Stretchable and transparent electronics have steadily attracted huge attention in wearable devices. Although Ag nanowire is the one of the most promising candidates for transparent and stretchable electronics, its electrochemical instability has forbidden its application to the development of electrochemical energy devices such as supercapacitors. Here, we introduce a highly stretchable and transparent supercapacitor based on electrochemically stable Ag-Au core-shell nanowire percolation network electrode. We developed a simple solution process to synthesize the Ag-Au core-shell nanowire with excellent electrical conductivity as well as greatly enhanced chemical and electrochemical stabilities compared to pristine Ag nanowire. The proposed core-shell nanowire-based supercapacitor still possesses fine optical transmittance and outstanding mechanical stability up to 60% strain. The Ag-Au core-shell nanowire can be a strong candidate for future wearable electrochemical energy devices.

To add more functionalities and overcome the limitation in conventional soft robots, highly anisotropic soft actuators with color shifting function during actuation is demonstrated for the first time. The electrothermally operating soft actuators with installed transparent metal nanowire percolation network heater allow easy programming of their actuation direction and instantaneous visualization of temperature changes through color change. Due to the unique direction dependent coefficient of thermal expansion mismatch, the suggested actuator demonstrates a highly anisotropic and reversible behavior with very large bending curvature (2.5 cm −1 ) at considerably low temperature (≈40 °C) compared to the previously reported electrothermal soft actuators. The mild operating heat condition required for the maximum curvature enables the superior long-term stability during more than 10 000 operating cycles. Also, the optical transparency of the polymer bilayer and metal nanowire percolation network heater allow the incorporation of the thermochromic pigments to fabricate color-shifting actuators. As a proof-of-concept, various color-shifting biomimetic soft robots such as color-shifting blooming flower, fluttering butterfly, and color-shifting twining tendril are demonstrated. The developed color-shifting anisotropic soft actuator is expected to open new application fields and functionalities overcoming the limitation of current soft robots.Unlike the conventional rigid actuators, the soft actuators are composed of elastic and lightweight materials with simple operating systems. [1] Due to their unique soft features, the soft actuators have been utilized in bioapplications such as artificial muscles, [2,3] soft manipulators, [4,5] biomimicking robots, [6][7][8][9] prosthesis, [10] and so on. The soft actuators operates by various physical, chemical, and optical stimulus such as electricity, [11][12][13][14][15] heat, [16][17][18] light, [7,8,19] magnetism, [20] pressure, [21] and humidity. [9,18,[22][23][24] Among them, considering the practical uses, the electrical signal has been the most popular input signal due to its easy and intuitive control of actuators. Typically the approaches to establish electrically operated soft actuators can be divided into two categories which are using electroactive polymeric (EAP) materials [4,5,12,15,25,26] and thermal expansive materials. [16][17][18]24,[27][28][29] However, since the EAP-based actuators need high operating voltage [4,5] and electrolyte environment, [12,25,26] their application in various fields is limited. On the other hand, the electrothermal actuator (ETA) which basically operates by different thermal expansive volume changes between the polymers composing a bilayer requires much lower operating voltage and Color-Changing Soft ActuatorsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

instruments, and wearable assistive devices, but which mostly are restricted to discrete motions. However, soft robotics with entirely soft bodied system often solve difficulties in conventional rigid robots by overcoming their constraints, exceeding the performances and creating new applications. [1][2][3] Therefore, these soft machines have already taken many roles in industrial processing, automation, marine engineering, etc. [4][5][6] Technological advances in robots and wearable devices are closely connected to optical and mechanical compliance depending on their use. By taking advantages of recent advancements in transparent actuators and sensors, combining their soft and stretchy mechanical compliance with optically transparent property affords to create a new class of soft robotics, which can be referred to as an imperceptible soft robotics (ISR). As shown in Figure 1, systematic diagram of imperceptible soft robotics describes that ISR will mainly consist of transparent systems and camouflage skin. Transparent systems embrace optically transparent soft actuators and sensors in order to build mechanically interactive robotics that are rarely seen by others. As a supportive component, camouflage skin aims to provide for transparent systems to adapt in natural environment or humans for undercover operation and safe user-friendly interactions. This new conception of imperceptible soft robotic system that exhibits optically transparent interface or visually imperceptions through camouflage skin provides new functionalities over ones without such properties. Imperceptions of an assistive wearable device can be crucially important in wearer's daily life. Mechanically compliant and visually imperceptive human assistive device can serve the user's rehabilitation process or support disabled parts in the body without discomfort, altering biomechanics, and obstructive to others. [7] In a similar fashion, robotic prosthetics that requires soft sensing capability of motherly touch for caring babies demand integrated sensors and actuators to be imperceptible. [8] Tactile sensation with an implementation of ISR delivering information to user in private also possesses a wide range of possibility in virtual/augmented reality for human-machine interface and smart-living environment. [9][10][11][12] Undercover mission enabled by disguising into nature through optical transparency or environmentally skin will also be achieved by imperceptibleThe advent of soft robotics has led to great advancements in robots, wear ables, and even manufacturing processes by employing entirely soft-bodied systems that interact safely with any random surfaces while providing great mechanical compliance. Moreover, recent developments in soft robotics involve advances in transparent soft actuators and sensors that have made it possible to construct robots that can function in a visually and mechanically unobstructed manner, assisting the operations of robots and creating more applications in various fields. In this aspect, imperceptible soft robo...

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.

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.