The magic touch: bringing sensory feedback to brain-controlled prosthetics

Researchers at the University of Chicago are leading a project to introduce the sense of touch to the latest brain-controlled prosthetic arms. Adding sensory feedback to already-complex neuroprosthetics is a towering task, but offers the chance to radically transform the lives of amputees and people living with paralysis.The future of prosthetics

Source of the Article: medicaldevice-network.com

Logan students spend year building special prosthetic leg

A group of Logan High School students spent the entire year creating a prosthetic limb, which simultaneously charges while the person walks.

The InvenTeam talked with members in the industry, who told stories of patients not being able to enjoy long trips outdoors for fear of losing power.

Logan teacher Steve Johnston said the class provides a unique opportunity.

“I try to always emphasize with the kids that we want to give them a unique engineering experience,” Johnston said. “We also want to make sure the item can help people in everyday life.”

The project faced several obstacles that the students had to overcome, including starting from scratch.

“We can’t test this on a human subject,” Johnston said. “We had to spend more time creating a tester to simulate the heel strike and foot motion to harvest energy from it.”

A bluetooth device in the leg allows a user to view the power remaining on their cellphone. The battery is charged by a person’s heel striking the ground.

A pair of engineers were brought in during the year to help students with the project.

The group will now give a presentation on their invention at the EurekaFest at MIT (Massachusetts Institute of Technology), as well as tour the area.

Source of the Article: wizmnews.com

Prosthetic leg for Amputees designed by Jae-Hyun An to encourage new genre of ballet

Source of the Article: Dezeen.com
Prosthetic ballet leg for amputees encourages new genre of dancePratt Institute graduate Jae-Hyun An has created a prosthetic leg that allows amputees to perform ballet like never before. Unlike regular artificial limbs, which are designed to mimic the human body, the Marie-T enables amputee ballet dancers to enhance their performance. Made up of three components, Marie-T features a weighty foam-injected rotational moulded foot, with a stainless-steel toe and rubber grip that help provide the dancer with balance and momentum during rotations.

In mainstream ballet, dancers typically move in and out of the pointe position – when all body weight is supported by the tips of fully extended feet within pointe shoes. However, because of the immense strain on the foot and ankle of a performer, it is impossible for a ballet dancer to constantly perform in this position. Jae-Hyun An, who studied on the Pratt’s Industrial Design programme, designed the carbon-fibre Marie-T to enable amputees to dance on pointe throughout a performance.Jae-Hyun An designs prosthetic leg for ballet called Marie-T

New York-based An said the design, which is named after 19th-century Swedish ballet dancer Marie Taglioni, could encourage amputees to develop a new choreography that has never been achieved by mainstream ballerinas. “I wanted to explore what would happen if you could allow a person to perform on pointe 100 per cent of the time,” said An, who developed Marie-T over the course of four months. “How would ballet change? I wanted to create a tool for someone to take and let their imagination define the capabilities of the product.”

Prosthetic ballet leg for amputees encourages new genre of dance

During research, An realised that a weak ankle can twist and cause a ballerina in pointe position to wobble. In response, An designed a strong and stable ankle area that helps the ballerina stay in balance. The ankle connects to a slightly curved carbon-fibre limb which helps absorb the shock from the impact of the ballet dancer stepping forward. The limb is topped by a 3D-printed socket with steel round head screws. Ill-fitting prosthetic limbs can cause blisters and rashes on dancers, so An designed the Marie-T so that the parts can be easily switched out when they become well worn or need to be resized. The designer told Dezeen: “Prosthetics by itself is such a powerful and inspirational design. Any form of it is really amazing! Whether it is Hugh Herr’s bionic legs from the Biomechatronics Group in MIT, or the Flex-Foot Cheetah Leg from Ossur, or even a peg leg from… whenever.”

“It is inspiring because the technology is incredible but even more so because of the immense struggle an amputee has to overcome to use these products. Some argue that some of these prostheses give amputees a certain advantage in specific tasks, but I am not sure they would say the same if they ever saw how much training and care it takes to handle a prosthesis,” he continued.

