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The development of ultra-compliant power sources is crucial for their seamless integration with next-generation skin-like wearable and implantable biomedical systems for long-term health monitoring. Toward this goal, stretchable energy storage and conversion devices (ESCDs), including supercapacitors, lithium-ion batteries (LIBs), solar cells, and generators are now attracting intensive worldwide research efforts. The purpose of this review is to discuss the latest achievements in the development of such stretchable energy devices in the context of biomedical applications. We first review the viable strategies and methodologies of fabricating stretchable energy storage and conversion devices. Then, we focus on description of various types of soft energy devices from a materials point of view. Furthermore, we discuss the challenges and opportunities in the design of truly conformal soft energy systems, including various key parameters, such as energy density, stability, and scalability. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Wetting behaviors on stretchable supports are very common in our daily lives, however, received limited attention even they show promising potentials in flexible electronics and other fields. In this study, stretchable wetting behaviors of conductive liquids deposited onto two horizontal rubber fibers are investigated. A firm liquid/solid interaction during the stretching process can contribute to a stable liquid bridge between the fibers even under extremely stretching, showing their proof-to-principle ability to monitor human movement toward early diagnosis of Parkinson's disease or sports injury prevention. [ABSTRACT FROM AUTHOR]

Conventional fuel cells are based on rigid electrodes, limiting their applications in wearable and implantable electronics. Here, it is demonstrated that enokitake‐like vertically‐aligned standing gold nanowires (v‐AuNWs) can also serve as powerful platform for stretchable fuel cells by using ethanol as model system. Unlike traditional fuel cell electrodes, the v‐AuNWs have "Janus Morphology" on both sides of the film and also are highly stretchable. The comparative studies demonstrate that tail side exposed v‐AuNWs based stretchable electrodes outperform the head‐side exposed v‐AuNWs toward the electro‐oxidation of ethanol due to the direct exposure of high‐surface‐area nanowires to the fuels. Therefore, a stretchable fuel cell is fabricated utilizing tail side based interdigitated electrodes, where v‐AuNWs and Pt black modified v‐AuNWs serve as the anode and cathode, respectively. The as‐prepared stretchable fuel cell exhibits good overall performance, including high power density, current density, open‐circuit voltage, stretchability, and durability. Most importantly, a wearable fuel cell is also achieved by integrating tattoo‐like interdigitated electrodes with a thin layer of sponge as a fuel container, exhibiting good performance under various deformations (compression, stretching, and twisting). Such attractive performance in conjunction with skin‐like in‐plane design indicates its great potential to power the next‐generation of wearable and implantable devices. [ABSTRACT FROM AUTHOR]