A Nature‐Inspired,Flexible Substrate Strategy for Future Wearable Electronics

Flexibility plays a vital role in wearable electronics. Repeated bending often leads to the dramatic decrease of conductivity because of the numerous microcracks formed in the metal coating layer, which is undesirable for flexible conductors. Herein, conductive textile‐based tactile sensors and metal‐coated polyurethane sponge‐based bending sensors with superior flexibility for monitoring human touch and arm motions are proposed, respectively. Tannic acid, a traditional mordant, is introduced to attach to various flexible substrates, providing a perfect platform for catalyst absorbing and subsequent electroless deposition (ELD). By understanding the nucleation, growth, and structure of electroless metal deposits, the surface morphology of metal nanoparticles can be controlled in nanoscale with simple variation of the plating time. When the electroless plating time is 20 min, the normalized resistance (R/R₀) of as‐made conductive fibers is only 1.6, which is much lower than a 60 min ELD sample at the same conditions (R/R₀ ≈ 5). This is because a large number of unfilled gaps between nanoparticles prevent metal films from cracking under bending. Importantly, the Kelvin problem is relevant to deposited conductive coatings because metallic cells have a honeycomb‐like structure, which is a rationale to explain the relationships of conductivity and flexibility.     

Polymer‐Assisted Metal Deposition (PAMD) for Flexible and Wearable Electronics: Principle,Materials, Printing,and Devices

The rapid development of flexible and wearable electronics favors low‐cost, solution‐processing, and high‐throughput techniques for fabricating metal contacts, interconnects, and electrodes on flexible substrates of different natures. Conventional top‐down printing strategies with metal‐nanoparticle‐formulated inks based on the thermal sintering mechanism often suffer from overheating, rough film surface, low adhesion, and poor metal quality, which are not desirable for most flexible electronic applications. In recent years, a bottom‐up strategy termed as polymer‐assisted metal deposition (PAMD) shows great promise in addressing the abovementioned challenges. Here, a detailed review of the development of PAMD in the past decade is provided, covering the fundamental chemical mechanism, the preparation of various soft and conductive metallic materials, the compatibility to different printing technologies, and the applications for a wide variety of flexible and wearable electronic devices. Finally, the attributes of PAMD in comparison with conventional nanoparticle strategies are summarized and future technological and application potentials are elaborated.     

Recent Progress of Textile‐Based Wearable Electronics: A Comprehensive Review of Materials,Devices, and Applications

Wearable electronics are emerging as a platform for next‐generation, human‐friendly, electronic devices. A new class of devices with various functionality and amenability for the human body is essential. These new conceptual devices are likely to be a set of various functional devices such as displays, sensors, batteries, etc., which have quite different working conditions, on or in the human body. In these aspects, electronic textiles seem to be a highly suitable possibility, due to the unique characteristics of textiles such as being light weight and flexible and their inherent warmth and the property to conform. Therefore, e‐textiles have evolved into fiber‐based electronic apparel or body attachable types in order to foster significant industrialization of the key components with adaptable formats. Although the advances are noteworthy, their electrical performance and device features are still unsatisfactory for consumer level e‐textile systems. To solve these issues, innovative structural and material designs, and novel processing technologies have been introduced into e‐textile systems. Recently reported and significantly developed functional materials and devices are summarized, including their enhanced optoelectrical and mechanical properties. Furthermore, the remaining challenges are discussed, and effective strategies to facilitate the full realization of e‐textile systems are suggested.