ArticleLiterature Review

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

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Abstract

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

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... The development of electronic skin (e-skin) technologies is still a current research topic, undertaken by scientific teams worldwide for over three decades [1]. The concept of an extensive, flexible network of sensors as an interface that mimics a biological organ is being developed, particularly in medicine, to enable smart healthcare [2], prosthesis [3], and amplifying human sensory abilities [4,5]. ...
... where F-force exerted on the e-skin surface in Newtons; p-touch pressure measured by e-skin sensor expressed as a decimal representation of 8-bit values; a 1 , a 2 , a 3 , a 4 -parameters of individual sensor model curve; each sensor and each curve model (1) or (2) can have different parameters. Figure 11 (left) shows a plot of the relationship described by Equation (1) in the loading phase of the e-skin sensor from row 15, column 29. ...
... Finally, it is difficult to define one specific characteristic for all sensors because it varies significantly from sensor to sensor, as shown in Figure 15. Each sensor should have its own parameters for the selected set of functions, e.g., according to Equation (1). Similarly, it is difficult to establish starting points for algorithms that optimise curve fitting parameters for a given set of functions. ...
Article
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The paper describes the semi-automatised calibration procedure of an electronic skin comprising screen-printed graphene-based sensors intended to be used for robotic applications. The variability of sensitivity and load characteristics among sensors makes the practical use of the e-skin extremely difficult. As the number of active elements forming the e-skin increases, this problem becomes more significant. The article describes the calibration procedure of multiple e-skin array sensors whose parameters are not homogeneous. We describe how an industrial robot equipped with a reference force sensor can be used to automatise the e-skin calibration procedure. The proposed methodology facilitates, speeds up, and increases the repeatability of the e-skin calibration. Finally, for the chosen example of a nonhomogeneous sensor matrix, we provide details of the data preprocessing, the sensor modelling process, and a discussion of the obtained results.
... Often encouraged by the growing needs for high diagnostic/therapeutic efficacy and for new fields of applications, the development of advanced array has been an active research topic with ever-challenging and ambitious technical requirements. Flexible array design and fabrication is more interested in size reduction, increased sensitivity, reduced number of elements, and wide bandwidth [14][15][16]. Ultrasonic array imaging places higher demands on increased flexibility, reduced array elements, and algorithm matching [17][18][19]. Flexible ultrasound array working on flat surfaces can achieve similar acoustic imaging functions to rigid ultrasound probes. ...
Article
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Advances in flexible integrated circuit technology and piezoelectric materials allow high-quality stretchable piezoelectric transducers to be built in a form that is easy to integrate with the body’s soft, curved, and time-dynamic surfaces. The resulting capabilities create new opportunities for studying disease states, monitoring health/wellness, building human–machine interfaces, and performing other operations. However, more widespread application scenarios are placing new demands on the high flexibility and small size of the array. This paper provides a 8 × 8 two-dimensional flexible ultrasonic array (2D-FUA) based on laser micromachining; a novel single-layer “island bridge” structure was used to design flexible array and piezoelectric array elements to improve the imaging capability on complex surfaces. The mechanical and acoustoelectric properties of the array are characterized, and a novel laser scanning and positioning method is introduced to solve the problem of array element displacement after deformation of the 2D-FUA. Finally, a multi-modal localization imaging experiment was carried out on the multi-target steel pin on the plane and curved surface based on the Verasonics system. The results show that the laser scanning method has the ability to assist the rapid imaging of flexible arrays on surfaces with complex shapes, and that 2D-FUA has wide application potential in medical-assisted localization imaging.
... Although there are already quite a few examples of such devices [1][2][3], most existing electronic elements on the industrial level are not compatible with stretching. Since the expected applications of flexible wearable devices are diverse [4][5][6][7], the stretchability, e.g., on the molecular scales, are often unnecessary. The necessary space resolution of stretchability depends on the specific applications. ...
Article
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Nanopapers fabricated from cellulose nanofibers (CNFs) are flexible for bending while they are rather stiff against stretching, which is a common feature shared by conventional paper-based materials in contrast with typical elastomers. Cellulose nanopapers have therefore been expected to be adopted in flexible device applications, but their lack of stretching flexibility can be a bottleneck for specific situations. The high stretching flexibility of nanopapers can effectively be realized by the implementation of Kirigami structures, but there has never been discussion on the mechanical resilience where stretching is not a single event. In this study, we experimentally revealed the mechanical resilience of nanopapers implemented with Kirigami structures for stretching flexibility by iterative tensile tests with large strains. Although the residual strains are found to increase with larger maximum strains and a larger number of stretching cycles, the high mechanical resilience was also confirmed, as expected for moderate maximum strains. Furthermore, we also showed that the round edges of cut patterns instead of bare sharp ones significantly improve the mechanical resilience for harsh stretching conditions. Thus, the design principle of relaxing the stress focusing is not only important in circumventing fractures but also in realizing mechanical resilience.
... Relying on advancements in functional materials, structural design, and state-of-art production/deposition techniques, a wide variety of single/ multi-stimuli responsive sensory systems, suitable for electronic skin (e-skin) applications, have been reported. [5][6][7][8] An efficient e-skin design requires a combination of functional materials with suitable mechanical and electrical properties, [9] in addition to the micro/nanoscale control of the layer's thickness and dimensions, which is optimized by the choice of suitable fabrication techniques. ...
Article
A force, humidity, and temperature‐responsive electronic skin is presented by combining piezoelectric zinc oxide (ZnO) and poly‐N‐vinylcaprolactam‐co‐di(ethylene glycol) divinyl ether hydrogel into core‐shell nanostructures using state‐of‐the‐art dry vapor‐based techniques. The proposed concept is realized with biocompatible materials in a simplified design that delivers multi‐stimuli sensitivity with high spatial resolution, all of which are prerequisites for an efficient electronic skin. While the piezoelectricity of ZnO provides sensitivity to external force, the thermoresponsiveness of the hydrogel core provides sensitivity to surrounding temperature and humidity changes. The hydrogel core exerts mechanical stress onto the ZnO shell, which is translated to a measurable piezoelectric signal. A localized force sensitivity of 364 ± 66 pC N−1 is achieved with very low cross talk between 0.25 mm2 pixels. Additionally, the sensor's sensitivity to humidity is demonstrated at 25 and 40 °C, i.e., above and below the hydrogel's lower critical solution temperature (LCST) of 34 °C. The largest response to temperature is obtained at high humidity and below the hydrogel's LCST. The sensor response to force, humidity, and temperature is significantly faster than the system's intrinsic or excitation‐induced time scale. Finally, the sensor response to touch and breath demonstrates its applicability as e‐skin in real‐life environment. A multi‐stimuli responsive sensor concept relying on a core‐shell nanostructure featuring a piezoelectric zinc thin film shell and an N‐vinylcaprolactam‐based hydrogel is presented. While the zinc oxide shell is directly sensitive to external applied force, the hydrogel responds to humidity and temperature by exerting stress onto the piezoelectric shell, which is converted into an electric signal.
... Artificial e-skins that can recognize tactile information are essential for the robotic and prosthetic applications. [163] By equipping with active matrix pressure sensors, the e-skins are capable of accurately perceiving spatially distributed tactile stimuli. The active matrix pressure sensors are constructed with different material combinations and device configurations. ...
Article
Full-text available
A variety of modern applications including soft robotics, prosthetics, and health monitoring devices that cover electronic skins (e‐skins), wearables as well as implants have been developed within the last two decades to bridge the gap between artificial and biological systems. During this development, high‐density integration of various sensing modalities into flexible electronic devices becomes vitally important to improve the perception and interaction of the human bodies and robotic appliances with external environment. As a key component in flexible electronics, the flexible thin‐film transistors (TFTs) have seen significant advances, allowing for building flexible active matrices. The flexible active matrices have been integrated with distributed arrays of sensing elements, enabling the detection of signals over a large area. The integration of sensors within pixels of flexible active matrices has brought the application scenarios to a higher level of sophistication with many advanced functionalities. Herein, recent progress in the active matrix flexible sensory systems is reviewed. The materials used to construct the semiconductor channels, the dielectric layers, and the flexible substrates for the active matrices are summarized. The pixel designs and fabrication strategies for the active matrix flexible sensory systems are briefly discussed. The applications of the flexible sensory systems are exemplified by reviewing pressure sensors, temperature sensors, photodetectors, magnetic sensors, and biosignal sensors. At the end, the recent development is summarized and the vision on the further advances of flexible active matrix sensory systems is provided. Recent progress in the active matrix flexible sensory systems is reviewed. The materials for constructing the active matrices are summarized. The design and fabrication for the sensory systems are discussed. The applications of the sensory systems are exemplified by taking pressure sensors, temperature sensors, photodetectors, magnetic sensors, and biosignal sensors.
... Considering the surface coverage and the softness of biological skins, large-area fabrication of electronic devices on flexible/stretchable substrates is needed. To this end, printed electronics could meet these requirements in a cost-effective manner (29)(30)(31)(32)(33)(34). Specifically, the printed semiconducting metal oxide nanowires (NWs) are promising candidates for the computational e-skin because of their high aspect ratio, unique electrical/optoelectrical properties, good mechanical flexibility, and compatibility with various printing technologies (35)(36)(37). ...
