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Herein, we present an unconventional method for multimodal characterization of three-dimensional cardiac organoids. This method can monitor and control the mechanophysiological parameters of organoids within a single device. In this method, local pressure distributions of human-induced pluripotent stem-cell-derived cardiac organoids are visualized spatiotemporally by an active-matrix array of pressure-sensitive transistors. This array is integrated with three-dimensional electrodes formed by the high-resolution printing of liquid metal. These liquid-metal electrodes are inserted inside an organoid to form the intraorganoid interface for simultaneous electrophysiological recording and stimulation. The low mechanical modulus and low impedance of the liquid-metal electrodes are compatible with organoids' soft biological tissue, which enables stable electric pacing at low thresholds. In contrast to conventional electrophysiological methods, this measurement of a cardiac organoid's beating pressures enabled simultaneous treatment of electrical therapeutics using a single device without any interference between the pressure signals and electrical pulses from pacing electrodes, even in wet organoid conditions.

The in situ diagnosis of cardiac activities with simultaneous therapeutic electrical stimulation of the heart is key to preventing cardiac arrhythmia. Here, we present an unconventional single-device platform that enables in situ monitoring even in a wet condition and control of beating heart motions without interferences to the recording signal. This platform consists of the active-matrix array of pressure-sensitive transistors for detecting cardiac beatings, biocompatible, low-impedance electrodes for cardiac stimulations, and an alginate-based hydrogel adhesive for attaching this platform conformally to the epicardium. In contrast to conventional electrophysiological sensing using electrodes, the pressure-sensitive transistors measured mechanophysiological characteristics by monitoring the spatiotemporal distributions of cardiac pressures during heart beating motions. In vivo tests show mechanophysiological readings having good correlation with electrocardiography and negligible interference with the electrical artifacts caused during cardiac stimulations. This platform can therapeutically synchronize the rhythm of abnormal heartbeats through efficient pacing of cardiac arrhythmia.

Continuous detection of raised intraocular pressure (IOP) could benefit the monitoring of patients with glaucoma. Current contact lenses with embedded sensors for measuring IOP are rigid, bulky, partially block vision or are insufficiently sensitive. Here, we report the design and testing in volunteers of a soft and transparent contact lens for the quantitative monitoring of IOP in real time using a smartphone. The contact lens incorporates a strain sensor, a wireless antenna, capacitors, resistors, stretchable metal interconnects and an integrated circuit for wireless communication. In rabbits, the lens provided measurements that match those of a commercial tonometer. In ten human participants, the lens proved to be safe, and reliably provided accurate quantitative measurements of IOP without inducing inflammation.

The brain is actuated by billions of neurons with trillions of interconnections that regulate human behaviors. Understanding the mechanisms of these systems that induce sensory reactions and respond to disease remains one of the greatest challenges in science, engineering, and medicine. Recent advances in nanomaterials and nanotechnologies have led to the extensive research of electronic devices for brain interfaces to better understand the neural activities of the brain’s complex nervous system. The development of sensor devices for monitoring the physiological signals of the brain related to traumatic injury status has accompanied by the progress of electronic neural probes in parallel. In addition, these neurological and stereotactic surgical revolutions hold immense potential for clinical analysis of pharmacological systems within cerebral tissues. Here, we review the progress of electronic devices interfacing with brain in terms of the materials, fabrication technologies, and device designs. Neurophysiological activity can be measured and modulated by brain probes based on newly developed nanofabrication methodologies. Furthermore, in vivo pathological monitoring of the brain and pharmacological assessment has been developed in miniaturized and wireless form. We also consider the key challenges and prospects for further development, and explore the future directions emerging in the latest research.

The eye is a complex sensory organ that contains abundant information for specific diseases and pathological responses. It has emerged as a facile biological interface for wearable healthcare platforms because of its excellent accessibility. Recent advances in electronic devices have led to the extensive research of point-of-care (POC) systems for diagnosing and monitoring diseases by detecting the biomarkers within the eye. Among these systems, contact lenses, which make direct contact with the ocular surfaces, have been utilized as one of the promising candidates for non-invasive POC testing of various diseases. The continuous and long-term measurement from the sensor allows the patients to manage their symptoms in an effective and convenient way. Herein, we review the progress of contact lens sensors in terms of the materials, methodologies, device designs, and target biomarkers. The anatomical structure and biological mechanisms of the eye are also discussed to provide a comprehensive understanding of the principles of contact lens sensors. Intraocular pressure and glucose, which are the representative biomarkers found in the eyes, can be measured with the biosensors integrated with contact lenses for the diagnosis of glaucoma and diabetes. Furthermore, contact lens sensors for various general pathologies as well as other ocular diseases are also considered, thereby providing the prospects for further developments of smart contact lenses as a future POC system.

