With so few people equipped with these devices, their longevity is still unknown. So far, the Utah network has lasted up to 10 years in monkeys. In Copeland’s case, his arrays still work, but not as well as they did in the first year after they were implanted, says Robert Gaunt, a biomedical engineer at the University of Pittsburgh and a member of Copeland’s research team. . “The body is a very difficult place to put engineering electronics and systems,” Gaunt says. “It’s an aggressive environment, and the body is always trying to get rid of these things.”
Implanted chips can provoke an immune response in the neural tissue that surrounds the electrodes, the sharp probes that stick into the brain. Studies have shown that this inflammation can lead to a decrease in signal quality. And scar tissue can form around brain implants, which also affects their ability to pick up signals from nearby neurons. The less a BCI can interpret information coming from neurons, the less efficient it is at performing its intended functions.
In particular, scientists are trying to extend the life of implants by experimenting with different types of materials. The Utah network is insulated with parylene, a protective polymer coating used in the medical device industry for its stability and low moisture permeability. But it can corrode and crack over time, and other materials may prove more durable.
Florian Solzbacher, co-founder and president of Blackrock Neurotech, which makes the Utah arrays, said the company was testing one coated with a combination of parylene and silicon carbide, which has been around as a material for more than 100 years. industrial. “We’ve seen benchtop lifespans of up to 30 years, and we currently have preliminary data in animals,” he says. But the company hasn’t implanted it in humans yet, so the real test will be how human tissue reacts to the new formulation.
Making the electrodes more flexible could also help reduce scarring. Angle’s Paradromics company is developing an implant similar to the Utah array, but with thinner electrodes intended to disrupt tissue less.
Some researchers are trying softer materials that might fit better in the brain than the stiff Utah lattice. A group at the Massachusetts Institute of Technology is experimenting hydrogel coatings designed to have an elasticity very similar to that of the brain. Scientists at the University of Pennsylvania are also developing “live” electrodescapillary microtissues made up of neurons and nerve fibers from stem cells.
But these approaches also have drawbacks. “You can get a stiff thing in a soft thing. But if you’re trying to put a very soft thing into another soft thing, it’s very difficult,” Gaunt says.
Another approach is to make the implants smaller, and therefore less invasive. For example, the researchers are testing neurograins, tiny shavings the size of a grain of sand that could hypothetically be sprinkled on the cortical surface. But no one has tried to disperse them on a human brain; the system has only been tested on rodents whose skulls have been removed.