“In my research I came across Viktoria Modesta and she re-interpreted performance with her prosthetics. It was visually so powerful and opened a completely new area of prosthetics for me. I fell in love with the idea of designing something that could expand the artistic and cultural scene of a community with prosthetic users.”

Prosthetic ballet leg for amputees encourages new genre of dance

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.

Story Source:

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>.

Capturing Touch for Prosthetic Limbs Through Artificial Skin

RESEARCH
Luke E. Osborn and Nitish V. Thakor

Those living with upper limb differences face numerous challenges, including lost limb movement and dexterity as well as missing sensory information during object manipulation. From a user’s perspective, upper limb prostheses still have several issues with control, general discomfort from the socket, and lack of sensory feedback 1. Significant efforts have resulted in sophisticated algorithms for decoding intended prosthesis movements along multiple degrees of freedom that have enabled amputees to regain more dexterous prosthesis control 2. Another seminal advancement is targeted muscle reinnervation surgery 3, which targets nerves to different intact muscle groups such as on the chest to provide a source of well differentiated myoelectric signals for prosthesis control.

Lack of sensory information and feedback has limited the perceptual capability of the amputees. Major advancements were made in 2014 when researchers used implanted stimulating electrodes to provide sensory information back to an upper limb amputee for detecting different objects during grasping 4, conveying pressure information to complete dexterous manipulation of a fragile object 5, and general tactile activation 6.

Touch Complexity

Sensory information, specifically touch, is an extremely complex and multifaceted percept that remains difficult to completely capture. Thousands of receptors in our hands work together to pass tactile information from our fingertips to the spinal cord and into the somatosensory regions of the cortex. For upper limb amputees, the peripheral nerves and feedback to the brain still exist, but these pathways are disrupted at the receptor level in the residual limb. Researchers can take advantage of the remaining intact neural pathways to provide some element of tactile information back to an amputee. One challenge is how to convey specific tactile information by stimulating remaining peripheral nerves either through the skin or directly. However, the disrupted distribution of the receptors in the amputee’s skin and their complex tactile encoding, both individually and as a population, make it hard to replicate complex touch sensations.

Tactile information is captured by various receptors in the skin. Mechanoreceptors are responsible for our ability to perceive sensations such as pressure, texture, vibration, and stretch whereas muscle spindles and Golgi tendons drives our innate ability to perceive position (i.e. proprioception). Thermoceptors convey sensations of temperature while nociceptors enable us to feel mechanical pain, such as a sharp prick or a cut 7. Researchers have been able to provide sensory percepts of pressure 4,5,8, vibrations 8, texture 9, illusory movements 10, and now even pain 11 to upper limb amputees. Extensive knowledge gained from studying skin receptor properties has spurred the development of artificial electronic skin (e-skin) and more specifically the electronic dermis (e-dermis).

Artificial Skin

Researchers have previously developed artificial electronic skins that take advantage of the developments in flexible electronics12,13 to produce e-skins. In one such implementation, the digital mechanoreceptor inspired sensor translates pressure into oscillatory spikes 14, and in another implementation the oscillatory output drives nerve stimulation of an artificial afferent in an invertebrate 15. Most advances in sensors and artificial skins are focused on materials and electronics and typically do not incorporate sensory feedback to a prosthesis or amputee. For upper limb prostheses, one challenge is translating the response of an artificial skin into meaningful sensory information to the user by mimicking the natural sensory encoding of touch.

E-dermis for Perception of Touch and Pain

Using biology as a model, we developed a multilayered electronic dermis (e-dermis) for capturing a range of tactile perceptions at the fingertips of a prosthetic hand. We implemented a neuromorphic model to transform the e-dermis measurements to biologically relevant spiking activity for nerve stimulation, which was then used for transcutaneous electrical nerve stimulation (TENS) to provide sensory feedback (Fig. 1A). A neuromorphic system is one that attempts to mimic components of a neural system through digital signals, in this case representing touch. The idea behind this implementation is to try and capture actual receptor characteristics to convey tactile information to an amputee.