There has been a great deal of interest in designing soft robots that can mimic a human system with haptic and proprioceptive functions. There is now a strong demand for soft robots that can sense their surroundings and functions in harsh environments. This is because the wireless sensing and actuating capabilities of these soft robots are very important for monitoring explosive gases in disaster areas and for moving through contaminated environments. To develop these wireless systems, complex electronic circuits must be integrated with various sensors and actuators. However, the conventional electronic circuits based on silicon are rigid and fragile, which can limit their reliable integration with soft robots for achieving continuous locomotion. In our study, we developed an untethered, soft robotic hand that mimics human fingers. The soft robotic fingers are composed of a thermally responsive elastomer composite that includes capsules of ethanol and liquid metals for its shape deformation through an electrothermal phase transition. And these soft actuators are integrated fully with flexible forms of heaters, with pressure, temperature, and hydrogen gas sensors, and wireless electronic circuits. Entire functions of this soft hand, including the gripping motion of soft robotic fingers and the real-time detections of tactile pressures, temperatures, and hydrogen gas concentrations, are monitored or controlled wirelessly using a smartphone. This wireless sensing and actuating system for somatosensory and respiratory functions of a soft robot provides a promising strategy for next-generation robotics.

Cracked tooth syndrome (CTS) is an incomplete fracture of a human tooth that commonly arises from chewing hard foods. Although it is a very common syndrome, CTS is often difficult to diagnose owing to the common small size of tooth cracks. Conventional techniques for the detection of cracks, such as transillumination and radiographic methods, are inaccurate and have poor imaging resolution. In this study, we devise a novel method for the in vivo detection of tooth microcracks by exploiting the mechanoluminescence (ML) phenomenon. ZrO2:Ti4+ (ZRT) phosphor particles are pasted onto suspected regions of tooth cracks and emit cyan-colored light as a result of masticatory forces. Then, a stretchable and self-healable photodetector (PD) array laminated on top of the phosphor particles converts the emitted photons into a photocurrent, which facilitates the two-dimensional mapping of the tooth cracks. Because of the high photosensitivity of the PD, intense ML and small size of ZRT phosphor particles, it is possible to image submicron- to micron-sized cracks with high resolution. Furthermore, the uniqueness of this technique over the conventional techniques stems from the application of a simple optical phenomenon, i.e., ML, for obtaining precise information regarding the locations, depth, and length of tooth cracks.

Tactile pressure sensors as flexible bioelectronic devices have been regarded as the key component for recently emerging applications in electronic skins, health-monitoring devices, or human-machine interfaces. However, their narrow range of sensible pressure and their difficulty in forming high integrations represent major limitations for various potential applications. Herein, we report fully integrated, active-matrix arrays of pressure-sensitive MoS2 transistors with mechanoluminescent layers and air dielectrics for wide detectable range from footsteps to cellular motions. The inclusion of mechanoluminescent materials as well as air spaces can increase the sensitivity significantly over entire pressure regimes. In addition, the high integration capability of these active-matrix sensory circuitries can enhance their spatial resolution to the level sufficient to analyze the pressure distribution in a single cardiomyocyte. We envision that these wide-range pressure sensors will provide a new strategy toward next-generation electronics at biomachine interfaces to monitor various mechanical and biological phenomena at single-cell resolution.

Recent approaches in self-healable electrodes use polymers with exhibiting significantly low electrical conductivity, compared to conventional metals. Such self-healable electrodes also require external stimuli to initiate self-healing, or present slow restoration for their intrinsic healing. Herein, we introduce an instantaneous and repeatable self-healing of highly conductive, fully metallic electrodes at ambient conditions. These electrodes consist of silver and liquid metal (with no polymer), and exhibit a sufficiently high conductivity of 2 S/μm. The liquid metal (LM) component enables instantaneous and repeatable self-healing of these electrodes (within a few milliseconds) under no external energy as well as high stretchability. Additionally, the inclusion of silver in this LM improves the mechanical strength of this composite, thereby overcoming the limitation of a pristine LM that has low mechanical strength. Moreover, this composite formation can be effective in preventing the penetration of gallium atoms into different metals, while preserving electrical contact properties. Also the self-healable nature of electrodes enables their outstanding sustainability against electrical breakdown at relatively high electric fields. Furthermore, the compatibility of these self-healable electrodes with conventional photolithography and wet etching facilitates high-resolution patterning for device fabrications, as demonstrated in an example with a self-healable organic light-emitting diode display.

