approach to fabricate 1.64 µm-thin black-gold fi lms on any elastomeric sheet (latex rubber, Eco-fl ex, polydimethylsiloxane (PDMS), etc.) resulting in highly stretchable strain sensors. The ultrathin sensors could detect strains as small as 0.01% and as large as 350%, simultaneously with a typical GF of 6.9-9.9, a fast response (<22 ms). We observed negligible loadingunloading signal changes over 5000 cycles. The superior sensing performances enabled real-time monitoring of a wide range of human motions (fore arm muscle movement, cheek motions, throat muscle stretching, and fi nger fl exion extension as well as human radial artery pulse).The fabrication process of AuNWs strain sensors is illustrated in Figure 1 a. First, a AuNWs solution (10 mg mL −1 ) was prepared following the previously published protocol. [ 38 ] Second, a latex rubber sheet was sandwiched between a fl at glass slide and a polyimide mask with a rectangular opening (25 × 5 mm 2 ). Then AuNWs solution (100 µL) was dropcasted onto the open area of polyimide mask and dried. After removing the glass slide and polyimide mask, a conductive AuNWs strip fi lm was obtained with a typical sheet resistance of 2.03 ± 0.95 MΩ.The AuNWs strip-fabrication approach was general, which could be extended to a variety of other polymeric substrates (PET, Eco-fl ex, PDMS, nitrile rubber, etc.) with uniform deposition and strong adhesion (Figure 1 b). After electrically wiring the AuNWs strip with two conductive threads, a skin-attachable and highly stretchable strain sensor was obtained (Figure 1 c). The conductive AuNWs fi lms were about 1.64 µm in thickness (Figure 1 c, top right), and with a top surface of nanowire-entangling and bundling morphologies resembling polymeric chains (Figure 1 c, bottom right).The thin AuNWs fi lms exhibited outstanding mechanical stretchability up to 300% without any observable cracking or fi lm detachment from latex rubber (Movie 1, Supporting Information). It also showed exceptional electrical conductivity recovery, superior to their corresponding sputter-coated gold fi lm or silver nanowires fi lm (Figure 1 d). The electrical resistance of AuNWs fi lm increased gradually and smoothly as the strain increased and recovered gradually and smoothly to the original conductivity as the strain was revered back to 0%. Such a fully reversible process was observed under a dynamic strain of 0%-100%-0% and almost no hysteresis was observed (Figure 1 d). In contrast, the sputter coated gold fi lm became completely insulative when the strain was over 30%, and remained insulative even when the strain was removed (0% strain) (Figure 1 e). It was also observed that irreversible cracks formed during stretching.Further investigation on silver nanowires (AgNWs) fi lm prepared by drop casting showed that its conductivity was lost Highly stretchable strain sensors will be key components in future wearable electronics with broad applications ranging from electronic skins, [1][2][3][4][5][6][7][8][9][10] intelligent human/machine interactions, [ 11,12 ]...

A bio-inspired flexible pressure sensor is generated with high sensitivity (50.17 kPa(-1)), quick responding time (<20 ms), and durable stability (negligible loading-unloading signal changes over 10 000 cycles). Notably, the key resource of surface microstructures upon sensor substrates results from the direct molding of natural mimosa leaves, presenting a simple, environment-friendly and easy scale-up fabrication process for these flexible pressure sensors.

Wearable and highly sensitive strain sensors are essential components of electronic skin for future biomonitoring and human machine interfaces. Here we report a low-cost yet efficient strategy to dope polyaniline microparticles into gold nanowire (AuNW) films, leading to 10 times enhancement in conductivity and ∼8 times improvement in sensitivity. Simultaneously, tattoolike wearable sensors could be fabricated simply by a direct "draw-on" strategy with a Chinese penbrush. The stretchability of the sensors could be enhanced from 99.7% to 149.6% by designing curved tattoo with different radius of curvatures. We also demonstrated roller coating method to encapusulate AuNWs sensors, exhibiting excellent water resistibility and durability. Because of improved conductivity of our sensors, they can directly interface with existing wireless circuitry, allowing for fabrication of wireless flexion sensors for a human finger-controlled robotic arm system.

www.advmat.de www.advancedsciencenews.com Such soft wearable devices will be lightweight and thin, soft, and elastic, inexpensive, and durable. These devices will be skinattachable, flexible, stretchable, bendable and twistable whilst maintaining excellent sensing performances. Such disruptive WT products will ultimately transform current rigid wearable 1.0 to future wearable 2.0 products (Figure 1), enabling sensitive, accurate yet specific health monitoring anytime and anywhere.While the disruptive soft WT is still in the embryonic stage of development, there have been intensive worldwide materials [1c,8] push with a purpose to develop thinner, softer, ideally invisible and unfeelable electronics. [9] Unlike wearable 1.0 which typically starts from device, wearable 2.0 requires the design starts from materials innovation. In this context, novel structural design and the use of novel materials are the two viable strategies. [1b,10] For the former, serpentine design and prestrained treatment enable the stretchabilities; [11] as for the later, various nanomaterials including silver nanowires, [12] gold nanowires, [13] carbon nanotubes, [14] and graphene [15] have been widely explored.A typical soft WT research covers comprehensively all the key components in progressive sequences, namely, wear → sense → communicate → analyze → interpret → decide (Figure 2). This requires multidisciplinary collaborations across interdisciplinary boundaries. As a starting point, wearable materials should be designed to consider factors such as in soft/hard material interface, breathability, biocompatibility, etc. Then wearable sensors may be fabricated and evaluated with regards to key parameters including sensitivity, specificity, reusability, and durability. Once the sensors' performances have been fully evaluated, their integration with wireless modules such as Bluetooth Low Energy (BLE) or wireless fidelity (WIFI) needs to be considered. One of key limitations is the wearable powering solution. It is encouraging to see the commercial products of paper lithium battery and development of soft energy devices in academia. [16] In addition to hardware, designing user-friendly graphical user interfaces (GUIs) is necessary and the development of suitable apps is important for seamless data acquisition of timelapsed biometric signals in a wireless manner. The signals will be then analyzed and interpreted, enabling efficient algorithm for rapid signal processing and decision support. The analysis of electrical signals will help understand and predict the relationship between biometric data and sensing signals generated by soft wearable materials. This will allow us to understand the key parameters related to biological conditions such as cardiac health, [17] sporting activities, [18] and aged care behaviors. [19] Here, we discuss all of the above key aspects of next-generation of disruptive soft wearable technologies but with a focus on materials aspect. Nevertheless, it also emphasizes the significance of cross-disciplinary colla...