Article
An electronic skin (e-skin) for the next generation of robots is expected to have biological skin-like multimodal sensing, signal encoding, and preprocessing. To this end, it is imperative to have high-quality, uniformly responding electronic devices distributed over large areas and capable of delivering synaptic behavior with long- and short-term memory. Here, we present an approach to realize synaptic transistors (12-by-14 array) using ZnO nanowires printed on flexible substrate with 100% yield and high uniformity. The presented devices show synaptic behavior under pulse stimuli, exhibiting excitatory (inhibitory) post-synaptic current, spiking rate-dependent plasticity, and short-term to long-term memory transition. The as-realized transistors demonstrate excellent bio-like synaptic behavior and show great potential for in-hardware learning. This is demonstrated through a prototype computational e-skin, comprising event-driven sensors, synaptic transistors, and spiking neurons that bestow biological skin-like haptic sensations to a robotic hand. With associative learning, the presented computational e-skin could gradually acquire a human body–like pain reflex. The learnt behavior could be strengthened through practice. Such a peripheral nervous system–like localized learning could substantially reduce the data latency and decrease the cognitive load on the robotic platform.
... Stretchable electronics enable a wide variety of previously unknown functions by offering various form factors not possible with rigid electronics (1)(2)(3)(4)(5)(6)(7). Recently, stretchable display (8)(9)(10), battery pack (11)(12)(13), sensor array (9,14,15), heater (16), and logic circuit (17) have been demonstrated. ...
Article
Integration of rigid components in soft polymer matrix is considered as the most feasible architecture to enable stretchable electronics. However, a method of suppressing cracks at the interface between soft and rigid materials due to excessive and repetitive deformations of various types remains a formidable challenge. Here, we geometrically engineered Ferris wheel-shaped islands (FWIs) capable of effectively suppressing crack propagation at the interface under various deformation modes (stretching, twisting, poking, and crumpling). The optimized FWIs have notable increased strain at failure and fatigue life compared with conventional circle- and square-shaped islands. Stretchable electronics composed of various rigid components (LED and coin cell) were demonstrated using intrinsically stretchable printed electrodes. Furthermore, electronic skin capable of differentiating various tactile stimuli without interference was demonstrated. Our method enables stretchable electronics that can be used under various geometrical forms with notable enhanced durability, enabling stretchable electronics to withstand potentially harsh conditions of everyday usage.
... Focusing on the computing hardware for e-skin, this Review complements previous review articles that have presented topics such as various types of tactile sensors (25)(26)(27)(28), techniques, and materials (for example, using liquid metal and hydrogel) to realize sensors in soft and flexible form factors (29,30), identification of object properties and interactions (31), and distributed energy (32,33). This article also complements previous reviews covering neuro-/bio-inspired e-skin (34)(35)(36), providing a systematic and comprehensive discussion on the computing element in tactile sensing. ...
Article
Touch is a complex sensing modality owing to large number of receptors (mechano, thermal, pain) nonuniformly embedded in the soft skin all over the body. These receptors can gather and encode the large tactile data, allowing us to feel and perceive the real world. This efficient somatosensation far outperforms the touch-sensing capability of most of the state-of-the-art robots today and suggests the need for neural-like hardware for electronic skin (e-skin). This could be attained through either innovative schemes for developing distributed electronics or repurposing the neuromorphic circuits developed for other sensory modalities such as vision and audio. This Review highlights the hardware implementations of various computational building blocks for e-skin and the ways they can be integrated to potentially realize human skin-like or peripheral nervous system-like functionalities. The neural-like sensing and data processing are discussed along with various algorithms and hardware architectures. The integration of ultrathin neuromorphic chips for local computation and the printed electronics on soft substrate used for the development of e-skin over large areas are expected to advance robotic interaction as well as open new avenues for research in medical instrumentation, wearables, electronics, and neuroprosthetics.
... Stretchable electronic devices have been developed using stretchable materials, such as conductive elastomers and organic semiconductors, or stretchable structures, such as origami-based structures with folds and kirigami structures with slits [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Hinged origami/kirigami stretchable electronic devices consist of panels (undeformed regions) and hinges (local bending deformation regions), and the stretchability of the entire device is achieved by the local bending deformation of the hinges [5][6][7][8][9][10][11][12][13][14][15]. ...
Article
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A self-folding method that can fold a thick (~10 μm) metal layer with a large curvature (>1 mm−1) and is resistant to repetitive folding deformation is proposed. Given the successful usage of hinged origami/kirigami structures forms in deployable structures, they show strong potential for application in stretchable electronic devices. There are, however, two key difficulties in applying origami/kirigami methods to stretchable electronic devices. The first is that a thick metal layer used as the conductive layer of electronic devices is too hard for self-folding as it is. Secondly, a thick metal layer breaks on repetitive folding deformation at a large curvature. To overcome these difficulties, this paper proposes a self-folding method using hinges on a thick metal layer by applying a meander structure. Such a structure can be folded at a large curvature even by weak driving forces (such as those produced by self-folding) and has mechanical resistance to repetitive folding deformation due to the local torsional deformation of the meander structure. To verify the method, the large curvature self-folding of thick metal layers and their mechanical resistance to repetitive folding deformation is experimentally demonstrated. In addition, an origami/kirigami hybrid stretchable electronic device with light-emitting diodes (LEDs) is fabricated using a double-tiling structure called the perforated extruded Miura-ori.
... Flexible electronics are a rapidly growing field due to their capacity to experience high deformations while keeping their electric functionality. They find use in technological applications such as wearable electronics and sensors [114,115], health care systems [116] and flexible batteries and supercapacitors [117]. There are two predominant manufacturing strategies for the mentioned systems: intrinsic flexible and conductive polymers or hybrid composites containing a soft elastomeric substrate with interconnected conductive particles dispersed. ...
Article
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Magnetic composites and self-healing materials have been drawing much attention in their respective fields of application. Magnetic fillers enable changes in the material properties of objects, in the shapes and structures of objects, and ultimately in the motion and actuation of objects in response to the application of an external field. Self-healing materials possess the ability to repair incurred damage and consequently recover the functional properties during healing. The combination of these two unique features results in important advances in both fields. First, the self-healing ability enables the recovery of the magnetic properties of magnetic composites and structures to extend their service lifetimes in applications such as robotics and biomedicine. Second, magnetic (nano)particles offer many opportunities to improve the healing performance of the resulting self-healing magnetic composites. Magnetic fillers are used for the remote activation of thermal healing through inductive heating and for the closure of large damage by applying an alternating or constant external magnetic field, respectively. Furthermore, hard magnetic particles can be used to permanently magnetize self-healing composites to autonomously re-join severed parts. This paper reviews the synthesis, processing and manufacturing of magnetic self-healing composites for applications in health, robotic actuation, flexible electronics, and many more.
... TENGs are a potential candidate for next-generation targeted drug delivery due to their efficient energy harvesting, low weightiness, biocompatibility, flexibility, ease to fabrication and self-powering features [8]. TENGs have revolutionised our lives by direct monitoring health status such as temperature, heartbeat, respiration, circulation and nervous system [9]. In the near future, TENGmediated electronics devices will be integrated deeply inside our bodies to perform fundamental roles in health by monitoring body temperature, drug delivery and human/machine interactions that intimately contact the human body effectively [10]. ...
Article
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In the current decade, remarkable efforts have been made to develop a self-regulated, on-demand and controlled release drug delivery system driven by triboelectric nanogenerators (TENGs). TENGs have great potential to convert biomechanical energy into electricity and are suitable candidates for self-powered drug delivery systems (DDSs) with exciting features such as small size, easy fabrication, biocompatible, high power output and economical. This review exclusively explains the development and implementation process of TENG-mediated, self-regulated, on-demand and targeted DDSs. It also highlights the recently used TENG-driven DDSs for cancer therapy, infected wounds healing, tissue regeneration and many other chronic disorders. Moreover, it summarises the crucial challenges that are needed to be addressed for their universal applications. Finally, a roadmap to advance the TENG-based drug delivery system developments is depicted for the targeted therapies and personalised healthcare.
... Wearable devices such as fitness trackers and smartwatches have been widely adopted in our daily lives for both health monitoring and digital interactivity. We are also witnessing the trend of wearable device minimization, where both the size of these devices and their distance from our bodies are reducing [13,19,20,46], suggesting a future where miniature wearable devices may seamlessly integrate with us for interaction, actuation and sensing. However, most wearables to date are resigned to a single location on our body. ...
Preprint
We explore Calico, a miniature relocatable wearable system with fast and precise locomotion for on-body interaction, actuation and sensing. Calico consists of a two-wheel robot and an on-cloth track mechanism or "railway," on which the robot travels. The robot is self-contained, small in size, and has additional sensor expansion options. The track system allows the robot to move along the user's body and reach any predetermined location. It also includes rotational switches to enable complex routing options when diverging tracks are presented. We report the design and implementation of Calico with a series of technical evaluations for system performance. We then present a few application scenarios, and user studies to understand the potential of Calico as a dance trainer and also explore the qualitative perception of our scenarios to inform future research in this space.
... The demands of sensing materials capable of detecting external stimuli and changes are dramatically increasing with the advancement of smart electronic devices in various applications. Especially, bendable, flexible, and stretchable functional sensing materials have been intensively developed by the rapidly growing demand for skin-inspired wearable devices [1][2][3] . The development of various wearable electronic skin (e-skin) sensors has been required for artificial skins for humans or robots and for individual health monitoring. ...
Article
Full-text available
The fabrication of freestanding bendable films without polymer substrates is demonstrated as a capacitive humidity-sensing material. The bendable and porous SiO2/Si films are simply prepared by electrochemical-assisted stripping, metal-assisted chemical etching, followed by oxidation procedures. The capacitive humidity-sensing properties of the fabricated porous SiO2/Si film are characterized as a function of the relative humidity and frequency. The remarkable sensing performance is demonstrated in the wide RH range from 13.8 to 79.0%. The sensing behavior of the porous SiO2/Si film is studied by electrochemical impedance spectroscopy analysis. Additionally, the reliability of the porous SiO2/Si sensing material is confirmed by cyclic and long-term sensing tests.
