Recent Advances in Skin‐Mounted Electronics

The skin, the largest organ of the human body, is characterized by its softness, stretchability, and multifunctionality. Being mechanically flexible and elastic, it plays critical roles in protection, sensation, and response to external stimuli. These unique properties have inspired the development of skin-mounted electronics—lightweight, soft, and stretchable devices capable of acquiring physiological and environmental data. This research area holds significant promise for various domains, including healthcare, robotics, and human–machine interfaces. The skin is also a highly complex system. Take the sense of touch as an example. As early as the 19th century, mechanoreceptors such as Pacinian corpuscles[1] and Merkel cells[2] were discovered, marking the beginning of somatosensory research. After more than a century, the 2021 Nobel Prize in Physiology or Medicine was awarded to Professors David Julius and Ardem Patapoutian for their discoveries of temperature and touch receptors. Patapoutian identified two mechanically activated ion channels, Piezo1 and Piezo2, elucidating the molecular bases for mammalian cells to sense mechanical force. These findings have significantly advanced our understanding of mechanosensation and spurred innovations in skin-mounted electronics. For instance, mimicking the 3D architecture of Merkel cells and Ruffini endings, researchers have developed electronic skins with force- and strain-sensing components arranged in 3D configurations, enabling decoupled detection of normal force, shear force, and strain.[3] Such systems allow for simultaneous modulus/curvature measurements during tactile interactions. Another group has replicated the neural network of the somatosensory system by integrating pressure sensors, ring oscillators, and ion-gel transistors to create artificial mechanoreceptors. These devices can process multiple pressure inputs and even drive robotic actuators, such as inducing oscillatory motion in a cockroach leg.[4] Drawing inspiration from biological skin, researchers are exploring innovations in materials, device design, fabrication techniques, and wireless communication for next-generation skin-mounted electronics. In this special issue, we have included reviews and reports from researchers across different disciplines mentioned above. Wireless solutions are crucial for enhancing the functionality and usability of skin-mounted devices. Jeong et al. (article number 202400884) provide a comprehensive review of short- and long-range wireless communication technologies, along with tether-free power solutions, including integrated energy sources and energy harvesting methods. These advancements enable real-time remote health monitoring while improving user comfort and versatility. Further exploring specific applications of wireless technology, Yu et al. (article number 202500184) discuss inductor-capacitor (LC)-based sensors, which use passive resonant circuits for wireless operation. These sensors, coupled with external readers via magnetic induction, eliminate the need for internal power sources, making them ideal for intracranial pressure monitoring, intraocular pressure sensing, and tumor microenvironment analysis. Wu et al. (article number 202400950) leverage triboelectric nanogenerators to develop a contactless motion-detection system, enabling 3D motion classification for wireless human-machine interfaces. Innovative fabrication methods are essential for producing high-performance skin-mounted electronics. Seo et al. (article number 202400979) introduce a photothermal approach for fabricating sub-50 µm polymer stencil masks using UV laser processing. This method overcomes challenges in mask reproducibility while maintaining cost and time efficiency. Zhu et al. (article number 202400983) employ electrohydrodynamic (EHD) printing to deposit silver nanowire inks on ultrathin polyimide substrates. Unlike conventional inkjet printing, EHD printing avoids nozzle clogging and achieves high-resolution patterning even with high-aspect-ratio nanowires. Post-printing annealing enhances conductivity, mechanical robustness, and chemical stability, ensuring performance under bending, peeling, and immersion in water or sweat. Beyond printing, nanostructure engineering enhances sensor performance. Yoo et al. (article number 202400980) fabricate a sub-100 nm valley nanograting via digital etching and nanoimprinting in their capacitive pressure sensor. By leveraging the percolation effect within the sub-100 nm nanograting structure, the sensitivity is increased by 4.2 times while maintaining insensitivity to bending. Microfluidics offers a versatile platform for building various on-skin sensors. Lim et al. (article number 202500010) review wearable electrochemical sensors for analyzing sweat, saliva, and interstitial fluid, offering real-time biomarker detection for personalized healthcare. Yue et al. (article number 202400982) integrate liquid metal into microfluidic systems and