Gallium-based liquid metals are promising for stretchable electronics due to their inherent deformability and excellent conductivity. However, the lack of a scalable and automated fabrication process has limited their practical applications. This study introduces a two-step method to create liquid metal emulsion gels suitable for 3D printing, characterized by densely packed liquid metal microcapsules within polymer matrices. The resulting emulsion gel demonstrates favorable rheological properties for 3D printing and minimal shrinkage through solidification. With a substantial fraction of sizable microcapsules, the printed features can be activated into compliant conductors with exceptional conductivity of ≈2.2× 104 S cm-1 and an ultrahigh stretchability of up to ≈1000% strain. Stretchable lighting emitting diode displays and near field communication tags are successfully fabricated through 3D printing to demonstrate the practicality of liquid metal microcapsule gels. These developments provide a versatile platform to design liquid metal inks for printed stretchable electronics.

Stretchable electronics are transforming next-generation wearables and robotics, creating a significant demand for compatible energy storage devices. Microbatteries, known for their compact and flat design, hold great promise but often face limitations of low strain tolerance and unidirectional stretchability. Here, we introduce omnidirectionally stretchable Zn-MnO2 microbatteries featuring innovative nanocomposite current collectors. These current collectors comprise serpentine-patterned silver nanowire and carbon nanotube nanocomposites embedded in a soft elastomer, which effectively dissipate strain across all directions. The resulting microbattery achieves impressive performance, including a high capacity (>1.5 mAh cm-2), excellent rate capability (up to 5.0 mA cm-2), and robust operation under omnidirectional/biaxial strains. Additionally, multiple microbattery cells are successfully integrated with a wireless charging circuit and a soft LED array, forming a wearable system that seamlessly conforms to body movements. This work establishes a novel design framework for deformable energy storage devices, merging superior electrochemical performance with multidirectional stretchability.

Stretchable supercapacitors are crucial for powering the next generation of wearable devices, but they face the challenge of insufficient areal capacitance. Although 3D electrodes improve the amount of active materials, their considerable thickness can increase stiffness and restrict deformability. Inspired by Armadillo's armor that incorporates rigid bony plates within elastic skin for optimal protection and flexibility, this study presents a 3D electrode designed to balance these conflicting requirements. The electrode comprises an array of densely packed, porous conductive pillars anchored to a soft current collector, effectively decoupling electrochemical and mechanical functions. The 900 mu m-thick pillars act as a porous scaffold, enabling high loading of active material PEDOT at 10 mg cm-2. Meanwhile, the current collector efficiently dissipates applied tension, resulting in exceptional deformability for the electrode. To demonstrate their practical application, these supercapacitors are integrated into a soft, untethered electronic system featuring a wireless charging circuit with a skin-conformal LED array for sustained operation. By effectively addressing the longstanding challenge of balancing high capacitance with mechanical compliance, this bioinspired electrode design establishes a transformative approach to create high-performance, deformation-resilient energy storage devices for wearable technologies.

Emerging intrinsically stretchable electroluminescent displays have the potential to transform future smart wearables by seamlessly integrating light-emitting capabilities with mechanical deformability. A significant challenge in constructing these devices is the lack of compliant transparent electrodes that possess excellent optoelectronic properties. This study presents a design concept for hybrid transparent electrodes that consist of liquid metal frames surrounding transparent ionic nanocomposite fluids. This electrode harnesses the highly conductive liquid metal component, achieving a low sheet resistance of just a few ohms even under extreme uniaxial and biaxial deformations. The central emitting region boasts an impressive optical transmittance of 96.6% at 465 nm thanks to the ionic nanocomposite. As a result, the overall optical transmittance of the entire electrode remains at 81.6% at 465 nm, even when including the opaque liquid metal frame. Stretchable matrix displays have been fabricated through a scalable process, demonstrating uniform luminous intensity, excellent deformability, and exceptional durability. This device can be bent, twisted, stretched, and conformed to curved surfaces, rendering it suitable for diverse applications. The hybrid transparent electrode developed here represents a promising design of mixed electron and ion conductors for advancing stretchable optoelectronic devices.

Stretchable transparent electrodes are crucial components for deformable electronics. While solid-state electrodes struggle to achieve significant stretchability, liquid metal electrodes have emerged as a potential alternative. However, their widespread application has been limited by their complex fabrication and reduced performance when stretched. This study introduces stretchable transparent electrodes composed of liquid metal in serpentine micromesh patterns. These electrodes are constructed cost-effectively to show high optical transmittance and low sheet resistance. They can endure 800% strain with limited variations in resistance due to the serpentine design. A transparent proximity and touch sensor is combined with soft pneumatic actuators to enable a deformable haptic interface. Additionally, transparent heaters are prepared to conform to the curvilinear body surface, allowing for thermotherapy on subcutaneous tumors while concurrently monitoring the skin's responses. Liquid metal serpentine micromeshes represent promising transparent electrodes for stretchable devices and systems.

