A prosthetic that restores the sense of where your hand is

Source: Ecole Polytechnique Fédérale de Lausanne

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.

Sensory feedback

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.

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Materials provided by Ecole Polytechnique Fédérale de Lausanne. Note: Content may be edited for style and length.


Journal Reference:

  1. 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>.

Researchers demonstrate key to success of nerve transfer technique in bionic reconstruction

Modern prostheses offer patients who have had a hand amputated much greater capability in everyday life than was possible with previous prosthetic reconstructive techniques. Redundant nerves from the amputated extremity can be surgically transferred to provide a much better connection between the patient’s body and the prosthesis. This technique has proven to be successful, although the specific reasons for its success were not fully understood. A team of researchers led by Konstantin Bergmeister and Oskar Aszmann from the Division of Plastic and Reconstructive Surgery and the Christian Doppler Laboratory for Recovery of Limb Function at MedUni Vienna, demonstrated, in an animal model, that the key to success lies in the muscle undergoing a change of identity triggered by the donor nerve.

Bionic prostheses are mentally controlled, in that they register the activation of residual muscles in the limb stump. Theoretically it should be possible for the latest generation prostheses to execute the same number of movements as a healthy human hand. However, the link between man and prosthesis is not yet capable of controlling all mechanically possible functions, because the interface between man and prostheses is limited in terms of signal transmission. “If we could solve this problem, the latest prostheses could actually become an intuitively operated replacement that functions just like a human hand,” underscore the researchers.

To enable the prosthesis to move at all, nerves have to be surgically transferred during the amputation procedure to increase the total number of muscle control signals. This involves connecting amputated peripheral nerves to residual muscles in the amputation stump. This method is very successful, because these muscles regenerate after a few months to provide better control of the prosthesis. However, until now, it was not clear what specific changes this nerve transfer technique produces in muscles and nerves.

Previously unknown neurophysiological effects discovered

As part of an experimental study conducted over several years, a research team led by Konstantin Bergmeister and Oskar Aszmann from MedUni Vienna’s Division of Plastic and Reconstructive Surgery (Head: Christine Radtke) and Christian Doppler Laboratory for Recovery of Limb Function have now shown that this nerve transfer technique has previously unidentified neurophysiological effects. These result in more accurate muscle contractility and much more finely controlled muscle signals than previously thought.

It was also found that muscles take on the identity of the donor nerves, that is to say the function of the muscle from which the nerve was originally harvested. This means that muscles can be modified very specifically to achieve the desired control of the lost extremity. This information will now be used in follow-up studies to refine the surgical technique of nerve transfer and adapt it more accurately to fine control systems. The vision of an intuitively controlled prosthesis that can perform all the natural manual functions could become a reality within the next few years.

Source:

https://www.meduniwien.ac.at/web/en/about-us/news/detailsite/2019/news-im-jaenner-2019/bionic-reconstruction-after-amputation-of-a-hand-muscles-can-be-repurposed-using-nerve-transfers/

Source of Article: https://www.news-medical.net/news/20190107/Researchers-demonstrate-key-to-success-of-nerve-transfer-technique-in-bionic-reconstruction.aspx

Vibrations Restore Sense of Movement in Prosthetics

Scientists recreate proprioception for people with artificial arms using a perceptual illusion.

Sep 1, 2018
By DIANA KWON

 

 

When Amanda Kitts’s car was hit head-on by a Ford F-350 truck in 2006, her arm was damaged beyond repair. “It looked like minced meat,” Kitts, now 50, recalls. She was immediately rushed to the hospital, where doctors amputated what remained of her mangled limb.

While still in the hospital, Kitts discovered that researchers at the Rehabilitation Institute of Chicago (now the Shirley Ryan AbilityLab) were investigating a new technique called targeted muscle reinnervation, which would enable people to control motorized prosthetics with their minds. The procedure, which involves surgically rewiring residual nerves from an amputated limb into a nearby muscle, allows movement-related electrical signals—sent from the brain to the innervated muscles—to move a prosthetic device.

Kitts immediately enrolled in the study and had the reinnervation surgery around a year after her accident. With her new prosthetic, Kitts regained a functional limb that she could use with her thoughts alone. But something important was missing. “I was able to move a prosthetic just by thinking about it, but I still couldn’t tell if I was holding or letting go of something,” Kitts says. “Sometimes my muscle might contract, and whatever I was holding would drop—so I found myself [often] looking at my arm when I was using it.”

