A new prosthetic hand offers amputees the ability to “feel” grasping and manipulating objects—and it’s already being used at home, outside the laboratory setting, for several months.
A new prosthetic hand offers amputees an ability to “feel” grasping and manipulating objects—and it’s already being used at home, outside the laboratory setting, for several months.
A team of biomedical engineers from Florida International University (FIU), Arizona State University, and Cochlear Corporation, has leveraged existing cochlear implant technology to create this Food and Drug Administration investigational device. The work shows the viability of wirelessly enabled peripheral nerve stimulation to help restore critical function to people with upper limb amputations.
A wide variety of motorized prosthetic hands exist on the market today, but such devices do not provide wearers information about contact, force, or grasp, said Ranu Jung, FIU’s chair of biomedical engineering.
“Users are heavily reliant on the visual, looking at the hand and looking at objects as they try to grab or manipulate them while doing different everyday tasks,” she said. “We wanted to create a technology that could fill those gaps, by providing sensory feedback to the residual limb to restore more function and improve quality of life.”
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Jung and her colleagues repurposed existing cochlear implant technology to create a portable wireless system that includes a commercially available motorized prosthetic hand, refitted with an electronic neurostimulator. Twelve fine wire longitudinal intrafascicular electrodes are placed in the median and ulnar nerves of the upper arm. The wires connect to a neurostimulator implanted in the shoulder. This allows for wireless bi-directional communication of signals to and from the native muscle and specific sensors placed on the artificial hand.
“We leveraged the wireless capabilities of the cochlear implant device and then modified the lead to create electrodes that would work in the upper arm as opposed to in the ear,” Jung said. “We then modified the firmware to meet our own needs, as there is a different kind of mapping that needs to be done for the signals, as well as different frequency ranges than are used in the ear.”
When tested in the laboratory, the system was able to successfully relay sensory information to the wearer about hand opening and closing, as well as grasp force.
The group presented the device at Neuroscience 2018, the annual Society for Neuroscience meeting held in November, showing a video of the study participant picking a grape off the bunch without any difficulty.
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“When different electrodes were stimulated, the user felt sensation on different regions of the prosthetic hand—and many of these percepts were stable over several months,” she said. “By changing the stimulation levels, those percepts helped the user gain greater control of hand opening and grasp force, performing better with the hand when the stimulation was on.”
That user is Jason Little, a real estate consultant who lost his arm in a traffic accident in 2011. Prior to this study, he preferred a prosthetic with a hook extension because of its durability. But he said that he has been impressed with what this system can offer. The sensations, he said, feel a little bit like “sticking your finger in a light socket,” but that the sensory feedback provided by the system lines up very closely to where he would feel contact or pressure in a natural hand.
“I’m noticing things now with the sensations that I didn’t before,” he said. “At one point, I was squeezing a stress ball, just opening and closing the prosthetic hand over the ball, and all of a sudden I started getting sensations in parts of the prosthetic hand—sensations I hadn’t felt in years. It’s a little crazy because it’s not even my real hand.”
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Little is already wearing the system at home and is working with the research team to highlight areas for improvement, including an updated hand that motorizes all five fingers, instead of just the thumb and first two fingers. He also asked for an option to change to limited or no sensation.
“The researchers aren’t amputees so they don’t know the day-to-day struggles of wearing a prosthesis,” he said. “They seemed a bit surprised when I said I wanted to be able to get the hand in a neutral position, without any sensory feedback. I had to explain, ‘Sometimes, you just want to put your hand in your pocket. You don’t want to feel everything in your pocket when you do so, you just want it to rest.’”
The team will follow Little for the next year, as well as recruit other amputees to participate in the study. As they do, Jung plans to continue improving the system, as well as refitting its components to design bilateral and lower limb prosthetic systems. The team also plans to see what it might offer to other medical conditions.
“This kind of implantable technology could be utilized in bioelectronic medicine, to target different nerves to influence other organs,” she said. “It’s possible that this kind of system may one day be used to help treat diabetes or chronic pain. It’s our hope that we can take advantage of existing technology with tested, biocompatible elements, to specifically stimulate peripheral nerves to restore function for a variety of conditions.”
Kayt Sukel is an independent writer who focuses on technology.
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