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Artificial Nerve System Could Give Prostheses a Sense of Touch

Researchers at Stanford
University and Seoul National University, Korea, have developed an
artificial sensory nerve system that can activate the twitch reflex in a
cockroach as well as identify letters in the Braille alphabet. The
work, published May 31 in Science, is a step toward creating artificial skin and restoring sensation to people who use prosthetic limbs, said Zhenan Bao, PhD, a professor of chemical engineering at Stanford and one of the senior authors.

“We
take skin for granted, but it’s a complex sensing, signaling, and
decision-making system,” Bao said. “This artificial sensory nerve system
is a step toward making skin-like sensory neural networks for all sorts
of applications.”

The
paper describes how the research team constructed an artificial sensory
nerve circuit that could be embedded in a future skin-like covering for
neuroprosthetic devices. This rudimentary artificial nerve circuit
integrates three previously described components. The first is a touch
sensor that can detect even minuscule forces. This sensor sends signals
through the second component—a flexible electronic neu ron. The touch
sensor and electronic neuron are improved versions of inventions
previously reported by Bao’s research lab. Sensory signals from these
components stimulate the third component, an
artificial synaptic transistor modeled after human synapses.
The synaptic transistor was created by Tae-Woo Lee, PhD, of Seoul
National University, who spent his sabbatical year in Bao’s lab at
Stanford to initiate the collaborative work.

“Biological
synapses can relay signals, and also store information to make simple
decisions,” said Lee, a second senior author on the paper. “The synaptic
transistor performs these functions in the artificial nerve circuit.”

Lee
used a knee reflex as an example of how more advanced artificial nerve
circuits might one day be part of an artificial skin that would give
prosthetic devices senses and reflexes.

The
researchers say artificial nerve technology remains in its infancy. For
instance, creating artificial skin coverings for prosthetic devices
will require new devices to detect heat and other sensations, the
ability to embed them into flexible circuits, and then a way to
interface them to the brain. Though it will be some time before the work
reaches that level of complexity, in the Science paper, the
group describes how the electronic neuron delivered signals to the
synaptic transistor, which was engineered in such a way that it learned
to recognize and react to sensory inputs based on the intensity and
frequency of low-power signals, just like a biological synapse.

The group members tested the ability of the system to generate reflexes and sense touch.

In
one test, researchers hooked up their artificial nerve to a cockroach’s
leg and applied small increments of pressure to their touch sensor. The
electronic neuron converted the sensor signal into digital signals and
relayed them through the synaptic transistor, causing the leg to twitch
as the pressure on the touch sensor increased or decreased.

They
also showed that the artificial nerve could detect various touch
sensations. In one experiment the artificial nerve was able to
differentiate Braille letters. In another, the researchers rolled a
cylinder over the sensor in different directions and it accurately
detected the direction of the motion.

To
read more about Bao’s research efforts into restoring the lost sense of
touch with stretchable, electronically-sensitive synthetic materials,
visit Skin-like Prosthetic Coverings Closer To Reality With Stanford
Breakthrough.

https://opedge.com/Articles/ViewArticle/2018-02-23/skin-like-prosthetic-coverings-closer-to-reality-with-stanford-breakthrough

Editor’s Note: This story was adapted from materials provided by Stanford University

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