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Electronic Skin Allows Prosthetic Hands to Touch, Feel Pain

A team of engineers at Johns Hopkins University has created an electronic skin that will enable individuals with amputations to perceive the sense of touch and pain through prosthetic fingertips. When
layered on top of prosthetic hands, the electronic skin, or e-dermis,
brings back a real sense of touch through the fingertips, said Luke
Osborn, a graduate student in biomedical engineering who coauthored a
paper about the device.

Tactile
information from object grasping is transformed into a neuromorphic
signal through the prosthesis controller. The neuromorphic signal is
used to transcutaneously stimulate peripheral nerves of an amputee to
elicit sensory perceptions of touch and pain.

The
skin, made of fabric and rubber laced with sensors to mimic nerve
endings, senses stimuli and relays the impulses back to the peripheral
nerves. “We’ve made a sensor that goes over the fingertips of a
prosthetic hand and acts like your own skin would,” Osborn said. “It’s
inspired by what is happening in human biology, with receptors for both
touch and pain. This is interesting and new because now we can have a
prosthetic hand that is already on the market and fit it with an
e-dermis that can tell the wearer whether he or she is picking up
something that is round or whether it has sharp points.”

The work, published June 20 in the journal Science Robotics,
shows it is possible to restore a range of natural, touch-based
feelings to people who use prosthetic limbs. The ability to detect pain
could be useful, for instance, not only in prosthetic hands but also in
lower-limb prostheses, alerting the user to potential damage to the
device.

Human skin
contains a complex network of receptors that relay a variety of
sensations to the brain. This network provided a biological template for
the research team, which includes members from the Johns Hopkins
departments of biomedical engineering, electrical and computer
engineering, and neurology, and from the Singapore Institute of
Neurotechnology.

Bringing
a more human touch to modern prosthetic designs is critical, especially
when it comes to incorporating the ability to feel pain, Osborn said.
That is where the e-dermis comes in, conveying information to the person
with the amputation by stimulating peripheral nerves in the arm, making
the phantom limb come to life. The e-dermis device does this by
electrically stimulating the nerves in a noninvasive way, through the
skin, according to the paper’s senior author, Nitish Thakor, PhD, a
professor of biomedical engineering and director of the Biomedical
Instrumentation and Neuroengineering Laboratory at Johns Hopkins.

“For
the first time, a prosthesis can provide a range of perceptions, from
fine touch to noxious to an amputee, making it more like a human hand,”
says Thakor, co-founder of Infinite Biomedical Technologies, the
Baltimore-based company that provided the prosthetic hardware used in
the study.

The
e-dermis was tested for one year on an individual with an amputation
who volunteered in the Neuroengineering Laboratory at Johns Hopkins. The
subject frequently repeated the testing to demonstrate consistent
sensory perceptions via the e-dermis. The team has worked with four
other volunteers with amputations in other experiments to provide
sensory feedback.

The
team created a “neuromorphic model” that mimicked the touch and pain
receptors of the human nervous system, allowing the e-dermis to
electronically encode sensations just as the receptors in the skin
would. Tracking brain activity via EEG, the team determined that the
test subject was able to perceive these sensations in his phantom hand.

The
researchers then connected the output to the volunteer using
transcutaneous electrical nerve stimulation. In a pain-detection task,
the team determined that the test subject and the prosthesis were able
to experience a natural, reflexive reaction to both pain while touching a
pointed object and non-pain when touching a round object.

This story was adapted from materials provided by Johns Hopkins University.

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