Printable elastic conductors promise large-area stretchable sensor/actuator networks for healthcare, wearables and robotics. Elastomers with metal nanoparticles are one of the best approaches to achieve high performance, but large-area utilization is limited by difficulties in their processability. Here we report a printable elastic conductor containing Ag nanoparticles that are formed in situ, solely by mixing micrometre-sized Ag flakes, fluorine rubbers, and surfactant. Our printable elastic composites exhibit conductivity higher than 4,000 S cm (highest value: 6,168 S cm) at 0% strain, and 935 S cm when stretched up to 400%. Ag nanoparticle formation is influenced by the surfactant, heating processes, and elastomer molecular weight, resulting in a drastic improvement of conductivity. Fully printed sensor networks for stretchable robots are demonstrated, sensing pressure and temperature accurately, even when stretched over 250%.

Next-generation biomedical devices will need to be self-powered and conformable to human skin or other tissue. Such devices would enable the accurate and continuous detection of physiological signals without the need for an external power supply or bulky connecting wires. Self-powering functionality could be provided by flexible photovoltaics that can adhere to moveable and complex three-dimensional biological tissues and skin. Ultra-flexible organic power sources that can be wrapped around an object have proven mechanical and thermal stability in long-term operation, making them potentially useful in human-compatible electronics. However, the integration of these power sources with functional electric devices including sensors has not yet been demonstrated because of their unstable output power under mechanical deformation and angular change. Also, it will be necessary to minimize high-temperature and energy-intensive processes when fabricating an integrated power source and sensor, because such processes can damage the active material of the functional device and deform the few-micrometre-thick polymeric substrates. Here we realize self-powered ultra-flexible electronic devices that can measure biometric signals with very high signal-to-noise ratios when applied to skin or other tissue. We integrated organic electrochemical transistors used as sensors with organic photovoltaic power sources on a one-micrometre-thick ultra-flexible substrate. A high-throughput room-temperature moulding process was used to form nano-grating morphologies (with a periodicity of 760 nanometres) on the charge transporting layers. This substantially increased the efficiency of the organophotovoltaics, giving a high power-conversion efficiency that reached 10.5 per cent and resulted in a high power-per-weight value of 11.46 watts per gram. The organic electrochemical transistors exhibited a transconductance of 0.8 millisiemens and fast responsivity above one kilohertz under physiological conditions, which resulted in a maximum signal-to-noise ratio of 40.02 decibels for cardiac signal detection. Our findings offer a general platform for next-generation self-powered electronics.

Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity—unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

functions in health monitoring, [12,13] medical therapy, [14] and soft robotics. [15,16] For applications to human skin and humanoid robots, stretchability of over 55% and good mechanical durability for thousands of cycles of deformation are needed for longterm stable operation. [9] High conductivity (over 5000 S cm −1 ) contributes to reducing power loss in wirings [3,17] and reducing noise for biosignal sensing electrodes. [18] Nanomesh-type elastic conductors with porous structure are effective in reducing skin inflammation owing to their gas permeability; [19] thus, they are very promising candidates for on-skin electronics. Achieving high stretchability and conductivity in single materials is very difficult and rare, and a successful approach for elastic conductors is to include two conductive and elastic components. [19][20][21] A pioneer study on porous elastic conductors coated Ag nanoparticles with poly(styrenebutadiene-styrene) fibers more than 150 µm thick, achieving 5215 S cm −1 conductivity with 140% maximum stretchability. [20] Replacing nanoparticles with nanowires is an effective approach to further increase conductivity and decrease resistance change from release status to stretch status. A 3 µm thick polyamide nanofiber (NF)/Ag nanowire (NW) bilayer conductor has been reported to achieve 8 Ω sq −1 sheet resistance (less than 500 S cm −1 ) and 50% stretchability with 85% transmittance at 550 nm wavelength. [21] However, it remains challenging for nanomesh-type elastic conductors to simultaneously achieve high conductivity (5000 S cm −1 ), stretchability (55%), and cyclic mechanical durability for skin-attachable electronics. Achieving high stretchability and good durability is very difficult when simply mixing conductive and polymer materials. Conductive networks and polymer scaffold can easily detach when stretched since the adhesion between them from van der Waals forces is very weak, resulting in rapid degradation of conductivity or even failure of nanomeshtype elastic conductors. On the other hand, adding large amounts of binder materials to enhance the bonding between conductive networks and elastic scaffold often results in lower conductivity, [22][23][24][25] and even the loss of their porous nanostructure. [26][27][28][29] Here, we report a simple bottom-up fabrication approach for porous nanomesh-type elastic conductors with high On-skin electronics require conductive, porous, and stretchable materials for a stable operation with minimal invasiveness to the human body. However, porous elastic conductors that simultaneously achieve high conductivity, good stretchability, and durability are rare owing to the lack of proper design for good adhesion between porous elastic polymer and conductive metallic networks. Here, a simple fabrication approach for porous nanomesh-type elastic conductors is shown by designing a layer-by-layer structure of nanofibers/nanowires (NFs/NWs) via interfacial hydrogen bonding. The as-prepared conductors, consisting of Ag NWs and polyurethane (PU) NFs, simultaneo...

