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Learning to Walk again

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paralyzed-ratsScientists at EPFL in Switzerland have designed a spinal implant which can join severed ends of the spinal cord together allowing paralysed rats to walk again once more. The implant has been named “e-Dura”, short for “Electronic Dura Mater” because the device electronically mimics the function of the dura mater, a protective layer of tissue surrounding the spinal cord. Its function is to prevent foreign substances from entering and damaging the spinal cord.

The spinal cord itself bridges the gap between the brain (where most of the decision making process takes place) and the rest of the body. It contains bundles and bundles of nerve fibres containing sensory inputs into the brain and motor outputs leaving the brain. When the spinal cord is damaged, for example when it has been broken or severed, the result is a break in this connectivity. The brain can then no longer send signals to parts of the body below the damaged region. Paralysis can often result from injuries to the spinal cord, with motor outputs from the brain not being sent past the damaged region, meaning certain body parts do not receive the signals to move.

In earlier research, the same team of scientists performed tests on paralysed rats showing that chemicals and electrodes implanted into the spinal cord past the damaged regions resulted in nerves being stimulated once again. The implanted electrodes stimulated the nerves to fire electrical signals and thus send messages while the chemicals acted as neurotransmitters. Following on from this research, they attempted to create a device to put into the spinal cord to act as a bridge between the two broken ends of spinal cord. By stimulating nerves located past the damaged area of the spinal cord, the electrical signals could travel as they normally would, activating muscles allowing the rats to walk.

e-Dura was built to contain electrodes and chemicals to excite nerves and tracks that conduct electricity between them. The tracks conduct signals from one severed end of the cord to the other, and the electrodes can stimulate the cord that lies after the break.

This is not the first spinal cord implant to be designed; previous implants have been constructed, but were unable to remain implanted for long term use. The implanted devices were placed above the spinal cord and the dura mater, but over time the dura mater would begin to rub against the rigid device implanted above it. This would often lead to swelling and inflammation. The damage to the tissue would result in the body mounting an immune response against the foreign object leading to rejection.

So how does e-Dura circumvent that? The device was made to be bendy and stretchy so it could move with the body tissues, and not hamper their movement. Because of its flexible design, e-Dura can be implanted directly onto the spinal cord below the dura mater. The implant is made of silicon and contains gold tracks on its surface which conduct electricity and are able to stretch and survive pulling. Electrodes in the device are made of silicon and platinum microbeads, which continue functioning while being squished in all directions. Within the device is a small channel which allows neurotransmitters to be delivered to the spinal cord below it. The resulting implant moves with the body instead of against it. A prototype was tested in rats for two months and it turned out that the device was not rejected.

Rats were paralysed through total severing of their spinal cord and the device was implanted at the point of this break. The implanted device allows the gap between the severed ends of spinal cord to be bridged allowing electrical signals to be conducted the whole way down the spinal cord from the brain. The combination of both chemical and electrical stimulation allowed the rats to send signals down the spinal cord to signal movement. In order to re-train the rats in walking, they were supported in harnesses for balancing but played no part in subsequent moving. e-Dura was tested for 6 weeks in these walking studies so the subsequent locomotion was demonstrated over weeks of implantation rather than in short time periods.

e-Dura was also tested as a brain implant and was shown to be effective in conducting signals through the brain.

The next step forward is to develop this device to work in humans, but such trials are still quite a few years off. Possible applications for this technology are to cure paralysis, and possibly to treat disorders and injuries of the brain such as epilepsy and Parkinson’s disease.

Aoife Hardesty

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