An In Situ Assembled, Sprayable Poly(Lipoic Acid) E‐Tattoo for Multimodal Health Monitoring

ABSTRACT Wearable electronics show promise in advancing personalized healthcare, with electronic skins (e‐skins) emerging as ideal candidates due to their intimate skin conformability. However, their widespread adoption is constrained by complex fabrication, insufficient conformability, and suboptimal biocompatibility. Herein, we propose a poly(lipoic acid)‐based sprayable electronic tattoo (LS e‐tattoo) formulated from lipoic acid (LA), tannic acid (TA), and silver flakes. This strategy uses spray‐coating for rapid polymerization, followed by a Zn 2+ spray for curing. As a result, a conformal, breathable, biocompatible, and robust conductive network forms in situ on the skin within 3 min. The secondary‐cured LS e‐tattoo exhibits an ultralow contact impedance of 95 kΩ at 50 Hz. The device also shows less than 1% resistance variation after 1,500 bending cycles, confirming its mechanical robustness. An integrated epidermal sensing system was further developed. This platform enables synchronous sweat chloride detection (12.5–70 mM, R 2 = 0.992). Concurrent measurements include body surface temperature (error < 0.1°C) and skin hydration ( R 2 = 0.998), while high‐fidelity electromyography signals (SNR: 14.4 dB) are acquired simultaneously. By combining in situ conformal integration with rapid on‐demand fabrication, this work offers a versatile platform for customized e‐skins.