Utah amputee could ‘feel’ his wife’s touch when they shook hands, thanks to motorized prosthetic arm

Researchers have developed a way for the prosthetic arm with fingers to mimic the way a human hand feels objects by sending the appropriate signals to the brain


                            Utah amputee could ‘feel’ his wife’s touch when they shook hands, thanks to motorized prosthetic arm

Keven Walgamott had a “good feeling” about picking up an egg without crushing it. What seems simple for nearly everyone else can be a Herculean task for Walgamott, who lost his left hand and part of his arm in an accident, 17 years ago.

He was testing out the prototype of a high-tech prosthetic arm with fingers, which can not only move, but they can move with his thoughts. And thanks to a biomedical engineering team at the University of Utah, Walgamott "felt" the egg well enough so his brain could tell the prosthetic hand not to squeeze too hard.

The team, led by University of Utah biomedical engineering associate professor Gregory Clark, has developed a way for the prosthetic arm (called LUKE Arm, so named after the robotic hand that Luke Skywalker got in The Empire Strikes Back) with fingers to mimic the way a human hand feels objects by sending the appropriate signals to the brain.

This implies that an amputee wearing the prosthetic arm can sense the touch of something soft or hard, understand better how to pick it up and perform delicate tasks that would otherwise be impossible with a standard prosthetic with metal hooks or claws for hands. 

The bionic hand user could "feel" up to 119 perceptions - ranging from pressure to vibration - enabling the person to identify and handle objects faster and more accurately than with the use of traditional sensation-mimicking systems. He could also successfully perform several daily-life tasks, even those he had previously found challenging, like putting a pillow in a pillowcase.

The bionic hand user was equipped with a sensory feedback system that can mimic natural sensory signals. This sensory feedback, according to the study published in Science Robotics, improved grasping performance.

Walgamott, a real estate agent from West Valley City, Utah, and one of seven test subjects was able to pluck grapes without crushing them and hold his wife’s hand with a sensation in the fingers similar to that of a non-disabled person.

Study participant performing daily tasks. (George et al., Sci. Robot. 4, eaax2352 - 2019)

As shown in the images above (George et al., Sci. Robot. 4, eaax2352 - 2019), the participant performed several one- and two-handed daily tasks while using the sensorized prosthesis, including moving an egg (A), picking grapes (B), texting on his phone, and shaking hands with his wife (D).

The experiments performed in this study were completed in two- to three-hour sessions, one to three times a week, across the 14-month duration of the study. The participant performed “activities of daily living”, which were divided into the following categories - basic (feeding and dressing); instrumental (housework, meal preparation, and technology use); and those that he had found challenging without the prosthesis (loading a pillow into a pillowcase, hammering, donning and doffing a ring). 

The researchers say while improvements are difficult to quantify with activities of daily living, but the participant noted that sensory feedback was particularly useful when manipulating fragile objects and spontaneously reported that he enjoyed the sensation of “feeling” objects in his hand. “One of the first things he wanted to do was put on his wedding ring. That’s hard to do with one hand. It was very moving,” says the team.

Participant performing a clinical test for hand dexterity. (George et al., Sci. Robot. 4, eaax2352 - 2019)

According to the researchers, the findings demonstrate that artificial sensory feedback can improve fine motor control, giving the user the ability to sense object properties through a bionic hand. Further, these artificial sensory experiences are enriched when the sensory feedback is designed to mimic the nervous system’s natural language, says the study.

“The present results build on previous work, demonstrating the potential of biologically inspired sensory feedback systems to restore “natural feeling” in the phantom hands of amputees. We extend these previous findings by showing that grasp force is achieved faster and more accurately and that fragile objects are transferred more quickly with sensory feedback than without,” says the research team from University of Utah (Salt Lake City); University of Chicago (US); and Lerner Research Institute, Cleveland Clinic (Cleveland).

The researchers say while current prosthetics can replace lost motor functions, users still express the desire to have their artificial limb feel more natural. Responsiveness has also been one of the main barriers to artificial limbs. Neuromyoelectric prosthetics – where electrodes placed on or implanted in muscles convey electrical signals from the organ to the prosthetic – have shown promise in providing accurate sensory feedback to users. However, demonstrations of these systems are very limited. 

Accordingly, the researchers developed a system that allows the prosthetic arm to tap into the wearer’s nerves, which are like biological wires that send signals to the arm to move.

“We developed a feedback system that mimics the temporally-changing activation patterns of nerve fibers in human hands, which was then implemented on an implanted prosthetic hand,” says the study. It was then evaluated on the study participant with a lower-arm amputation, allowing him to report size, texture correctly, and compliance of different objects even while blindfolded and wearing headphones.

The quality of the perceptions also varied - some were described as “vibration” (36%), “pressure” (29%), or “tapping” (3%); others were described as pain (16%); a few were described as “tightening” (12%) and joint movement (3%). The participant also reported decreased phantom pain and described the emotional impact of artificial touch when he used the bionic hand to shake hands with his wife and “felt her touch through it for the first time.” 

“Sensory feedback improved grip precision. Sensory feedback was provided on some experimental blocks but not others. The participant’s grip performance was more precise with sensory feedback than without, as evidenced by less variable grip force on six of eight objects. The participant moved the object without breaking it significantly more often with sensory feedback than without (32 of 40 times versus 22 of 40 times; and did so more rapidly,” show the results from the study. 

The participant used electromyographic signals from residual arm muscles to move the prosthetic hand and manipulate a large lacrosse ball or a small golf ball, all while blindfolded. Artificial sensory feedback from electrode array stimulation of residual nerves was driven by sensors on the prosthetic hand. (George et al., Sci. Robot. 4, eaax2352 - 2019)

Further, to assess the degree to which the prosthesis could convey object information, the participant’s task was to report the size of the object (small versus large). The participant was able to perform this task almost perfectly with the sensory feedback, correctly reporting the size on 31 of 32 object presentations.

“Amputees have expressed a desire for sensory feedback to reduce their dependence on visual feedback. The ability to feel grip force while grasping and holding objects is the most important aspect of sensory feedback for amputees. The sensory feedback provided here allowed the participant to perform object discrimination tasks without visual or auditory feedback and enabled the participant to exert grip forces more precisely,” says the study

In addition to creating a prototype of the arm with a sense of touch, the team is currently developing a version that is completely portable and does not need to be wired to a computer outside the body. Instead, everything would be connected wirelessly, giving the wearer complete freedom, say the researchers.

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