... Due to intramolecular charge transfer (ICT), organic chemical compounds having electron-donating (D) and electron-withdrawing (W) teams within the same chemical structure area unit are believed to own optoelectronic importance and high spectrum characteristics. This development features a big selection of applications, together with optical and nonlinear devices [5,6] and photochemical and photobiological method verification [7]. The photophysical characteristics of those compounds area unit extremely influenced by the polarity of solvents [8], with increasing polarity shifting the emission spectrum to an extended wavelength [9,10]. ...
Article
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In different solvents, the electronic UV-Vis absorption and emission spectra of 7-(Dimethylamino)-4-(Trifluoromethyl)Coumarin (C152) were monitored. For the C152 molecular structure, the impact of solvent polarity on fluorescence quantum yield is explored. What is more, the critical micelle concentration (cmc) magnitude was calculable employing a plot of fluorescence intensity against cetrimonium bromide (CTAB) and sodium dodecyl sulfate concentrations (SDS). What is more, the photostability of the C152 model structure exploitation utterly varied solvents like acetone, methyl isobutyl ketone, and amyl alcohol in terms of approach for calculating half-life methodology (pumping with nitrogen laser 337.1 nm), yet because of the range of pulses needed to cut back the studied molecule intensity to 50% of its original value. The B3LYP/6-311G(d) level of theory was wont to optimize the C152 molecular structure. Natural bond orbital (NBO) analysis is additionally wont to explore the electronic hyper-conjugation of the C152 modeling structure. B3LYP/6-311Gþþ(d, p) is employed to get NBO studies for the molecule under investigation. The computational electronic UV-Vis absorption spectra of the C152 molecule were computed exploitation time-dependent density functional theory (TD-DFT) at the B3LYP/6-311Gþþ(d, p) level in gas and several other solvents. Theoretical findings were contrasted with experimental findings. The results reveal that the computational optical characteristics of the investigated molecular structure accord with the experimental findings. KEYWORDS 7-(Dimethylamino)-4-(Trifluoromethyl)Coumarin; density functional theory (DFT); fluorescence spectra; optical spectra; time dependent density functional theory (TD-DFT)
... [1][2][3] In recent years, electronic skins (e-skins) with protection, perception, and adjustment functions have been developed, which show promising applications in wearable devices, human-computer interface, intelligent prostheses, medical diagnostics, and other areas. [4][5][6][7][8][9] The temperature sensing and thermoregulating function of e-skin is attracting increasing attention, particularly in the intellectualization of bionic robots and mechanical prostheses. [10][11][12] Human beings perceive different degrees of heat and cold through four types of temperature sensory receptors. ...
Article
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The realization of the thermoregulating function of electronic skin (e‐skin) by simulating the human temperature perception system can greatly improve the intelligence of the e‐skin. Here, we report a thermoregulating e‐skin that fits on the surface of a prosthetic limb based on a hybrid structure consisting of a flexible thermoelectric device and a phase‐change heat sink. The hybrid e‐skin possesses outstanding temperature adaptability similar to that of the human body; it can maintain the surface temperature at 35°C in environmental temperatures ranging from 10 to 45°C. The power expenditure of the e‐skin is essentially the same as the energy required by the human body to regulate temperature and is only 14.22 mW cm−2 in the thermoneutral zone. Thermoregulation based on this e‐skin can greatly improve the temperature distribution of the target surface, providing a promising solution for the biomimetic thermoregulation of robots and the next generation of intelligent prostheses. The thermoregulating electronic skin based on a flexible thermoelectric device and a phase change material heat sink has the ability of heating and cooling, allowing the surface temperature to be maintained at 35°C in a cold/hot environment from 10 to 45°C, making it a promising solution for biomimetic thermoregulation of robots and the next generation of intelligent prostheses.
... With the increasing demand for applying electronics to the areas with complex shapes, the stretchability of the electronics has been increasingly concerned. Improving the stretchability of the electronics from materials, structure, connection, and fabrication has been a focus of research [1]. As an example, stretchability can enable electronics to be applied to the human skin and textiles [2]. ...
Article
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In this study, bending reliability of the surface mounted devices (SMD) attached using isotropic conductive adhesive (ICAs) on screen printed stretchable devices polyurethane substrate are investigated. The performance of polyurethane and polyurethane-acrylic ICAs and the impact of rolling speed are studied. The rolling test was performed using the customized automatic rolling test device. It was found that the polyurethane-acrylic blend gives poorer adhesion with the silver conductor and very high cohesive force. The polyurethane resin brings adhesive high adhesive force with the silver conductive layer while lower adhesion with the Tin surface of the SMD, and it exhibited poorer cohesive force. The resistance of all samples experienced a steady and slow increase period before it accelerated to failure. During the slow and steady increase phase, the increased resistance was mainly from the conductive layer, whereas during the dramatic increase phase, it was mainly from the ICA connected area. The increased rolling speed had accelerated the resistance evolution process and lowered the samples' reliability severely. It also lowered the adhesion of the polyurethane-acrylic blend with the ink layer and lowered cohesive force of polyurethane ICA.
... An ambitious goal is to manufacture an electronic skin (named Eskin) inspired by human skin, which means to develop a network of sensing elements embedded in tough, high stretchable, skin adhering, biocompatible materials with good cell affinity. More ambitious goals are to supply these artificial skins with more functionalities such as chemical sensing, diagnostic and monitoring capabilities, odor, and taste sensing (electronic nose and tongue) 275 . More efficient robots can be designed through the application of these smart skins. ...
Article
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After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis – blue mussel and Mytilus californianus ‐ California mussel are the most well‐known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesive and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle‐inspired chemistry is a versatile technique when designing not only wet adhesive, but in several more applications, especially in the bioengineering area. The applications of muscle‐inspired biomaterials in various medical applications are summarized to shed some light on future ahead of available strategies. This article is protected by copyright. All rights reserved.
... Bionic perception systems integrated with different sensors could perceive different external stimuli information, which have great potential in communicating with complex environments, recognizing objects, and engaging in social interaction. Traditional sensory systems relying on microprocessors and external circuits show high power consumption faced with the explosive growth of data 8 . Recently, the advancement in flexible electronics and neuromorphic electronics has opened up opportunities to construct artificial perception systems to emulate biological functions. ...
Article
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The advancement in flexible electronics and neuromorphic electronics has opened up opportunities to construct artificial perception systems to emulate biological functions which are of great importance for intelligent robotics and human-machine interactions. However, artificial systems that can mimic the somatosensory feedback functions have not been demonstrated yet despite the great achievement in this area. In this work, inspired by human somatosensory feedback pathways, an artificial somatosensory system with both perception and feedback functions was designed and constructed by integrating the flexible tactile sensors, synaptic transistor, artificial muscle, and the coupling circuit. Also, benefiting from the synaptic characteristics of the designed artificial synapse, the system shows spatio-temporal information-processing ability, which can further enhance the efficiency of the system. This research outcome has a potential contribution to the development of sensor technology from signal sensing to perception and cognition, which can provide a special paradigm for the next generation of bionic tactile perception systems towards e-skin, neurorobotics, and advanced bio-robots.
Article
Conductive hydrogels based on two-dimensional (2D) nanomaterials, MXene, have emerged as promising materials for flexible wearable sensors. In these applications, the integration of high toughness, ultrastretchability, low hysteresis, self-adhesiveness, and multiple sensory functions into one gel is essential. However, serious issues, such as easy restacking and inevitable oxidation of MXene nanosheets in aqueous media and weak interfacial bindings between MXene and the gel network, make it almost impossible to achieve the multiple performances mentioned above. Here we present a conductive MXene-composited polymer (MCP) hydrogel by incorporating gelatin-modified MXene into polyacrylamide (PAAm) hydrogel for the fabrication of multifunctional sensors. The presence of gelatin not only greatly improves the stability of the MXene nanosheets by forming a protective sheath, but also largely enhances the interfacial interactions between the MXene and the hydrogel network as molecular glues. Thus, the MCP hydrogel exhibits a high strength (430 kPa), remarkable stretchability (1100%), low hysteresis (<10% at 500% cyclic tensile), and excellent repeatable adhesion. The resultant MCP hydrogel-based versatile sensors display a high strain sensitivity with a broad working range (gauge factor (GF) = 8.83, up to 1000%), realizing the detection of various human motions. Moreover, the prepared sensors possess superior thermosensitive capacities (1.110/°C) for the measurement of body temperature. This strategy opens horizons to designing high-performance MXene-based hydrogels for advanced sensing platforms.
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Current stretchable strain sensors possess limited linear working ranges and it is still a formidable challenge to develop sensors that concurrently possess high gauge factors and high stretchability (ε ~ 100%). Herein, we report a facile method for creating unidirectional strain sensors to address the above issues. Using the 3D printing technique, we introduced thickness variations to control microcracking patterns in a carbon nanofibers-containing PEDOT:PSS (poly(3,4-ethylene dioxythiophene) polystyrene sulfonate) thin-film sensor. As a result, the sensor is capable of exceptionally linear response for up to 97% tensile strain while maintaining a high gauge factor of 151.
