Wearable and implantable devices require conductive, stretchable and biocompatible materials. However, obtaining composites that simultaneously fulfil these requirements is challenging due to a ...trade-off between conductivity and stretchability. Here, we report on Ag-Au nanocomposites composed of ultralong gold-coated silver nanowires in an elastomeric block-copolymer matrix. Owing to the high aspect ratio and percolation network of the Ag-Au nanowires, the nanocomposites exhibit an optimized conductivity of 41,850 S cm
(maximum of 72,600 S cm
). Phase separation in the Ag-Au nanocomposite during the solvent-drying process generates a microstructure that yields an optimized stretchability of 266% (maximum of 840%). The thick gold sheath deposited on the silver nanowire surface prevents oxidation and silver ion leaching, making the composite biocompatible and highly conductive. Using the nanocomposite, we successfully fabricate wearable and implantable soft bioelectronic devices that can be conformally integrated with human skin and swine heart for continuous electrophysiological recording, and electrical and thermal stimulation.
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IJS, NUK, SBMB, UL, UM, UPUK
Deformable full-colour light-emitting diodes with ultrafine pixels are essential for wearable electronics, which requires the conformal integration on curvilinear surface as well as retina-like ...high-definition displays. However, there are remaining challenges in terms of polychromatic configuration, electroluminescence efficiency and/or multidirectional deformability. Here we present ultra-thin, wearable colloidal quantum dot light-emitting diode arrays utilizing the intaglio transfer printing technique, which allows the alignment of red-green-blue pixels with high resolutions up to 2,460 pixels per inch. This technique is readily scalable and adaptable for low-voltage-driven pixelated white quantum dot light-emitting diodes and electronic tattoos, showing the best electroluminescence performance (14,000 cd m(-2) at 7 V) among the wearable light-emitting diodes reported up to date. The device performance is stable on flat, curved and convoluted surfaces under mechanical deformations such as bending, crumpling and wrinkling. These deformable device arrays highlight new possibilities for integrating high-definition full-colour displays in wearable electronics.
Abstract
Soft bioelectronic devices provide new opportunities for next-generation implantable devices owing to their soft mechanical nature that leads to minimal tissue damages and immune responses. ...However, a soft form of the implantable optoelectronic device for optical sensing and retinal stimulation has not been developed yet because of the bulkiness and rigidity of conventional imaging modules and their composing materials. Here, we describe a high-density and hemispherically curved image sensor array that leverages the atomically thin MoS
2
-graphene heterostructure and strain-releasing device designs. The hemispherically curved image sensor array exhibits infrared blindness and successfully acquires pixelated optical signals. We corroborate the validity of the proposed soft materials and ultrathin device designs through theoretical modeling and finite element analysis. Then, we propose the ultrathin hemispherically curved image sensor array as a promising imaging element in the soft retinal implant. The CurvIS array is applied as a human eye-inspired soft implantable optoelectronic device that can detect optical signals and apply programmed electrical stimulation to optic nerves with minimum mechanical side effects to the retina.
Extended reality (XR) refers to a space where physical and digital elements coexist and comprises three elements, namely, environment, human, and computer, which interact with each other. Image ...sensors and displays are the core elements of XR systems because visual information is important for recognizing and judging objects. Recently, new features of image sensors and displays that are useful for developing next‐generation XR systems have been reported. For example, a miniaturized version of image sensors with the superb object detection and recognition capability offers new opportunities for machine vision technology. Furthermore, transparent and deformable displays are the key components of XR systems because they not only provide highly realistic virtual image information but also serve as efficient user interfaces. Herein, the recent progresses in such unconventional image sensors and display technologies are reviewed. First, image sensors with features of wavelength‐selective photodetection for color discrimination, neuromorphic image acquisition for facile pattern recognition, and curved image sensor designs inspired by biological eyes for miniaturization and unconventional imaging performances are discussed. Then, light‐emitting device technologies focusing on devices with transparency and deformable form factors are described. Finally, the review is concluded with a brief summary and a future outlook.
