Recent advances in soft materials and system integration technologies have provided a unique opportunity to design various types of wearable flexible hybrid electronics (WFHE) for advanced human ...healthcare and human–machine interfaces. The hybrid integration of soft and biocompatible materials with miniaturized wireless wearable systems is undoubtedly an attractive prospect in the sense that the successful device performance requires high degrees of mechanical flexibility, sensing capability, and user‐friendly simplicity. Here, the most up‐to‐date materials, sensors, and system‐packaging technologies to develop advanced WFHE are provided. Details of mechanical, electrical, physicochemical, and biocompatible properties are discussed with integrated sensor applications in healthcare, energy, and environment. In addition, limitations of the current materials are discussed, as well as key challenges and the future direction of WFHE. Collectively, an all‐inclusive review of the newly developed WFHE along with a summary of imperative requirements of material properties, sensor capabilities, electronics performance, and skin integrations is provided.
Recent advances in soft materials and system integration technologies have provided a unique opportunity to design various types of wearable flexible hybrid electronics (WFHE) for advanced human healthcare and human–machine interfaces. The most up‐to‐date materials, sensors, and system‐packaging technologies to develop advanced WFHE are provided.
Optogenetics is a powerful technique that allows target-specific spatiotemporal manipulation of neuronal activity for dissection of neural circuits and therapeutic interventions. Recent advances in ...wireless optogenetics technologies have enabled investigation of brain circuits in more natural conditions by releasing animals from tethered optical fibers. However, current wireless implants, which are largely based on battery-powered or battery-free designs, still limit the full potential of in vivo optogenetics in freely moving animals by requiring intermittent battery replacement or a special, bulky wireless power transfer system for continuous device operation, respectively. To address these limitations, here we present a wirelessly rechargeable, fully implantable, soft optoelectronic system that can be remotely and selectively controlled using a smartphone. Combining advantageous features of both battery-powered and battery-free designs, this device system enables seamless full implantation into animals, reliable ubiquitous operation, and intervention-free wireless charging, all of which are desired for chronic in vivo optogenetics. Successful demonstration of the unique capabilities of this device in freely behaving rats forecasts its broad and practical utilities in various neuroscience research and clinical applications.
Conventional electronic (e‐) skins are a class of thin‐film electronics mainly fabricated in laboratories or factories, which is incapable of rapid and simple customization for personalized ...healthcare. Here a new class of e‐tattoos is introduced that can be directly implemented on the skin by facile one‐step coating with various designs at multi‐scale depending on the purpose of the user without a substrate. An e‐tattoo is realized by attaching Pt‐decorated carbon nanotubes on gallium‐based liquid‐metal particles (CMP) to impose intrinsic electrical conductivity and mechanical durability. Tuning the CMP suspension to have low‐zeta potential, excellent wettability, and high‐vapor pressure enables conformal and intimate assembly of particles directly on the skin in 10 s. Low‐cost, ease of preparation, on‐skin compatibility, and multifunctionality of CMP make it highly suitable for e‐tattoos. Demonstrations of electrical muscle stimulators, photothermal patches, motion artifact‐free electrophysiological sensors, and electrochemical biosensors validate the simplicity, versatility, and reliability of the e‐tattoo‐based approach in biomedical engineering.
A new class of e‐tattoo that can be directly implemented on the skin by rapid one‐step coating with various designs at a multi‐scale for personalized healthcare is introduced. The e‐tattoo is realized by tuning the electrically conductive and mechanically durable liquid metal composite based suspension to have low repulsion between particles, excellent wettability, and high vapor pressure.
Robotic skin with human‐skin‐like sensing ability holds immense potential in various fields such as robotics, prosthetics, healthcare, and industries. To catch up with human skin, numerous studies ...are underway on pressure sensors integrated on robotic skin to improve the sensitivity and detection range. However, due to the trade‐off between them, existing pressure sensors have achieved only a single aspect, either high sensitivity or wide bandwidth. Here, an adaptive robotic skin is proposed that has both high sensitivity and broad bandwidth with an augmented pressure sensing ability beyond the human skin. A key for the adaptive robotic skin is a tunable pressure sensor built with uniform gallium microgranules embedded in an elastomer, which provides large tuning of the sensitivity and the bandwidth, excellent sensor‐to‐sensor uniformity, and high reliability. Through the mode conversion based on the solid–liquid phase transition of gallium microgranules, the sensor provides 97% higher sensitivity (16.97 kPa−1) in the soft mode and 262.5% wider bandwidth (≈1.45 MPa) in the rigid mode compared to the human skin. Successful demonstration of the adaptive robotic skin verifies its capabilities in sensing a wide spectrum of pressures ranging from subtle blood pulsation to body weight, suggesting broad use for various applications.
S. Lee, S.‐H. Byun, C. Y. Kim, S. Cho, S. Park, J. Y. Sim, J.‐W. Jeong
An adaptive robotic skin with augmented pressure sensing ability is introduced. Integrated tunable pressure sensors built with uniform gallium microgranules provide high sensitivity and bandwidth and excellent sensor‐to‐sensor uniformity, enabling a large‐scale robotic skin with sensing performance superior to human skin. Proof‐of‐concept demonstrations show its unique sensing capability and versatility covering a broad range of pressure.
