Temporary scalp tattoo can be used to record brain activity

Analysing brainwaves could be made easier by printing a temporary tattoo onto a person’s head.

Electroencephalography (EEG) is a way of measuring electrical activity in the brain via electrodes placed on the scalp. It can be used to test patients for neurological conditions such as epilepsy, tumours or injury from stroke or traumatic impacts to the head.

Because people’s skulls vary in size and shape, technicians have to spend considerable amounts of time measuring and marking the scalp to get accurate readings. A gel helps the electrodes detect brain signals, but it stops working well as it dries. The cables that connect to the electrodes can also cause discomfort and may interfere with subtle electric signals.

Nanshu Lu at the University of Texas at Austin and her team want to avoid these issues by printing a temporary tattoo onto the subject’s scalp. The ink for the tattoo is made of two polymers called poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS). It is highly conductive and durable and doesn’t irritate the skin.

A computer program creates a personalised design of the tattoo based on a 3D scan of the scalp, then a printer controlled by a robotic arm applies the ink straight onto the scalp. There are two different formulations of the ink: one for the electrodes that pick up brain signals and one for connections that run to the back of the neck. From there, physical wires carry the signals to a small device that records the data.

“Our technology embodies the first hair-compatible temporary e-tattoo that allows for high-quality brain monitoring,” says Lu.

The tattoo has been shown to work well on people with bald heads and buzz-cut hairstyles. “While the method has not yet been tested extensively on long, thick, curly hair, modified nozzle designs or incorporating robotic fingers for hair parting could make it feasible in the future,” she says. Data transmitters embedded in the tattoos could also make the process fully wireless, according to the team.