For decades, one of the most-studied and elusive cures in medical science has been biotechnology that would allow humans to walk again after spinal cord trauma. Other prosthetic devices haveadvanced enormously over the last 50 years, thanks to the integration of miniaturized motors, space-age materials, and cutting edge fabrication, while repairing damage to the nervous system has advanced at a comparative snail’s pace. Now, a group of researchers has demonstrated a new device that allows paralyzed rats to walk again, and they’re hoping it can do the same for humans.
To understand the significance of this new device, dubbed the e-Dura, we need to talk a bit about the underlying problem. When a neuron in the central nervous system is damaged, the neuron’s support cells (glia) move in. Astrocytes, one kind of glial cells, build up scar tissue around the damaged region to protect it from further damage. Oligodendrocytes, another kind of glia, block axons from wayfinding, preventing them from attaching to the damaged region in the CNS. This combined formation is what’s known as a glial scar.
A glial scar. Image from the University of Rochester
Glial cells have positive effects — they repair the integrity of the central nervous system and they stimulate the restoration of blood flow and metabolic support to the remaining nervous tissue. Unfortunately, one side effect of this prioritization is that they stymie the nervous system’s attempt to repair itself.
One of the complications that has prevented previous classes of implants from being effective long term is that these same glial cells appear shortly after implants are inserted into patients. Devices may work in the short term, but in the long term the body takes action to isolate the implants and prevent them from functioning. What the e-Dura’s manufacturers hypothesized was that it was the stiffness of the implants that caused neural damage that led to glial cell formation.
To understand this, think about a fiberglass cast. The reason doctors put a liner in between cast and skin is because without one, you’ll be rubbed raw in a matter of days as your skin flexes around the cast. We don’t think of nerve tissue as being stretchy, but it has to be able to expand and contract — astronauts have been known to come back from space missions nearly an inch taller than when they left, and they don’t come back as paraplegics confined to wheelchairs. Standing, sitting, and walking all produce minute movements in the spinal column, and the e-Dura’s design is built to allow the device to shift without causing abrasion.
So far, the technique appears to have worked, at least in rats. If that’s true, it could be an enormous step forward towards implantable devices to treat spinal damage. To date, most implants have focused on demonstrating that nerve signals can still be conducted to the legs, proving that if the connection is restored, the signals can be received again. This was critical knowledge, particularly in long-term quadriplegic or paraplegics who hadn’t walked in years, but it didn’t automatically point to a long-term solution for the problem.
The e-Dura program isn’t the only research tackling the difficult task of creating a long-term synthetic interface between two halves of a partially or completely severed spinal column, but it could be one of the most important. Solving the glial cell formation issue around implants would vastly simplify a great many other projects that are focused on finding the best method of transmitting information and returning function to critical areas.
Even a partial success would be revolutionary. Paraplegics who were unable to walk again might still regain bowel/bladder control or sexual function, or the ability to exercise and exert more control over their day-to-day lives. The e-Dura is only in the rat-testing phase at the moment, which means human trials are still an indeterminate time in the future — but this technology could truly matter to people who have lost function below the waist or neck.
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