Temporary Tattoo-Inspired, Skin-Adaptable Epidermal Electrode from an Ultrathin PU-PVA Film

Long-term, high-fidelity electrophysiological monitoring requires epidermal electrodes that simultaneously offer conformability, breathability, and mechanical durability─attributes rarely achieved in current designs─through a scalable, simple, and low-cost fabrication strategy. We report a 5.2-μm-thick, transparent, air- and vapor-permeable "tattoo" electrode that adheres to the human skin through water-activated hydrogen bonding provided by a NaCl/glycerol/water hydrating solution, echoing the mechanism of temporary tattoos. The fabrication process is easy, efficient, and scalable. The device consists of a poly(vinyl alcohol) matrix reinforced by an electrospun polyurethane nanomesh, yielding an interfacial area adhesion energy of 2060.8 μJ cm^-2, and a low skin contact impedance of 21.0 kΩ at 100 Hz. Unlike conventional hydrogel or dry electrodes, our design needs no external adhesive layer, resists dehydration, and withstands everyday mechanical stress while remaining comfortable to wear. It exhibits an air permeance of 0.94 cm³ cm^-2 s^-1 cmHg^-1, a water-vapor transmission rate of 1856.5 ± 36.9 g m^-2 day^-1, and survives 1000 cycles of 100% uniaxial strain. The electrode also retains >81.4 ± 1.7% of its initial water content after 7 days of storage and maintains its stretchability, adhesion, skin contact impedance, and conductivity even after 60 days. These properties enable reliable, minimized motion artifact acquisition of biosignals during vigorous activities and extended daily use. Finally, we demonstrate wireless surface electromyogram that tracks muscle-recruitment dynamics during strength-training and rehabilitation exercises, including push-ups and climbing, underscoring the potential of the tattoo electrode for real-world wearable health monitoring.