November 8, 2013
Advances In Robotics Make For Better Prosthetics
Brett Smith for redOrbit.com - Your Universe Online
More naturally moving prosthetic legs currently in development will dramatically boost the mobility of lower-limb amputees and allow them to effectively navigate stairs, slopes and uneven ground, according to a recent perspective article in the journal Science Translational Medicine from Michael Goldfarb, a mechanical engineering professor at Vanderbilt University.
Over the last decade, Goldfarb and his team have been conducting research in lower-limb prosthetics, resulting in the development of the first robotic prosthesis. With both powered knee and ankle joints, the prosthesis became the first man-made prosthetic leg controlled by thought when scientists at the Rehabilitation Institute of Chicago developed a neural interface for it.
Along with his graduate students, co-authors Brian Lawson and Amanda Shultz, Goldfarb’s article said lithium-ion batteries, powerful brushless electric motors with rare-Earth magnets, miniaturized sensors, and low-power computer chips are some of the technological advances responsible for the Vanderbilt team’s groundbreaking technology.
“The size and weight of these components is small enough so that they can be combined into a package comparable to that of a biological leg and they can duplicate all of its basic functions,” Vanderbilt research writer David Salisbury wrote in a recent article about the prosthetic technology. “The electric motors play the role of muscles. The batteries store enough power so the robot legs can operate for a full day on a single charge. The sensors serve the function of the nerves in the peripheral nervous system, providing vital information such as the angle between the thigh and lower leg and the force being exerted on the bottom of the foot, etc.
“The microprocessor provides the coordination function normally provided by the central nervous system,” Salisbury added. “And, in the most advanced systems, a neural interface enhances integration with the brain.”
The robotic legs must interact with a user’s nervous system to coordinate the actions of the prosthesis during an activity and recognize a user’s intent to switch from one type of movement to another, such as from walking to climbing a ladder.
Currently, there are several different approaches to connecting a robotic leg to the nervous system that vary greatly in invasiveness. The least invasive approach uses physical sensors to coordinate prosthesis behavior based on body posture. The most invasive approaches involve placing electrodes into a patient’s peripheral nerves or into their brain.
“Approaches that entail a greater degree of invasiveness must obviously justify the invasiveness with substantial functional advantage,” the Vanderbilt team wrote in their article.
Previous research has found patients who have lower-limb prostheses with powered knee and heel joints naturally walk quicker with less hip effort and while expending less energy than when they do using passive prostheses. Amputees with more passive artificial legs also have falls that lead to high rates of hospitalization, particularly among younger amputees.
Because patients with a robotic prosthesis don’t have to compensate for movement deficiencies like they do for passive legs, the artificial limb moves like a natural leg, meaning it can compensate better for uneven ground and reduce the chances of a fall. The limbs can also be programmed to help users recover from a fall.
The Vanderbilt team said the limbs currently being developed win eventually have to win approval from the Food and Drug Administration as a Class I or Class II medical device.