Liquid metal is being regarded as a promising material for soft electronics owing to its distinct combination of high electrical conductivity comparable to that of metals and exceptional ...deformability derived from its liquid state. However, the applicability of liquid metal is still limited due to the difficulty in simultaneously achieving its mechanical stability and initial conductivity. Furthermore, reliable and rapid patterning of stable liquid metal directly on various soft substrates at high-resolution remains a formidable challenge. In this work, meniscus-guided printing of ink containing polyelectrolyte-attached liquid metal microgranular-particle in an aqueous solvent to generate semi-solid-state liquid metal is presented. Liquid metal microgranular-particle printed in the evaporative regime is mechanically stable, initially conductive, and patternable down to 50 μm on various substrates. Demonstrations of the ultrastretchable (~500% strain) electrical circuit, customized e-skin, and zero-waste ECG sensor validate the simplicity, versatility, and reliability of this manufacturing strategy, enabling broad utility in the development of advanced soft electronics.
Thin, soft, and elastic electronics with physical properties well matched to the epidermis can be conformally and robustly integrated with the skin. Materials and optimized designs for such devices ...are presented for surface electromyography (sEMG). The findings enable sEMG from wide ranging areas of the body. The measurements have quality sufficient for advanced forms of human‐machine interface.
Recent developments of micro‐sensors and flexible electronics allow for the manufacturing of health monitoring devices, including electrocardiogram (ECG) detection systems for inpatient monitoring ...and ambulatory health diagnosis, by mounting the device on the chest. Although some commercial devices in reported articles show examples of a portable recording of ECG, they lose valuable data due to significant motion artifacts. Here, a new class of strain‐isolating materials, hybrid interfacial physics, and soft material packaging for a strain‐isolated, wearable soft bioelectronic system (SIS) is reported. The fundamental mechanism of sensor‐embedded strain isolation is defined through a combination of analytical and computational studies and validated by dynamic experiments. Comprehensive research of hard‐soft material integration and isolation mechanics provides critical design features to minimize motion artifacts that can occur during both mild and excessive daily activities. A wireless, fully integrated SIS that incorporates a breathable, perforated membrane can measure real‐time, continuous physiological data, including high‐quality ECG, heart rate, respiratory rate, and activities. In vivo demonstration with multiple subjects and simultaneous comparison with commercial devices captures the SIS's outstanding performance, offering real‐world, continuous monitoring of the critical physiological signals with no data loss over eight consecutive hours in daily life, even with exaggerated body movements.
This paper reports a new class of strain‐isolating materials, hybrid interfacial physics, and soft material packaging for a strain‐isolated, wearable soft bioelectronic system (SIS). In vivo demonstration during daily activities over 8 h captures the SIS's feasibility as a realistic ambulatory health monitor, which can find applications in both clinical uses and consumer healthcare technologies.
The priority of synaptic device researches has been given to prove the device potential for the emulation of synaptic dynamics and not to functionalize further synaptic devices for more complex ...learning. Here, we demonstrate an optic-neural synaptic device by implementing synaptic and optical-sensing functions together on h-BN/WSe
heterostructure. This device mimics the colored and color-mixed pattern recognition capabilities of the human vision system when arranged in an optic-neural network. Our synaptic device demonstrates a close to linear weight update trajectory while providing a large number of stable conduction states with less than 1% variation per state. The device operates with low voltage spikes of 0.3 V and consumes only 66 fJ per spike. This consequently facilitates the demonstration of accurate and energy efficient colored and color-mixed pattern recognition. The work will be an important step toward neural networks that comprise neural sensing and training functions for more complex pattern recognition.
Low modulus, compliant systems of sensors, circuits and radios designed to intimately interface with the soft tissues of the human body are of growing interest, due to their emerging applications in ...continuous, clinical-quality health monitors and advanced, bioelectronic therapeutics. Although recent research establishes various materials and mechanics concepts for such technologies, all existing approaches involve simple, two-dimensional (2D) layouts in the constituent micro-components and interconnects. Here we introduce concepts in three-dimensional (3D) architectures that bypass important engineering constraints and performance limitations set by traditional, 2D designs. Specifically, open-mesh, 3D interconnect networks of helical microcoils formed by deterministic compressive buckling establish the basis for systems that can offer exceptional low modulus, elastic mechanics, in compact geometries, with active components and sophisticated levels of functionality. Coupled mechanical and electrical design approaches enable layout optimization, assembly processes and encapsulation schemes to yield 3D configurations that satisfy requirements in demanding, complex systems, such as wireless, skin-compatible electronic sensors.
Materials and fabrication procedures are described for bioresorbable transistors and simple integrated circuits, in which the key processing steps occur on silicon wafer substrates, in schemes ...compatible with methods used in conventional microelectronics. The approach relies on an unusual type of silicon on insulator wafer to yield devices that exploit ultrathin sheets of monocrystalline silicon for the semiconductor, thin films of magnesium for the electrodes and interconnects, silicon dioxide and magnesium oxide for the dielectrics, and silk for the substrates. A range of component examples with detailed measurements of their electrical characteristics and dissolution properties illustrate the capabilities. In vivo toxicity tests demonstrate biocompatibility in sub‐dermal implants. The results have significance for broad classes of water‐soluble, “transient” electronic devices.
Materials, designs, and integration techniques are presented for a class of water‐soluble electronics capable of fabrication using wafer‐based processes. The active components exploit biocompatible and bioresorbable materials that are capable of dissolution in biofluids. Characterization of the electronic properties of the devices, their kinetics for dissolution, and preliminary evaluations in animal models highlight key aspects of the materials and concepts.
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