On-Scalp Printing of Personalized EEG E-Tattoos

Electroencephalography (EEG) is a non-invasive method essential for diagnosing neurological conditions and enabling brain-computer interfaces (BCI). Traditional EEG setups, which rely on wet conductive gels and cumbersome cables, are often labor-intensive, uncomfortable, and prone to signal degradation. Although e-tattoos—soft, skin-conformable wearable devices—have advanced various biomedical applications, they have struggled with EEG compatibility due to hair interference. Here, we report a significant advancement in EEG e-tattoo technology through the automated, on-scalp but non-contact printing of biocompatible and electrically conductive inks. Our PEDOT:PSS-based inks are specially designed for low-skin-contact-impedance electrodes and highly conductive interconnects, can be jetted through hair, dampen the scalp, and rapidly self-dry into ultrathin, skin-soft, and stretchable films. This innovation markedly enhances breathability and longevity compared to traditional gel electrodes, as well as hair compatibility and skin adhesion compared to transferred e-tattoos. Our manufacturing system employs an automated sensor layout design algorithm, customized for individual head shapes, in conjunction with a 5-axis printing robot to achieve safe and precise sensor placement. These printed e-tattoos successfully capture critical EEG markers, such as motion imagery (MI) and error-related potentials (ErrP), representing a transformative step towards personalized, comfortable, and long-term EEG monitoring.