Wireless communication through linkage with a smartphone and other portable devices in the sensor area are essential for increasing the efficiency of utilization by storing sensing-value data. Thus, the demand for wireless technology is increasing due to the advantages it provides for the various applications that use these data. However, there is still considerable ambiguity concerning the low portability of such technology due to the increased volume with component integration, the high consumption of power, and the necessity of having a separate battery. Herein, we present solutions for these problems with demonstrations that involve 1) the miniaturization of the device by altering the structure of the built-in battery, 2) the use of a pressure-activated switch for the low-power driving technology, and 3) the implementation of a wireless communication platform by integrating a Bluetooth module with the devices. In addition, we demonstrate a human-interactive display that enables users to instantly observe the changes in the brightness of the organic light-emitting diodes (OLED) as the pressure changes. We show that the system can display the measured, real-time pressure values on the screens of mobile devices, which represents a significant advancement in the fields of energy science and biomedical science.

One of the key strategies for developing modern transparent optoelectronic devices is to achieve more conductive, transparent, and thermally-stable electrodes at minimal costs. Herein, we report a simple and cost-effective coaxial electrospinning process that produces continuous and ultra-long copper nanofibers (CuNFs) conformally covered with a shell layer of carbon black (CB). The electrospinning of Cu nanoparticles and CB inks enabled the fabrication of Cu (core)/CB (shell) nanofibers as network forms that were dispersed directly on target substrates with no additional deposition or lithography process. By virtue of the presence of the CB shell, the reflection of light from the metal surface, a critical limitation in existing metallic transparent conductive electrodes (TCEs), was reduced dramatically. Its reflection of light was even lower than that of bare quartz due to the suppressed backscattering of individual CuNFs, and this provided a high-clarity view through the black CuNF-TCEs while maintaining the high transparency of 91% and the low sheet resistance of 0.8 Ω/sq. Current-voltage experiments on single NF showed that a CuNF sustained a breakdown current density of 5 × 106 A/cm2, outperforming its counterpart silver NF and indicating the robustness of black CuNF-TCEs against electromigration. Such haze-free, thermally-stable black CuNF-TCEs enabled the demonstration of transparent heaters capable of working at extremely high temperatures; the maximum working temperature of the heaters was up to 800 °C, and the temperature was maintained for >90 min under an alternating current bias. We believe that the coaxial electrospinning of metal inks with other products will enable a variety of multi-functional metal NFs, leading to the development of next-generation displays, touch panels, and smart windows.

Integration of a smart contact lens and a heat patch realizes personal management of ocular surface diseases wirelessly., Wearable electronic devices that can monitor physiological signals of the human body to provide biomedical information have been drawing extensive interests for sustainable personal health management. Here, we report a human pilot trial of a soft, smart contact lens and a skin-attachable therapeutic device for wireless monitoring and therapy of chronic ocular surface inflammation (OSI). As a diagnostic device, this smart contact lens enables real-time measurement of the concentration of matrix metalloproteinase-9, a biomarker for OSI, in tears using a graphene field-effect transistor. As a therapeutic device, we also fabricated a stretchable and transparent heat patch attachable on the human eyelid conformably. Both diagnostic and therapeutic devices can be incorporated using a smartphone for their wireless communications, thereby achieving instantaneous diagnosis of OSI and automated hyperthermia treatments. Furthermore, in vivo tests using live animals and human subjects confirm their good biocompatibility and reliability as a noninvasive, mobile health care solution.

Despite recent substantial advances in perovskite materials, their 3D integration capability for next-generation electronic devices is limited owing to their inherent vulnerability to heat and moisture with degradation of their remarkable optoelectronic properties during fabrication processing. Herein, a facile method to transfer the patterns of perovskites to planar or nonplanar surfaces using a removable polymer is reported. After fabricating perovskite devices on this removable polymer film, the conformal attachment of this film on target surfaces can place the entire devices on various substrates by removing this sacrificial film. This transfer method enables the formation of a perovskite image sensor array on a soft contact lens, and in vivo tests using rabbits demonstrate its wearability. Furthermore, 3D heterogeneous integration of a perovskite photodetector array with an active-matrix array of pressure-sensitive silicon transistors using this transfer method demonstrates the formation of a multiplexed sensing platform detecting distributions of light and tactile pressure simultaneously.

