Integration of Electrohydrodynamic Printing and Hydroprinting for the Cost-Effective Fabrication of Microscale Conformal Transparent Electrodes on Diverse Curved Surfaces

Hydroprinting has emerged as a cost-effective solution to transfer planar flexible electronics onto diverse curved surfaces for the fabrication of conformal transparent electrodes (CTEs) in the fields of microelectronics and healthcare monitoring. However, current hydroprinting strategies commonly rely on intricate multiple-step microfabrication processes or inkjet/direct/screen printing, largely limiting accessibility or resolution for microscale CTEs. Here, an integration strategy is proposed by combining electrohydrodynamic printing and hydroprinting, simplifying the fabrication of microscale CTEs with remarkable electrical/thermal/sensing capabilities and robust mechanical stability. Stable electrohydrodynamic printing of microscale silver mesh electrodes on non-conductive water-soluble polyvinyl alcohol films achieves excellent compatibility with diverse curved surfaces and distinct substrate materials. The smallest feature size of the CTEs is 48.5 +/- 3.7 mu m, showing a figure of merit of 1304. Interestingly, the CTEs hydroprinted on rough surfaces demonstrate better adhesion and scratching resistances than those hydroprinted on smooth counterparts, maintaining a negligible sheet resistance increase after 100 cyclic mechanical tests. The CTEs on a cylindrical glass bottle exhibit excellent transparency and electrothermal properties. The CTEs onto human skin for electrocardiogram sensing and monitoring realize a notable 30.24% signal enhancement, improved motion artifact resistance and negligible skin irritation compared to the commercialized Ag/AgCl electrodes.