The body’s ability to repair damaged nerves is something of a mystery. For neurologists, it seems clear that damage to the central nervous system—the brain and spinal cord—cannot be repaired. However, damage to the nerves in the rest of the body—the peripheral nervous system—is a different matter.
Much evidence suggests the body can repair certain types of peripheral nerve damage. But only in certain circumstances and often in limited ways. So new ways to reconnect severed nerves and to trigger repair and regrowth are of considerable interest.
Which is why the work of Ashour Sliow at Western Sydney University in Australia and a few colleagues is important. These guys have developed a new way to reconnect a severed nerve with a biodegradable scaffold and then stimulate it electrically using a magnetic field outside the body.
They say their technique is minimally invasive, unlike other nerve regeneration approaches and can repair severed nerves in rats.
In recent years, neurologists have discovered that brief electrical stimulation can significantly improve the way nerves repair and regrow.
But there are significant challenges in perfecting this kind of treatment. One is that severed nerves are often stitched back together again and the sutures are a significant source of scaring and inflammation.
Then there is the problem of applying electrical stimulation. This is often done using a conducting band around the reconnected part of the nerve that is connected to a wire that extends out of the body.
This often causes in problems. Any invasive connection is prone to infection and any small tug on the wire can dislodge the band. In practice, the conducting band often migrates, which significantly reduces its therapeutic effectiveness.
“Repairing and electrically stimulating peripheral nerves with a non-invasive device is very challenging and the current scientific and technological know-how has yet to produce an effective system to combine and perform these two tasks together,” says Sliow and co.
They take a different approach. These guys have developed a band made of chitosan, a biodegradeable material made from shrimp shells. The team bond this directly to the nerve using a laser that does not damage the nerve tissue.
The chitosan band then acts as a scaffold for the nerve during the healing process. “This scaffold is anchored to tissue by a laser without sutures, thus exploiting the photo-adhesive properties of the scaffold,” say Sliow and co.
The chitosan scaffold also performs another role. Sliow and his colleagues have integrated a gold band into the scaffold. This band has a diameter of about a 1 millimetre and acts as a kind of radio antenna that can pick up for electromagnetic signals generated outside the body.
The idea is that these signals induce a current in the gold band and that this stimulates the nerve itself.
To find out how well this so-called “graft-antenna” works, the team used the device to stimulate and repair sciatic nerves in anesthetised Wistar rats. They stimulated the severed nerves using transcranial magnetic stimulation for 1 hour a week over three months, using a pattern of signals known to trigger nerves.
They found that the sciatic nerves regenerated during this period and that the antenna was able to stimulate muscle action during this time. In addition, the graft antenna was stable throughout and did not migrate during the experiment.
That’s interesting work with significant potential. The ability to repair nerves has benefitted from scaffolds that support the nerve and from electrical stimulation. But nobody has worked out how to do both these things at the same time. Until now.
Of course, there is work ahead. For example, the device needs to be compared in controlled trials to repairs effected by sutures to quantify how much better it is.
After that, will come trials in humans and there is very reason to be cautiously optimistic. “The graft-antenna is stable in the body after implantation and can facilitate axon regeneration with no significant adverse effect,” say the team.
Ref: arxiv.org/abs/1807.02788 : Bioadhesive Graft-Antenna for Stimulation and Repair of Peripheral Nerves
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