The e-dermis mimics the skin and its receptors in several ways: it has an array of sensors (receptors); the sensors are arranged over multiple layers (Fig. 1B); it produces receptor like signals; and it encodes sensor information the manner encoded by nerves. The e-dermis was made up of piezoresistive fabric (Eeonyx), which was placed between intersecting conductive traces (LessEMF) to create pressure sensitive taxels. A 1-mm layer of silicone rubber (Dragon Skin 10, Smooth-On) was added between the epidermal and dermal layers of the e-dermis and a 2-mm rubber layer added protection and compliance to the fingertip e-dermis.

Our goal was to model the skin and its receptors, and to mimic the range of perceptions from light touch to noxious, or painful. To detect pressure and pain, we treated the epidermal (upper) layer of the e-dermis as a nociceptor and the sensing elements in the dermal (bottom) layer as mechanoreceptors. The neuromorphic output from the e-dermis was then used as the stimulation signal for sensory feedback.

To understand the sensory perceptions perceived by an amputee during nerve stimulation. We performed sensory mapping of the phantom hand of one amputee as well as a quantification of the various sensory perceptions, including discomfort resulting from stimulation at a noxious level produced by controlling different stimulation parameters. Additional details can be found in 11.

To evaluate the ability of the amputee wearing the prosthesis to differentiate between tactile pressure and pain, we used 3 objects of varying curvature for a simple prosthesis grasping task (Fig. 2A). The prosthesis was able to reliably detect pain when grasping the sharpest item (Fig, 2B). Indeed, the prosthesis responded with a reflex to drop the object, similar to what happens in biology when we experience pain (i.e. withdrawal reflex). In another experiment where the user’s vision was occluded from the object being grasped, the sharper object was perceived by the user as being more painful (Fig. 2C).

One question that should be addressed: why pain? Our perception of pain is valuable because it protects our bodies by conveying information on things in our environment that are potentially damaging or harmful. A prosthetic arm doesn’t have this ability. Our recent research investigated how the idea of sensing pain could potentially benefit a prosthesis user. Because a prosthesis doesn’t have the ability to heal itself, we created a prosthesis pain reflex to compliment the sensory information being sent back to the user. In a way, this additional sensation of pain enables the prosthesis itself to become a little more lifelike and “self-aware” in its ability to understand the environment. At the same time, the tactile information being sent back to the user hopefully helps create a more realistic and feature-rich sensation of touch.

The combination of the biologically inspired e-dermis with neuromorphic stimulation models attempts to capture some of the nuanced characteristics of natural receptors, specifically those that convey innocuous and noxious signals. As upper limb prostheses continue to advance we turn to the human body as a template for developing sophisticated sensors and techniques for making these prosthetic devices more lifelike. Recreating the complex sensation of touch requires continued research of how nerve stimulation is perceived by a prosthesis user as well as how we can more accurately convey artificial neural signals that can be perceived as natural sensations.

Acknowledgements

This work was partially funded by the Space@Hopkins funding initiative through Johns Hopkins University. The results of this study were published in the June 2018 edition of Science Robotics:

Osborn, L. E., Dragomir, A., Betthauser, J. L., Hunt, C. L., Nguyen, H. H., Kaliki, R. R., & Thakor, N. V. Prosthesis with neuromorphic multilayered e-dermis perceives touch and pain. Science Robotics, 2018;3(19):eaat3818. DOI: 10.1126/scirobotics.aat3818.

