Futuristic bionic arm helps amputees feel the sensation of touch and movement

  • January 06, 2022

Dreaming of a future where Luke Skywalker’s replacement hand is more than a sci-fi fantasy, scientists have designed a “bionic arm” that enlists help from tiny robots to re-create the vital sensations forfeited when one loses an upper limb.  The bots do that by safely vibrating muscles at the amputation site.

By 2028, the global prosthetics and orthotics market is expected to reach over $8 billion, according to a 2021 report from Grand View Research; however, artificial limbs have hit a mechanical roadblock.  They cannot really account for many intuitive sensations that help us in our everyday lives, such as the way it feels to open and close our hands.  “We’re still using technology that kind of reached its zenith around World War II,” explained Paul Marasco, an Associate Professor in the Cleveland Clinic Lerner Research Institute’s Department of Biomedical Engineering and lead author of a study on the new bionic arm published in early September 2021 in the journal Science Robotics.

Enter the bionic arm, a hybrid of metal and realistic skin tones.

Though there are several other teams working on bionic arms, such as the groups behind popular cyberpunk video game Deus Ex and Metal Gear Solid, Marasco touts a few advantages of his version.  The sci-fi-looking device translates information directly to and from the brain via powerful robots about half the size of a standard matchbox.  While turning thoughts into action, the arm can simultaneously contact the brain to deliver sensations corresponding to that intended action.

Not only does the artificial limb appear to be the first bionic arm to simultaneously test several metrics of its benefits over typical prosthetics, those metrics indicate that it replicates the mechanics of natural arms precisely enough to restore unconscious reflexes in amputees who use it.  We rely on such reflexes every day.  For instance, when we pick up a cup of coffee, our hand finds the mug on the table, grips the handle with the right level of firmness and lets go at the perfect time to prevent spills.  We can achieve this task thoughtlessly even on the groggiest of mornings because nerves in our arm muscles automatically respond to our choices — in this case, “I must drink that coffee.”

Traditional prosthetic limbs cannot re-create such seamless movement because they run in manual drive — amputees have to keep their eyes on them at all times and worry about things a nondisabled person usually chalks up to intuition.

After testing the device on two study subjects and using unprecedented analytic tools, the team was excited to discover that the subjects reverted back to reflexive behaviors from before their amputation, including intuitive grip and natural eye movements — they could focus their sight away from the limb.  The metallic arm requires three components:  realignment of nerve endings; mini-robots that work as a sort of control center; and the bionic arm itself.

First, a surgical procedure takes an amputee’s unused nerve endings within the healthy part of the arm — those that used to be dedicated to removed parts, such as fingertips — and “plugs” them into the site of amputation.  “Your brain is like, ‘My fingers are connected to a muscle,’ [it just doesn’t] know that it’s a muscle on your shoulder versus a muscle down in your forearm,” Marasco explained.

The bionic arm is placed onto the amputation site and little robots are fit into the socket.  Those robots press on relevant areas of the site, stimulating the nerve endings that are now attached, when the patient engages the arm.  “You can buzz their muscles and generate these really kind of interesting things — these perceptual illusions of complex hand movement,” Marasco said.

The researchers modified off-the-shelf prosthetic limbs rather than starting from scratch, hoping to fast-track the devices to rehabilitation clinics and make them more cost-effective than traditional prosthetics.  People who use those less advanced artificial limbs often overuse the side of their body without an amputation, leading to back or shoulder problems that ultimately require costly medical care.  “These advanced systems are more expensive to fit to start with, but if you use them, they don’t injure you, because you don’t have to account for them,” Marasco said.  “This is going to be something that’s going to cost less money in the future.”

REFERENCE:  CNet; 01 SEP 2021; Monisha Ravisetti

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