Prosthetic Limb

The 9-pound MPL undergoing research provides 22 degrees of motion and independent movement of the fingers. It provides nearly as much dexterity as a natural limb and, like a natural limb, is designed to respond to a user’s thoughts, according to APL.

‘‘House legs’’ are simply shortened prostheses that are light- weight and easy to don and doff much akin to slippers. This design and concept addresses needs of household ambulation to very active aswell as very inactive persons with bilateral transfemoral and knee disarticulation amputation levels.

“No other arm has the level of dexterity and sensorization that this arm is. It is the most advanced arm in the world,” Michael McLoughlin, who serves as the program manager at the APL, told U.S. Medicine.

McLoughlin said the ultimate objective is to provide a prosthetic that has a level of functionality approaching that of the lost limb.

“That means to be able to form a very complex grasp and to be able to use it very intuitively,” he said. “When we start thinking about interfacing with the nervous system, the real power of what we are doing is that, for the amputee, they are really thinking about moving their arm, they are not learning how to do something new,” he said.

Putting together an advanced system such as this has required widespread expertise, McLoughlin explained, with numerous industry, government and academic contributors.

In addition to working with the University of Pittsburgh and the California Institute of Technology for their experience in brain-computer interfaces, APL is partnering with the University of Chicago for its expertise in sensory perception and with the University of Utah for its expertise to develop implantable devices suitable for interfacing with the human brain.

“This has always been a technically extremely challenging program, on a number of levels — just building the arm that has all the ability of a natural limb is very challenging. The brain-computer interface, just understanding what to do with the signals and how to interpret neural patterns and convert those into the motions of the arm, that is challenging,” McLoughlin said.    

In the case of Hemmes, an electrocortigraphy (ECoG) grid “adapted from seizure-mapping brain electrode arrays was placed on the surface of his brain during surgery,” according to a UPMC release. The researchers used computer software developed in earlier studies to interpret the neural signals sensed by the brain grid. When Hemmes imagined flexing his thumb, a brain signal pattern was created, then interpreted by the computer, allowing him to perform tasks with the prosthetic.

Research on direct brain control of this advanced prosthetic continues. It was announced last year that DARPA-funded researchers at UPMC and the California Institute of Technology would conduct pre-clinical trials with five spinal cord-injured volunteers, testing brain control of mechanical limbs.

The Defense Advanced Research Agency’s Revolutionizing Prosthetics program seeks to expand prosthetic arm options for today’s wounded warriors. Photo from DARPA website.

In another project with Walter Reed National Military Medical Center, a prosthetic controlled in a less invasive manner is undergoing testing. Rather than implanting electrodes in the brain, as may be necessary with spinal cord injured patients, noninvasive surface electrodes allow control for patients who have the functionality to use it.

“We want to be able to adapt the technology to a very wide range of patients,” McLoughlin said. “So someone who is an amputee that has a fairly intact peripheral system, to someone who has a spinal-cord injury or other neurodegenerative condition that is no longer able to utilize their arms, would be able to utilize the prosthetics. We try to adapt to what the patient needs.”