Scientists have created temporary tattoos that can be sprayed onto the scalp as a non-intrusive method to measure brain activity.

A study published in Cell Biomaterials has shown how liquid ink printed onto a patient’s scalp could monitor high-quality brain activity.

The invention, known as EEG e-tattoos, may also have the potential to improve devices and applications that scientists use to repair sensory-motor and cognitive functions in the human brain.

“Our study can potentially revolutionize the way non-invasive brain-computer interface devices are designed,” says José Millán, author of the study and Chair of Neuroengineering at the University of Texas at Austin.

An Electroencephalograph (EEG) is a test that doctors use to measure the electrical activity of a brain. Analysing these brainwaves can help diagnose and monitor conditions such as brain tumours, epilepsy and brain injuries.

Currently, setting up an EEG is time-consuming. Patients have to sit and wait as a technician measures their head with pencils and rulers before placing the electrodes on the patient’s head manually.

Traditionally, EEGs also involve using bulky cables which can be uncomfortable and are also prone to signal degradation over time.

“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, one of the authors of the study.

Using the patient’s 3D head scan, the technology uses a computer algorithm to determine where the EEG electrodes should be placed on a patient’s scalp.

Printing electrodes on a hairy scalp. Credit: Nanshu Lu

Lu’s team then operates a digitally controlled inkjet printer which sprays a thin layer of ink on the electrode spots.

The ink goes through the hair until it reaches the scalp. Once the ink has dried, it acts as a thin-film sensor that can measure brain activity. To collect the brain wave data, wires are attached to the tattoos although in the team hopes to create a fully wireless EEG experience.

Unlike a traditional EEG, the process causes no discomfort to patients, the researchers say. 

Lu and her team have previously worked on similar e-tattoos that can be used on the chest for Seismocardiography (SCG) tests too.

However, these previous e-tattoos have only been effective on hairless areas of the body and require a thin layer of adhesive material before being placed on the skin.

“Designing materials that are compatible with hairy skin has been a persistent challenge in e-tattoo technology,” Lu says.

To solve this issue, Lu and her team created the liquid from conductive polymers, meaning they can conduct electricity.

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