Summary: Researchers have developed a next-generation bionic hand that allows amputees to regain their proprioception. The results of the study are the culmination of ten years of robotics research.
The next-generation bionic hand, developed by researchers from EPFL, the Sant’Anna School of Advanced Studies in Pisa and the A. Gemelli University Polyclinic in Rome, enables amputees to regain a very subtle, close-to-natural sense of touch. The scientists managed to reproduce the feeling of proprioception, which is our brain’s capacity to instantly and accurately sense the position of our limbs during and after movement — even in the dark or with our eyes closed.
The new device allows patients to reach out for an object on a table and to ascertain an item’s consistency, shape, position and size without having to look at it. The prosthesis has been successfully tested on several patients and works by stimulating the nerves in the amputee’s stump. The nerves can then provide sensory feedback to the patients in real time — almost like they do in a natural hand.
The findings have been published in the journal Science Robotics. They are the result of ten years of scientific research coordinated by Silvestro Micera, a professor of bioengineering at EPFL and the Sant’Anna School of Advanced Studies, and Paolo Maria Rossini, director of neuroscience at the A. Gemelli University Polyclinic in Rome.
Current myoelectric prostheses allow amputees to regain voluntary motor control of their artificial limb by exploiting residual muscle function in the forearm. However, the lack of any sensory feedback means that patients have to rely heavily on visual cues. This can prevent them from feeling that their artificial limb is part of their body and make it more unnatural to use.
Recently, a number of research groups have managed to provide tactile feedback in amputees, leading to improved function and prosthesis embodiment. But this latest study has taken things one step further.
“Our study shows that sensory substitution based on intraneural stimulation can deliver both position feedback and tactile feedback simultaneously and in real time,” explains Micera. “The brain has no problem combining this information, and patients can process both types in real time with excellent results.”
Intraneural stimulation re-establishes the flow of external information using electric pulses sent by electrodes inserted directly into the amputee’s stump. Patients then have to undergo training to gradually learn how to translate those pulses into proprioceptive and tactile sensations.
This technique enabled two amputees to regain high proprioceptive acuity, with results comparable to those obtained in healthy subjects. The simultaneous delivery of position information and tactile feedback allowed the two amputees to determine the size and shape of four objects with a high level of accuracy (75.5%).
“These results show that amputees can effectively process tactile and position information received simultaneously via intraneural stimulation,” says Edoardo D’Anna, EPFL researcher and lead author of the study.
Edoardo D’Anna, Giacomo Valle, Alberto Mazzoni, Ivo Strauss, Francesco Iberite, Jérémy Patton, Francesco M. Petrini, Stanisa Raspopovic, Giuseppe Granata, Riccardo Di Iorio, Marco Controzzi, Christian Cipriani, Thomas Stieglitz, Paolo M. Rossini, Silvestro Micera. A closed-loop hand prosthesis with simultaneous intraneural tactile and position feedback. Science Robotics, 2019; 4 (27): eaau8892 DOI: 10.1126/scirobotics.aau8892
Source of the Article: Ecole Polytechnique Fédérale de Lausanne. “A prosthetic that restores the sense of where your hand is.” ScienceDaily. ScienceDaily, 21 February 2019. <www.sciencedaily.com/releases/2019/02/190221110357.htm>.
‘Electronic skin’ allows user to experience a sense of touch and pain; ‘After many years, I felt my hand, as if a hollow shell got filled with life again,’ amputee volunteer says
By Amy Lunday
/Published Jun 20, 2018
Amputees often experience the sensation of a “phantom limb”—a feeling that a missing body part is still there.
That sensory illusion is closer to becoming a reality thanks to a team of engineers at Johns Hopkins University that has created an electronic skin. 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,” says the amputee who served as the team’s principal volunteer. (The research protocol used in the study does not allow identification of the amputee volunteers.)
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.
“We’ve made a sensor that goes over the fingertips of a prosthetic hand and acts like your own skin would,” says Luke Osborn, a graduate student in biomedical engineering. “It’s inspired by what is happening in human biology, with receptors for both touch and pain.
Image caption:Luke Osborn interacts with a prosthetic hand sporting the e-dermis
IMAGE CREDIT: LARRY CANNER / HOMEWOOD PHOTOGRAPHY
“This is interesting and new,” Osborn adds, “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 online in the journal Science Robotics, shows it’s possible to restore a range of natural, touch-based feelings to amputees 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.
