Self-Healable Multifunctional Electronic Tattoos Based on Silk and Graphene

Electronic tattoos (E-tattoos), which can be intimately mounted on human skin for noninvasive and high-fidelity sensing, have attracted the attention of researchers in the field of wearable electronics. However, fabricating E-tattoos that are capable of self-healing and sensing multistimuli, similar to the inherent attributes of human skin, is still challenging. Herein, a healable and multifunctional E-tattoo based on a graphene/silk fibroin/Ca2+ (Gr/SF/Ca2+) combination is reported. The highly flexible E-tattoos are prepared through printing or writing using Gr/SF/Ca2+ suspension. The graphene flakes distributed in the matrix form an electrically conductive path that is responsive to environmental changes, such as strain, humidity, and temperature variations, endowing the E-tattoo with high sensitivity to multistimuli. The performance of the E-tattoo is investigated as a strain, humidity, and temperature sensor that shows high sensitivity, a fast response, and long-term stability. The E-tattoo is remarkably healed after damage by water because of the reformation of hydrogen and coordination bonds at the fractured interface. The healing efficiency is 100% in only 0.3 s. Finally, as proof of concept, its applications for monitoring of electrocardiograms, breathing, and temperature are shown. Based on its unique properties and superior performance, the Gr/SF/Ca2+ E-tattoo may be a promising candidate material for epidermal electronics.