Synthetic skin allows amputees to 'feel and touch'

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Synthetic skin allows amputees to 'feel and touch'

A highly advanced form of technology was integrated in prosthetics and robotics. Synthetic skin which is grafted onto prosthetic limbs are able to impose the feeling of actual skin and the sense of touch onto the arms of amputees.


Prosthetics and Robotics

Current prosthetic limbs aren’t capable of transmitting complex sensations like texture or pain to the user and those people who have prosthetic limbs especially those who suffered severe trauma are unable to regain the loss of sensation and feel what is lost in them.

A recent breakthrough by scientists at Johns Hopkins School of Medicine, developed  a synthetic layer of skin on an artificial hand which transmitted feelings of pain directly to the user.

“Pain helps protect our bodies from damage by giving us the sensation that something may be harmful, such as the sharp edge of a knife,” says Luke Osborn, a co-author of the new study and a graduate student at Johns Hopkins University in the Department of Biomedical Engineering. “For a prosthesis, there is no concept of pain, which opens it up to the possibility of damage. We found a way to provide sensations of pain in a meaningful way to the prosthesis as well as the amputee user.”

In the new study, an ideal prosthesis would “allow the user to maintain complete control” and choose to “overrule pain reflexes” if desired.

The new technology which is known as phantom limb allows amputees to feel that a missing part of their body is still there intact. This also allows certain robots to perform certain movements that only a prosthetic limb can do.


E- Dermis

JHU neuroengineer Nitish Thakor, [Luke] Osborn and his colleagues called this technology, e-dermis—a skin-like layer that gives prosthetic limbs the capacity to perceive touch and pain. Pressure applied to the e-dermis is transmitted to the user’s brain via  nerve stimulators implanted in the arm above the prosthesis, allowing the system to emulate actual sensations including pain. In tests of the e-dermis system, a volunteer amputee said he could tell the difference between objects that were rounded or sharp.

But in the meantime, the JHU researchers are seeking to create more realistic prosthetic limbs capable of delivering a rich diversity of tactile information, involving other sensations.

In experiments, an amputee volunteer could almost feel pressure and even objects that elicit painful sensations. He could tell the difference between non-painful and painful tactile perceptions, including an object’s curvature and its sharp edges.

When layered on top of prosthetic hands, this e-dermis brings back a real sense of touch through the fingertips.

"After many years, I felt my hand, as if a hollow shell got filled with life again," an anonymous amputee, who served as the team's principal volunteer tester, said.

Made of fabric and rubber laced with sensors to mimic nerve endings, e-dermis recreates a sense of touch as well as pain by sensing stimuli and relaying the impulses back to the peripheral nerves.

The team also created a neuromorphic model mimicking 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. They tracked brain activity using EEG or electroencephalography which determined if the test subject were able to perceive sensations in the prosthetic hand.

The researchers then connected the e-dermis output to the volunteer by using a noninvasive method known as transcutaneous electrical nerve stimulation, or TENS. 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 various objects.

The e-dermis is not sensitive to temperature. For this study, the team focused on detecting object curvature (for touch and shape perception) and sharpness (for pain perception).

The researchers next goal is to further develop the technology and better understand how to provide meaningful sensory information to amputees, in the hopes of making the system ready for widespread patient use.


Solar powered synthetic skin

Harnessing the sun’s rays to power synthetic skin could help create advanced prosthetic limbs capable of returning the sense of touch to amputees.

Graphene’s remarkable physical properties to use energy from the sun was used to power up this synthetic skin. Allowing its inspiration from our own human skin, this allows robots to eventually have a sense touch and also respond to nerve sensations just like our neurons that relay signals to our brain.

Professor Ravinder Dahiya and colleagues from his Bendable Electronics and Sensing Technologies (BEST) group’s initial breakthrough was to develop a touch-sensitive covering for prosthetic hands made from graphene.

Graphene is a highly flexible form of graphite, stronger than steel, and electrically conductive. It’s optical transparency, which allows around 98% of the light to pass directly through it, makes it ideal for gathering energy from the sun to generate power.

The group of researchers were able to integrate power-generating photovoltaic cells into their electronic skin which remains flexible and totally tactile for a sensation just like a normal person has.   

Human skin is an incredibly complex system capable of detecting pressure, temperature and texture through an array of neural sensors which carry signals from the skin to the brain. With this technology, functionality can also be mimicked not just the morphology of the skin. And this allows robots to be able to feature this kind of complexity within them.


"We have already made significant steps in creating prosthetic prototypes which integrate synthetic skin and are capable of making very sensitive pressure measurements," says Prof. Dahiya.

Skin capable of touch sensitivity also opens the possibility of creating robots capable of making better decisions about human safety. This would essentially maximize the benefits of having robots in our midst as it makes us prevent some risks of doing our jobs. Robots can now able to performs tasks like gripping materials which prosthetics struggle doing.

The group has advanced their synthetic skin prototype to so it that is now fully flexible. It comprises a flexible graphene-based touch-sensitive layer integrated on flexible solar cell. Detailed movements required by an advanced prosthetic is comparable to the prototype with its full potential. The new skin requires just 20 nanowatts of power per square centimetre, which is easily met even by the poorest-quality photovoltaic cells currently available on the market.

Their research has now allowed solar energy can be harnessed and stored using flexible ultra-thin high-performance supercapacitors based within the skin. Not only does this improve the effective use of skin in robotics and prosthetics, this advance opens up new possibilities for other technologies.

“The next step for us is to further develop the power-generation technology which underpins this research and use it to power the motors which drive the prosthetic hand itself. This could allow the creation of an entirely energy-autonomous prosthetic limb," Prof. Dahiya said further.




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