What Kitts’s prosthetic limb failed to provide was a sense of kinesthesia—the awareness of where one’s body parts are and how they are moving. (Kinesthesia is a form of proprioception with a more specific focus on motion than on position.) Taken for granted by most people, kinesthesia is what allows us to unconsciously grab a coffee mug off a desk or to rapidly catch a falling object before it hits the ground. “It’s how we make such nice, elegant, coordinated movements, but you don’t necessarily think about it when it happens,” explains Paul Marasco, a neuroscientist at the Cleveland Clinic in Ohio. “There’s constant and rapid communication that goes on between the muscles and the brain.” The brain sends the intent to move the muscle, the muscle moves, and the awareness of that movement is fed back to the brain (see “Proprioception: The Sense Within,” The Scientist, September 2016).

GOOD VIBRATIONS: The prosthetic makes use of a kinesthetic phenomenon whereby vibrating a person’s muscle provides a false sense of movement.
PAUL MARASCO, LABORATORY FOR BIONIC INTEGRATION

Prosthetic technology has advanced significantly in recent years, but proprioception is one thing that many of these modern devices still cannot reproduce, Marasco says. And it’s clear that this is something that people find important, he adds, because many individuals with upper-limb amputations still prefer old-school body-powered hook prosthetics. Despite being low tech—the devices work using a bicycle brake–like cable system that’s powered by the body’s own movements—they provide an inherent sense of proprioception.

To restore this sense for amputees who use the more modern prosthetics, Marasco and his colleagues decided to create a device based on what’s known as the kinesthetic illusion: the strange phenomenon in which vibrating a person’s muscle gives her the false sense of movement. A buzz to the triceps will make you think your arm is flexing, while stimulating the biceps will make you feel that it’s extending (Exp Brain Res, 47:177–90, 1982). The best illustration of this effect is the so-called Pinocchio illusion: holding your nose while someone applies a vibrating device to your bicep will confuse your brain into thinking your nose is growing (Brain, 111:281–97, 1988). “Your brain doesn’t like conflict,” Marasco explains. So if it thinks “my arm’s moving and I’m holding onto my nose, that must mean my nose is extending.”

To test the device, the team applied vibrations to the reinnervated muscles on six amputee participants’ chests or upper arms and asked them to indicate how they felt their hands were moving. Each amputee reported feeling various hand, wrist, and elbow motions, or “percepts,” in their missing limbs. Kitts, who had met Marasco while taking part in the studies he was involved in at the institute in Chicago, was one of the subjects in the experiment. “The first time I felt the sense of movement was remarkable,” she says.

In total, the experimenters documented 22 different percepts from their participants. “It’s hard to get this sense reliably, so I was encouraged to see the capability of several different subjects to get a reasonable sense of hand position from this illusion,” says Dustin Tyler, a biomedical engineer at Case Western Reserve University who was not involved in the work. He adds that while this is a new, noninvasive approach to proprioception, he and others are also working on devices that restore this sense by stimulating nerves directly with implanted devices (Sci Rep, 8:9866, 2018).

Marasco and his colleagues then melded the vibration with the movement-controlled prostheses, so that when participants decided to move their artificial limbs, a vibrating stimulus was applied to the muscles to provide them with proprioceptive feedback. When the subjects conducted various movement-related tasks with this new system, their performance significantly improved (Sci Transl Med, 10:eaao6990, 2018).

The first time I felt the sense of movement was remarkable.

“This was an extremely thorough set of experiments,” says Marcia O’Malley, a biomedical engineer at Rice University who did not take part in that study. “I think it is really promising.”

Although the mechanisms behind the illusion largely remain a mystery, Marasco says, the vibrations may be activating specific muscle receptors that provide the body with a sense of movement. Interestingly, he and his colleagues have found that the “sweet spot” vibration frequency for movement perception is nearly identical in humans and rats—about 90 Hz (PLOS ONE, 12:e0188559, 2017).

For Kitts, a system that provides proprioceptive feedback means being able to use her prosthetic without constantly watching it—and feeling it instead. “It’s whole new level of having a real part of your body,” she says.

Source of the article: www.the-scientist.com