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Liquid‐metal (LM)‐based soft and stretchable electronics (SSEs) provide unique advantages for wearable computing, soft robotics, and implantable devices applications involving physical interaction with biological tissues and delicate objects. However, the lack of scalable manufacturing techniques prevents their mainstream adoption and commercialization. This paper introduces a scalable and reproducible manufacturing technique for wafer‐level fabrication of LM‐based SSEs, including LM‐only devices and hybrid circuits with LM and solid‐state microelectronics. The approach combines selective metal‐alloy wetting (SMAW) and controlled dip‐coating of eutectic gallium‐indium (EGaIn). The alloying of EGaIn and metal enables depositing EGaIn selectively onto the circuit layout defined by lithographically patterned copper traces on elastomer‐coated wafers. An automated, wafer‐level dip‐coating (DC) approach is developed to enable controllable and reproducible deposition of EGaIn. Wafer‐level simultaneous fabrication of many LM capacitors is demonstrated, and their geometric and electrical reproducibility is evaluated. The results indicate that the SMAW‐DC process can fabricate LM circuits reproducibly and rapidly. Hybrid SSEs are demonstrated by fabricating multiple wearable patches of ultra‐high frequency circuits with an LM dipole antenna, an LM strain gauge, and a solid‐state temperature sensor. Importantly, the presented technique can be integrated into the standard microfabrication flow for microelectronics, ensuring a high level of scalability. A scalable fabrication method is introduced for reproducible manufacturing of liquid‐metal‐based (LM) soft and stretchable circuits with integrated microchips. Proposed method incorporates a facile two‐layer dip‐coating process to lithography used in the microelectronics industry, thus takes advantage of the established scalability. LM dip‐coating automates the LM deposition step, thereby rendering the process scalable while yielding the fabricated geometries consistent.
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This review summarizes the adhesion mechanism and design strategies of underwater adhesion hydrogels, and generalizes their underwater application fields (adhesives, motion monitoring, marine environmental exploration and coatings).
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Use of flexible electronic devices use in different applications of Internet of thing especially in robot technology has been gotten importance to measured different physical factors like temperature. Also there is a need of a flexible and more informative approach to analysis the data. In this work, we have reported two flexible temperature sensors based reduce graphene and multi wall carbon nanotubes with high sensitivity and quick response time as well as recovery time. The electric properties of the sensor have been studied through the LCR meter associated with controlled chamber at 1 kHz. We use classical and neutrosophic method for analyzing the measured data of temperature sensors and find more effective of them by comparing their methods of analysis.
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Surface treatment for the polymer gate dielectric plays a significant role in achieving the high-performance flexible field-effect transistors. In this work, the direct SAM treatment on the polar polymer gate dielectric is introduced and the effects on the electrical performance of OFETs are investigated. After an appropriate SAM treatment for the polar polymer dielectric, the mobility can be improved and the hysteresis and interfacial trap states are decreased obviously. Moreover, the SAM treated polymer dielectric is used to achieve the ultra-flexible OFET successfully, with a stable electrical performance under various deformations. These results demonstrate that the direct SAM treatment on polar polymer dielectric is a promising strategy for the high-performance flexible organic transistors, presenting the huge potential for the next-generation flexible electronics.
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Single-walled carbon nanotubes (SWCNTs) present excellent electronic and mechanical properties desired in wearable and flexible devices. The preparation of SWCNT films is the first step for fabricating various devices. This work developed a scalable and feasible method to assemble SWCNT thin films on water surfaces based on Marangoni flow induced by surface tension gradient. The films possess a large area of 40 cm × 30 cm (extensible), a tunable thickness of 15 ∼ 150 nm, a high transparency of up to 96%, and a decent conductivity. They are ready to be directly transferred to various substrates, including flexible ones. Flexible strain sensors were fabricated with the films on flexible substrates. These sensors worked with high sensitivity and repeatability. By realizing multi-functional human motion sensing, including responding to voices, monitoring artery pulses, and detecting knuckle and muscle actions, the assembled SWCNT films demonstrated the potential for application in smart devices.
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The control of cross-linking of polythiophene with cyclic siloxane was achieved and provided to their mechanical properties and elastic recovery. The cross-links led to high recovery of crystallite orientation under stretching.
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There is growing recognition that the developments in piezoresistive devices from personal healthcare to artificial intelligence, will emerge as de novo translational success in electronic skin. Here, we review the updates with regard to piezoresistive sensors including basic fundamentals, design and fabrication, and device performance. We also discuss the prosperous advances in piezoresistive sensor application, which offer perspectives for future electronic skin.
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Nowadays, multifunctional, easily prepared, and highly sensitive flexible sensors have attracted extensive attention and are gradually used in various scenarios. Here, we report the design of the Ti2C3Tx/polyurethane composites prepared by a facile gas-liquid interface self-assembly. The obtained flexible sensor has a wide detection range (∼900%), a low-stress detection limit (<1%), a high sensitivity (GF = 1.3, strain from 0 to 100%), and a fast response time (<140 ms). The multifunctional stress sensor can be applied to not only wearable motion monitoring and detection of various signals but also the detection of underwater human motion, as well as different motion states and swimming frequencies of toy fish in water, demonstrating its great prospects in a variety of applications, such as human movement monitoring and marine biological detection and research.
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Resistive random access memory (ReRAM) based on resistive switching (RS) effect is a new type of non-volatile memory device that stores information based on the reversible conversion of resistance states...
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The excessive usage and demand of consumer electronics have caused an elevation of electronic waste. Typically, consumer electronics are produced with non-biodegradable, non-biostable, and sometimes fatal materials, resulting in global alarming biological summons. Thence, to mend the drawbacks, an emerging field—named transient electronics—takes effect where the biomaterial, device, substrate, and total systems disappear untraceably after steady-state operation. Conspicuously, transient electronics have induced immense curiosity in researchers to perform interesting investigations due to the feature of disintegration after stable operation. The idea of transient electronics has been implemented in biomedical, military, and nanotechnology fields. Although rapid development is evident in transient technology in a short period, it is believed that the technology will deliver the utmost prospects in advanced electronic applications. Essentially, in transient technology, the vital challenge is to determine the platform materials that offer stability, resistance, biocompatibility, and mainly, the solubility to accommodate the transient devices. In this Review, a detailed overview of different soluble substrates, such as organic, polymer, and solid-state substrates, is described, along with the feasibility of the fabricated devices on the respective substrates to support transient electronics. Second, the dissolving mechanism of the corresponding substrates is analyzed.
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Artificial intelligent skins hold the potential to revolutionize artificial intelligence, health monitoring, soft robotics, biomedicine, flexible, and wearable electronics. Present artificial skins can be characterized into electronic skins ( e-skins) that convert external stimuli into electrical signals and photonic skins ( p-skins) that convert deformations into intuitive optical feedback. Merging both electronic and photonic functions in a single skin is highly desirable, but challenging and remains yet unexplored. We report herein a brand-new type of artificial intelligent skin, an optoelectronic skin ( o-skin), which combines the advantages of both e-skins and p-skins in a single skin device based on one-dimensional photonic crystal-based hydrogels. Taking advantage of its anisotropic characteristics, the resulting o-skin can easily distinguish vector stimuli such as stress type and movement direction to meet the needs of multi-dimensional perception. Furthermore, the o-skin also demonstrates advanced functions such as full-color displays and intelligent response to the environment in the form of self-adaptive camouflage. This work represents a substantial advance in using the molecular engineering strategy to achieve artificial intelligent skins with multiple anisotropic responses that can be integrated on the skin of a soft body to endow superior functions, just like the natural organisms that inspire us.
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High-performance piezoresistive nanocomposites have attracted extensive attention because of their significant potential as next-generation sensing devices for a broad range of applications, such as monitoring structural integrity and human performance. While various piezoresistive nanocomposites have been successfully developed using different material compositions and manufacturing techniques, current development procedures typically involve empirical trial and error that can be laborious, inefficient, and, most importantly, unpredictable. Therefore, this paper proposed and validated a topological design-based methodology to strategically manipulate the piezoresistive effect of nanocomposites to achieve a wide range of strain sensitivities without changing the material system. In particular, patterned nanocomposite thin films with stress-concentrating and stress-releasing topologies were designed. The strain sensing properties of the different topology nanocomposites were characterized and compared via electromechanical experiments. Those results were compared to both linear and nonlinear piezoresistive material model numerical simulations. Both the experimental and simulation results indicated that the stress-concentrating topologies could enhance strain sensitivity, whereas the stress-releasing topologies could significantly suppress bulk film piezoresistivity.
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Over the past several years, wearable electrophysiological sensors with stretchability have received significant research attention because of their capability to continuously monitor electrophysiological signals from the human body with minimal body motion artifacts, long-term tracking, and comfort for real-time health monitoring. Among the four different sensors, i.e., piezoresistive, piezoelectric, iontronic, and capacitive, capacitive sensors are the most advantageous owing to their reusability, high durability, device sterilization ability, and minimum leakage currents between the electrode and the body to reduce the health risk arising from any short circuit. This review focuses on the development of wearable, flexible capacitive sensors for monitoring electrophysiological conditions, including the electrode materials and configuration, the sensing mechanisms, and the fabrication strategies. In addition, several design strategies of flexible/stretchable electrodes, body-to-electrode signal transduction, and measurements have been critically evaluated. We have also highlighted the gaps and opportunities needed for enhancing the suitability and practical applicability of wearable capacitive sensors. Finally, the potential applications, research challenges, and future research directions on stretchable and wearable capacitive sensors are outlined in this review.
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A soft bending sensor based on the inverse pyramid structure is demonstrated, revealing that it can effectively suppress microcrack formation in designated regions, thus allowing the cracks to open gradually with bending in a controlled manner. Such a feature enabled the bending sensor to simultaneously have a wide dynamic range of bending strain (0.025-5.4%), high gauge factor (∼74), and high linearity (R2 ∼ 0.99). Furthermore, the bending sensor can capture repeated instantaneous changes in strain and various types of vibrations, owing to its fast response time. Moreover, the bending direction can be differentiated with a single layer of the sensor, and using an array of sensors integrated on a glove, object recognition was demonstrated via machine learning. Finally, a self-monitoring proprioceptive ionic electroactive polymer (IEAP) actuator capable of operating in liquid was demonstrated. Such features of our bending sensor will enable a simple and effective way of detecting sophisticated motion, thus potentially advancing wearable healthcare monitoring electronics and enabling proprioceptive soft robotics.