References

  1. Biddiss, E., Beaton, D., and Chau, T. Consumer design priorities for upper limb prosthetics. Disability and Rehabilitation: Assistive Technology. 2007;2(6):346-57. DOI: 10.1080/17483100701714733.
  2. Farina, D. et al. Man/machine interface based on the discharge timings of spinal motor neurons after targeted muscle reinnervation. Nature Biomedical Engineering. 2017;1(2):25. DOI: 10.1038/s41551-016-0025.
  3. Kuiken, T. A. et al. Targeted reinnervation for enhanced prosthetic arm function in a woman with a proximal amputation: a case study. Lancet. 2007;369(9559):371-80. DOI: 10.1016/S0140-6736(07)60193-7.
  4. Raspopovic, S. et al. Restoring natural sensory feedback in real-time bidirectional hand prostheses. Science Translational Medicine. 2014;6(222):222ra19. DOI: 10.1126/scitranslmed.3006820.
  5. Tan, D. W. et al. A neural interface provides long-term stable natural touch perception. Science Translational Medicine. 2014;6(257):257ra138. DOI: 10.1126/scitranslmed.3008669.
  6. Ortiz-Catalan, M., Håkansson, B., and Brånemark, R. An osseointegrated human-machine gateway for long-term sensory feedback and motor control of artificial limbs. Science Translational Medicine. 2014;6(257):257re6. DOI: 10.1126/scitranslmed.3008933.
  7. Abraira, V. and Ginty, D. The sensory neurons of touch. Neuron. 2013;79(4):618-39. DOI: 10.1016/j.neuron.2013.07.051.
  8. Wendelken, S. et al. Restoration of motor control and proprioceptive and cutaneous sensation in humans with prior upper-limb amputation via multiple utah slanted electrode arrays (USEAs) implanted in residual peripheral arm nerves. Journal of Neuroengineering and Rehabilitation. 2017;14(1):121. DOI: 10.1186/s12984-017-0320-4.
  9. Oddo, C. M. et al. Intraneural stimulation elicits discrimination of textural features by artificial fingertip in intact and amputee humans. eLife. 2016;5:e09148. DOI: 10.7554/eLife.09148.
  10. Marasco, P. D. et al. Illusory movement perception improves motor control for prosthetic hands. Science Translational Medicine. 2018;10(432):eaao6990. DOI: 10.1126/scitranslmed.aao6990.
  11. Osborn, L. E. et al. Prosthesis with neuromorphic multilayered e-dermis perceives touch and pain. Science Robotics. 2018;3(19):eaat3818. DOI: 10.1126/scirobotics.aat3818.
  12. Kim, J. et al. Stretchable silicon nanoribbon electronics for skin prosthesis. Nature Communications. 2014;5:5747. DOI: 10.1038/ncomms6747.
  13. Yokota, T. et al. Ultraflexible organic photonic skin. Science Advances. 2016;2(4):e1501856. DOI: 10.1126/sciadv.1501856.
  14. Tee, B. C. K. et al. A skin-inspired organic digital mechanoreceptor. Science. 2015;350(6258):313-6. DOI: 10.1126/science.aaa9306.
  15. Kim, Y. et al. A bioinspired flexible organic artificial afferent nerve. Science. 2018;360(6392):998-1003. DOI: 10.1126/science.aao0098.

Biography

Luke Osborn
Luke Osborn, MSE, is a PhD student in biomedical engineering at Johns Hopkins University. His research in the Neuroengineering and Biomedical Instrumentation Lab focuses on developing tactile sensing technologies, neuromorphic modeling of sensory information, and sensory feedback for upper limb prostheses. He is a student member of the IEEE.

Nitish Thakor
Nitish Thakor, PhD, is a professor of biomedical engineering, electrical and computer engineering, and neurology at Johns Hopkins and directs the Laboratory for Neuroengineering. He is also the director the Singapore Institute for Neurotechnology (SINAPSE) at the National University of Singapore. His research focus is in the field of neuroengineering, including neural diagnostic instrumentation, neural microsystems, neural signal processing, optical imaging of the nervous system, neural control of prostheses, and brain-machine interfaces. He is a recipient of a Research Career Development Award from the National Institutes of Health and a Presidential Young Investigator Award from the US National Science Foundation. He is a founding fellow of the Biomedical Engineering Society and fellow of the IEEE.

