The potential of the electrospun nanofiber membrane (ENM)-based soft electronics in epidermal bioelectronics has gained huge attention with their conformal compatibility with the human body and associated performance improvements. This study presents a novel filtration-based direct local nanowire patterning method on the ENM using dispenser systems, aiming to fabricate stretchable, breathable, and highly conductive epidermal electronics harnessing various types of metal nanowires, including Ag, Ag@Au core-shell, and Ag@(Au-Pt) core-shell nanowires. By utilizing capillary force from a support bed beneath the ENM, efficient fluid flow can be achieved, eliminating the requirement for expensive vacuum equipment typically employed in filtration processes. In the postprocessing phase, the photothermal effect of a laser is harnessed to improve the mechanical stability of the nanowire-ENM interface. The maskless fabrication process is instrumental in crafting epidermal bioelectronics in that the design can be spontaneously replicated according to diverse human body geometries in situ. The selective insulation process can be also executed with the same dispenser system, streamlining the overall fabrication system. Applications are demonstrated showcasing the advantages of the presented fabrication system and the resulting devices, including an in vivo epicardial signal recording electrode, an epidermal electrochemical biosensor, and a customized epidermal electromyography (EMG)-based human-machine interface (HMI). This study presents an innovative method for fabricating electrospun nanofiber membrane (ENM)-based adaptive epidermal bioelectronics, utilizing capillary force-assisted nanowire dispensing. The use of a highly absorbent supporting medium facilitates efficient drainage of the suspension liquid, enabling high resolution printing of nanowires. In combination with a laser-based nanowire embedding process, the fabricated ENM-based devices demonstrate promising advancements in functionality and reliability. image

Metal nanomaterials are highly valued for their enhanced surface area and electrochemical properties, which are crucial for energy devices and bioelectronics. However, their practical applications are often limited by challenges, such as scalability and dimensional constraints. In this study, we developed a synthesis method for highly porous Ag-Au core-shell nanowire foam (AACNF) using a one-pot process based on a simultaneous nanowelding synthesis method. The unique characteristics of AACNF as metal-based electrodes show the lowest density among metal-based electrodes while demonstrating high electrical conductivity (99.33-753.04 S/m) and mechanical stability. The AACNF's excellent mass transport properties enable multiscale hierarchical incorporation with functional materials including polymeric precursors and living cells. The enhanced mechanical stability at the nanowelded junctions allows AACNF-hydrogel composites to exhibit large stretching (∼700%) and 10,000 times higher electrical conductivity than hydrogel-nanowire composites without the junction. Large particles in the 1-10 μm scale, including fibroblast cells and exoelectrogenic microbes, are also successfully incorporated with AACNF. AACNF-based microbial fuel cells show high power density (∼330.1 W/m3) within the optimal density range. AACNF's distinctive ability to form a hierarchical structure with substances in various scales showcases its potential for advanced energy devices and biohybrid electrodes in the future.

Photolithography is a well-established fabrication method for realizing multilayer electronic circuits. However, it is challenging to adopt photolithography to fabricate intrinsically stretchable multilayer electronic circuits fully composed of an elastomeric matrix, due to the opacity of thick stretchable nanocomposite conductors. Here, we present photothermal lithography that can pattern elastomeric conductors and via holes using pulsed lasers. The photothermal-patterned stretchable nanocomposite conductor exhibits 3 times higher conductivity (5940 S cm-1) and 5 orders of magnitude lower resistance change (R/R0 = 40) under a 30% strained 5000th cyclic stretch, compared to those of a screen-printed conductor, based on the percolation network formed by spatial heating of the laser. In addition, a 50 μm sized stretchable via holes can be patterned on the passivation without material ablation and electrical degradation of the bottom conductor. By repeatedly patterning the conductor and via holes, highly conductive and durable multilayer circuits can be stacked with layer-by-layer material integration. Finally, a stretchable wireless pressure sensor and passive matrix LED array are demonstrated, thus showing the potential for a stretchable multilayer electronic circuit with durability, high density, and multifunctionality.

In situ monitoring system on the food package based on biodegradable materials to examine the food status is of great significance for practical application since food poisoning and non-degradable package waste have raised critical healthcare and environmental issues recently. Here, we report a laser-induced paper sensor (LIPS) that is comprised of a laser-induced graphene (LIG)/paper hybrid structure for wireless, real-time monitoring of the food status by the chemical- and thermo- sensing capabilities of LIPS. Direct laser irradiation on any type or structure of commercial paper converts the laser-irradiated paper surface into LIPS with a decent sheet resistance of 105 omega sq(-1) and porous structure which enables smart monitoring of key parameters such as gas concentration and temperature for the food spoilage prior to the food intake. Optimized laser irradiation conditions on the paper substrate produced the temperature and chemical gas coefficient of resistance change of 0.15%degrees C-1 and 0.0041% ppm(-1). As a proof-of-concept, we fabricated LIPS on the surface of the paper to both detect the temperature and monitor the chemical degradation of the food, of which data can be directly delivered to the user's mobile device through continuous wireless communication. We believe that LIPS proposed herein will make significant contributions to the next-generation food-related green electronics to provide users with a smart and high-fidelity monitoring platform for simple detection of the real-time status of food products.