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What is the role of touch in inviting social interaction with robots? Forms of functional haptics in collaboration and socially assistive robots for example indicate one pathway. But what of more naturalistic and affective forms of touch that are more inviting, that encourage pro-social behaviors? This is a tale of three loops. First, the haptic feedback loop, where human-human touch still remains underexplored, and where human-machine touch is produced through mechanical engineering as ‘force display’ and perceived by the user as tactile (e.g. Srinivasan and Basdogan 1997). Second, the affective feedback loop, courtesy of Höök (2008; 2009) and Dumouchel and Damiano (2017), where technical systems influence, and are influenced by, a human user corporeally. Bringing these loops together encourages interaction design to consider how touch and affect may more effectively invite a range of users to interact with social robots, and their role in the perception of Artificial Empathy (AE).
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Precise control over the smart materials exhibiting reversible shape changes in response to environmental stimuli presents a considerable challenge. Here, with a self-assembly strategy by extracting natural materials from pigskin, a single layer bio-inspired, transparent, soft biological film (BF) with the primary characteristics of self-actuation and self-sensing is successfully developed. The self-assembly constructed BF can exchange water and reflect environmental humidity gradients rapidly to activate continuous rotary movement. Temperature which affects the thermal motion of water molecules will induce different orientation movement of the film, and on this basis, a humidity-driven energy transfer motor is developed. More characterizations highlight the behavior mechanism of BF through water exchanging by a hydrogen bonding interaction with the hydrophilic group of amino acids residues on the BF surface. Finally, a wearable, steady and ultrafast-response sensor to detect human breathing, especially for real-time obstructive sleep apnea (OSA) state, is fabricated. This study offers great potential in emerging applications including micro-sensors, switches, soft robots and power source technologies.
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Flexible capacitive and resistive pressure sensors are promising candidates due to their various artificial intelligent applications, human body physiological monitoring, medical diagnostic systems, human-machine interaction, and electronic skin. The key functional parameters and transduction mechanisms decide the performance and applications of any pressure sensors. In recent years, various reports on flexible pressure sensing devices with colossal improvement in the key parameters has been reported. In this review article, a brief introduction about working principle of the transduction mechanism, key parameters, and sensors functional materials is described. Later, a summary has been provided on the recent developments in the flexible pressure sensors with their key parameters, namely sensitivity, response time, and limit of pressure detection. A brief study about the various applications of the sensing devices in human motion, healthcare monitoring, human-machine interaction and electronic skin are also discussed. This review article will provide a innovative direction to the readers working in this field to improve the pressure sensor’s quality and to explore their applications.
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Pressure sensors are a promising design paradigm for wearable devices required to interact gently with the environment. To enable flexible sensors to respond intelligently to the surroundings, microstructures for subtle pressure and force waveform detection are needed. Here, a self‐adaptive pressure sensor is reported in which graphene‐based flakes adhere to the melamine sponge backbones forming hierarchical structures and exhibiting high‐pressure resolution. Under a high preload pressure of 100 kPa, the pressure sensor demonstrates a high‐pressure resolution ability of ≈1‰. The self‐adaptive microstructure change and mechanical behavior are observed simultaneously and dynamically using in situ electron microscopy. The high‐pressure resolution of the pressure sensor enables it to monitor subtle human ballistocardiogram signals, which demonstrates excellent potential in multifarious applications of human motion detection and health monitoring. It is challenging for a pressure sensor to detect a tiny pressure under high pressure. Herein, a self‐adaptive in situ pressure sensor with a hierarchical gradient structure is proposed. It exhibits a high‐pressure resolution on the order of 104 Pa under a 100 kPa high pressure preloaded. The sensing mechanism is revealed by in situ scanning electron microscopy technique.
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Tactile sensation is one of the most important senses in living things and smart devices to obtain the required data from the outside world, and slip is one of the main tactile information. In the present study, a slip sensor made of conductive sponge and polyvinylidene fluoride (PVDF) is proposed to sense the magnitude and direction of the sliding force. The structure and working principle of the sensor are analyzed using the finite element method. Compared with the conventional room temperature vulcanized (RTV) silicone rubber and polydimethylsiloxane (PDMS) substrates, the conductive sponge not only provides good support for PVDF film and increases its output voltage but also can be used as an electrode to transfer electric charges. The performed experiments show that the response time of the tactile unit using the conductive sponge substrate is 48 ms, and the detection range of the tactile unit is 0.1–15 N. It is found that the designed sensor has a response time of 80 ms, a recovery time of 160 ms, and a measurement error of the angle perception is 4.54° ± 1.53°. Moreover, its detection error for shear force is 8.04% ± 5.8%. Accordingly, this method can be effectively applied to distinguish the magnitude and direction of the shear force and detect the object sliding in real‐time. This paper provides a sliding detection sensor to sense the magnitude and direction of sliding force. The conductive sponge can increase the polyvinylidene fluoride (PVDF) deformation and improve the output signal. The experimental results show that the sensor can be used in the field of robotics.
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Hydrogel-based ionic skins are ionic conductive artificial skin-like materials that are promising for a broad range of applications such as wearable sensory devices, soft robotics and machines, and bioelectronics. However, fabricating hydrogel skins with satisfying mechanical performance and intelligent sensing functions is still a significant challenge. Herein, we have developed an ionic conductive nanocomposite hydrogel with ultra stretchability and self-evolving sensing functions. By leveraging the dynamic feature of synergetic interfacial ionic interactions, a trace amount of carbon nanotubes endows the hydrogel networks with excellent mechanical performances (i.e., tensile strength, stretchability and toughness up to 1.09 MPa, 4075% and 12.8 MJ/m³, respectively). Additionally, the hydrogel is soft, elastic, transparent and self-healing. The rational combination of the mechanical and electrical properties renders the as-prepared hydrogel with excellent sensing performances and cycling stability, and therefore enables it to perform as a sensory unit of a complete platform for the recognition of some complicated human behaviors, outperforming the previously reported hydrogels due to its intelligent sensing functions. Specifically, with the integration of machine learning module, the hydrogel-based platform exhibits great recognition accuracies to human handwriting motions from single letters to words, phrases, and short sentences after proper training. The combination of superior mechanical performances and self-evolving sensing functions within this hydrogel-based ionic skin unlocks its potential as the intelligent human-device interface, which promotes the application of artificial intelligence in customized electronic devices.
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The unique molecular chain and aggregation structures of Eucommia ulmoides gum (EUG) lead to unique mechanical and thermal behavior. By regulating the microstructure of EUG via chemical reactions, changes in the mechanical and thermal behavior as well as the addition of specific functionalities of EUG can be achieved. Herein, we report a simple method to prepare intrinsic, autonomous, low-temperature self-healing materials by introducing pendent polyol moieties onto the chain of epoxidized EUG (EEUG). The relationship between the microstructure and properties of the resultant hydroxyl-functionalized EEUG (FEEUG) was analyzed by Fourier transform infrared spectrometry (FTIR), nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), tensile tests, and lap shear tests. As the modification degree of FEEUG increased, the mechanical behavior of FEEUG gradually changed from plastic to elastic and then to viscous, and the material showed highly efficient self-healing behavior. The self-healing efficiency was 77.8 % after 1 h of free contact at 30 °C and reached up to 90.2 % after 4 h. During five repeated lap shear tests, the adhesive strength of FEEUG28.6 (sample with a modification degree of 28.6 mol. %) decreased by only 10.9 %. The specific high chain mobility due to the diffusion and randomization of EUG at low temperatures and the reversible recovery of hydrogen bonds are believed to be the main causes for this phenomenon.
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Bionic hydrogel sensors have been known as promising alternatives to biomimetic skins. Here, a bionic hydrogel sensor based on sodium alginate (Alg), polyacrylamide (PAAM) and Fe³⁺ have been fabricated by a simple one-pot method, shows super stretchability, excellent adhesion and conductivity. The Fe³⁺/Alg-PAAM hydrogel was endowed with a dynamic coordination dual-network structure based on controllable Fe³⁺ penetration and free radical polymerization dual effect, which was equipped with the synergistic properties of high storage modulus (2200 KPa), super stretchability (1800%) and strong adhesion to various substrates (glass adhesion with 61.8 KPa). Moreover, due to abundant free ions, the Fe³⁺/Alg-PAAM hydrogel displays good conductive behavior, and further shows excellent sensing behavior and strain sensitivity as a skin sensor to monitor human movement. This work enriches the design and preparation strategies of flexible hydrogels to promote the application of Alg-based materials for the wearable electronic devices and intelligent monitoring systems.
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A mechanoreceptor is a sensor in the human body used to detect signals from the environment, and it induces bodily responses via the brain. We designed a transparent mechanoreceptor using a metal-oxide heterojunction to develop the skin-adopted concept. A highly transparent device (>60%) on PET substrate is obtained using wide bandgap oxide heterostructure. These layers spontaneously provide photovoltaic power (15 μW) to operate the mechanoreceptor without an external power supply system. We show that flexible device provides fast photo response of order of µs, offers solutions ultrafast mechanoreceptor for self-powered skin application. The mechanoreceptor can also operate well above 200 Hz for future ultrafast e-skin. In addition, the photovoltaic mechanoreceptor can be developed on a flexible substrate that is compatible with skin applications such as speedy responses to stimuli (<100 µs). The transparent photovoltaic mechanoreceptor has a self-operational mode and has flexible options in human electronics.
Chapter
Conductive polymers (CPs) have gained significant attraction in recent years, and their applications range from optoelectronics to material science. In this chapter, we provide a broad overview of recent advances in the development of CP nanomaterials and their biomedical applications. We highlight the potential biomedical applications of biodegradable CPs (specifically those for electronic skin, tissue engineering, actuators, and biosensors). We conclude this review by offering our perspectives on the current challenges and future opportunities facing the development and practical applications of CP nanomaterials.
