Ultrathin, Breathable, Permeable, and Skin‐Adhesive Charge Storage Electronic Tattoos Based on Biopolymer Nanofibers and Carbon Nanotubes

Ultrathin, breathable, and skin-compatible epidermal electronics are attractive for wearable and implantable healthcare and biomedical applications. However, materializing and integrating all electronic components on ultrathin platforms is still challenging. Here, a charge-storing electronic tattoo (E-tattoo) device with ultrathin, breathable, and skin-compatible properties is reported. Silk protein nanofibers (SNFs) and carbon nanotubes (CNTs) form the top and bottom electrodes that sandwich the intermediate dielectric layer fabricated using poly(vinyl alcohol) nanofibers. The E-tattoo capacitors on the deformed skin, show excellent mechanical and electrical stability, and 60 mu m-thick capacitors exhibit frequency-dependent capacitances (up to 350 pF at 5 kHz) and capability for memory operation. Mechanical bending induces capacitance change, which increases as the bending radius is decreased, indicating mechanical sensing capability of the E-tattoo. SNF/CNT-based triboelectric nanogenerator E-tattoos can be connected to the capacitor E-tattoo, and the charges generated by multiple bare-finger touches can be stored in the capacitor (0.23 V for 200 touches). Due to the micro/nanopores in the NF networks, the device exhibits a water vapor transmission rate of 115.04 g m(-2) d(-1), which is better than that of a commercial band-aid, as well as ethanol sensing capability. Developed E-tattoo capacitor can be used for constructing multicomponent integrated ultrathin and epidermal electronics.