Physical and digital worlds combine to form extended reality (XR). Image‐sensing and light‐emitting devices are the core components of XR because they enable intuitive interaction between physical and digital elements. This review focuses on unconventional features of image‐sensing and light‐emitting devices, which are useful for the next‐generation XR systems. Future outlook and remaining challenges are also described.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Transparent electrodes have been widely used for various electronics and optoelectronics, including flexible ones. Many nanomaterial‐based electrodes, in particular 1D and 2D nanomaterials, have been ...proposed as next‐generation transparent and flexible electrodes. However, their transparency, conductivity, large‐area uniformity, and sometimes cost are not yet sufficient to replace indium tin oxide (ITO). Furthermore, the conventional ITO is quite rigid and susceptible to mechanical fractures under deformations (e.g., bending, folding). In this study, the authors report new advances in the design, fabrication, and integration of wearable and transparent force touch (touch and pressure) sensors by exploiting the previous efforts in stretchable electronics as well as novel ideas in the transparent and flexible electrode. The optical and mechanical experiment, along with simulation results, exhibit the excellent transparency, conductivity, uniformity, and flexibility of the proposed epoxy‐copper‐ITO (ECI) multilayer electrode. By using this multi‐layered ECI electrode, the authors present a wearable and transparent force touch sensor array, which is multiplexed by Si nanomembrane p‐i‐n junction‐type (PIN) diodes and integrated on the skin‐mounted quantum dot light‐emitting diodes. This novel integrated system is successfully applied as a wearable human–machine interface (HMI) to control a drone wirelessly. These advances in novel material structures and system‐level integration strategies create new opportunities in wearable smart displays.
A novel transparent and flexible electrode, composed of an epoxy‐copper‐indium tin oxide (ECI) multilayer is presented. Enhanced optical transparency, mechanical deformability, and electrical conductivity of the ECI multilayer allow for the development of a transparent and wearable human–machine interface system. The system is composed of the touch and pressure sensor array multiplexed by Si nanomembrane diodes and is integrated with wearable quantum dot light‐emitting diodes. A drone can be wirelessly controlled by the developed wearable force touch sensor array.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
With the rapid advances in wearable electronics, the research on carbon-based and/or organic materials and devices has become increasingly important, owing to their advantages in terms of cost, ...weight, and mechanical deformability. Here, we report an effective material and device design for an integrative wearable cardiac monitor based on carbon nanotube (CNT) electronics and voltage-dependent color-tunable organic light-emitting diodes (CTOLEDs). A p-MOS inverter based on four CNT transistors allows high amplification and thereby successful acquisition of the electrocardiogram (ECG) signals. In the CTOLEDs, an ultrathin exciton block layer of bis2-(diphenylphosphino)phenylether oxide is used to manipulate the balance of charges between two adjacent emission layers, bis2-(4,6-difluorophenyl)pyridinato-C 2,N(picolinato)iridium(III) and bis(2-phenylquinolyl-N,C(2′))iridium(acetylacetonate), which thereby produces different colors with respect to applied voltages. The ultrathin nature of the fabricated devices supports extreme wearability and conformal integration of the sensor on human skin. The wearable CTOLEDs integrated with CNT electronics are used to display human ECG changes in real-time using tunable colors. These materials and device strategies provide opportunities for next generation wearable health indicators.
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IJS, KILJ, NUK, PNG, UL, UM
Sensory receptors in human skin transmit a wealth of tactile and thermal signals from external environments to the brain. Despite advances in our understanding of mechano- and thermosensation, ...replication of these unique sensory characteristics in artificial skin and prosthetics remains challenging. Recent efforts to develop smart prosthetics, which exploit rigid and/or semi-flexible pressure, strain and temperature sensors, provide promising routes for sensor-laden bionic systems, but with limited stretchability, detection range and spatio-temporal resolution. Here we demonstrate smart prosthetic skin instrumented with ultrathin, single crystalline silicon nanoribbon strain, pressure and temperature sensor arrays as well as associated humidity sensors, electroresistive heaters and stretchable multi-electrode arrays for nerve stimulation. This collection of stretchable sensors and actuators facilitate highly localized mechanical and thermal skin-like perception in response to external stimuli, thus providing unique opportunities for emerging classes of prostheses and peripheral nervous system interface technologies.
