Stretchable and Soft Organic–Ionic Devices for Body‐Integrated Electronic Systems

Abstract Ion‐conducting polymers such as hydrogels have soft, flexible, and stretchable properties that enable humans to intimately interact with other living things. They are important components of cells, tissue, and organs of the human being. Interestingly, these polymers possess sufficient mobile ions that are more sensitive to external stimuli of tactility, temperature, biological molecules, and electrical polarization than conventional solid‐state materials such as metals and oxides. The objective of this review is to summarize recent advances in such unconventional electronics using soft ion‐conducting polymers in various types of sensors and electronic components for signal processing, stimulation, and display devices for integrated systems. Differences in properties (such as soft and elastic properties, formation of electrical double layer, and direct doping/dedoping of active layer) between ion‐conducting polymer‐based electronic devices and conventional electronics are discussed, considering essential conditions for their biomedical applications, including decreased driving voltage due to mobility of ions, high stability and sensitivity in a biological environment, and biocompatible and biodegradable characteristics. Each part of an integrated system is successfully demonstrated using novel materials and geometries with advanced fabrications and low‐voltage operation for diverse bio‐interfaces. Finally, representative research efforts are introduced for integrating each part of electronics for biomedical applications.