Scientists have created a new type of liquid ink that can be printed onto a patient’s scalp to monitor brain activity. This innovative technology, highlighted in the December 2 edition of the journal Cell Biomaterials, presents a promising substitute for the currently intricate methods used for brainwave analysis and diagnosing neurological disorders. It also shows promise for improving non-invasive brain-computer interface systems.
Recently, researchers have developed a liquid ink that allows doctors to print directly onto a patient’s scalp to assess brain activity. Introduced on December 2 in the journal Cell Biomaterials, this technology could serve as a much simpler alternative to the complex current methods used for tracking brainwaves and diagnosing neurological issues. Additionally, it could improve applications of non-invasive brain-computer interfaces.
“Our advancements in sensor technology, biocompatible ink, and rapid printing techniques are paving the path for the creation of electronic tattoo sensors on the body, with extensive uses in both clinical and other areas,” states Nanshu Lu, one of the lead authors from the University of Texas at Austin.
Electroencephalography (EEG) is crucial for diagnosing numerous neurological conditions like seizures, brain tumors, epilepsy, and head injuries. In conventional EEG procedures, technicians measure the scalp with rulers and pencils, marking multiple points for attaching electrodes, which connect to a data-gathering device via long cables to monitor brain activity. This method is often lengthy and cumbersome and can be uncomfortable for patients, who typically must endure a prolonged testing period.
Lu and her team have been at the forefront of developing small sensors to pick up bodily signals from the skin’s surface, a technology referred to as electronic tattoos, or e-tattoos. These e-tattoos have been applied on various parts of the body, such as the chest to monitor heart activities, on muscles to assess fatigue, and even under the armpit to analyze sweat components.
Previously, e-tattoos were printed onto thin adhesive layers before being transferred to the skin, but this method only worked on areas without hair.
“Creating materials suitable for use on hairy skin has been a long-standing issue in e-tattoo technology,” explains Lu. To address this, the team has developed a liquid ink made from conductive polymers. This ink is capable of flowing through hair to reach the scalp, and once it dries, it functions as a thin-film sensor that can detect brain activity through the scalp.
By using a computer algorithm, the researchers can define where EEG electrodes should be placed on the scalp. They then utilize a digital inkjet printer to precisely spray a layer of the e-tattoo ink onto the specified areas. This method is rapid, non-invasive, and does not cause discomfort to the patients, according to the researchers.
The research team applied e-tattoo electrodes on the scalps of five individuals with short hair and placed traditional EEG electrodes alongside them. They discovered that the e-tattoos efficiently detected brainwaves with minimal interference.
After six hours, the gel on the standard electrodes began to dry, resulting in over a third of these electrodes failing to detect any signals. The remaining electrodes experienced reduced contact with the skin, leading to less accurate readings. In contrast, the e-tattoo electrodes maintained consistent connectivity for at least 24 hours.
The researchers also modified the ink’s formulation to create printed lines that extend from the electrodes down to the base of the head, replacing the wires used in conventional EEG setups. “This adjustment allowed the printed connections to transmit signals without interference,” notes co-author Ximin He from the University of California, Los Angeles.
The team subsequently connected shorter wires between the e-tattoos to a compact device that gathers brainwave data. They suggested plans to embed wireless data transmitters into the e-tattoos for a fully wireless EEG setup in the future.
“Our research could potentially transform how non-invasive brain-computer interface devices are developed,” adds co-author José Millán from the University of Texas at Austin. These brain-computer interface devices measure brain activities linked to functions like speech or movement, enabling users to control external devices without physical movement. Presently, these devices often require bulky headsets, but e-tattoos may replace these cumbersome external devices by printing the necessary electronics directly onto a patient’s scalp, enhancing accessibility for brain-computer interface technology, according to Millán.
