Spray-Coated Fully Water-Soluble Composites for Waterproof Breathable E-Tattoos

Electronic tattoos (e-tattoos), which can be conformally attached to the human skin for real-time, continuous, and noninvasive sensing of physiological signals, hold great promise for personalized healthcare applications. However, e-tattoos based on these water-soluble materials are easily degraded by sweat in the course of daily exercise, leading to the inaccuracy of human signal sensing for long-term monitoring. Herein, enhanced waterproof breathable e-tattoos via spray deposition of a water-soluble composite ink containing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS), single-walled carbon nanotubes, waterborne polyurethane, and maltitol (as a plasticizer) is developed. The sprayed e-tattoos exhibit a distinctive 3D network structure. This unique architecture endows them with exceptional waterproof properties, excellent conformal adhesion, breathability, and biocompatibility, thereby ensuring their long-term wearability. As epidermal electronic devices, the highly conformal e-tattoos serve as ion-selective interdigital electrodes and seamlessly integrated with a flexible printed circuit board. Such integration enabled wireless, continuous, and real-time monitoring of potassium ion (K + ) concentrations in human sweat during daily activities. Therefore, the waterproof and breathable e-tattoos with excellent comprehensive performance could provide a promising platform for next-generation wearable epidermal electronics.