# Recent Advances in Fiber-Shaped Electronic Devices for Wearable Applications
## 5 Challenges and Outlook  
During the past decade, research into 1D electronic devices has grown rapidly due to their potential as promising structural and functional components of future electronics. However, fiber electronics still suffer from several problems, such as high power consumption, low integration density, poor mechanical and environmental stability, and complex fabrication methods [35]. For instance, FETs using fiber and textile structures show low field-effect mobilities and low on-current states that offer considerably worse performance than those made using flexible planar substrates. Therefore, the electrical performance of 1D devices needs to be improved, while maintaining fiber structures with good mechanical properties. Additionally, 1D devices should be protected by encapsulation because of the  
Figure 8: **(a)** Left: Schematic of the woven display textile. Each contacting luminescent warp and transparent conductive wet forms an EL unit (inset). Right: photograph of a multicolor display textile under complex deformations. **(b)** Left: photograph of an integrated textile system composed of display, information input, and power supply modules. Right: system-level block diagram of the integrated textile system **(c)** Left: conceptual illustration presents the idea that textiles integrated with a display and keyboard can be used as a communication platform. Middle: information is input onto the clothing by pressing the keys that are woven into the textile. Right: receiving and sending messages between the integrated textile system and a smartphone. **(a–c)** Reproduced with permission Ref. [20]. Copyright 2021, Springer Nature. **(d)** Schematic illustration of the scalable manufacturing of tactile sensing textiles using a customized coaxial piezoresistive fiber fabrication system and digital machine knitting. A commercial conductive stainless-steel thread is coated with a piezoresistive nanocomposite. **(e)** Examples of tactile frames collected during human–environment interactions, and their applications explored using machine learning techniques. **(d,e)** Reproduced with permission Ref. [83]. Copyright 2021, Springer Nature. high sensitivity of many active and electrode materials to oxygen and moisture in the atmosphere, which could accelerate device degradation [2]. Another critical issue in the field of fiber electronics is developing suitable electrodes and a predominant technology for connecting 1D devices. Most emerging wearable devices include many connecting electrodes that interact with other functional devices. Those interactions exchange information between the external environment and the human body. Electrode materials are typically more rigid than either human bodies or fabric. Therefore, wearable electrodes must be made to withstand human motion, moisture, and the mechanical stress of deforming fabric. Designing and interfacing electrodes with soft materials are thus one of the major barriers to the implementation of electronic fibers. Wearable electrodes surrounded by active layers need to be structurally stable to prevent disconnection, delamination, and cracks during deformation. Although 1D stretchable and flexible electrodes have been studied extensively, their long-term stability is much lower than expected. Despite the realization of various stretchable systems, effective long-term connections between circuit elements in fiber systems are still technically difficult. On the one hand, it is extremely important to find new and efficient conductive threads that can be industrially woven or knit. On the other hand, comfortable and stable electrodes that are suitable for fiber substrates should be developed to realize their practical applications. Reliable operation and long-term durability, such as resistance to washing and temperature changes, are also important requirements to meet before smart e-textiles can be blended into garments.