Researchers at the University of Texas and the University of California, Los Angeles (UCLA) say they have created a liquid ink that can be directly printed onto a patient’s scalp to measure brain activity, offering an alternative to traditional electroencephalography (EEG). The new technology, detailed in the journal Cell Biomaterials, is part of ongoing research into electronic tattoos (e-tattoos) and their potential to improve both clinical diagnostics and brain-computer interface applications.
“Our innovations in sensor design, biocompatible ink, and high-speed printing pave the way for future on-body manufacturing of electronic tattoo sensors, with broad applications both within and beyond clinical settings,” said lead researcher Nanshu Lu, PhD, whose lab at the University of Texas at Austin focuses on the development of bio-integrated electronics.
EEGs are commonly used to diagnose neurological conditions such as epilepsy, brain tumors, and injuries. The current technology involves applying multiple electrodes to the scalp using adhesives, which are then connected to a machine via wires to collect brain wave activity. This method is not only time-intensive and uncomfortable but also prone to signal degradation as the adhesive gel dries.
Electronic-tattoo technology has previously been used on the chest to measure heart activity, on muscles to measure fatigue, and on armpits to measure components found in sweat. Early versions usually require the e-tattoo to be printed in a thin layer of adhesive material which was then transferred to the skin. But these methods proved to be effective only on hairless skin. Lu’s team, working with collaborators from UCLA and other institutions, developed an ink made from conductive polymers that can flow through hair to reach the scalp. Once dried, the ink forms a thin-film sensor capable of detecting brain activity.
“Designing materials that are compatible with hairy skin has been a persistent challenge in e-tattoo technology,” Lu said.
The technology leverages a computer algorithm to help design the spots for the EEG electrodes on the patients’ scalps which is then applied by an inkjet printer to a patient’s scalp. The process is quick, contactless, and is not uncomfortable to the patients, the investigators noted.
In a test involving five participants with short hair, the researchers compared the performance of these printed e-tattoos against conventional EEG electrodes. Both methods showed comparable results in detecting brainwaves, but the e-tattoos demonstrated greater longevity and stability. While the gel on standard electrodes began to dry out after six hours—leading to signal loss in over a third of the electrodes—the e-tattoos maintained strong connectivity for at least 24 hours.
The team also replaced traditional EEG wires with inkjet-printed lines that conduct signals directly to a small data-collection device. This adjustment reduced the need for bulky wiring, a significant improvement current methods. “This tweak allowed the printed wires to conduct signals without picking up new signals along the way,” said Ximin He, PhD, co-corresponding author and leader of a lab at UCLA researching “bio-inspired dynamic materials.”
The potential applications of these electronic tattoos extend beyond clinical EEG diagnostics. Brain-computer interfaces (BCIs), which translate neural signals into commands for external devices, could also benefit. Current BCI systems rely on cumbersome headsets to capture brain activity. Electronic tattoos may provide a more efficient alternative by integrating electronics directly onto the scalp.
“Our study can potentially revolutionize the way non-invasive brain-computer interface devices are designed,” said co-author José Millán, PhD a professor of neuroengineering at the University of Texas at Austin. By simplifying the design and application process, electronic tattoos may increase the accessibility of BCIs for individuals with disabilities or other neurological conditions.