Soft and stretchable electrodes are essential components for skin-tight wearable devices, which can provide comfortable, unobtrusive, and accurate physiological monitoring and physical sensing for applications such as healthcare, medical treatment, and human-machine interfaces. Metal–elastomer nanocomposites are a promising approach, enabling high conductivity and stretchability derived from metallic conduction and percolation networks of metal nano/micro fillers. However, their practical application is still limited by their inferior cyclic stability and long-term durability. Here, we report on a highly durable nanofiber-reinforced metal–elastomer composite consisting of (i) metal fillers, (ii) an elastomeric binder matrix, and (iii) electrospun polyvinylidene fluoride nanofibers for enhancing both cyclic stability and conductivity. Embedded polyvinylidene fluoride (PVDF) nanofibers enhance the toughness and suppress the crack growth by providing a fiber reinforcing effect. Furthermore, the conductivity of nanofiber-reinforced elastic conductor is four times greater than the pristine material because the silver-rich layer is self-assembled on the top surface by a filtering effect. As a result, a stretchable electrode made from nanofiber-reinforced elastic conductors and wrinkled structures has both excellent cyclic durability and high conductivity and is stretchable up to 800%. The cyclic degradation (ΔR/R 0) remains at 0.56 after 5000 stretching cycles (50% strain), whereas initial conductivity and sheet resistance are 9903 S cm–1 and 0.047 Ω sq–1, respectively. By utilizing a highly conductive and durable elastic conductor as sensor electrodes and wirings, a skin-tight multimodal physiological sensing suit is demonstrated. Continuous long-term monitoring of electrocardiogram, electromyogram, and motions during weight-lifting exercises are successfully demonstrated without significant degradation of signal quality.

Mechanically durable transparent electrodes are needed in flexible optoelectronic devices to realize their long-term stable functioning, for applications in various fields such as energy, healthcare, and soft robotics. Several promising transparent electrodes based on nanomaterials have been previously reported to replace the conventional and fragile indium-tin oxide (ITO); however, obtaining feasible printed transparent electrodes for ultraflexible devices with a multistack structure is still a great challenge. Here, a printed ultrathin (uniform thickness of 100 nm) Ag mesh transparent electrode is demonstrated, simultaneously achieving high conductance, high transparency, and good mechanical properties. It shows a 17 Ω sq sheet resistance (R ) with 93.2% transmittance, which surpasses the performance of sputtered ITO electrodes and other ultrathin Ag mesh transparent electrodes. The conductance is stable after 500 cycles of 100% stretch/release deformation, with an insignificant increase (10.6%) in R by adopting a buckling structure. Furthermore, organic photovoltaics (OPVs) using our Ag mesh transparent electrodes achieve a power conversion efficiency of 8.3%, which is comparable to the performance of ITO-based OPVs.

A smart face mask that can conveniently monitor breath information is beneficial for maintaining personal health and preventing the spread of diseases. However, some challenges still need to be addressed before such devices can be of practical use. One key challenge is to develop a pressure sensor that is easily triggered by low pressure and has excellent stability as well as electrical and mechanical properties. In this study, a wireless smart face mask is designed by integrating an ultrathin self‐powered pressure sensor and a compact readout circuit with a normal face mask. The pressure sensor is the thinnest (totally compressed thickness of ≈5.5 µm) and lightest (total weight of ≈4.5 mg) electrostatic pressure sensor capable of achieving a peak open‐circuit voltage of up to ≈10 V when stimulated by airflow, which endows the sensor with the advantage of readout circuit miniaturization and makes the breath‐monitoring system portable and wearable. To demonstrate the capabilities of the smart face mask, it is used to wirelessly measure and analyze the various breath conditions of multiple testers.

Flexible and biocompatible integrated photo‐charging devices consisting of photovoltaic cells and energy storage units can provide an independent power supply for next‐generation wearable electronics or biomedical devices. However, current flexible integrated devices exhibit low total energy conversion and storage efficiency and large device thickness, hindering their applicability towards efficient and stable self‐powered systems. Here, a highly efficient and ultra‐thin photo‐charging device with a total efficiency approaching 6% and a thickness below 50 µm is reported, prepared by integrating 3‐µm‐thick organic photovoltaics on 40 µm‐thick carbon nanotube/polymer‐based supercapacitors. This flexible photo‐charging capacitor delivers much higher performance compared with previous reports by tuning the electrochemical properties of the composite electrodes, which reduce the device thickness to 1/8 while improving the total efficiency by 15%. The devices also exhibit a superior operational stability (over 96% efficiency retention after 100 charge/discharge cycles for one week) and mechanical robustness (94.66% efficiency retention after 5000 times bending at a radius of around 2 mm), providing a high‐power and long‐term operational energy source for flexible and wearable electronics.