Stretchable conductive nanocomposites and their applications in wearable devices

Recently, highly conductive polymer nanocomposites, particularly soft polymer nanocomposites, have received extensive attention as promising material candidates for wearable devices. Compared with the cases of the wearable devices based on conventional rigid electronic materials, the wearable devices based on polymer nanocomposites exhibit excellent conformal contacts with the skin due to the soft mechanical properties of these nanocomposites; therefore, soft polymeric nanocomposites can be applied to stretchable wirings, electrodes, and sensor units in various on-skin electronics. The types of polymers and nanofillers used for the synthesis of these nanocomposites are critical factors determining the properties of polymer nanocomposites. The overall physical properties of nanocomposites depend on the type of polymer used, whereas the electrical properties of nanocomposites are governed by the type of nanofiller employed. Herein, we review the latest studies on the polymer nanocomposites constructed using different polymers and nanofillers that are applied to wearable devices. We have classified the polymers into non-elastic polymers, hydrogels, chemically crosslinked elastomers, and physically crosslinked elastomers and the nanofillers into C, liquid metal, Ag, Au, and other emerging nanomaterials. Detailed characteristics, fabrication methods, applications, and limitations of these nanocomposites are reviewed. Finally, a brief outlook for future research is provided.