Researchers have created a groundbreaking liquid ink that can be printed directly onto the scalp, offering a less intrusive alternative to traditional EEG (electroencephalography) methods for tracking brain activity. This new innovation opens up new possibilities for brain-computer interface technologies by allowing for continuous monitoring of brainwaves more comfortably and efficiently.

Innovative Ink for Brain Activity Monitoring

For the first time, scientists have developed a liquid ink that can be printed onto a patient’s scalp, providing a simpler and more efficient way to monitor brain activity. This advancement, published on December 2 in Cell Biomaterials, not only simplifies the tracking of brainwaves but also has the potential to enhance non-invasive brain-computer interface technologies.

“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,” says Nanshu Lu, co-corresponding author and researcher at the University of Texas at Austin.

A Game Changer for EEG with E-Tattoos

EEG is a crucial tool for diagnosing neurological conditions, such as seizures, brain tumors, epilepsy, and brain injuries. However, traditional EEG setups are cumbersome and time-consuming, often requiring patients to sit still for hours while electrodes are glued to the scalp and connected to data-collection machines through wires.

Lu and her team have been working on electronic tattoos (e-tattoos) that can track bodily signals from the surface of the skin. These tattoos have already been used for heart rate monitoring, muscle fatigue detection, and even measuring sweat components.

Overcoming Past Challenges

Previous e-tattoos were ineffective on hairy skin, which made them difficult to use for brainwave monitoring on the scalp. To address this, the researchers designed a conductive liquid ink that can pass through hair and adhere directly to the scalp. Once dry, the ink forms a thin-film sensor that is capable of tracking brain activity in real time.

The process involves using a computer algorithm to determine the spots for EEG electrodes on the patient’s scalp. A digitally controlled inkjet printer then sprays the e-tattoo ink onto those spots. This method is quick, non-invasive, and doesn’t cause discomfort for the patient.

E-Tattoos vs. Traditional EEG

In tests conducted on five participants with short hair, the e-tattoos performed similarly to traditional EEG electrodes in detecting brainwaves with minimal interference. Over a six-hour period, the gel on conventional EEG electrodes began to dry out, causing more than a third to fail and the remaining electrodes to lose contact with the skin, resulting in less accurate readings. In contrast, the e-tattoo electrodes maintained stable connectivity for up to 24 hours.

Researchers also improved the ink formula and added e-tattoo lines that run from the electrodes down to the base of the head, effectively replacing the wires used in traditional EEG setups. These printed wires ensured that signals were transmitted without introducing additional interference.

Advancing Brain-Computer Interface Technology

The potential impact of this technology on brain-computer interfaces (BCIs) is enormous. BCIs allow users to control external devices through brain activity, making them valuable for individuals with mobility impairments. However, current BCI systems often require large, cumbersome headsets. E-tattoos offer the possibility of embedding the electronics directly onto the patient’s scalp, reducing the need for bulky equipment.

“Our study can potentially revolutionize the way non-invasive brain-computer interface devices are designed,” says José Millán, co-corresponding author from the University of Texas at Austin. With e-tattoos, BCI devices could become more accessible and comfortable for users, replacing external devices with on-scalp electronics.

Looking Toward the Future

In future developments, the team plans to integrate wireless transmitters into the e-tattoos, making the entire EEG process wireless. This would provide a truly portable and non-intrusive method for continuous brainwave monitoring.

Reference: “On-scalp printing of personalized electroencephalography e-tattoos,” Scalco de Vasconcelos et al., 2 December 2024, Cell Biomaterials. DOI: 10.1016/j.celbio.2024.100004