minimal invasiveness advantage [2], [3]. However, the treatment temperature strongly depends on the dose of MNPs which will diffuse and even vanish in the human body thereby reducing the heating effectiveness. An alternative way is replacing the MNPs with metallic loops. Although metallic loops can be precisely located and will not be diffused over time, implanting them into the tissue is more invasive[4]. In this paper, we propse to use injectable metallic loop coils as the mediator by using liquid metal coatedg with biocompatible materials.
As a preliminary prototype, we use gelatin (25% consistence) to analog the human tissue. Agar solution mixed with konjaku flour (6% and 0.3% consistence, respectively) is injected into geltain with 1 ml/s speed by using a syringe needle. After about 5 seconds, the agar solution freezes and the syringe needle can be reomved. Four the syringe needles with 1.2-mm deameter are used to injected one by one to shape a square-shaped hole inside the agar. After removing the four syringle needles, the square-shaped hole is actually not hermetically-sealed. Additonal agar (red dye is mixed intendedly in order to let them be obvious) is injected to seal the square- shaped hole and form a sealed hallow tube. And then the liquid metal (GaInSn alloy with 0°C melting temperature) is injected into this hole with the help of a 0.5-mm diameter syringe needle. The final prototy flexible liquid metal coil is shown in Fig. 1a.

Authors:Minwoo Choi1, Yong Ju Park1, Bhupendra K. Sharma1, Sa-Rang Bae2, Soo Young Kim2*, Jong-Hyun Ahn1*

Abstract:
Recently, there has been an increasing demand for electronic devices which has ultra-thin thickness, wide area, irregular surface wrapping, and easy attachment to human body for the implementation of intelligent electronic systems. [1, 2]. Transition-metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) at two-dimensional (2D) atomic scale have been realized much superior as compared to conventional materials due to their exceptional dominant combination of semiconducting and mechanical properties.
However, atomically thin MoS2 which performs extensive research on semiconductor electronic devices has not yet been studied in real active matrix driven large organic light emitting diode (OLED) displays. The biggest obstacle that restricts its applicability as drive element is to impart a large contact resistance at metal/MoS2 interface and hindered carrier transport at conventional SiO2 dielectric surface which greatly deteriorate the mobility [3].
In this study, we propose the modified switching device architecture to efficiently utilize the high-k Al2O3 layer that can drive an ultra-thin OLED display even under dynamic folding when integrated into the active matrix system. The modified structure in combination of Al2O3 layer showed 28 times increment in mobility over normal back gated TFT and is readily adapted for demonstrating the operation of display while attached to human wrist with 66 pixel array.

Authors:Zengyong Chu*, Yinlong Tan, Jia Song

Abstract:
Recently, flexible and wearable devices are increasingly in demand and graphene has been widely used due to its exceptional chemical, mechanical and electrical properties. Building complex buckling patterns of graphene is an essential strategy to increase its flexible and stretchable properties. Herein, a facile dimensionally controlled four-dimensional (4D) shrinking method was proposed to generate hierarchical reduced graphene oxide (rGO) buckling patterns on curved substrates mimicking different parts of the uniforms.
The reduced graphene oxide ridges (rGORs) generated on the spherical substrate seem isotropic, while those generated on the cylindrical substrate are obviously more hierarchical or oriented, especially when the cylindrical substrate are shrinking via two steps. The sensitivity of rGORs along the axial direction is much higher than those along the circumferential direction. The flexible rGORs-based strain sensors can be used to detect both large and subtle human motions and activities by achieving high sensitivity (maximum gauge factor up to 48), high unidirectional stretchability (300−530%), and ultrahigh areal stretchability (up to 2690%). Excellent durability was also demonstrated for human motion monitoring with resistance to hand rubbing, ultrasonic cleaning, machine washing, and chemical immersion.

Authors:Cui Wenjie*, Zheng Hongxing* , Wang Lu* , Liu Ruipeng*, Wang Mengjun* ,Li Erping #

Abstract:
A flexible antenna fed by coplaner waveguide(CPW) is designed. The simulation and experimental results verify the design for the medical application in the 1.4 GHz WMTS band [1]. A CPW is chosen over a coupling line for feeding because this simplifies the design by using only 1 layer of conductive material without an extra layer, which guaranteed low profile and compact size. We first investigated that the geometry of the proposed antenna. The overall structure consisted of L-shape ground plane and meander-type radiation patch and were etched a polyimide substrate (εr=3.6, tanδ=0.0652, thickness=0.05mm), and depicted in Fig. 1. Meanwhile, in order to make the antenna suitable for implantation, biocompatible superstrate silicon block was used to encapsulate the overall design [2]. The superstrate layer is mainly used to shield the antenna from direct contact of the living tissue. Also, the superstrate acts as a buffer between the metal radiator and human tissues by reducing RF power at the locations of loss human tissues. The proposed antenna has been designed and optimized using CST studio suite [3]. The final dimensions of the optimized antenna are the following: L=16, W=15, L1=12.12, L2=10, L3=2.3, L4=3.6, L5=4.3, Ls=3.65, Lg1=13，Wg1=6.25, Lg2=3, Wg2=7.25, Wg=1, Ws=0.8, Wc=0.5, Lc=4 (unit: mm)。