The patterning of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hydrogels with excellent electrical property and spatial resolution is a challenge for bioelectronic applications. However, most PEDOT:PSS hydrogels are fabricated by conventional manufacturing processes such as photolithography, inkjet printing, and screen printing with complex fabrication steps or low spatial resolution. Moreover, the additives used for fabricating PEDOT:PSS hydrogels are mostly cytotoxic, thus requiring days of detoxification. Here, we developed a previously unexplored ultrafast and biocompatible digital patterning process for PEDOT:PSS hydrogel via phase separation induced by a laser. We enhanced the electrical properties and aqueous stability of PEDOT:PSS by selective laser scanning, which allowed the transformation of PEDOT:PSS into water-stable hydrogels. PEDOT:PSS hydrogels showed high electrical conductivity of 670 S/cm with 6-μm resolution in water. Furthermore, electrochemical properties were maintained even after 6 months in a physiological environment. We further demonstrated stable neural signal recording and stimulation with hydrogel electrodes fabricated by laser.

Sustaining a long-term but viable power source for underwater electronics has been an engineering conundrum due to a lack of feasible physical mechanisms to harvest energy in the underwater environment. In this regard, thermoelectricity, which converts heat into electricity, can suggest a potent solution, since the ocean and other water bodies maintain the constant water temperature and therefore serve as a permanent thermal differential. In addition to energy harvesting, the same thermoelectric device can be also utilized to both heat and cool, thereby providing an effective means of controlling the temperature of the arbitrary subject in the underwater environment. In this light, we present a soft and stretchable multi-modal thermoelectric skin (TES) that can both (i) generate electricity across the temperature differential between the ocean water and the human body and (ii) thermoregulate the body temperature in the underwater environment. The soft and elastic nature of TES enables an intimate and thorough contact with the deformable and irregular surfaces of the human skin, therefore maximizing the heat conduction at the human-device interface that the rigid or flexible thermoelectric devices can not fully attain. To the authors’ best knowledge, TES produces the highest electrical power density when compared to the stretchable thermoelectric devices reported so far, mainly owing to its optimum design factors. Along with the outstanding device performance, the underwater environment further boosts the thermoelectric efficiency of TES both in energy harvesting and thermoregulatory perspectives due to the much more favorable thermal properties of water than those of air. Furthermore, to verify the practical usage of TES and demonstrate its high wearability, we incorporated multiple TES units into the neoprene dry-suit. The TES units can self-power multiple embedded sensors that wirelessly monitor the physiological condition and further provide the spatial information of the tactical diver, such that the TES units and embedded system can function as a wearable underwater rescue platform. Lastly, the temperature feedback loop algorithm embedded in the thermoregulatory system allows the TES units to constantly regulate the temperature of the human body and thus prevent underwater hypo-/hyperthermia.

Recently, several studies have been conducted on wearable biosensors. Despite being skin-adhesive and mountable diagnostic devices, flexible biosensor patches cannot truly be considered wearable biosensors if they need to be connected to external instruments/processors to provide meaningful data/readings. A realistic and usable wearable biosensor should be self-contained, with a fully integrated device framework carefully designed and configured to provide reliable and intelligent diagnostics. There are several major challenges to achieving continuous sweat monitoring in real time for the systematic and effective management of type II diabetes (e.g., prevention, screening, monitoring, and treatment) through wearable sweat glucose biosensors. Consequently, further in-depth research regarding the exact interrelationship between active or passive sweat glucose and blood glucose is required to assess the applicability of wearable glucose biosensors in functional health monitoring. This review provides some useful insights that can enable effective critical studies of these unresolved issues. In this review, we first classify wearable glucose biosensors based on their signal transduction, their respective challenges, and the advanced strategies required to overcome them. Subsequently, the challenges and limitations of enzymatic and non-enzymatic wearable glucose biosensors are discussed and compared. Ten basic criteria to be considered and fulfilled in the development of a suitable, workable, and wearable sweat-based glucose biosensor are listed, based on scientific reports from the last five years. We conclude with our outlook for the controllable, well-defined, and non-invasive monitoring of epidermal glucose for maximum diagnostic potential in the effective management of type II diabetes.

