Medicine these days entertains all kinds of ambitious plans for reading off brain signals to control wheelchairs, or using electronics to bypass spinal injuries. But most of these ideas for implants that can interface with the nervous system run up against a basic materials problem: wires are stiff and bodies are soft.
What’s new is how stretchable electronics are merging with a widening effort to invent new ways to send and receive signals from nerves. “People are pushing the limits because everyone wants to precisely interact with the brain and nervous system,” says Polina Anikeeva
That motivated some researchers at the École Polytechnique Fédérale, in Lausanne, Switzerland, to design a soft, flexible electronic implant, which they say has the same ability to bend and stretch as dura mater, the membrane that surrounds the brain and spinal cord.
The scientists, including Gregoire Courtine, have previously showed that implants can allow mice with spinal injuries to walk again. They did this by sending patterns of electrical shocks to the spinal cord via electrodes placed inside the spine. But the rigid wires ended up damaging the mice’s nervous systems.
The reason metal or plastic electrodes eventually cause damage, or stop working, is that they cause compression and tissue damage. A stiff implant, even if it’s very thin, will still not stretch as the spinal cord does. “It slides against the tissue and causes a lot of inflammation,” says Lacour. “When you bend over to tie your shoelaces, the spinal cord stretches by several percent.”
The implant mimics a property of human tissue called viscoelasticity—somewhere between rubber and a very thick fluid. Pinch the skin on your hand with force and it will deform, but then flow back into place.
The ultimate aim of this kind of research is an implant that could restore a paralyzed person’s ability to walk. Lacour says that is still far off, but believes it will probably involve soft electronics. “If you want a therapy for patients, you want to ensure it can last in the body,” she says. “If we can match the properties of the neural tissue we should have a better interface.”
Bendable Implant Taps Nervous System With No Damage.