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.
Soft strain sensors are needed for a variety of applications including human motion and health monitoring, soft robotics, and human/machine interactions. Capacitive-type strain sensors are excellent candidates for practical applications due to their great linearity and low hysteresis; however, a big limitation of this sensor is its inherent property of low sensitivity when it comes to detecting various levels of applied strain. This limitation is due to the structural properties of the parallel plate capacitor structure during applied stretching operations. According to this model, at best the maximum gauge factor (sensitivity) that can be achieved is 1. Here, we report the highest gauge factor ever achieved in capacitive-type strain sensors utilizing an ultrathin wrinkled gold film electrode. Our strain sensor achieved a gauge factor slightly above 3 and exhibited high linearity with negligible hysteresis over a maximum applied strain of 140%. We further demonstrated this highly sensitive strain sensor in a wearable application. This work opens up the possibility of engineering even higher sensitivity in capacitive-type strain sensors for practical and reliable wearable applications.
Ultraconformable strain gauge can be applied directly to human skin for continuous motion activity monitoring, which has seen widespread application in interactive robotics, human motion detection, personal health monitoring, and therapeutics. However, the development of an on-skin strain gauge that can detect human body motions over a long period of time without disturbing the natural skin movements remains a challenge. Here, we present an ultrathin and durable nanomesh strain gauge for continuous motion activity monitoring that minimizes mechanical constraints on natural skin motions. The device is made from reinforced polyurethane-polydimethylsiloxane (PU-PDMS) nanomeshes and exhibits excellent sustainability, linearity, and durability with low hysteresis. Its thinness geometry and softness provide minimum mechanical interference on natural skin deformations. During speech, the nanomesh-attached face exhibits skin strain mapping comparable to that of a face without nanomeshes. We demonstrate long-term facial stain mapping during speech and the capability for real-time stable full-range body movement detection.
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...
A reliable and low-cost solution-processing procedure to synthesize a highly adhesive flexible metal antenna with low resistivity for radio-frequency identification device (RFID) tags on paper substrates via inkjet printing combined with surface modification and electroless deposition (ELD) is demonstrated in this paper. Through the surface modification of colloidal solution of hydrolyzed stannous chloride and chitosan solution, the paper-based substrate is able to reduce the penetration rate of ink and further increase the adsorption amount of silver ions, which could create a catalytic activating layer to catalyze the subsequent ELD of a conductive deposited metal antenna. The resulting metal antenna for RFID tags presents good adhesive strength and low resistivity of 2.58 × 10 −8 Ω·m after 40 min of ELD, and maintains a reliable reading range of RFID tags even after over 1000 times of bending and mechanical stress. Consequently, the developed technology proposed allows for cheap, efficient, and massive production of metal antenna for paper-based RFID tags with excellent mechanical and electrical properties. Furthermore, this process is especially advantageous for the fabrication of next-generation flexible electronic devices based on paper substrates.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201902579.identification technology in IOT. [2] Different kinds of substrates have been applied to fabricate RFID tags, including polyethylene terephthalate, [3][4][5] polyethylene naphthalate, [6][7][8] polyimide (PI), [9][10][11] and paper. [12,13] Paper is not only widely available, inexpensive, and well established but also lightweight, biodegradable, and can be creased for storage in small spaces or made into 3D self-standing structures; [14,15] so it is an ideal flexible substrate for RFID tags. Using paper as an insulating substrate, it is possible to fabricate RFID tags i) that do not need extra coarsening process because of enough surface roughness; [16] ii) that can naturally degrade; [17] iii) that is an abundantly available renewable material; [18] iv) that involves little absorption of electromagnetic energy due to its low dielectric constant and loss tangent angle. [19][20][21][22] Commercial paper-based RFID tags comprise metal antenna, integrated circuit (IC), and paper substrate, of which metal antenna accounts for 80% of the whole tag cost. [23] At present, the most mature method for preparing metal antenna RFID tag based on organic plastic substrate in industry is the subtractive etching method. [24] Although this traditional method of manufacturing metal antenna shows some superior characteristics, including high accuracy, low resistivity, and good weather resistance, it does generate some disadvantages such as high cost, restriction about substrate type, and environmental pollution. [20,25] In addition, the damage to fiber structure in paper substrate cannot be avoided due to the oxidation of fiber by the strong acid etching s...
A simple strategy to simultaneously improve power conversion efficiency (PCE) and mechanical stability of ultraflexible organic solar cells is reported. By using a fullerene/non-fullerene mixed acceptor, 3-mm-thick ultraflexible organic solar cells achieve a PCE of 13% (a certified value of 12.3%) with 97% PCE retention after 1,000 bending cycles and 89% PCE retention after 1,000 compression-stretching cycles.
Robust polymeric nanofilms can be used to construct gas-permeable soft electronics that can directly adhere to soft biological tissue for continuous, long-term biosignal monitoring. However, it is challenging to fabricate gas-permeable dry electrodes that can self-adhere to the human skin and retain their functionality for long-term (>1 d) health monitoring. We have succeeded in developing an extraordinarily robust, self-adhesive, gas-permeable nanofilm with a thickness of only 95 nm. It exhibits an extremely high skin adhesion energy per unit area of 159 μJ/cm2. The nanofilm can self-adhere to the human skin by van der Waals forces alone, for 1 wk, without any adhesive materials or tapes. The nanofilm is ultradurable, and it can support liquids that are 79,000 times heavier than its own weight with a tensile stress of 7.82 MPa. The advantageous features of its thinness, self-adhesiveness, and robustness enable a gas-permeable dry electrode comprising of a nanofilm and an Au layer, resulting in a continuous monitoring of electrocardiogram signals with a high signal-to-noise ratio (34 dB) for 1 wk.
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