Wearable healthcare devices have garnered substantial interest for the realization of personal health management by monitoring the physiological parameters of individuals. Attaining the integrity between the devices and the biological interfaces is one of the greatest challenges to achieving high-quality body information in dynamic conditions. Liquid metals, which exist in the liquid phase at room temperatures, are advanced intensively as conductors for deformable devices because of their excellent stretchability and self-healing ability. The unique surface chemistry of liquid metals allows the development of various sensors and devices in wearable form. Also, the biocompatibility of liquid metals, which is verified through numerous biomedical applications, holds immense potential in uses on the surface and inside of a living body. Here, the recent progress of liquid metal-based wearable electronic devices for healthcare with respect to the featured properties and the processing technologies is discussed. Representative examples of applications such as biosensors, neural interfaces, and a soft interconnection for devices are reviewed. The current challenges and prospects for further development are also discussed, and the future directions of advances in the latest research are explored.

Visual and tactile information are the key intuitive perceptions in sensory systems, and the synchronized detection of these two sensory modalities can enhance accuracy of object recognition by providing complementary information between them. Herein, multimodal integration of flexible, high-resolution X-ray detectors with a synchronous mapping of tactile pressure distributions for visualizing internal structures and morphologies of an object simultaneously is reported. As a visual-inspection method, perovskite materials that convert X-rays into charge carriers directly are synthesized. By incorporating pressure-sensitive air-dielectric transistors in the perovskite components, X-ray detectors with dual modalities (i.e., vision and touch) are attained as an active-matrix platform for digital visuotactile examinations. Also, in vivo X-ray imaging and pressure sensing are demonstrated using a live rat. This multiplexed platform has high spatial resolution and good flexibility, thereby providing highly accurate inspection and diagnoses even for the distorted images of nonplanar objects.

This study presents a smart, soft contact lens that provides real-time sensing for the wireless immunosensing of cortisol., Despite various approaches to immunoassay and chromatography for monitoring cortisol concentrations, conventional methods require bulky external equipment, which limits their use as mobile health care systems. Here, we describe a human pilot trial of a soft, smart contact lens for real-time detection of the cortisol concentration in tears using a smartphone. A cortisol sensor formed using a graphene field-effect transistor can measure cortisol concentration with a detection limit of 10 pg/ml, which is low enough to detect the cortisol concentration in human tears. In addition, this soft contact lens only requires the integration of this cortisol sensor with transparent antennas and wireless communication circuits to make a smartphone the only device needed to operate the lens remotely without obstructing the wearer’s view. Furthermore, in vivo tests using live rabbits and the human pilot experiment confirmed the good biocompatibility and reliability of this lens as a noninvasive, mobile health care solution.

International audience; Here we demonstrate an unconventional fabrication of highly transparent supercapacitors and electrodes using random networks of nanostructured metallic glass nanotroughs for their integrations as wirelessly rechargeable and invisible, skin heat patches. Transparent supercapacitors with fine conductive patterns were printed using an electrohydrodynamic jet-printing. Also, transparent and stretchable electrodes, for wireless antennas, heaters and interconnects, were formed using random network based on nanostructured CuZr nanotroughs and Ag nanowires with superb optoelectronic properties (sheet resistance of 3.0 Ω/sq at transmittance of 91.1%). Their full integrations, as an invisible heat patch on skin, enabled the wireless recharge of supercapacitors and the functions of heaters for thermal therapy of skin tissue. The demonstration of this transparent thermotherapy patch to control the blood perfusion level and hydration rate of skin suggests a promising strategy toward next-generation wearable electronics.

In recent years, to develop more spontaneous and instant interfaces between a system and users, technology has evolved toward designing efficient and simple gesture recognition (GR) techniques. As a tool for acquiring human motion, a tactile sensor system, which converts the human touch signal into a single datum and executes a command by translating a bundle of data into a text language or triggering a preset sequence as a haptic motion, has been developed. The tactile sensor aims to collect comprehensive data on various motions, from the touch of a fingertip to large body movements. The sensor devices have different characteristics that are important for target applications. Furthermore, devices can be fabricated using various principles, and include piezoelectric, capacitive, piezoresistive, and field-effect transistor types, depending on the parameters to be achieved. Here, we introduce tactile sensors consisting of field-effect transistors (FETs). GR requires a process involving the acquisition of a large amount of data in an array rather than a single sensor, suggesting the importance of fabricating a tactile sensor as an array. In this case, an FET-type pressure sensor can exploit the advantages of active-matrix sensor arrays that allow high-array uniformity, high spatial contrast, and facile integration with electrical circuitry. We envision that tactile sensors based on FETs will be beneficial for GR as well as future applications, and these sensors will provide substantial opportunities for next-generation motion sensing systems.