About BrainInsight

BrainInsight, the IEEE Brain Initiative eNewsletter, is a quarterly online publication, featuring practical and timely information and forward-looking commentary on neurotechnologies. BrainInsight describes recent breakthroughs in research, primers on methods of interests, or report recent events such as conferences or workshops.


IEEE
Source of the article: Brain.ieee.org

Solar-powered synthetic skin could give robots a sense of touch and allow amputees to feel again

Synthetic skin capable of touch sensitivity could make smart prosthetic hands more useful for amputees

AI IS FUELING SMARTER PROSTHETICS THAN EVER BEFORE

By Andrea Powell

THE DISTANCE BETWEEN prosthetic and real is shrinking. Thanks to advances in batteries, brain-controlled robotics, and AI, today’s mechanical limbs can do everything from twist and point to grab and lift. And this isn’t just good news for amputees. “For something like bomb disposal, why not use a robotic arm?” says Justin Sanchez, manager of Darpa’s Revolutionizing Prosthetics program. Well, that would certainly be handy.

Brain-Operated Arm

Capable of: Touching hands, reaching out
Mind-controlled limbs aren’t new, but University of Pittsburgh scientists are working on an arm that can feel. Wires link the arm and brain, so when pressure is applied, a signal alerts the sensory cortex.

Hand That Sees

Capable of: Looking for an opportunity
Researchers at Newcastle University have designed a hand with a tiny camera that snaps pics of objects in its view. Then an AI determines an action. Like, grasp that beer and raise it to my mouth.

The Linx

Capable of: Climbing every mountain
Unlike older lower-limb prosthetics, the Linx can tell when it’s sitting in a chair. At just under 6 pounds, it relies on seven sensors that collect data on activity and terrain, helping the leg adapt to new situations.

Bebionic

Capable of: Making rude gestures
It’s the only prosthetic hand with air-bubbled fingertips—great for typing and handling delicate objects (like eggs). And because individual motors power natural movements, wearers can flip the bird in an instant.

The Michelangelo

Capable of: Painting masterpieces
Whereas many prosthetics have a stiff thumb, Ottobock designed this model with a secondary drive unit in the fattest finger—making it opposable. So it’s easier to hold, say, a paintbrush. Big thumbs up!

The LUKE Arm

Capable of: Wielding lightsabers
Yep, LUKE as in Skywalker. The Life Under Kinetic Evolution arm is the first muscle- controlled prosthetic to be cleared by the FDA. With up to 10 motors in the arm, the Force is definitely with this one.

Source of the Article: Wired.com

Low-cost prosthetic foot mimics natural walking

New design can be tuned to an individual’s body weight and size.

Jennifer Chu | MIT News Office

Prosthetic limb technology has advanced by leaps and bounds, giving amputees a range of bionic options, including artificial knees controlled by microchips, sensor-laden feet driven by artificial intelligence, and robotic hands that a user can manipulate with her mind. But such high-tech designs can cost tens of thousands of dollars, making them unattainable for many amputees, particularly in developing countries.

Now MIT engineers have developed a simple, low-cost, passive prosthetic foot that they can tailor to an individual. Given a user’s body weight and size, the researchers can tune the shape and stiffness of the prosthetic foot, such that the user’s walk is similar to an able-bodied gait. They estimate that the foot, if manufactured on a wide scale, could cost an order of magnitude less than existing products.

The custom-designed prostheses are based on a design framework developed by the researchers, which provides a quantitative way to predict a user’s biomechanical performance, or walking behavior, based on the mechanical design of the prosthetic foot.

“[Walking] is something so core to us as humans, and for this segment of the population who have a lower-limb amputation, there’s just no theory for us to say, ‘here’s exactly how we should design the stiffness and geometry of a foot for you, in order for you to walk as you desire,’” says Amos Winter, associate professor of mechanical engineering at MIT. “Now we can do that. And that’s super powerful.”

