Humans, however, are very different beasts, and Berggren knows from experience that what works in one organism doesn’t always work in another. For this project, he started by trying to use a molecule he had previously designed to form a conductive polymer in plants. But when he tried to use the molecule in animals, nothing happened. “The first year of this project was a complete failure,” he says.
Eventually, Xenofon Strakosas, an assistant professor working in Berggren’s lab, figured out the problem: In plants, hydrogen peroxide helps the injected material bind together, but there isn’t enough peroxide in animals. for the reaction to work. So Strakosas added a few more things to the mix: an enzyme that uses glucose or lactate, which are common in animal tissues, to produce peroxide, and another enzyme that breaks down peroxide. Suddenly, the electrodes formed perfectly.
For experts like Maria Asplund, professor of bioelectronic microtechnology at Chalmers University of Technology in Sweden, the idea of forging electrodes inside the body is totally new. “Chemists can make things happen that I never imagined,” she says. But Asplund, which has spent more than a decade working to create more brain-friendly electrodes, doesn’t plan to abandon its proven methods for creating electrodes just yet. For one, this new tool has not been tested on mammals and no one knows how long it will last inside the body. More importantly, although electrodes may be able to successfully conduct electrical signals, Berggren and his colleagues have no solution for getting those signals out of the brain so scientists can actually see them, or for sending current so that the electrodes can be used for brain stimulation.
They have a number of options. One would be to stick an insulated wire directly into the electrode to carry its signals from deep within the brain to the surface of the skull, where scientists could measure them. This wire, however, could damage brain tissue, which the team is trying to avoid. Instead, they can try to design other components that, like the electrode, could self-assemble in the brain so that a signal could be read wirelessly from the outside.
If Berggren and his colleagues figure out how to communicate with their electrodes, they’ll still have a hard time competing with cutting-edge devices like Neuropixels, which can record from hundreds of neurons at once. Achieving that degree of precision with a soft electrode could prove difficult, says Jacob Robinson, an associate professor of electrical and computer engineering at Rice University in Texas. “There’s usually a trade-off between performance and invasiveness,” he says. “The engineering challenge is to push that limit.”
At least to start with, brain stimulation might be a better application for soft electrodes because it doesn’t need to be so precise. And even inaccurate recordings could benefit completely paralyzed people, says Aaron Batista, a professor of bioengineering at the University of Pittsburgh who studies brain-computer interfaces in monkeys. Soft electrodes might not be able to produce fluent speech by directly measuring someone’s brain signals, but for patients who can’t move at all, just being able to convey “yes” or “no” would a huge difference.