Compliant materials are crucial for stretchable electronics. Stretchable solids and gels have limitations in deformability and durability, whereas active liquids struggle to create complex devices. This study presents multifunctional yield-stress fluids as printable ink materials to construct stretchable electronic devices. Ionic nanocomposites comprise silica nanoparticles and ion liquids, while electrical nanocomposites use the natural oxidation of liquid metals to produce gallium oxide nanoflake additives. These nanocomposite inks can be printed on an elastomer substrate and stay in a solid state for easy encapsulation. However, their transition into a liquid state during stretching allows ultrahigh deformability up to the fracture strain of the elastomer. The ionic inks produce strain sensors with high stretchability and temperature sensors with high sensitivity of 7% °C-1. Smart gloves are further created by integrating these sensors with printed electrical interconnects, demonstrating bimodal detection of temperatures and hand gestures. The nanocomposite yield-stress fluids combine the desirable qualities of solids and liquids for stretchable devices and systems.

Stretchable displays that combine light-emitting capabilities with mechanical compliance are essential building blocks of next-generation wearable electronics. However, their widespread applications are currently limited by complex device architecture, limited pixel density, and immature fabrication processes. In this study, we present the device design and material developments of intrinsically stretchable light-emitting drawing displays that can show arbitrary hand-drawing features. The alternating-current electroluminescent display uses a simplified architecture comprising coplanar interdigitated liquid metal electrodes, an electroluminescent layer, and a dielectric encapsulation layer. Ink patterns on the device are coupled with the interdigitated electrodes under alternating voltage stimulations, generating localized electric fields for bright emissions. Various inks are prepared for painting, stamping, and stencil printing. Arbitrary luminous features on the devices can be either long-lasting or transient in characteristics. These skin-like devices are made entirely of compliant materials that can withstand bending, twisting, and stretching manipulations. Due to the excellent mechanical deformability, the drawing displays can be conformally laminated on the skin as body-integrated optoelectronic communication devices for graphic information.

Stretchable sweat sensors are promising technology that can acquire biomolecular insights for health and fitness monitoring by intimate integration with the body. However, current sensors often require microfabricated microfluidic channels to control sweat flow during lab-on-body analysis, which makes effective and affordable sweat sampling a significant practical challenge. Here, we present stretchable and sweat-wicking patches that utilize bioinspired smart wettable membranes for the on-demand manipulation of sweat flow. In a scalable process, the membrane is created by stacking hydrophobic elastomer nanofibers onto soft microfoams with predefined two-dimensional superhydrophobic and superhydrophilic patterns. The engineered heterogeneous wettability distribution allows these porous membranes to achieve enhanced extraction and selective collection of sweat in embedded assays. Despite the simplified architecture, the color reactions between sweat and chemical indicators are inhibited from directly contacting the skin to achieve a largely improved operation safety. The sensing patches can simultaneously quantify pH, urea, and calcium in sweat through digital colorimetric analysis with smartphone images. The construction with all compliant materials renders these patches soft and stretchy to achieve conformal attachment to the skin. Successfully analyzing sweat compositions after physical exercises illustrates the practical suitability of these skin-attachable sensors for health tracking and point-of-care diagnosis.

Stretchable sweat sensors have become a personalized wearable platform for continuous, noninvasive health monitoring through conformal integration with the human body. Typically, these devices are coupled with soft microfluidic systems to control sweat flow during advanced analysis processes. However, the implementation of these soft microfluidic devices is limited by their high fabrication costs and the need for skin adhesives to block natural perspiration. To overcome these limitations, a stretchable and smart wettable patch has been proposed for multiplexed in situ perspiration analysis. The patch includes a porous membrane in the form of a patterned microfoam and a nanofiber layer laminate, which extracts sweat selectively from the skin and directs its continuous flow across the device. The integrated electrochemical sensor array measures multiple biomarkers simultaneously such as pH, K+, and Na+. The soft sensing patch comprises compliant materials and structures that allow deformability of up to 50% strain, which enables a stable and seamless interface with the curvilinear human body. During continuous physical exercise, the device has demonstrated a special operating mode by actively accumulating sweat from the skin for multiplex electrochemical analysis of biomarker profiles. The smart wettable membrane provides an affordable solution to address the sampling challenges of in situ perspiration analysis.