Animal locomotion offers valuable references as it is a critical component of survival as animals adapting to a specific environment. Especially, underwater locomotion poses a challenge because water exerts a high antagonistic drag force against the direction of progress. However, marine vertebrates usually use much lower aerobic energy for locomotion than aerial or terrestrial vertebrates due to their unique intermittent gliding locomotion. None of the prior works demonstrate the locomotive strategies of marine vertebrates. Herein, an untethered soft robotic fish capable of reconstructing the marine vertebrates’ effective locomotion and traveling underwater by controlling localized buoyancy with thermoelectric pneumatic actuators is introduced. The actuators enable both heating and cooling to control a localized buoyancy while providing a substantial driving force to the system. Besides mimicking the locomotion, the bidirectional communication system enables the untethered delivery of commands to the underwater subject and real‐time acquisition of the robotic fish's physical information. Underwater imaging validates the fish's practical use as a drone, allowing for inspecting the aquatic environment that is not easily accessible to humans. Future work studies the operation of the robotic fish as a collective swarm to examine a broader range of the underwater area and conduct various strategic missions.

Latest developments in thin-film electronics have put skin electronics in the limelight. Integration of multiple skin sensors and wireless power transferring ability are cardinal components for continuous acquisition of the human signals, enabling higher level of applications in wearable healthcare and AR/VR devices. Skin sensor is considerably influenced by target body parts and users where it is attached, and thus face various design adjustments for the best performance. However, most skin electronics using conventional fabrication methods have a fixed design for specific targets and users only and face great challenge when they need design changes, for it has to re-initialize entire fabrication process even for the simplest design modification. Here, in situ and in operando adaptation (SOA) is presented, a revolutionary customizable electronic fabrication platform that allows simultaneous evolvable design modification and addition of new functionality to original skin electronics while they are in operation on a human skin. SOA renders immediate response to various user specifications possible, offering concurrent customization for various wearable and wireless applications including human physiology/motion sensors. Furthermore, SOA offers simultaneous impedance optimization in different body parts and users which enables on-skin wireless power supply. These findings will prove a boon to the development of customizable wearable skin-like electronics.

With the help of machine learning, electronic devices-including electronic gloves and electronic skins-can track the movement of human hands and perform tasks such as object and gesture recognition. However, such devices remain bulky and lack an ability to adapt to the curvature of the body. Furthermore, existing models for signal processing require large amounts of labelled data for recognizing individual tasks for every user. Here we report a substrate-less nanomesh receptor that is coupled with an unsupervised meta-learning framework and can provide user-independent, data-efficient recognition of different hand tasks. The nanomesh, which is made from biocompatible materials and can be directly printed on a person's hand, mimics human cutaneous receptors by translating electrical resistance changes from fine skin stretches into proprioception. A single nanomesh can simultaneously measure finger movements from multiple joints, providing a simple user implementation and low computational cost. We also develop a time-dependent contrastive learning algorithm that can differentiate between different unlabelled motion signals. This meta-learned information is then used to rapidly adapt to various users and tasks, including command recognition, keyboard typing and object recognition.

Soft pneumatic actuators play an important role in the technological advancement of soft robotics, but they face intrinsic limitations due to the presence of complex and bulky air compressors and tubes, that make it difficult to design completely soft robotic systems. In this study, we develop a first demonstration of the soft thermo-pneumatic actuating module that operates based on the thermally controlled gas-liquid phase transition with the soft thermoelectric device. The bi-directional thermal managing ability (heating and cooling) of the thermoelectric device is capable of controlling the inflation and deflation of the pneumatic chamber with the aid of the thermally conductive silicone rubber that enhances the heat transfer. For the first time to the authors' best knowledge, we demonstrate the active cooling of the thermoelectric device that accelerates the deflation rate by the active cooling functionality that significantly reduces the whole operating time. Additionally, to validate its practical usage in soft robotics, the soft actuating module shows different motions, such as bending and rectilinear stretching, based on the assembly design that is employed to develop the soft gripper and the entirely untethered soft earthworm robot without a complicated and bulky compressor system.

Development of an artificial camouflage at a complete device level remains a vastly challenging task, especially under the aim of achieving more advanced and natural camouflage characteristics via high-resolution camouflage patterns. Our strategy is to integrate a thermochromic liquid crystal layer with the vertically stacked, patterned silver nanowire heaters in a multilayer structure to overcome the limitations of the conventional lateral pixelated scheme through the superposition of the heater-induced temperature profiles. At the same time, the weaknesses of thermochromic camouflage schemes are resolved in this study by utilizing the temperature-dependent resistance of the silver nanowire network as the process variable of the active control system. Combined with the active control system and sensing units, the complete device chameleon model successfully retrieves the local background color and matches its surface color instantaneously with natural transition characteristics to be a competent option for a next-generation artificial camouflage.