Winter and former graduate student Kathryn Olesnavage report details of this framework in IEEE’s Transactions on Neural Systems and Rehabilitation. They have published their results on their new prosthetic foot in the ASME Journal of Mechanical Design, with graduate student Victor Prost and research engineer William Brett Johnson.

Following the gait

In 2012, soon after Winter joined the MIT faculty, he was approached by Jaipur Foot, a manufacturer of artificial limbs based in Jaipur, India. The organization manufactures a passive prosthetic foot, geared toward amputees in developing countries, and donates more than 28,000 models each year to users in India and elsewhere.

“They’ve been making this foot for over 40 years, and it’s rugged, so farmers can use it barefoot outdoors, and it’s relatively life-like, so if people go in a mosque and want to pray barefoot, they’re likely to not be stigmatized,” Winter says. “But it’s quite heavy, and the internal structure is made all by hand, which creates a big variation in product quality.”

The organization asked Winter whether he could design a better, lighter foot that could be mass-produced at low cost.

“At that point, we started asking ourselves, ‘how should we design this foot as engineers? How should we predict the performance, given the foot’s stiffness and mechanical design and geometry? How should we tune all that to get a person to walk the way we want them to walk?’” Winter recalls.

The team, led by Olesnavage, first looked for a way to quantitatively relate a prosthesis’ mechanical characteristics to a user’s walking performance — a fundamental relationship that had never before been fully codified.

While many developers of prosthetic feet have focused on replicating the movements of able-bodied feet and ankles, Winter’s team took a different approach, based on their realization that amputees who have lost a limb below the knee can’t feel what a prosthetic foot does.

“One of the critical insights we had was that, to a user, the foot is just kind of like a black box — it’s not connected to their nervous system, and they’re not interacting with the foot intimately,” Winter says.

Instead of designing a prosthetic foot to replicate the motions of an able-bodied foot, he and Olesnavage looked to design a prosthetic foot that would produce lower-leg motions similar to those of an able-bodied person’s lower leg as they walk.

“This really opened up the design space for us,” Winter says. “We can potentially drastically change the foot, so long as we make the the lower leg do what we want it to do, in terms of kinematics and loading, because that’s what a user perceives.”

With the lower leg in mind, the team looked for ways to relate how the mechanics of the foot relate to how the lower leg moves while the foot is in contact with the ground. To do this, the researchers consulted an existing dataset comprising measurements of steps taken by an able-bodied walker with a given body size and weight. With each step, previous researchers had recorded the ground reaction forces and the changing center of pressure experienced by a walker’s foot as it rocked from heel to toe, along with the position and trajectory of the lower leg.

Winter and his colleagues developed a mathematical model of a simple, passive prosthetic foot, which describes the stiffness, possible motion, and shape of the foot. They plugged into the model the ground reaction forces from the dataset, which they could sum up to predict how a user’s lower leg would translate through a single step.

With their model, they then tuned the stiffness and geometry of the simulated prosthetic foot to produce a lower-leg trajectory that was close to the able-bodied swing — a measure they consider to be a minimal “lower leg trajectory error.”

“Ideally, we would tune the stiffness and geometry of the foot perfectly so we exactly replicate the motion of the lower leg,” Winter says. “Overall, we saw that we can get pretty darn close to able-bodied motion and loading, with a passive structure.”

Evolving on a curve

The team then sought to identify an ideal shape for a single-part prosthetic foot that would be simple and affordable to manufacture, while still producing a leg trajectory very similar to that of able-bodied walkers.

To pinpoint an ideal foot shape, the group ran a “genetic algorithm” — a common technique used to weed out unfavorable options, in search of the most optimal designs.

“Just like a population of animals, we made a population of feet, all with different variables to make different curve shapes,” Winter says. “We loaded them into simulation and calculated their lower leg trajectory error. The ones that had a high error, we killed off.”

