Mask‐Free Direct Printing of Highly Customizable, Conformable, Robust, and Recyclable Microelectrodes for Advanced Curvy Electronics

Highly conformal and mechanically robust curvy electronics that seamlessly adapt to sophisticated and unpredictable 3D geometries provide breakthrough solutions in advanced fields such as health monitoring, wireless energy transmission, and human-computer interface. Nevertheless, existing material choices along with manufacturing techniques substantially impede these electronics from achieving their full potential. This study presents a mask-free and straightforward direct writing and transfer (DW&T) technique that employs a polytetrafluoroethylene film as a temporary substrate, utilizing the phase transition of printed electrodes between hydrogel and dry states to enable cost-effective fabrication of conformally adhering conductive microelectrode patterns on nearly all 3D surfaces. The resultant microelectrodes demonstrate extensively adjustable feature dimensions (linewidth 50-400 µm; height 0.07-2.3 µm; pitch 20 µm in minimum) and possess distinct electrical and optical characteristics, in addition to exhibiting significant stability under severe bending and stretching strains and recyclability. To demonstrate the capabilities of the DW&T, imperceptible and customizable substrate-free electronic skin (e-skin) on human skin is developed. The e-skin maintains ultraconformal and seamless contact with the skin, does not impede the natural sensations and physiological changes of its hosts, and achieves high-fidelity recording of diverse electrophysiological signals.