Flexible Spinal Implants Help Paralyzed Rats Walk Again

Researchers have created an ultra-flexible brain implant that may help restore injured spinal cords and nervous systems without inflammation or infection.

“E-dura,” named after the dura mater protective layer of the brain and spinal cord, is composed of soft silicone, with gold wiring laid down in a special mesh-like layer that allows it to bend and stretch. Implants need to be flexible because the spinal cord is flexible — stiff wiring can cause inflammation or even rejection. The e-dura, however, caused no reaction at all in rats in which it was implanted. A more impressive test put e-dura implants in rats that were paralyzed via spinal injury. After a few weeks with e-dura sending electrical and chemical signals along the spinal cord patterned on the rat’s brains’ own “walk” signal, the rats were on their feet again.

It’s not that simple in humans, of course, but having implants that are safe and effective in less complex nervous systems is a promising place to start for human-centric treatment. The research, conducted at the Swiss Federal Institute of Technology (EPFL), appears in the Jan. 9 issue of the journal Science.

An Easy-Does-It Implant
Flexible and stretchy, the implant developed by Swiss researchers is placed beneath the dura mater, directly onto the spinal cord. Its elasticity and its potential for deformation are almost identical to the living tissue surrounding it. This reduces friction and inflammation to a minimum. When implanted into rats, the e-Dura prototype caused neither damage nor rejection, even after two months. More rigid traditional implants would have caused significant nerve tissue damage during this period of time, according to experts.

The researchers tested the device prototype by applying their rehabilitation protocol — which combines electrical and chemical stimulation — to paralyzed rats. Not only did the implant prove its biocompatibility, but it also did its job perfectly, allowing the rats to regain the ability to walk on their own again after a few weeks of training.

“Our e-Dura implant can remain for a long period of time on the spinal cord or the cortex, precisely because it has the same mechanical properties as the dura mater itself. This opens up new therapeutic possibilities for patients suffering from neurological trauma or disorders, particularly individuals who have become paralyzed following spinal cord injury,” said professor Stéphanie Lacour, co-author of the paper, and holder of EPFL’s Bertarelli Chair in Neuroprosthetic Technology.

Flexibility of Tissue, Efficiency of Electronics
Developing the e-Dura implant was quite the challenge. As flexible and stretchable as living tissue, it nonetheless includes electronic elements that stimulate the spinal cord at the point of injury. The silicon substrate is covered with cracked gold electric conducting tracks that can be pulled and stretched. The electrodes are made of an innovative composite of silicon and platinum microbeads. They can be deformed in any direction, while still ensuring optimal electrical conductivity. Finally, a fluidic microchannel enables the delivery of pharmacological substances – neurotransmitters in this case – that will reanimate the nerve cells beneath the injured tissue.

The implant also can be used to monitor electrical impulses from the brain in real time. When they did this, the scientists were able to extract with precision the animal’s motor intention before it was translated into movement.

“It’s the first neuronal surface implant designed from the start for long-term application. In order to build it, we had to combine expertise from a considerable number of areas,” noted professor Grégoire Courtine, co-author and holder of EPFL’s IRP Chair in Spinal Cord Repair. “These include materials science, electronics, neuroscience, medicine, and algorithm programming.”

For the time being, the e-Dura implant primarily has been tested in cases of spinal cord injury in paralyzed rats. But the potential for applying these surface implants is huge –– for example in epilepsy, Parkinson’s disease and pain management. The scientists are planning to move towards clinical trials in humans, and to develop their prototype in preparation for commercialization.