(PHILADELPHIA) – Investigators at the University
of Pennsylvania School of Medicine describe the basis
for developing a biological interface that could link a patient's
nervous system to a thought-driven artificial limb. Their conceptual
framework - which brings together years of spinal-cord
injury research - is published in the January issue of Neurosurgery.
"We're at a junction now of developing a new approach for
a brain-machine interface," says senior author Douglas
H. Smith, MD, Professor of Neurosurgery
and Director of the Center
for Brain Injury and Repair at Penn. "The nervous system
will certainly rebel if you place hard or sharp electrodes into
it to record signals. However, the nervous system can be tricked
to accept an interface letting it do what it likes - assimilating
new nerve cells into its own network."
develop the next generation of prosthetics
the idea is to use regions of undamaged nervous tissue to provide
command signals to drive a device, such as an artificial limb. The
challenge is for a prosthesis to perform naturally, relaying two-way
communication with the patient’s brain. For example, the patient's
thoughts could convert nerve signals into movements of a prosthetic,
while sensory stimuli, such as temperature or pressure provides
feedback to adapt the movements.
The central feature of the proposed interface is the ability to
create transplantable living nervous tissue already coupled to electrodes.
Like an extension cord, of sorts, the non-electrode end of the lab-grown
nervous tissue could integrate with a patient’s nerve, relaying
the signals to and from the electrode side, in turn connected to
an electronic device.
This system may one day be able to return function to people who
have been paralyzed by a spinal-cord injury, lost a limb, or in
other ways. "Whether it is a prosthetic device or a disabled
body function, the mind could regain control," says Smith.
To create the interface, the team used a newly developed process
of stretch growth of nerve fibers called axons,
previously pioneered in Smith’s
lab. Two adjacent plates of neurons
are grown in a bioreactor.
Axons sprout out to connect the neuron populations on each plate.
The plates are then slowly pulled apart over a series of days, aided
by a precise computer-controlled motor system, until they reached
a desired length.
For the interface, one of the plates is an electrical microchip.
Because Smith and his team have shown that stretch-grown
axons can transmit active electrical signals, they propose that
the nervous-tissue interface - through the microchip - could detect
and record real-time signals conducted down the nerve and stimulate
the sensory signals back through the axons.
In another study, Smith and colleagues showed that these
stretch-grown axons could grow when transplanted into a rat model
of spinal-cord damage. The team is now is the midst of studies
measuring neuronal electrical activity across newly engineered nerve
bridges and the restoration of motor activity in experimental animals.
Co-authors are Niranjan
Kameswaran, and Eric
L. Zager, all from Penn and Bryan
J. Pfister, New
Jersey Institute of Technology (Newark, NJ), and Jason
Huang at the University
of Rochester, N.Y.
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