Those that had a lower error, the researchers further mixed and matched with other shapes, to evolve the population toward an ideal shape, with the lowest possible lower leg trajectory error. The team used a wide Bezier curve to describe the shape of the foot using only a few select variables, which were easy to vary in the genetic algorithm. The resulting foot shape looked similar to the side-view of a toboggan.

Olesnavage and Winter figured that, by tuning the stiffness and shape of this Bezier curve to a person’s body weight and size, the team should be able to produce a prosthetic foot that generates leg motions similar to able-bodied walking. To test this idea, the researchers produced several feet for volunteers in India. The prostheses were made from machined nylon, a material chosen for its energy-storage capability.

“What’s cool is, this behaves nothing like an able-bodied foot — there’s no ankle or metatarsal joint — it’s just one big structure, and all we care about is how the lower leg is moving through space,” Winter says. “Most of the testing was done indoors, but one guy ran outside, he liked it so much. It puts a spring in your step.”

Going forward, the team has partnered with Vibram, an Italian company that manufactures rubber outsoles — flexible hiking boots and running shoes that look like feet. The company is designing a life-like covering for the team’s prosthesis, that will also give the foot some traction over muddy or slippery surfaces. The researchers plan to test the prosthetics and coverings on volunteers in India this spring.

Winter says the simple prosthetic foot design can also be a much more affordable and durable option for populations such as soldiers who want to return to active duty or veterans who want to live an active lifestyle.

“A common passive foot in the U.S. market will cost $1,000 to $10,000, made out of carbon fiber. Imagine you go to your prosthetist, they take a few measurements, they send them back to us, and we send back to you a custom-designed nylon foot for a few hundred bucks. This model is potentially game-changing for the industry, because we can fully quantify the foot and tune it for individuals, and use cheaper materials.”

This research was funded, in part, by the MIT Tata Center for Technology and Design.

Source of Article: http://news.mit.edu/2018/low-cost-prosthetic-foot-mimics-natural-walking-0627

Surgical technique improves sensation, control of prosthetic limb

Surgical technique improves sensation, control of prosthetic limb
A schematic demonstrating the control mechanism of the neural interface. The subject’s leg movement is sent to the prosthesis as an EMG signal (blue arrows), and the movement of the prosthesis is communicated back to the subject’s nervous system (green arrow). Credit: T.R. Clites et al., Science Translational Medicine (2018)

Humans can accurately sense the position, speed, and torque of their limbs, even with their eyes shut. This sense, known as proprioception, allows humans to precisely control their body movements.

Despite significant improvements to prosthetic devices in recent years, researchers have been unable to provide this essential sensation to people with artificial limbs, limiting their ability to accurately control their movements.

Researchers at the Center for Extreme Bionics at the MIT Media Lab have invented a new neural interface and communication paradigm that is able to send movement commands from the central nervous system to a robotic prosthesis, and relay proprioceptive feedback describing movement of the joint back to the central nervous system in return.

This new paradigm, known as the agonist-antagonist myoneural interface (AMI), involves a novel surgical approach to  amputation in which dynamic muscle relationships are preserved within the amputated limb. The AMI was validated in extensive preclinical experimentation at MIT prior to its first surgical implementation in a human patient at Brigham and Women’s Faulkner Hospital.

In a paper published today in Science Translational Medicine, the researchers describe the first human implementation of the agonist-antagonist myoneural interface (AMI), in a person with below-knee amputation.

The paper represents the first time information on joint position, speed, and torque has been fed from a prosthetic limb into the nervous system, according to senior author and project director Hugh Herr, a professor of media arts and sciences at the MIT Media Lab.

“Our goal is to close the loop between the peripheral nervous system’s muscles and nerves, and the bionic appendage,” says Herr.

To do this, the researchers used the same biological sensors that create the body’s natural proprioceptive sensations.

