Flexible implants that connect directly to the central nervous system have restored independent movement in laboratory rats. Although the test subjects are rodents, these new devices, which are inspired by neural tissue, represent a step toward long-lasting neural prosthetics that may help people recover abilities lost to brain or spinal injuries, researchers say.
Scientists have been working on such implants for years and some have similarly restored locomotive abilities in previously paralyzed animals. But existing devices are usually rigid and can irritate tissue in the spine or brain. A research team led by Stéphanie P. Lacour and Grégoire Courtine of the Swiss Federal Polytechnic Institute of Lausanne (EPFL) has now developed an implant it calls electronic dura mater, or e-dura, that appears to overcome these problems.
Inspired by the tough but pliable membrane called dura mater that surrounds mammalian brains and spinal cords, the EPFL team built a device with an elasticity much more like biological tissue than earlier implants. Unlike dura mater, however, the new implant can also deliver drugs and communicate electronically with the outside world—hence the name (Science 2015, DOI: 10.1126/science.1260318).
The researchers used a silicone elastomer as e-dura’s substrate, which contains microfluidic channels for drug delivery. Soft electrodes made from a platinum-silicone composite provide a solid but gentle electrical contact with tissue in the brain or spine.
Thin layers of gold run through the polymer like wires, allowing the team to connect the electrodes to equipment outside the body. These gold interconnects are extremely flexible thanks to microscopic cracks that allow the metal to bend and stretch, not unlike an accordion, Lacour says.
“These ideas will help to pave the way toward medical devices of the future,” says John A. Rogers, a materials scientist at the University of Illinois, Urbana-Champaign, who was not involved with the project. “I’m extremely impressed by the work.”
E-dura can remain implanted for months without harming rats, Lacour says. She adds that the device can be used as a diagnostic tool—to monitor brain activity, for instance—or as a neural prosthetic that electrochemically stimulates neural tissue, as the team demonstrated with paralyzed rats.
In that case, the team used the e-dura to stimulate healthy tissue in a rat’s spine beneath the lesion that caused paralysis. This effectively circumvents the injury, enabling the rat to move its legs once more.
There will be challenges in building similar implants for humans, Lacour tells C&EN, but that is exactly where this research is headed. “We are convinced we can translate this technology to humans,” she says. “The question is how long it will take.”