Recent progress in electronic skin or e‐skin research is broadly reviewed, focusing on technologies needed in three main applications: skin‐attachable electronics, robotics, and prosthetics. First, since e‐skin will be exposed to prolonged stresses of various kinds and needs to be conformally adhered to irregularly shaped surfaces, materials with intrinsic stretchability and self‐healing properties are of great importance. Second, tactile sensing capability such as the detection of pressure, strain, slip, force vector, and temperature are important for health monitoring in skin attachable devices, and to enable object manipulation and detection of surrounding environment for robotics and prosthetics. For skin attachable devices, chemical and electrophysiological sensing and wireless signal communication are of high significance to fully gauge the state of health of users and to ensure user comfort. For robotics and prosthetics, large‐area integration on 3D surfaces in a facile and scalable manner is critical. Furthermore, new signal processing strategies using neuromorphic devices are needed to efficiently process tactile information in a parallel and low power manner. For prosthetics, neural interfacing electrodes are of high importance. These topics are discussed, focusing on progress, current challenges, and future prospects.

An ultrahigh sensitive capacitive pressure sensor based on a porous pyramid dielectric layer (PPDL) is reported. Compared to that of the conventional pyramid dielectric layer, the sensitivity was drastically increased to 44.5 kPa −1 in the pressure range <100 Pa, an unprecedented sensitivity for capacitive pressure sensors. The enhanced sensitivity is attributed to a lower compressive modulus and larger change in an effective dielectric constant under pressure. By placing the pressure sensors on islands of hard elastomer embedded in a soft elastomer substrate, the sensors exhibited insensitivity to strain. The pressure sensors were also nonresponsive to temperature. Finally, a contact resistance-based pressure sensor is also demonstrated by chemically grafting PPDL with a conductive polymer, which also showed drastically enhanced sensitivity.

This work reports an ultrasensitive wearable temperature sensor based on GNWs/PDMS for personalized healthcare and human–machine interface systems.

Spotlight on lipids: One of the major limitations of tetrazine bioorthogonal cycloadditions is the requirement of bulky dienophile reaction partners. Methylcyclopropene tags were designed capable of reacting rapidly with tetrazines while maintaining stability in aqueous solution. The suitability of these probes for bioconjugation is shown by imaging cyclopropene‐modified phospholipids in live human cancer cells (see picture).

High-performance flexible pressure sensors are highly desirable in health monitoring, robotic tactile, and artificial intelligence. Construction of microstructures in dielectrics and electrodes is the dominating approach to improving the performance of capacitive pressure sensors. Herein, we have demonstrated a novel three-dimensional microconformal graphene electrode for ultrasensitive and tunable flexible capacitive pressure sensors. Because the fabrication process is controllable, the morphologies of the graphene that is perfectly conformal with the electrode are controllable consequently. Multiscale morphologies ranging from a few nanometers to hundreds of nanometers, even to tens of micrometers, have been systematically investigated, and the high-performance capacitive pressure sensor with high sensitivity (3.19 kPa–1), fast response (30 ms), ultralow detection limit (1 mg), tunable-sensitivity, high flexibility, and high stability was obtained. Furthermore, an ultrasensitivity of 7.68 kPa–1 was successfully achieved via symmetric double microconformal graphene electrodes. The finite element analysis indicates that the microstructured graphene electrode can enhance large deformation and thus effectively improve the sensitivity. Additionally, the proposed pressure sensors are demonstrated with practical applications including insect crawling detection, wearable health monitoring, and force feedback of robot tactile sensing with a sensor array. The microconformal graphene may provide a new approach to fabricating controllable microstructured electrodes to enhance the performance of capacitive pressure sensors and has great potential for innovative applications in wearable health-monitoring devices, robot tactile systems, and human–machine interface systems.

Rationally designed nanoparticles that can bind toxins show great promise for detoxification. However, the conventional intravenous administration of nanoparticles for detoxification often leads to nanoparticle accumulation in the liver, posing a risk of secondary poisoning especially in liver-failure patients. Here we present a liver-inspired three-dimensional (3D) detoxification device. This device is created by 3D printing of designer hydrogels with functional polydiacetylene nanoparticles installed in the hydrogel matrix. The nanoparticles can attract, capture and sense toxins, while the 3D matrix with a modified liver lobule microstructure allows toxins to be trapped efficiently. Our results show that the toxin solution completely loses its virulence after treatment using this biomimetic detoxification device. This work provides a proof-of-concept of detoxification by a 3D-printed biomimetic nanocomposite construct in hydrogel, and could lead to the development of alternative detoxification platforms.

The lifetime and power conversion efficiency are the key issues for the commercialization of perovskite solar cells (PSCs). In this paper, the development of 2D/3D perovskite hybrids (CAPbI/MAPbICl) was firstly demonstrated to be a reliable method to combine their advantages, and provided a new concept for achieving both stable and efficient PSCs through the hybridization of perovskites. 2D/3D perovskite hybrids afforded significantly-improved moisture stability of films and devices without encapsulation in a high humidity of 63 ± 5%, as compared with the 3D perovskite (MAPbICl). The 2D/3D perovskite-hybrid film did not undergo any degradation after 40 days, while the 3D perovskite decomposed completely under the same conditions after 8 days. The 2D/3D perovskite-hybrid device maintained 54% of the original efficiency after 220 hours, whereas the 3D perovskite device lost all the efficiency within only 50 hours. Moreover, the 2D/3D perovskite hybrid achieved comparable device performances (PCE: 13.86%) to the 3D perovskite (PCE: 13.12%) after the optimization of device fabrication conditions.

In spite of the wide application potential of 1,2,4,5-tetrazines, particularly in live-cell and in-vivo imaging, a major limitation has been the lack of practical synthetic methods. Here we report the in situ synthesis of (E)-3-substituted-6-alkenyl-1,2,4,5-tetrazine derivatives via an elimination-Heck cascade reaction. Using this strategy, we provide 24 examples of π-conjugated tetrazine derivatives that can be conveniently prepared from tetrazine building blocks and related halides. These include tetrazine analogs of biological small molecules, highly conjugated buta-1,3-diene substituted tetrazines, and a diverse array of fluorescent probes suitable for live-cell imaging. These highly conjugated probes show dramatic fluorescent turn-on (up to 400-fold) when reacted with dienophiles such as cyclopropenes and trans-cyclooctenes, and we demonstrate their application for live-cell imaging. This work provides an efficient and practical synthetic methodology for tetrazine derivatives and will facilitate the application of conjugated tetrazines, particularly as fluorogenic probes for live-cell imaging.