The AMI consists of two opposing muscle-tendons, known as an agonist and an antagonist, which are surgically connected in series so that when one muscle contracts and shortens—upon either volitional or electrical activation—the other stretches, and vice versa.

This coupled movement enables natural biological sensors within the muscle-tendon to transmit electrical signals to the central nervous system, communicating muscle length, speed, and force information, which is interpreted by the brain as natural joint proprioception.

“Because the muscles have a natural nerve supply, when this agonist-antagonist muscle movement occurs information is sent through the nerve to the brain, enabling the person to feel those muscles moving, both their position, speed, and load,” he says.

By connecting the AMI with electrodes, the researchers can detect electrical pulses from the muscle, or apply electricity to the muscle to cause it to contract.

“When a person is thinking about moving their phantom ankle, the AMI that maps to that bionic ankle is moving back and forth, sending signals through the nerves to the brain, enabling the person with an amputation to actually feel their bionic ankle moving throughout the whole angular range,” Herr says.

Decoding the electrical language of proprioception within nerves is extremely difficult, according to Tyler Clites, first author of the paper and graduate student lead on the project.

“Using this approach, rather than needing to speak that electrical language ourselves, we use these  to speak the language for us,” Clites says. “These sensors translate mechanical stretch into electrical signals that can be interpreted by the brain as sensations of position, speed, and force.”The AMI was first implemented surgically in a human patient at Brigham and Women’s Faulkner Hospital, Boston, by Matthew Carty, one of the paper’s authors, a surgeon in the Division of Plastic and Reconstructive Surgery, and an MIT research scientist.

In this operation, two AMIs were constructed in the residual limb at the time of primary below-knee amputation, with one AMI to control the prosthetic ankle joint, and the other to control the prosthetic subtalar joint.

“We knew that in order for us to validate the success of this new approach to amputation, we would need to couple the procedure with a novel prosthesis that could take advantage of the additional capabilities of this new type of residual limb,” Carty says. “Collaboration was critical, as the design of the procedure informed the design of the robotic limb, and vice versa.”

Toward this end, an advanced prosthetic limb was built at MIT and electrically linked to the patient’s peripheral nervous system using electrodes placed over each AMI muscle following the amputation surgery.

Surgical technique improves sensation, control of prosthetic limb
Credit: Massachusetts Institute of Technology

The researchers then compared the movement of the AMI patient with that of four people who had undergone a traditional below-knee amputation procedure, using the same advanced prosthetic limb.

They found that the AMI patient had more stable control over movement of the prosthetic device and was able to move more efficiently than those with the conventional amputation. They also found that the AMI patient quickly displayed natural, reflexive behaviors such as extending the toes toward the next step when walking down a set of stairs.

These behaviors are essential to natural human movement and were absent in all of the people who had undergone a traditional amputation.

What’s more, while the patients with conventional  reported feeling disconnected to the prosthesis, the AMI patient quickly described feeling that the bionic ankle and foot had become a part of their own body.

“This is pretty significant evidence that the brain and the spinal cord in this patient adopted the prosthetic leg as if it were their biological limb, enabling those biological pathways to become active once again,” Clites says. “We believe proprioception is fundamental to that adoption.”

Surgical technique improves sensation, control of prosthetic limb
Credit: Massachusetts Institute of Technology

The researchers have since carried out the AMI procedure on nine other below-knee amputees and are planning to adapt the technique for those needing above-knee, below-elbow, and above-elbow amputations.

“Previously humans have used technology in a tool-like fashion,” Herr says. “We are now starting to see a new era of human-device interaction, of full neurological embodiment, in which what we design becomes truly part of us, part of our identity.”

Source of the Article: https://medicalxpress.com/news/2018-05-surgical-technique-sensation-prosthetic-limb.html

Source of the Article: https://medicalxpress.com/news/2018-05-surgical-technique-sensation-prosthetic-limb.html

New artificial nerves could transform prosthetics

Source of the Article: www.sciencemag.org

 

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.