We report on a low-cost, simple yet efficient strategy to fabricate ultralightweight aerogel monoliths and conducting rubber ambers from copper nanowires (CuNWs). A trace amount of poly(vinyl alcohol) (PVA) substantially improved the mechanical robustness and elasticity of the CuNW aerogel while maintaining a high electrical conductivity. The resistivity was highly responsive to strains manifesting two distinct domains, and both followed a power law function consistent with pressure-controlled percolation theory. However, the values of the exponents were much less than the predicted value for 3D systems, which may be due to highly porous structures. Remarkably, the CuNW-PVA aerogels could be further embedded into PDMS resin, forming conducting rubber ambers. The ambers could be further manufactured simply by cutting into any arbitrary 1D, 2D, and 3D shapes, which were all intrinsically conductive without the need of external prewiring, a condition required in the previous aerogel-based conductors. The outstanding electrical conductivity in conjunction with high mechanical compliance enabled prototypes of the elastic piezoresistivity switches and stretchable conductors.

2 nm thin gold nanowires (AuNWs) have extremely high aspect ratio (≈10 000) and are nanoscale soft building blocks; this is different from conventional silver nanowires (AgNWs), which are more rigid. Here, highly sensitive, stretchable, patchable, and transparent strain sensors are fabricated based on the hybrid films of soft/hard networks. They are mechanically stretchable, optically transparent, and electrically conductive and are fabricated using a simple and cost-effective solution process. The combination of soft and more rigid nanowires enables their use as high-performance strain sensors with the maximum gauge factor (GF) of ≈236 at low strain (<5%), the highest stretchability of up to 70% strain, and the optical transparency is from 58.7% to 66.7% depending on the amount of the AuNW component. The sensors can detect strain as low as 0.05% and are energy efficient to operate at a voltage as low as 0.1 V. These attributes are difficult to achieve with a single component of either AuNWs or AgNWs. The outstanding sensing performance indicates their potential applications as "invisible" wearable sensors for biometric information collection, as demonstrated in applications for detecting facial expressions, respiration, and apexcardiogram.The ORCID identification number(s) for the author(s) of this article can be found under http://dx.

Sensitive, specific, yet multifunctional tattoo‐like electronics are ideal wearable systems for “any time, any where” health monitoring because they can virtually become parts of the human skin, offering a burdenless “unfeelable” wearing experience. A skin‐like, multifunctional electronic tattoo made entirely from gold using a standing enokitake‐mushroom‐like vertically aligned nanowire membrane in conjunction with a programmable local cracking technology is reported. Unlike previous multifunctional systems, only a single material type is needed for the integrated gold circuits involved in interconnects and multiplexed specific sensors, thereby avoiding the use of complex multimaterials interfaces. This is possiblebecause the programmable local cracking technology allows for the arbitrary fine‐tuning of the properties of elastic gold conductors from strain‐insensitive to highly strain‐sensitive simply by adjusting localized crack size, shape, and orientations—a capability impossible to achieve with previous bulk cracking technology. Furthermore, in‐plane integration of strain/pressure sensors, anisotropic orientation‐specific sensors, strain‐insensitive stretchable interconnects, temperature sensors, glucose sensors, and lactate sensors without the need of soldering or gluing are demonstrated. This strategy opens a new general route for the design of next‐generation wearable electronic tattoos.

Stretchable electronics may enable electronic components to be part of our organs-ideal for future wearable/implantable biodiagnostic systems. One of key challenges is failure of the soft/rigid material interface due to mismatching Young's moduli, which limits stretchability and durability of current systems. Here, we show that standing enokitake-like gold-nanowire-based films chemically bonded to an elastomer can be stretched up to 900% and are highly durable, with >93% conductivity recovery even after 2000 stretching/releasing cycles to 800% strain. Both experimental and modeling reveal that this superior elastic property originates from standing enokitake-like nanowire film structures. The closely packed nanoparticle layer sticks to the top of the nanowires, which easily cracks under strain, whereas the bottom part of the nanowires is compliant with substrate deformation. This leads to tiny V-shaped cracks with a maintained electron transport pathway rather than large U-shaped cracks that are frequently observed for conventional metal films. We further show that our standing nanowire films can serve as current collectors in supercapacitors and second skin-like smart masks for facial expression detection.