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Silk fibroin has become a promising biomaterial owing to its remarkable mechanical property, biocompatibility, biodegradability, and sufficient supply. However, it's difficult to directly construct materials with other formats except for yarn, fabric and nonwoven based on natural silk. A promising bioinspired strategy is firstly extracting desired building blocks of silk, then reconstructing them into functional regenerated silk fibroin (RSF) materials with controllable formats and structures. This strategy could give it excellent processability and modifiability, thus well meet the diversified needs in biomedical applications. Recently, to engineer RSF materials with properties similar to or beyond the hierarchical structured natural silk, novel extraction and reconstruction strategies have been developed. In this review, we seek to describe varied building blocks of silk at different levels used in biomedical field and their effective extraction and reconstruction strategies. This review also present recent discoveries and research progresses on how these functional RSF biomaterials used in advanced biomedical applications, especially in the fields of cell-material interactions, soft tissue regeneration, and flexible bioelectronic devices. Finally, potential study and application for future opportunities, and current challenges for these bioinspired strategies and corresponding usage were also comprehensively discussed. In this way, it aims to provide valuable references for the design and modification of novel silk biomaterials, and further promote the high-quality-utilization of silk or other biopolymers.
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Liquid metal (LM)-based polymer composites are currently new breakthrough and emerging classes of soft multifunctional materials (SMMs) having immense transformative potential for soft technological applications. Currently, room-temperature LMs, mostly eutectic gallium‑indium and Galinstan alloys are used to integrate with soft polymer due to their outstanding properties such as high conductivity, fluidity, low adhesion, high surface tension, low cytotoxicity, etc. The microstructural alterations and interfacial interactions controlling the efficient integration of LMs with rubber are the most critical aspects for successful implementation of multifunctionality in the resulting material. In this review article, a fundamental understanding of microstructural alterations of LMs to the formation of well-defined percolating networks inside an insulating rubber matrix has been established by exploiting several existing theoretical and experimental studies. Furthermore, effects of the chemical modifications of an LM surface and its interfacial interactions on the compatibility between solid rubber and fluid filler phase have been discussed. The presence of thin oxide layer on the LM surface and the effects and challenges it poses to the adequate functionalization of these materials have been discussed. Plausible applications of SMMs in different soft matter technologies, like soft robotics, flexible electronics, soft actuators, sensors, etc. have been provided. Finally, the current technical challenges and further prospective to the development of SMMs using non‑silicone rubbers have been critically discussed. This review is anticipated to infuse a new impetus to the associated research communities for the development of next generation SMMs.
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Novel nanomaterials for bioassay applications represent a rapidly progressing field of nanotechnology and nanobiotechnology. Here, we present an exploration of single-walled carbon nanotubes as a platform for investigating surface-protein and protein-protein binding and developing highly specific electronic biomolecule detectors. Nonspecific binding on nanotubes, a phenomenon found with a wide range of proteins, is overcome by immobilization of polyethylene oxide chains. A general approach is then advanced to enable the selective recognition and binding of target proteins by conjugation of their specific receptors to polyethylene oxide-functionalized nanotubes. This scheme, combined with the sensitivity of nanotube electronic devices, enables highly specific electronic sensors for detecting clinically important biomolecules such as antibodies associated with human autoimmune diseases.
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Electronics can be made on elastically stretchable “skin.” Such skins conform to irregularly curved surfaces and carry arrays of thin-film devices and integrated circuits. Laypeople and scientists intuitively grasp the concept of electronic skins; material scientists then ask “what materials are used?” and “how does it work?” Stretchable circuits are made of diverse materials that span more than 12 orders of magnitude in elastic modulus. We begin with a brief overview of the materials and the architecture of stretchable electronics, then we discuss stretchable substrates, encapsulation, interconnects, and the fabrication of devices and circuits. These components and techniques provide the tools for creating new concepts in biocompatible circuits that conform to and stretch with living tissue. They enable wireless energy transfer via stretchable antennas, stretchable solar cells that convert sunlight to electricity, supercapacitors, and batteries that store energy in stretchable electronic devices. We conclude with a brief outlook on the technical challenges for this revolutionary technology on its road to functional stretchable electronic systems.
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We present a novel and flexible system to be employed for tactile transduction in the realization of artificial "robot skin". The mechanical deformation detection, which functionally reproduces the sense of touch, is based on Organic Thin Film Transistors (OTFTs) assembled on a flexible plastic foil, where each device acts as a strain sensor. OTFT-based mechanical sensors were fabricated employing a solution-processable organic semiconductor, namely 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) deposited by drop casting. It will be shown that the surface deformation induced by an external mechanical stimulus gives rise in both cases to a marked, reproducible, and reversible (within a certain range of surface deformation) variation of the device output current. Starting from these results, more complex structures, such as arrays and matrices of OTFT-based mechanical sensors, have been fabricated by means of inkjet printing. Thanks to the flexibility of the introduced structure, we will show that the presented system can be transferred on different surfaces (hard and soft) and employed for a wide range of applications. In particular, it can be successfully employed for tactile transduction in the realization of artificial "robot skin".
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The use of carbon nanotubes for piezoresistive strain sensors has acquired significant attention due to its unique electromechanical properties. In this comprehensive review paper, we discussed some important aspects of carbon nanotubes for strain sensing at both the nanoscale and macroscale. Carbon nanotubes undergo changes in their band structures when subjected to mechanical deformations. This phenomenon makes them applicable for strain sensing applications. This paper signifies the type of carbon nanotubes best suitable for piezoresistive strain sensors. The electrical resistivities of carbon nanotube thin film increase linearly with strain, making it an ideal material for a piezoresistive strain sensor. Carbon nanotube composite films, which are usually fabricated by mixing small amounts of single-walled or multiwalled carbon nanotubes with selected polymers, have shown promising characteristics of piezoresistive strain sensors. Studies also show that carbon nanotubes display a stable and predictable voltage response as a function of temperature.
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Dielectric elastomer generators offer great potential for soft applications involving fluid or human interactions. These scavengers are light, compliant, have a wide range of functions and develop an important energy density. Nevertheless, these systems are passive and require an external bias source, namely a high voltage source and complex power circuits. This cumbersome polarization complexes the system in a drastic way and slows down the development of dielectric generators. In order to remove these problems, we propose here new transducers based on the use of an electret coupled with dielectric elastomer, thus avoiding the use of a high external voltage source, and leading to the design of a soft autonomous dielectric generator. By combining a dielectric model and the electret theory, an electromechanical model was developed to evaluate the capabilities of such a generator. This generator was then produced starting from Teflon™ as electret and silicone PolyPower™ as electroactive polymer. A good agreement between the model and the experiment were obtained. An experimental energy density of 0.55 mJ g−1 was reached for 50% strain (electret potential of −1000 V). Once optimized in its design, such a soft generator could produce energy density up to 1.42 mJ g−1. An energy density of 4.16 mJ g−1 is expected with an electret potential of −2000 V.
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Sensitive skin is a large-area, flexible array of sensors with data processing capabilities, which can be used to cover the entire surface of a machine or even a part of a human body. Depending on the skin electronics, it endows its carrier with an ability to sense its surroundings via the skin's proximity, touch, pressure, temperature, chemical/biological, or other sensors. Sensitive skin devices will make possible the use of unsupervised machines operating in unstructured, unpredictable surroundings-among people, among many obstacles, outdoors on a crowded street, undersea, or on faraway planets. Sensitive skin will make machines "cautious" and thus friendly to their environment. This will allow us to build machine helpers for the disabled and elderly, bring sensing to human prosthetics, and widen the scale of machines' use in service industry. With their ability to produce and process massive data flow, sensitive skin devices will make yet another advance in the information revolution. This paper surveys the state of the art and research issues that need to be resolved in order to make sensitive skin a reality. The paper is partially based on the report of the Sensitive Skin Workshop conducted jointly by the National Science Foundation (NSF) and Defense Advanced Research Projects Agency (DARPA) in October 1999 in Arlington, VA, of which the three co-authors were the co-chairs [1].
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The piezoelectric performance of polyvinylidene fluoride (PVDF) is shown to double through the controlled incorporation of carbon nanomaterial. Specifically, PVDF composites containing carbon fullerenes (C60) and single-walled carbon nanotubes (SWNT) are fabricated over a range of compositions and optimized for their Young's modulus, dielectric constant, and d31 piezoelectric coefficient. Thermally stimulated current measurements show a large increase in internal charge and polarization in the composites over pure PVDF. The electromechanical coupling coefficients (k31) at optimal loading levels are found to be 1.84 and 2 times greater than pure PVDF for the PVDF-C60 and PVDF-SWNT composites, respectively. Such property-enhanced nanocomposites could have significant benefit to electromechanical systems employed for structural sensing, energy scavenging, sonar, and biomedical imaging.
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Stripes of thin gold films are made on an elastomeric substrate with built-in compressive stress to form surface waves. Because these waves can be stretched flat they function as elastic electrical conductors. Surprisingly, we observe electrical continuity not only up to an external strain of ∼ 2% reached by stretching the films first flat ( ∼ 0.4%) and then to the fracture strain of free-standing gold films ( ∼ 1%), but up to ∼ 22%. Such large strains will permit making stretchable electric conductors that will be essential to three-dimensional electronic circuits.
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Dielectric generators require an external circuit with a high bias voltage source to polarize them. To drastically reduce this circuit and to avoid external polarization, we propose here original transducers combining electrets and dielectric elastomer. Two operating modes have been studied and electromechanical analytical models have been developed from the combination of electrets theory and dielectric model. These concepts are applied on e-textile application: scavenging energy during human motion. An energy density around 6 mJ g−1 is expected on an optimal load of 10 MΩ. More generally, the flexibility, the lightness, the absence of high-voltage supply open many fields of applications beyond e-textiles.