Human–Machine Interfaces In article number 2002286, Seung Hwan Ko and co-workers review the cutting edge of wearable devices. Recent development of untethered devices consists of a range of cutting-edge technologies such as electromagnetic, triboelectric, and thermoelectric energy harvesting. Recent advances in bio-fuel-based electronics show numerous solutions to the remaining practical issues of continuous measurement without an external power source. Key advancements in untethered devices in various power sources are introduced with their principles and working mechanisms.

Advances in wearable and stretchable electronic technologies have yielded a wide range of electronic devices that can be conformably worn by, or implanted in humans to measure physiological signals. Moreover, various cutting‐edge technologies for battery‐free electronic devices have led to advances in healthcare devices that can continuously measure long‐term biosignals for advanced human–machine interface and clinical diagnostics. This report presents the recent progress in battery‐less, wearable devices using a wide range of energy harvesting sources, such as electromagnetic energy, mechanical energy, and biofuels. Additionally, this report also discusses the principles and working mechanisms of near/far‐field communications, triboelectric, thermoelectric, and biofuel technologies.

The recent emergence of highly contagious respiratory disease and the underlying issues of worldwide air pollution jointly heighten the importance of the personal respirator. However, the incongruence between the dynamic environment and nonadaptive respirators imposes physiological and psychological adverse effects, which hinder the public dissemination of respirators. To address this issue, we introduce adaptive respiratory protection based on a dynamic air filter (DAF) driven by machine learning (ML) algorithms. The stretchable elastomer fiber membrane of the DAF affords immediate adjustment of filtration characteristics through active rescaling of the micropores by simple pneumatic control, enabling seamless and constructive transition of filtration characteristics. The resultant DAF-respirator (DAF-R), made possible by ML algorithms, successfully demonstrates real-time predictive adapting maneuvers, enabling personalizable and continuously optimized respiratory protection under changing circumstances.

State monitoring of the complex system needs a large number of sensors. Especially, studies in soft electronics aim to attain complete measurement of the body, mapping various stimulations like temperature, electrophysiological signals, and mechanical strains. However, conventional approach requires many sensor networks that cover the entire curvilinear surfaces of the target area. We introduce a new measuring system, a novel electronic skin integrated with a deep neural network that captures dynamic motions from a distance without creating a sensor network. The device detects minute deformations from the unique laser-induced crack structures. A single skin sensor decodes the complex motion of five finger motions in real-time, and the rapid situation learning (RSL) ensures stable operation regardless of its position on the wrist. The sensor is also capable of extracting gait motions from pelvis. This technology is expected to provide a turning point in health-monitoring, motion tracking, and soft robotics.

Cephalopods' extraordinary ability to hide into any background has inspired researchers to reproduce the intriguing ability to readily camouflage in the infrared (IR) and visible spectrum but this still remains as a conundrum. In this study, a multispectral imperceptible skin that enables human skin to actively blend into the background both in the IR-visible integrated spectrum only by simple temperature control with a flexible bi-functional device (active cooling and heating) is developed. The thermochromic layer on the outer surface of the device, which produces various colors based on device surface temperature, expands the cloaking range to the visible spectrum (thus visible-to-IR) and ultimately completes day-and-night stealth platform simply by controlling device temperature. In addition, the scalable pixelization of the device allows localized control of each autonomous pixel, enabling the artificial skin surface to adapt to the background of the sophisticated pattern with higher resolution and eventually heightening the level of imperceptibility. As this proof-of-concept can be directly worn and conceals the human skin in multispectral ranges, the work is expected to contribute to the development of next-generation soft covert military wearables and perhaps a multispectral cloak that belongs to cephalopods or futuristic camouflage gadgets in the movies.

A thermal haptic device was developed to replicate thermal feelings for virtual reality applications.

Accurate temperature field measurement provides critical information in many scientific problems. Herein, a new paradigm for highly sensitive, flexible, negative temperature coefficient (NTC) thermistor-based artificial skin is reported, with the highest temperature sensing ability reported to date among previously reported NTC thermistors. This artificial skin is achieved through the development of a novel monolithic laser-induced reductive sintering scheme and unique monolithic structures. The unique seamless monolithic structure simultaneously integrates two different components (a metal electrode and metal oxide sensing channel) from the same material at ambient pressure, which cannot be achieved by conventional heterogeneous integration through multiple, complex steps of photolithography or vacuum deposition. In addition to superior performance, electronic skin with high temperature sensitivity can be fabricated on heat-sensitive polymer substrates due to the low-temperature requirements of the process. As a proof of concept, temperature-sensitive artificial skin is tested with conformally attachable physiological temperature sensor arrays in the measurement of the temperatures of exhaled breath for the early detection of pathogenic progression in the respiratory system. The proposed highly sensitive flexible temperature sensor and monolithic selective laser reductive sintering are expected to greatly contribute to the development of essential components in various emerging research fields, including soft robotics and healthcare systems.