It's many small steps for rats, but a huge step for people with spinal injuries; a flexible implant has been shown to circumvent damage to the spinal cord of rats.
The last few years have seen rapid progress in efforts to restore the capacity to walk in people with spinal injuries. One man, Darek Fidyka, is actually walking after two years of paralysis, while rats in harnesses are climbing stairs.
However, none of these projects are yet ready for widespread application. Fidyka had special circumstances that made him a far more promising candidate than most paraplegics, and the techniques that work on rats often prove temporary. One reason for the latter is that electronic devices tend to lack the flexibility of human body parts, and when fitted to the spinal cord can do damage that eventually blocks the implant from the nerves with which it needs to communicate.
“The spinal cord can stretch and relax,” says Professor Stéphanie Lacour of the Swiss Federal Institute of Technology. "If the implant doesn't accommodate this deformation then there will be a lot of sheering and rubbing at the interface which will create inflammation." She adds that even materials that are flexible on the scale we see them at are often still microscopically rigid.
The Institute was also responsible for the previous stair-climbing rat announcement, but the researchers there knew that for transference to humans something better was required.
Their answer is a device they call “e-dura” in reference to the dura mater, one of the membranes that protects the spinal cord from damage. When implanted within the dura mater, the e-dura passes electrical signals across the damaged part of the spinal cord directly to the nerves. It also releases drugs to stimulate serotonin release, which besides keeping us happy also helps to maintain neurons.
The e-dura uses a flexible polymer for the structure and gold as the conductor. Gold is highly ductile and bends well, but does not normally stretch, a key requirement here. The gold was applied in layers just 35 nanometers thick, with tiny cracks between that allow the material as a whole to stretch and compress while still conducting electricity.
Credit: © EPFL. Tiny cracks in the gold layering make it elastic while still transmitting energy.
The capacity to pass signals is no use if the wrong messages are sent. Lacour's team tracked the signals in healthy rats associated with different motions and programmed the implant to be able to recognize the ones needed to walk.
Lacour has published the six-week success of the e-dura in Science, announcing it can “sustain millions of mechanical stretch cycles, electrical stimulation pulses and chemical injections.”
H/T Live Science