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Highly flexible transparent capacitive sensors have been demonstrated for the detection of deformation and pressure. The elastomeric sensors employ a pair of compliant electrodes comprising silver nanowire networks embedded in the surface layer of polyurethane matrix, and a highly compliant dielectric spacer sandwiched between the electrodes. The capacitance of the sensor sheets increases linearly with strains up to 60% during uniaxial stretching, and linearly with externally applied transverse pressure from 1 MPa down to 1 kPa. Stretchable sensor arrays consisting of 10 × 10 pixels have also been fabricated by patterning the composite electrodes into X-Y addressable passive matrix.
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This paper presents a highly sensitive capacitive pressure sensor composed of a polymer dielectric film with a nano-needle structure. The nano-needle polymer films were prepared by facile fabrication methods including breath figures formation followed by stamping. The pressure sensitivity of the sensor reached 1.76 kPa−1 in the low pressure range (<1 kPa), which is comparable to the sensitivity of human skin. Analysis of the geometries and densities effect was shown, and the nano-needle film showed better sensitivity in comparison to films with hemispherical or conical structures. The pressure sensors were integrated with printed organic thin film transistors to enable flexible, large-area tactile sensing applications.
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We investigated the field-effect characteristics of mechanically stretched regio-regular poly(3-hexylthiophene) (P3HT) on a supporting poly(vinyl alcohol) (PVA) film. After stretching the P3HT/PVA film, large dichroism was observed in the polarized UV-Vis absorption spectra. The stretched P3HT films were applied parallel or orthogonal to the conduction channel of the transistor. The field-effect mobility was highly anisotropic, with larger mobility along the stretched direction of the films. The mobility increased with increasing stretch ratio (Sr) for the parallel devices but decreased for the orthogonal devices.
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Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO2 or NH3, the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.
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Dielectric elastomers are progressively emerging as one of the best performing classes of electroactive polymers for electromechanical transduction. They are used for actuation devices driven by the so-called Maxwell stress effect. At present, the need for high driving electric fields limits the diffusion of these transduction materials in some areas of potential application, especially in the case of biomedical disciplines. A reduction of the driving fields may be achieved with new elastomers offering intrinsically superior electromechanical properties. So far, most of attempts in this direction have been focused on the development of composites between elastomer matrixes and high-permittivity ceramic fillers, yielding to limited results. In this work, a different approach was adopted for increasing the electromechanical response of a common type of dielectric elastomer. The technique consisted in blending, rather than loading, the elastomer (poly-dimethyl-siloxane) with a highly polarizable conjugated polymer (undoped poly-hexyl-thiophene). The resulting material was characterised by dielectric spectroscopy, SEM microscopy, tensile mechanical analysis and electromechanical transduction tests. Very low percentages (1-6 wt%) of poly-hexyl-thiophene yielded both an increase of the relative dielectric permittivity and an unexpected reduction of the tensile elastic modulus. Both these factors synergically contributed to a remarkable increase of the electromechanical response, which reached a maximum at 1 wt% content of conjugated polymer. Estimations based on a simple linear model were compared with the experimental electromechanical data and a good agreement was found up to 1 wt%. This approach may lead to the development of new types of materials suitable for several types of applications requiring elastomers with improved electromechanical properties.
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Recent advances in stretchable electronics have seen the emergence of new technologies, and intensive efforts are being dedicated to embed some form of “intelligence” in various types of surfaces. However, the primary challenge in the field of stretchable electronics has been the development of stretchable or elastic electrical wiring that is both highly conductive and highly stretchable. Another challenge has been the development of manufacturing processes for integrating active device components as non-stretchable regions with electrical wiring as stretchable regions; the rigid/stretchable interfaces of these components require both high conductivity and high mechanical stability. In this article, we review the fabrication of carbon-nanotube-based elastic conductors with high electrical conductivity and mechanical stretchability as a representative example of stretchable organic integrated circuit electronics. Furthermore, we demonstrate the development of rubber-like stretchable integrated circuits for large-area human/machine interfaces. The fabrication process described in this article exploits the advantages of integrating a variety of electrical functional materials, ranging from rigid and semi-rigid elastomers to gels, with electronic circuits. The stretchable devices can be spread over a wide range of surfaces, including free surface curvatures and movable parts, thereby significantly increasing the scope of application of stretchable electrical and electronic circuits.
Article
Two levels of aligned stencil lithography were used to fabricate pentacene thin film transistors on 12 mu m thick flexible polyimide substrates. Flexible transistors with 20 x 40 mu m(2) channels were electrically measured under strain up to 2.6%. After one stretching cycle, their average mobility was decreased by 21%, remaining constant after the next 100 cycles. In order to decouple ageing from stretching effects for long-term cycling, transistors with 10 x 20 mu m(2) channels were stretched up to 28,000 times and measured in the relaxed state, in parallel with reference samples left on the wafer. Their mobility decreased by 25% after the first cycle, while the consequent stretching did not affect the mobility more than natural ageing.
Article
Chip als Spürnase: Empfindlicher denn je lassen sich Explosivstoffe mit Siliciumnanodraht-Feldeffekttransistor-Sensoranordnungen nachweisen, die mit Monoschichten eines elektronenreichen Aminosilans modifiziert sind und Komplexe mit den Analyten bilden (siehe Bild). Diese Nano-„Spürnasen“ bemerken TNT-Konzentrationen von nur 1×10−6 ppt und sind somit Spürhunden und allen anderen bekannten Nachweismethoden für Explosivstoffe überlegen.
Article
The development of an experimental tactile sensor system fitted on a robot work-table is analyzed in this paper. In the first stage of this research a 16 × 16 piezoresistive sensor was used, attached on the work-table of an ASEA IRB-2000 robot. The keypoint of the above design is that the sensor is not used just to obtain texture information, as it is happens when it is fitted on the gripper, but also to obtain tactile data from the object nonvisible base-surface and finally the object weight. The experimental system is designed so as to allow variation in the design parameters to determine the best set of parameter values for optimal performance of the sensor. Experiments carried out show the operability of the above system and, furthermore, the advantages using this sensor topology.
Article
Wavy ribbons of carbon nanotubes (CNTs) are embedded in elastomeric substrates to fabricate stretchable conductors that exhibit excellent performance in terms of high stretchability and small resistance change. A CNT ribbon with a thin layer of sputtered Au/Pd film is transferred onto a prestrained poly(dimethylsiloxane) (PDMS) substrate and buckled out-of-plane upon release of the prestrain. Embedded in PDMS, the wavy CNT ribbon is able to accommodate large stretching (up to the prestrain) with little change in resistance. For a prestrain of 100%, the resistance increases only about 4.1% when the wavy CNT ribbon is stretched to the prestrain. A simple stretchable circuit consisting of a light-emitting diode and two wavy ribbons is demonstrated and shows constant response on significant twisting, folding, or stretching. Fabricated with a simple buckling approach, the wavy CNT-ribbon-based stretchable conductors (e.g., interconnects and electrodes) could play an important role in stretchable electronics, sensors, photovoltaics, and energy storage.
Article
Understanding and controlling the morphology of donor/acceptor blends is critical for the development of solution processable organic solar cells. By crosslinking a poly(3-n-hexylthiophene-2,5-diyl) (P3HT) film we have been able to spin-coat [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) onto the film to form a structure that is close to a bilayer, thus creating an ideal platform for investigating interdiffusion in this model system. Neutron reflectometry (NR) demonstrates that without any thermal treatment a smaller amount of PCBM percolates throughout the crosslinked P3HT when compared to a non-crosslinked P3HT film. Using time-resolved NR we also show thermal annealing increases the rate of diffusion, resulting in a near-uniform distribution of PCBM throughout the polymer film. XPS measurements confirm the presence of both P3HT and PCBM at the annealed film's surface indicating that the two components are intermixed. Photovoltaic devices fabricated using this bilayer approach and suitable annealing conditions yielded comparable power conversion efficiencies to bulk heterojunction devices made from the same materials. The crosslinking procedure has also enabled the formation of patterned P3HT films by photolithography. Pillars with feature sizes down to 2 μm were produced and after subsequent deposition of PCBM and thermal annealing devices with efficiencies of up to 1.4% were produced.
Article
Carbon nanotube (CNT) based continuous fiber, a CNT assembly that could potentially retain the superb properties of individual CNTs on a macroscopic scale, belongs to a fascinating new class of electronic materials with potential applications in electronics, sensing, and conducting wires. Here, the fabrication of CNT fiber based stretchable conductors by a simple prestraining-then-buckling approach is reported. To enhance the interfacial bonding between the fibers and the poly(dimethylsiloxane) (PDMS) substrate and thus facilitate the buckling formation, CNT fibers are first coated with a thin layer of liquid PDMS before being transferred to the prestrained substrate. The CNT fibers are deformed into massive buckles, resulting from the compressive force generated upon releasing the fiber/substrate assembly from prestrain. This buckling shape is quite different from the sinusoidal shape observed previously in otherwise analogous systems. Similar experiments performed on carbon fiber/PDMS composite film, on the other hand, result in extensive fiber fracture due to the higher fiber flexural modulus. Furthermore, the CNT fiber/PDMS composite film shows very little variation in resistance (≈1%) under multiple stretching-and-releasing cycles up to a prestrain level of 40%, indicating the outstanding stability and repeatability in performance as stretchable conductors.