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Bringing a more human touch to modern prosthetic designs is critical, especially when it comes to incorporating the ability to feel pain, Osborn says.
“Pain is, of course, unpleasant, but it’s also an essential, protective sense of touch that is lacking in the prostheses that are currently available to amputees,” he says. “Advances in prosthesis designs and control mechanisms can aid an amputee’s ability to regain lost function, but they often lack meaningful, tactile feedback or perception.”
That’s where the e-dermis comes in, conveying information to the amputee by stimulating peripheral nerves in the arm, making the so-called phantom limb come to life. Inspired by human biology, the e-dermis enables its user to sense a continuous spectrum of tactile perceptions, from light touch to noxious or painful stimulus.
“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 TEAM FOCUSED ON DEVELOPING A SYSTEM CAPABLE OF DETECTING OBJECT CURVATURE (FOR TOUCH AND SHAPE PERCEPTION) AND SHARPNESS (FOR PAIN PERCEPTION).
The team 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. Tracking brain activity via electroencephalography, or EEG, the team determined that the test subject was able to perceive these sensations in his phantom 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 a pointed object and non-pain when touching a round object.
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 e-dermis technology could be used to make robotic systems more human, and it could also be used to expand or extend to astronaut gloves and space suits, Osborn says.
The researchers plan to further develop the technology and work to better understand how to provide meaningful sensory information to amputees in the hopes of making the system ready for widespread patient use.
Johns Hopkins is a pioneer in the field of upper limb dexterous prosthesis. More than a decade ago, the university’s Applied Physics Laboratory led the development of the advanced Modular Prosthetic Limb, which an amputee patient controls with the muscles and nerves that once controlled his or her real arm or hand.
Prosthetics may soon take on a whole new feel. That’s because researchers have created a new type of artificial nerve that can sense touch, process information, and communicate with other nerves much like those in our own bodies do. Future versions could add sensors to track changes in texture, position, and different types of pressure, leading to potentially dramatic improvements in how people with artificial limbs—and someday robots—sense and interact with their environments.
“It’s a pretty nice advance,” says Robert Shepherd, an organic electronics expert at Cornell University. Not only are the soft, flexible, organic materials used to make the artificial nerve ideal for integrating with pliable human tissue, but they are also relatively cheap to manufacture in large arrays, Shepherd says.
Modern prosthetics are already impressive: Some allow amputees to control arm movement with just their thoughts; others have pressure sensors in the fingertips that help wearers control their grip without the need to constantly monitor progress with their eyes. But our natural sense of touch is far more complex, integrating thousands of sensors that track different types of pressure, such as soft and forceful touch, along with the ability to sense heat and changes in position. This vast amount of information is ferried by a network that passes signals through local clusters of nerves to the spinal cord and ultimately the brain. Only when the signals combine to become strong enough do they make it up the next link in the chain.
Now, researchers led by chemist Zhenan Bao at Stanford University in Palo Alto, California, have constructed an artificial sensory nerve that works in much the same way. Made of flexible organic components, the nerve consists of three parts. First, a series of dozens of sensors pick up on pressure cues. Pressing on one of these sensors causes an increase in voltage between two electrodes. This change is then picked up by a second device called a ring oscillator, which converts voltage changes into a string of electrical pulses. These pulses, and those from other pressure sensor/ring oscillator combos, are fed into a third device called a synaptic transistor, which sends out a series of electrical pulses in patterns that match those produced by biological neurons.
Bao and her colleagues used their setup to detect the motion of a small rod moving in different directions across their pressure sensors, as well as identify Braille characters. What’s more, they managed to connect their artificial neuron to a biological counterpart. The researchers detached a leg from a cockroach and inserted an electrode from the artificial neuron to a neuron in the roach leg; signals coming from the artificial neuron caused muscles in the leg to contract, they report today in Science.
Because organic electronics like this are inexpensive to make, the approach should allow scientists to integrate large numbers of artificial nerves that could pick up on multiple types of sensory information, Shepherd says. Such a system could provide far more sensory information to future prosthetics wearers, helping them better control their new appendages. It could also give future robots a greater ability to interact with their ever-changing environments—something vital for performing complex tasks, such as caring for the elderly.
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