The Quest for Injectable Brain Implants Has Begun

The hard electrodes inserted into the brain to treat Parkinson’s and paralysis damage the organ’s soft tissue. A new invention could change that.

OUR WORLD IS populated by hundreds of thousands of cyborgs. Some are Parkinson’s patients, who can shut off their tremors by activating metal electrodes implanted deep within their brains. Others—albeit far fewer—are completely paralyzed people who can move robotic limbs with their minds, thanks to their own implants. Such technologies can radically improve someone’s quality of life. But they have a major problem: Metal and the brain get along very, very poorly. 

Brains have the texture of Jell-O—push on them too hard, and they’ll come apart into fragile clumps. There’s a violence to probing the brain with wires. “It’s like sticking a knife into the tissue,” says Magnus Berggren, professor of organic electronics at Linköping University in Sweden.

Worse, while electrodes remain relatively fixed in place, the brain jiggles and shifts around them, causing even more injury. The body responds by forming scar tissue, which gradually walls off the electrode from the neurons that it is supposed to record or stimulate. Because of scarring, Utah arrays—the tiny, hairbrush-like devices implanted in the brains of paralyzed people—are typically removed after around five years, and patients who have regained the ability to move or speak once again become silent and still.

Scientists have recognized the extensive damage that electrodes can cause since at least the 1950s. Generations of engineers have labored to solve the problem by crafting ever-smaller and ever-more-flexible devices, but these have their own shortcomings. There’s no good way to get a flexible electrode deep into the brain, and even when placed at the brain’s surface, such electrodes may not function well over long time periods.

But Berggren and his colleagues think they may have developed a solution. Rather than making an electrode outside of the brain and then trying to implant it, they have designed a gel that, when injected into bodily tissue, solidifies into an electrically conductive polymer. The process isn’t unlike pouring molten metal into a mold, except that the gel is apparently harmless, and the electrode, once it forms, is just as soft and movable as the brain tissue around it.

The team published their results in February in the journal Science. So far, they have tested the material in living zebra fish and dead leeches—in both cases, it formed electrodes that could successfully carry a current. And the electrodes seem safe: The zebra fish swam around happily after having the substance pumped into their heads, and when the scientists killed the fish and sliced up their brains, they didn’t see any scarring. Even neurons that ended up fully embedded within the electrodes appeared healthy.

Source: wired.com