Article
Highly conductive and transparent poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) films, incorporating a fluorosurfactant as an additive, have been prepared for stretchable and transparent electrodes. The fluorosurfactant-treated PEDOT:PSS films show a 35% improvement in sheet resistance (Rs) compared to untreated films. In addition, the fluorosurfactant renders PEDOT:PSS solutions amenable for deposition on hydrophobic surfaces, including pre-deposited, annealed films of PEDOT:PSS (enabling the deposition of thick, highly conductive, multilayer films) and stretchable poly(dimethylsiloxane) (PDMS) substrates (enabling stretchable electronics). Four-layer PEDOT:PSS films have an Rs of 46 Ω per square with 82% transmittance (at 550 nm). These films, deposited on a pre-strained PDMS substrate and buckled, are shown to be reversibly stretchable, with no change to Rs, during the course of over 5000 cycles of 0 to 10% strain. Using the multilayer PEDOT:PSS films as anodes, indium tin oxide (ITO)-free organic photovoltaics are prepared and shown to have power conversion efficiencies comparable to that of devices with ITO as the anode. These results show that these highly conductive PEDOT:PSS films can not only be used as transparent electrodes in novel devices (where ITO cannot be used), such as stretchable OPVs, but also have the potential to replace ITO in conventional devices.
Article
Despite the ubiquity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a transparent conducting electrode in flexible organic electronic devices, its potential as a stretchable conductor has not been fully explored. This paper describes the electronic and morphological characteristics of PEDOT:PSS on stretchable poly(dimethylsiloxane) (PDMS) substrates. The evolution of resistance with strain depends dramatically on the methods used to coat the hydrophobic surface of PDMS with PEDOT:PSS, which is cast from an aqueous suspension. Treatment of the PDMS with an oxygen plasma produces a brittle skin that causes the PEDOT:PSS film to fracture and an increase in resistivity by four orders of magnitude at only 10% strain. In contrast, a mild treatment of the PDMS surface with ultraviolet/ozone (UV/O3) and the addition of 1% Zonyl fluorosurfactant to the PEDOT:PSS solution produces a mechanically resilient film whose resistance increases by a factor of only two at 50% strain and retains significant conductivity up to 188% strain. Examination of the strained surfaces of these resilient PEDOT:PSS films suggests alignment of the grains in the direction of strain. Wave-like buckles that form after the first stretch >10% render the film reversibly stretchable. Significant cracking (2 cracks mm–1) occurs at 30% uniaxial strain, beyond which the films are not reversibly stretchable. Cyclic loading (up to 1000 stretches) produces an increase in resistivity whose net increase in resistance increases with the value of the peak strain. As an application, these stretchable, conductive films are used as electrodes in transparent, capacitive pressure sensors for mechanically compliant optoelectronic devices.
Article
Polyurethane (PU)–polypyrrole (PPy) composite films and nanofibers were successfully prepared for the purpose of combining the properties of PU and PPy. Pyrrole (Py) monomer was polymerized and dispersed uniformly throughout the PU matrix by means of oxidative polymerization with cerium(IV) [ceric ammonium nitrate Ce(IV)] in dimethylformamide. Films and nanofibers were prepared with this solution. The effects of the PPy content on the thermal, mechanical, dielectric, and morphological properties of the composites were investigated with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR)–attenuated total reflection (ATR) spectroscopy, dielectric spectrometry, and scanning electron microscopy. The Young's modulus and glass‐transition temperatures of the composites exhibited an increasing trend with increases in the initially added amount of Py. The electrical conductivities of the composite films and nanofibers increased. The crystallinity of the composites were followed with DSC, the mechanical properties were followed with DMA, and the spectroscopic results were followed with FTIR–ATR spectroscopy. In the composite films, a new absorption band located at about 1650 cm−1 appeared, and its intensity improved with the addition of Py. The studied composites show potential for promising applications in advanced electronic devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Article
Stretchable device systems with suspended SnO2 nanowires (NWs) as channel materials: Oxygen plasma is used to remove the underlying polymer to float the NWs. These suspended NW field-effect transistors exhibit high electrical performance. By adopting a neutral mechanical plane and curved interconnection, electrical performance of the suspended NW field-effect transistors is maintained under stretching up to approximately 40%.
Conference Paper
Elastomers are emerging as an alternative to inorganic materials for electromechanical transducers. The rubber-like polymers are characterized by high elasticity (their equivalent elastic modulus is typically 2 orders of magnitude lower than that of silicon) and high yield strain (>;100%). They offer a unique opportunity to design and fabricate transducers, which can then shape complex, three-dimensional structures and accommodate moving structures. This paper reports on the design and technology to manufacture stretchable mechanical sensors and demonstrate an ultra-compliant 3×3 touch sensor matrix.
Article
The development of organic transistors for flexible electronics requires the understanding of device behavior upon the application of strain. Here, a comprehensive study of the effect of polymer-dielectric and semiconductor chemical structure on the device performance under applied strain is reported. The systematic change of the polymer dielectric results in the modulation of the effects of strain on the mobility of organic field-effect transistor devices. A general method is demonstrated to lower the effects of strain in devices by covalent substitution of the dielectric surface. Additionally, the introduction of a hexyl chain at the peripheries of the organic semiconductor structure results in an inversion of the effects of strain on device mobility. This novel behavior may be explained by the capacitative coupling of the surface energy variations during applied strain.
Article
A pressure sensor functionalised with vertically aligned carbon nanotubes is presented. The sensor is fabricated to have a multi-walled carbon-nanotube forest supported by a deflectable 8 m-thick Parylene-C membrane that is suspended by the silicon frame. The responses of the fabricated sensors are experimentally characterised. The sensitivities to positive and negative gauge pressures are found to be comparable in magnitude with the average values of -986 and +816 ppm/kPa, respectively. The measurement also reveals that the temperature coefficient of resistance for the forest suspended with the Parylene membrane is -515 ppm/°C and ~3× smaller than that for the forest fixed onto the silicon substrate.
Article
The three major types of tactile sensors currently available, namely optical sensors, conductive elastomer sensors, and silicon strain gauges, are discussed. Attention is also given to the new tactile sensing possibilities that are opening up as more data on the human skin become available. The principles of ultrasonic sensing are discussed.
Article
In this paper, we propose a new method to estimate the shape and irregularity of objects by a vision-based tactile sensor, which consists of a CCD camera, LED lights, transparent acrylic plate, and a touchpad which consists of an elastic membrane filled with translucent red water. Intensities of red, green and blue bands of the traveling light in the touchpad are analyzed in this study to estimate the shape/irregularity of the object. The LED light traveling in the touchpad is scattered and absorbed by the red pigment in the fluid. The depth of the touchpad is estimated by using the intensity of the light obtained from the red-green-blue (RGB) values of the image, in consideration of the scattering and reflection effects. The reflection coefficient that depends on the shape of the membrane, was decoupled in the proposed formulation. The intensity of the traveling light is represented with the geometrical parameters of the touchpad surface. In order to reduce the approximation error caused by unmodeled factors, we compensate the error by using a function of the deformation of the membrane. The validation of the proposed method is confirmed through experimental results.
Article
In the center of an otherwise unremarkable office stand six large robotic torsos mounted on pedestals and positioned along a bench that's covered with piles of plastic widgets.
Article
In this paper, we report a novel flexible tactile sensor array for an anthropomorphic artificial hand with the capability of measuring both normal and shear force distributions using quantum tunneling composite as a base material. There are four fan-shaped electrodes in a cell that decompose the contact force into normal and shear components. The sensor has been realized in a 2 × 6 array of unit sensors, and each unit sensor responds to normal and shear stresses in all three axes. By applying separated drops of conductive polymer instead of a full layer, cross-talk between the sensor cells is decreased. Furthermore, the voltage mirror method is used in this circuit to avoid crosstalk effect, which is based on a programmable system-on-chip. The measurement of a single sensor shows that the full-scale range of detectable forces are about 20, 8, and 8 N for the x-, y-, and z-directions, respectively. The sensitivities of a cell measured with a current setup are 0.47, 0.45, and 0.16 mV/mN for the x-, y-, and y-directions, respectively. The sensor showed a high repeatability, low hysteresis, and minimum tactile crosstalk. The proposed flexible three-axial tactile sensor array can be applied in a curved or compliant surface that requires slip detection and flexibility, such as a robotic finger.
Article
While diffuse-illumination touch sensing has the advantage of being sensitive enough to detect an object over a touch surface, it has the drawback of being unable to distinguish touches from approaches reliably. As a solution to this problem, proposed is a novel optical sensing structure that exploits the phenomenon of internal scattering. A prototype touch surface realising the proposed concept confirmed that it is indeed effective for better touch classification while retaining proximal sensitivity.
Article
Stretchable electronics can go beyond what might commonly be considered “electronics.” They can exploit their inherent elasticity to enable new types of transducers that convert between electrical energy and mechanical energy. Dielectric elastomer actuators are “stretchable capacitors” that can offer muscle-like strain and force response to an applied voltage. As generators, dielectric elastomers offer the promise of energy harvesting with few moving parts. Power can be produced simply by stretching and contracting a relatively low-cost rubbery material. This simplicity, combined with demonstrated high energy density and high efficiency, suggests that dielectric elastomers are promising for a wide range of energy-harvesting applications. Indeed, dielectric elastomers have been demonstrated to harvest energy from human walking, ocean waves, flowing water, blowing wind, pushing buttons, and heat engines. While the technology is promising and advances are being made, there are challenges that must be addressed if dielectric elastomers are to be a successful and economically viable energy-harvesting technology. These challenges include developing materials and packaging that sustain a long lifetime over a range of environmental conditions, designing the devices that stretch the elastomer material uniformly, and system issues such as practical and efficient energy-harvesting circuits.
Article
A thin metal film vapor deposited on thick elastomer substrate develops an equi-biaxial compressive stress state when the system is cooled due to the large thermal expansion mismatch between the elastomer and the metal. At a critical stress, the film undergoes buckling into a family of modes with short wavelengths characteristic of a thin plate on a compliant elastic foundation. As the system is further cooled, a highly ordered herring-bone pattern has been observed to develop. Here it is shown that the herringbone mode constitutes a minimum energy configuration among a limited set of competing modes.