Implantable electronic devices for recording electrophysiological signals and for stimulating muscles and nerves have been widely used throughout clinical medicine. Mechanical mismatch between ...conventional rigid biomedical devices and soft curvilinear tissues, however, has frequently resulted in a low signal to noise ratio and/or mechanical fatigue and scarring. Multifunctionality ranging from various sensing modalities to therapeutic functions is another important goal for implantable biomedical devices. Here, a stretchable and transparent medical device using a cell‐sheet–graphene hybrid is reported, which can be implanted to form a high quality biotic/abiotic interface. The hybrid is composed of a sheet of C2C12 myoblasts on buckled, mesh‐patterned graphene electrodes. The graphene electrodes monitor and actuate the C2C12 myoblasts in vitro, serving as a smart cell culture substrate that controls their aligned proliferation and differentiation. This stretchable and transparent cell‐sheet–graphene hybrid can be transplanted onto the target muscle tissue, to record electromyographical signals, and stimulate implanted sites electrically and/or optically in vivo. Additional cellular therapeutic effect of the cell‐sheet–graphene hybrid is obtained by integrated myobalst cell sheets. Any immune responses within implanted muscle tissues are not observed. This multifunctional device provides many new opportunities in the emerging field of soft bioelectronics.
Stretchable and transparent cell‐sheet–graphene hybrid composed of cultured C2C12 myoblast sheets on mesh‐patterned, and buckled graphene electrodes brings high quality biotic/abiotic interface with multifunctional properties ranging from various sensing and actuating modalities to therapeutic functions in vitro and in vivo. Reduced acute immune responses due to the cell sheet support the advantage of the cell‐sheet–graphene hybrid.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Graphene has been highlighted as a platform material in transparent electronics and optoelectronics, including flexible and stretchable ones, due to its unique properties such as optical ...transparency, mechanical softness, ultrathin thickness, and high carrier mobility. Despite huge research efforts for graphene‐based electronic/optoelectronic devices, there are remaining challenges in terms of their seamless integration, such as the high‐quality contact formation, precise alignment of micrometer‐scale patterns, and control of interfacial‐adhesion/local‐resistance. Here, a thermally controlled transfer printing technique that allows multiple patterned‐graphene transfers at desired locations is presented. Using the thermal‐expansion mismatch between the viscoelastic sacrificial layer and the elastic stamp, a “heating and cooling” process precisely positions patterned graphene layers on various substrates, including graphene prepatterns, hydrophilic surfaces, and superhydrophobic surfaces, with high transfer yields. A detailed theoretical analysis of underlying physics/mechanics of this approach is also described. The proposed transfer printing successfully integrates graphene‐based stretchable sensors, actuators, light‐emitting diodes, and other electronics in one platform, paving the way toward transparent and wearable multifunctional electronic systems.
A thermally controlled transfer printing method that is specially designed for the multiple aligned transference of patterned graphene is developed. Through this approach, accurate and high‐yield transference of patterned graphene onto diverse substances is achieved, allowing a transparent, stretchable, and wearable all‐graphene electronic/optoelectronic system to be fabricated.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Implantable bioelectronic devices are becoming useful and prospective solutions for various diseases owing to their ability to monitor or manipulate body functions. However, conventional implantable ...devices (e.g., pacemaker and neurostimulator) are still bulky and rigid, which is mostly due to the energy storage component. In addition to mechanical mismatch between the bulky and rigid implantable device and the soft human tissue, another significant drawback is that the entire device should be surgically replaced once the initially stored energy is exhausted. Besides, retrieving physiological information across a closed epidermis is a tricky procedure. However, wireless interfaces for power and data transfer utilizing radio frequency (RF) microwave offer a promising solution for resolving such issues. While the RF interfacing devices for power and data transfer are extensively investigated and developed using conventional electronics, their application to implantable bioelectronics is still a challenge owing to the constraints and requirements of in vivo environments, such as mechanical softness, small module size, tissue attenuation, and biocompatibility. This work elucidates the recent advances in RF‐based power transfer and telemetry for implantable bioelectronics to tackle such challenges.
This review covers the recent progresses in various radio‐frequency (RF)‐based wireless implantable devices. The studies highlight the significance and potential of the RF‐based wireless power transfer and telemetry schemes and the adoption of the soft materials and device designs for the development of sustainable and versatile implantable bioelectronics.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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