Prosthetic wearers all have a common goal in mind – to regain the functionality of an amputated limb. While their prosthetics may restore some degree of movement, it doesn’t carry the feeling of touch when it’s worn. Now scientists at the University of Utah are on the right path to changing that with their latest prosthetic creation. There have been attempts on developing prosthetics capable of providing the wearer with sensation, but those sensations aren’t very precise, and they have some limitations, according to the team. The work developed by a biomedical engineering team at the University of Utah is similar to how our hands function in terms of feeling and sensation.
University of Utah biomedical engineering student, Jacob Geroge, left and professor Greg Clark, right, help to develop the LUKE arm that can operate through the wearer’s thoughts. (Image Credit: Dan Hixson/University of Utah College of Engineering)
Their inventive technology is a collaborative effort between numerous institutions with the University of Utah, according to Gregory Clark, a biomedical engineer and neuroscientist working at the university. The Utah Slanted Electrode Array (USEA) is a new development created by the university’s researchers, which allows the wearer to have an interface between a prosthetic hand and the rest of their sensory and motor nerves found in their arm. This is significant because it provides a link to their nerves and the interface to keep the device operational. It’s done through a surgical process where hundreds of microelectrodes and wires are implanted next to nerve fibers in the arm, which is then connected to a computer. The microelectrodes can interact with small subsets of nerve fibers very selectively and comprehensively. This allows sensory and motor signals to be transferred back and forth between the prosthesis and the nervous system, enabling the arm to move.
However, to lift up objects requires more than the brain’s signals telling the prosthetic to move. It would need to learn how to sense the object through feeling so it would know how much force to apply to the object, which can’t be taught by looking at the object alone. The arm contains sensors in its hand that sends signals to the nerves through the USEA to imitate the sensation of touching something. When contact is made with an object, a set of impulses shoot up the nerves, reaches the brain, which then tapers off. To create this effect, the team used mathematical calculations with documented impulses from a primate’s arm. This was done to model how humans receive different signal patterns. The model was then put into the LUKE prosthetic arm system.
The team hired the help of Keven Walgamott in 2016 to test the new device. Keven had his hand and part of his arm amputated in an electrical accident 17 years ago. He was surgically implanted with the USEA, which connected to a prosthetic arm developed by DEKA Research & Development Corp., who then named the arm LUKE, after the famed prosthetic hand Luke Skywalker wore in the Star Wars franchise. LUKE has been in development for 15 years and consists of metal motors and parts with clear silicon “skin” placed over the hand. It also runs on an external battery, wired to a computer. Walgamott participated in more tests over a 14 month period in the university’s lab. The results of the project can be found on Science Robotics, published July 24th, 2019.
When the USEA interface was activated, Walgamott was able to feel the same things the LUKE hand touched and was also about to determine if an object was soft or hard to the touch. Due to the added sensitivity of the device, Walgamott was also able to carry out more complex movements in his prosthetic, like picking grapes, gently lifting a fragile box, and he was even able to insert a pillow into its case. Walgamott also wanted to clasp both of his hands together. Which is what he did – by reaching out, placing both his hands together and rubbing them side-by-side, he was able to gain feeling in his prosthetic hand as if it were an actual human hand. This was the first time he had regain sensation in 17 years.
Keven Walgamott uses the LUKE prosthetic arm to perform a series of tasks, including picking grapes at the University of Utah’s lab, where tests were carried out. (Image Credit: University of Utah Center for Neural Interfaces)
While LUKE is an imperfect copy of the human arm and hand, it still has room for potential and improvements. For instance, there are more nerve fibers in the arm than there are electrodes found in the USEA, which results in a weaker feeling when wearing the prosthetic, making it invaluable to patients wearing the device. LUKE could also tone down the severity and frequency of pain an amputee feels. Such was the case with Walgamott.
The team hopes to enhance the design of LUKE by creating a more portable version of the prosthesis, allowing wearers to use it in their home. They would also like to switch to wireless implants for the interface, making it less bothersome for the wearer and can also reduce the risk of infection or breakage. Pending approval from the Food and Drug Administration, the team will also start at-home trials within a few months. It will take an additional few years for the devices to be made available commercially, even if trials go as planned and error-free. It’s still enough time for amputees to benefit from the advanced prosthetics.
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