In the final analysis, the persistence of paralysis in human history might seem a bit absurd. After all, in some forms of paralysis we have a nervous system that is, at least, 99% functional. Brain-to-break can be working fine, and break-to-limb can work just fine, too. Sever just one link in the most crucial portions of the chain, and now that whole chain is worthless. But technology is well on the way to finding a solution to this maddeningly simple problem, and a promising idea called e-dura is showing how close some of these solutions are to real human testing.
The biggest problem for neural implants has never been the neural part, but the implant part. Any interface between human flesh and machine metal is, to state it simply, hard to do. You can put your device entirely internal, but then you have issues with power supply, communication, maintenance, upgrading — and you still haven’t fixed the compatibility problem. Spinal implants have made incredible leaps in their ability to read and even create neural signals, but all that is meaningless if the curative implants go on to break down the spine in a whole new way, ultimately leading to rejection by the body. In particular, incredible studies that can let paralyzed mammals regain some of their former mobility have had a hard time letting the rats maintain the effect.
It’s a cruel irony that the dura mater, a thick outer membrane surrounding the brain and spinal cord, has for a long time been far from durable enough for our needs. Implants in the head and spine can easily attach to this relatively tough scaffold, but once there they have historically caused a whole new set of ailments. Unlike bone, the dura mater moves and stretches as we go through life — and that causes real problems when there’s a piece of hard technology rubbing and scraping the tissue.
The meaning of this is visible in the behavior of implanted rats. Non-paralyzed rats were given e-dura and regular implants, and over time the traditional implants caused the rats to lose their manual dexterity, stumble and eventually fall while climbing over ladders. The rats with e-dura showed no such signs of deterioration in the spine. The team also tested e-dura’s ability to read and ferry on both both electrical and chemical neural signals, healing paralysis — right now.
What really sets e-dura apart, though, is that its effects can last in mammals with life expectancies longer than those of lab rats.
To achieve that, e-dura had to get more advanced than you might imagine. E-dura is designed to have the same stiffness and elasticity as the dura mater itself, in theory allowing it to deform properly with real movement and keeping it from abrading and inflaming the tissue. Everything has to be non-toxic, bio-durable, and mechanically compatible with the dura mater, not only flexible but stretchable. Gold wires have embedded cracks that allow the wires to stretch without losing their conductivity, and the electrodes have a stretchable polymer coating. It’s all designed to sum to the same overall properties as the implant’s surroundings.
This has larger implications than just physical rubbing — e-dura rats did not show a heightened immune response to the implant, which is another cause of problems in rats with traditional implants. Being so clearly foreign, the body identifies stiff implants as foreign and attacks them, to its own detriment, causing immune rejection. It’s incredible that this sort of technology has gotten to the point of, essentially, bug-fixing, and the simple fact of partially healing paralysis is no longer enough to impress.
The question isn’t if they’ll start selecting humans for testing these newly practical implants, but when.