P. Vidal
University of Texas at Austin,
United States
Keywords: EEG, e-tattoos, printing, robot, hair-compatible
Summary:
Electroencephalography (EEG) is a non-invasive technique that records brain activity from the scalp, offering the advantage of high temporal resolution, affordability, and versatility compared to alternative modalities such as functional magnetic resonance imaging (fMRI) and invasive electrocorticography (ECoG). It has been widely used in sleep monitoring, clinical diagnosis and treatment of neurological disorders, and brain-computer interfaces (BCIs). Current clinically used electrodes, including conductive gel and conductive paste, require precise manual positioning by trained professionals, making the process labor-intensive and inconvenient for both patients and clinicians. In addition, these electrodes tend to dehydrate over time, resulting in compromised signal quality and limiting their use for long-term recordings. Dry electrodes, particularly ultrathin tattoo-like designs, can achieve stable, long-term EEG recordings, owing to their conformal contact with the skin. However, these electrodes can only record signals from hairless regions. It is still challenging to apply these electrodes to the hairy scalp due to hair interference. We introduce a non-contact, on-body digital printing technology that allows high-throughput, personalized e-tattoo printing on human hairy scalp. This advanced manufacturing process combines individualized 3D head scans with a custom electrode layout algorithm, enabling rapid and automated placement compared to the labor-intensive methods used in conductive gel/paste-based systems. Using a five-axis microjet printing robot, the process ensures safe and uniform ink deposition through the hair by maintaining a perpendicular jetting axis at a fixed distance from the scalp, effectively overcoming the limitations of traditional e-tattoo electrodes. Through the rational design of ionic-electrically conductive electrode ink with low contact impedance and highly electrically conductive interconnect ink, the printed e-tattoo eliminates traditional wiring and suppresses signal interference. After printing, these inks self-dries into micrometer-thin conductive membranes, forming a low-impedance, long-term stable interface with the skin while remaining breathable and easy to remove. With the introduction of the adhesive additives, the electrodes maintained stable EEG recording performance for 48 hours, even under mechanical deformation and external abrasion. Physiologically imperceptible to the wearer, the printed e-tattoo is compatible with other setups, such as VR headsets, enabling stable EEG recording in a virtual reality environment. This personalized advanced manufacturing technology has the potential to transform BCIs across various industries, including neurological research, prosthetics control, virtual reality integration, and human-robot interactions. It also opens the door to on-body digital manufacturing of other e-tattoo devices for applications beyond the head, enabling large-area, skin-conformal, and multifunctional wearable systems.