AbstractEpidermal electronics is an emerging wearable platform that involves attaching deformable forms of devices to the skin. Epidermal electrodes represent a vital component of this technology, as they provide a direct electronic interface with the skin for sensing and stimulation. However, most of the current electrodes are built on non‐permeable elastomer substrates, which can limit their long‐term, continuous operations in a non‐invasive manner. Fortunately, recent advancements in conductive materials and fabrication techniques have enabled high‐performance epidermal electrodes that are comfortable to wear. In order to track the latest progress, this review article first introduces the designs of permeable structures and the preparation of conductive electrodes. The subsequent discussion elaborates on effective strategies to achieve desirable properties, such as high conductivity, stretchability, skin adhesion, and biocompatibility. The emerging applications of permeable epidermal electrodes are also summarized. Finally, this review concludes with the current challenges and future directions of breathable epidermal electrodes.

Textile-based light-emitting devices are attracting more and more attention because of their potential applications in smart clothing, human-computer interfaces, safety warnings, entertainment fashion, etc. However, simple and efficient manufacturing of luminescent devices on fabrics even clothing with excellent stretchability and washability remains challenging. Here, a solvent-free thermal lamination process combined with laser engraving has been proposed to fabricate electroluminescent (EL) devices on textiles. All the preprepared components, such as the bottom electrode, the EL layer, and the top transparent electrode, were thermally laminated on the surface of textiles employing thermoplastic polyurethane (TPU) as the binding matrix. The stretchability, luminance, and interface adhesion of the EL devices were systematically studied, showing excellent mechanical durability at high temperature, in humid environments, withstanding repeated machine washing, and resistant to various forms of physical damage. As a demonstration of potential application, textile-based EL devices were fabricated, which could display colored and pixelated patterns as well as dynamic images. The thermal lamination technology developed in this work can potentially enable people to DIY (do it yourself) fabricate light-emitting devices on clothing using daily tools, which could facilitate the widespread use of textile-based wearable displays.

Stretchable alternating current electroluminescent devices represent an emerging optoelectronic technology with skin-like deformability. Despite robust construction and reliable performances, the conventional sandwiched device is only compatible with simple luminous features instead of complicated patterns. An unconventional design of intrinsically stretchable ACEL panels is reported here, featuring capacitively coupled bottom interdigitated liquid metal electrodes and top hydrogel transparent electrodes. Arbitrary luminous feature resembling the top electrode pattern is readily accessible without tailored designs. A facile procedure is established to construct functional devices exhibiting ultrahigh stretchability to 400% strain and durable performance under repetitive deformations. The successful integration in a soft pneumatic actuator further demonstrates the promising potential of stretchable ACEL panels for graphic information display in soft devices and systems.

College of Engineering and Applied Sciences, State Key Laboratory of Analytical Chemistry for Life Science, and Jiangsu Key Laboratory of Artificial Functional Materials, Nanjing University, Nanjing 210046, China Key Laboratory of High Performance Polymer Materials and Technology of Ministry of Education, Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210046, China

In contrast to ionically conductive liquids and gels, a new type of yield-stress fluid featuring reversible transitions between solid and liquid states is introduced in this study as a printable, ultrastretchable, and transparent conductor. The fluid is formulated by dispersing silica nanoparticles into the concentrated aqueous electrolyte. The as-printed features show solid-state appearances to allow facile encapsulation with elastomers. The transition into liquid-like behavior upon tensile deformations is the enabler for ultrahigh stretchability up to the fracture strain of the elastomer. Successful integrations of yield-stress fluid electrodes in highly stretchable strain sensors and light-emitting devices illustrate the practical suitability. The yield-stress fluid represents an attractive building block for stretchable electronic devices and systems in terms of giant deformability, high ionic conductivity, excellent optical transmittance, and compatibility with various elastomers.

Stretchable optoelectronics represent an emerging technology featuring soft mechanical properties. The advancements in this active area rely on the development of compliant electronic materials. Currently, the deformable forms of light-emitting devices often exhibit double-side emissions due to the lack of stretchable reflective electrodes. This study reports a facile procedure to deposit smooth and uniform liquid metal films over large-area elastomeric substrates as stretchable reflective electrodes. The as-prepared electrodes exhibit low sheet resistance (0.15 Omega sq(-1)), high optical reflectance (95% at 550 nm), and ultrahigh deformability (500% strain). The electrode shows sufficient durability to survive repetitive tensile deformations. Successful implementation of a liquid metal electrode in a stretchable light-emitting device achieves single-side emission with enhanced light extraction. The stretchable reflective electrode reported here represents a key building component to enable a broad range of applications such as deformable lighting, wearable displays, and soft robotics.