A wearable smart sensing system is capable of continuously monitoring biometric information such as respiration, pulse, and body temperature while attached to an arbitrary surface on the user's body to be utilized freely during activities. Research conducted on new materials, fabrication processes, structure of electrodes, and wireless communication technologies has made constant progress in the development of smart sensing systems that use entirely wearable forms of devices to go beyond conventional devices that are based on intrinsically rigid components, such as silicon. Among various platforms that can be used in the development of smart sensing systems, optoelectronics provides innovative sensing functions (e.g., human–machine interfaces and phototherapy) that can be transferred from traditional healthcare to smart healthcare, such as point of care. Optoelectronics are light‐mediated displays that allow a light source to be controlled and a large light spectrum to be detected. Recently, this platform that uses smart and wearable optoelectronic sensing systems has become increasingly advanced to better help human beings treat their diseases through self‐healthcare. Herein, recent advanced technologies in materials, structures, and wireless platforms for smart sensors using wearable optoelectronics are reviewed.

Wavelength-scale objects usually diffuse incident light into all directions, thereby resulting in a low transmittance accompanied by a thick haze. The degradation of visibility remains a more challenging problem for metal nanostructures due to the excitation of localized surface plasmon resonances, which impedes their practical use in display applications. Here, we report a broadband, polarization- and angle-independent near-unity transmittance from a network of submicron Ag wires via the suppression of backward scattering. Electromagnetic simulations on a single Ag wire predicted that a conformal, dielectric shell suppresses backward scattering while only boosting the zeroth-order forward scattering. A facile oxidation process on electrospun Ag wires produced Ag/Ag2O core/shell wires randomly dispersed on a glass substrate. Measurements of spatially (1.5 × 1.5 cm2) and spectrally (λ = 480–880 nm) averaged transmittance revealed that Ag/Ag2O wires (with an Ag filling ratio of 3.4%) recorded a transmittanc...

Structured metals can sustain a very large scattering cross-section that is induced by localized surface plasmons, which often has an adverse effect on their use as transparent electrodes in displays, touch screens, and smart windows due to an issue of low clarity. Here, we report a broadband optical cloaking strategy for the network of mesoscopic metal wires with submicrometer to micrometer diameters, which is exploited for manufacturing and application of high-clarity metal-wires-based transparent electrodes. We prepare electrospun Ag wires with 300–1800 nm in diameter and perform a facile surface oxidation process to form Ag/Ag2O core/shell heterogeneous structures. The absorptive Ag2O shell, together with the coating of a dielectric cover, leads to the cancellation of electric multipole moments in Ag wires, thereby drastically suppressing plasmon-mediated scattering over the full visible spectrum and rendering Ag wires to be invisible. Simultaneously with the effect of invisibility, the transmittance ...

We report the facile fabrication of transparent and high-performance moisture barrier material (SC nanocomposite) using surface-modified bentonite clay (SC) as nanofiller and glycidyl silane as a surface-modifier/binder via simple, cost-effective and mass-producible process. SC is synthesised using a base-catalysed sol-gel process; their hydroxyl surfaces are decorated with glycidyl ligands to endure the densely stacked structure and high clay content in the final nanocomposite. The SC nanocomposite barrier exhibits high optical transparency (>90), dense multi-stacked clay structure, and considerably enhanced moisture barrier performance. We discuss the fabrication and physical properties of the SC nanocomposite. To assess the applicability of the nanocomposite as a high-performance barrier material in practical applications, typical organic light-emitting devices are encapsulated, and their lifetime is evaluated.

An unconventional method is developed to fabricate flexible and transparent sensors for real-time, wireless sensing of alcohol vapors using hybrid nanostructures of indium oxide and Pt nanoparticles (as an active channel) with random networks of metal nanowires (as electrodes and antennas). The hybrid structures of indium oxide and Pt nanoparticles present high response and selectivity for ethanol vapor sensing with detecting the blood alcohol concentration range corresponding to the license suspension or revocation in the Road Traffic Act of many countries (blood alcohol concentration 200 ppm). The integration of a Bluetooth system or an inductive antenna enables wireless operations of the alcohol sensor using smartphones for applications as wearable and hands-free devices with flexible, transparent film geometries. Furthermore, these sensor systems exhibit outstanding thermal reliabilities for their stable operations over wide temperature ranges between −40 °C and 125 °C, which can extend their practical use for automobile electronics. Such devices can be transferable onto diverse nonplanar surfaces including steering wheels and curved glasses of phones, which suggests substantial promise for their applications in next-generation automobile or wearable electronics.