Ultraflexible tattoo electrodes for epidermal and in vivo electrophysiological recording

Tattoo electronics, flexible patches that mount directly onto the skin with the ease and flexibility of a temporary tattoo, have foreseen remarkable application potentials in personalized healthcare monitoring and human-machine interfaces. Documented tattoo electronics mostly have an on-skin form factor to date. Using dermal tattoos for in vivo diagnostics presents an unexplored paradigm. Here, we extend the application scenario of "tattoo electrodes" from an on-skin fashion to an actual under-skin configuration, enabled by a highly soft, conductive, and biocompatible polymer matrix. With printed ultrathin electrodes, we achieve a record-high conductivity and record-low skin contact impedance, allowing the design of a single-lead electrocardiogram system for seamless wearing and precise detection of intervals and rhythms in dynamic conditions. Furthermore, the biocompatible ink enables the development of dermal electrodes by virtue of tattoo artistry. It shows enormous potential for electrical communication between bioelectronics and biological tissues at a deep-tissue level.