develop a hardness sensor based on a multi-layer structure. By laminating multiple PDMS microfluidic layers, pressure, and deformation are simultaneously measured in a decoupled manner, enabling identification of the hardness of contact materials. This compact design is suitable for robotic surgical applications. Materials innovation is always a core part of skin-mounted electronics. This special issue also covers some of the most important materials in this area. Kwon et al. (article number 202400997) summarize advances in bioresorbable polymers, semiconductors, and metals, enabling transient biomedical devices that minimize electronic waste. Zhao and Li's works focus on hydrogels. Zhao et al. (article number 202400987) leverage the redox pair of Mo2C-derived molybdenum polyoxometalates/ammonium persulfate to achieve rapid initiation of in situ free radical polymerization of hydrogels at room temperature. Additionally, the incorporation of LiCl provides exceptional frost resistance, water retention, durability, and stability even under prolonged load cycling. Li et al. (article number 202400961) report an elastomer-encapsulated hydrogel as a couplant for wearable ultrasonic devices. They use a prefabricated hydrogel as a template and add a large amount of glycerol to obtain an ultrasmooth hydrogel-elastomer interface and long-term water retention over 8 days. Carbon has versatile electrical properties and can be used in various scenarios in skin-mounted electronics. Xiang et al. (article number 202400991) review the recent advances of carbon nanotube (CNT)-based epidermal amplifiers. The direct integration with sensors on the skin facilitates signal amplification prior to transmission, thereby enhancing signal amplitudes and output impedance. Among various semiconducting materials, CNTs are one of the most promising candidates due to their high mobility, low-temperature processability, good stability, uniformity, and printability. Lee et al. (article number 202400984) report partially reduced graphene oxide for on-skin temperature sensing. Using a flash-thermal reduction technique, they can control its material properties by adjusting the flash energy and achieve flexibility, reversibility, high sensitivity, excellent linearity, long-term stability, and rapid response time, surpassing conventional metal-based temperature sensors. Shi et al. (article number 202400985) report a mesoporous carbon spheres-polymer composite film for flexible capacitive pressure sensors. Leveraging the percolation mechanism for transduction, the film achieves high sensitivity (0.16 kPa−¹), outstanding precision (<2.987%), high linearity (R2 = 0.995 across 0–10 kPa), and an impressive measurement range (1,000 kPa). The design of polymers is crucial for the performance of skin-mounted devices. For example, with regard to gas sensing, Yang et al. and Song et al. propose different strategies. In Yang's paper (article number 202400981), they focus on stretchable organic field-effect transistor-based gas sensors. They develop a tri-layer dielectric design consisting of a high-κ polymer film, a non-polar polymer layer, and a crosslinking layer, enabling the transistors to operate at a low voltage of −5 V. In Song's work (article number 202400977), they choose colorimetric sensing. Leveraging ultrathin resonators, they achieve enhanced chromaticity and angular stability. The active layer of polyvinyl alcohol allows fast detection of relative humidity and various volatile organic compounds. The diverse research presented in this issue underscores the vast potential of skin-mounted electronics. From wireless sensing to advanced materials and fabrication, these innovations pave the way for breakthroughs in health monitoring, robotics, and human–machine interaction. We encourage readers to explore these contributions, which will undoubtedly shape the field in the coming decade. The authors declare no conflict of interest. Zhuo Li is a Full Professor at the College of Smart Materials and Future Energy, Fudan University, China. She received her Ph.D. in Materials Science and Engineering from Georgia Institute of Technology in 2014. She is an Associate Editor of IEEE Transactions on Components, Packaging, and Manufacturing Technology. Her research interests include flexible sensors and electronic packaging materials. Jae-Woong Jeong is a KAIST Endowed Chair Professor and Associate Professor of Electrical Engineering at Korea Advanced Institute of Science and Technology (KAIST). He earned his Ph.D. in Electrical Engineering from Stanford University in 2012 and subsequently worked as a postdoctoral researcher at the University of Illinois at Urbana-Champaign from 2012 to 2014. Prior to joining KAIST, he was an Assistant Professor of Electrical, Computer, and Energy Engineering at the University of Colorado Boulder from 2015 to 2017. His research focuses on developing innovative electronics design concepts and fabrication strategies to advance the scope and applications of bio-integrated electronics.