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 In 2012 the researchers showed how electrical-chemical stimulation
could restore lower body movement in rats with spinal cord injuries.
They showed that a severed section of the spinal cord can regain its
use when a rat's innate intelligence and regenerative capacity is
awakened with a treatment of chemicals. The scientists then
stimulated the spinal cord with electrodes implanted in the
outermost layer of the spinal canal, called the epidural space. They
found that a stimulated rat spinal column, physically isolated from
the brain, started taking over the task of modulating leg movement,
allowing previously paralyzed rats to walk, albeit involuntarily.
"By combining this electro-chemical stimulation of the spinal cord
tissue we then tested whether we could then restore locomotion in
the hind limbs. And this is what we found. Indeed we can - using
this technology - we were able over weeks of time to stimulate the
spinal cord in spinal cord-injured animals and allow then to walk,"
explained Professor Stéphanie Lacour, co-author of the study at the
Swiss Federal Institute of Technology in Lausanne.
However, applying these so-called 'surface implants' to humans
presented a host of problems. By applying them directly to the
spinal cord, any movement or stretching of the nerve tissues would
cause the implant to rub, with repeated friction leading to
inflammation, build-up of scar tissue and, ultimately, rejection of
the implant.
Lacour, who is leading the research alongside study co-author
Grégoire Courtine, said they needed to come up with a more viable
material.
"To define whether or not the softness of the mechanical compliance
of the device mattered in terms of its long-term integration with
the tissue. Because one important aspect of our studies is that we
design the implant so that it could, one day, be used in a
therapeutical context. So we wanted an implant that could stay for
quite some time in vivo without inducing any detrimental effect. And
so the first question we asked was: is soft making a difference?"
she said.
The soft and stretchy prototype device was designed and built on
site. The silicon substrate is covered with gold electric conducting
tracks, with the electrodes made from a composite of silicon and
platinum microbeads. A tiny microchannel enables the delivery of
drugs -- in this case, neurotransmitters that reanimate the nerve
cells beneath the injured tissue.
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"We implanted the device subdurally; so just below the natural skin
that protects the spinal cord, so that we could be at the very
surface of the spinal cord. And then we used this to stimulate
electrically, and also chemically. And we added to the implant a
very small conduit, like a micro channel where we could deliver also
drugs," said Lacour.
Implanted beneath the dura mater, directly onto the spinal cord, the
elastic e-Dura prototype can be bent and deformed almost exactly
like the living tissue that surrounds it. When the prototype was
implanted into rats it caused neither damage nor rejection, even
after two months.
Lacour added that one of e-Dura's unique properties is the embedded
metallic electrodes that can be bent and stretched without breaking:
"The innovation in e-Dura is that the metallic track can also
withstand a very large deformation. So we have stretchable metal
integrated in e-Dura."
While the team is confident the technology can be successfully
implanted without rejection, the spinal cord of the paralyzed rat is
currently stimulated from an external source, with no correlation
between the its brain and spine. Lacour concedes this is the next
hurdle to overcome: "There's no link at the moment between the
brain; so the motor command between the brain and the actual
stimulation pattern on the spinal cord. So we now also have to find
a way to link the two so that the person will think about moving
and, indeed, the stimulation will be synchronized."
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