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...

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.

We have recently demonstrated that vertically aligned gold nanowires (v-AuNWs) are outstanding material candidates for wearable biomedical sensors toward real-time and noninvasive health monitoring because of their excellent tunable electrical conductivity, biocompatibility, chemical inertness, and wide electrochemical window. Here, we show that v-AuNWs could also be used to design a high-performance wearable pressure sensor when combined with rational structural engineering such as pyramid microarray-based hierarchical structures. The as-fabricated pressure sensor featured a low operation voltage of 0.1 V, high sensitivity in a low-pressure regime, a fast response time of <10 ms, and high durability with stable signals for the 10 000 cycling test. In conjunction with printed electrode arrays, we could generate a multiaxial map for spatial pressure detection. Furthermore, our flexible pressure sensor could be seamlessly connected with a Bluetooth low-energy module to detect high-quality artery pulses in a wireless manner. Our solution-based gold coating strategy offers the benefit of conformal coating of nanowires onto three-dimensional microstructured elastomeric substrates under ambient conditions, indicating promising applications in next-generation wearable biodiagnostics.

An artificial basilar membrane (ABM) is an acoustic transducer that mimics the mechanical frequency selectivity of the real basilar membrane, which has the potential to revolutionize current cochlear implant technology. While such ABMs can be potentially realized using piezoelectric, triboelectric, and capacitive transduction methods, it remains notoriously difficult to achieve resistive ABM due to the poor frequency discrimination of resistive‐type materials. Here, a point crack technology on noncracking vertically aligned gold nanowire (V‐AuNW) films is reported, which allows for designing soft acoustic sensors with electric signals in good agreement with vibrometer output—a capability not achieved with corresponding bulk cracking system. The strategy can lead to soft microphones for music recognition comparable to the conventional microphone. Moreover, a soft resistive ABM is demonstrated by integrating eight nanowire‐based sensor strips on a soft trapezoid frame. The wearable ABM exhibits high‐frequency selectivity in the range of 319–1951 Hz and high sensitivity of 0.48–4.26 Pa−1. The simple yet efficient fabrication in conjunction with programmable crack design indicates the promise of the methodology for a wide range of applications in future wearable voice recognition devices, cochlea implants, and human–machine interfaces.

Two-dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few-layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co-existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier-transformed alternating current voltammetry (FTacV) are attributed to CO reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO is the rate determining step for bismuth catalysed CO reduction.

We report on unconventional Janus material properties of vertically aligned gold nanowire films that conduct electricity and interact with light and water in drastically different ways on its two opposing sides. These Janus-like properties originate from enokitake-like nanowire structures, causing the nanoparticle side ("head") to behave like bulk gold, yet the opposing nanowire side ("tail") behaves as discontinuous nanophases. Due to this Janus film structure, its head side is hydrophilic but its tail side is hydrophobic; its head side reflects light like bulk gold, yet its tail side is a broadband superabsorber; its tail side is less conductive but with tunable resistance. More importantly, the elastomer-bonded Janus film exhibits unusual mechatronic properties when being stretched, bent, and pressed. The tail-bonded elastomeric sheet can be stretched up to ∼800% strain while remaining conductive, which is about 10-fold that of head-bonded film. In addition, it is also more sensitive to bending forces and point loads than the corresponding tail-bonded film. We further demonstrate the versatility of nanowire-based Janus films for pressure sensors using bilayer structures in three different assembly layouts.