|University of Alabama associate professor of mechanical engineering Xiangrong Shen (right) discusses a prototype of a propellant-driven below-the-knee prosthesis with graduate student Molei Wu.|
Researchers at the Georgia Institute of Technology (Atlanta), University of Alabama (Birmingham), and Vanderbilt University (Nashville, TN) announced a joint program that would develop ankle prostheses that are powered by a gas or liquid-based propellant. The cornerstone of this program is based on research by Michael Goldfarb, a professor of mechanical engineering at Vanderbilt University. Goldfarb has been working on an exoskeleton for the military research group DARPA.
Electric prostheses have several significant limitations. Since batteries have a limited energy density, an individual using a prosthesis motored by an electric motor will have to recharge the unit on a regular basis. With the use of a propellant, an individual may get several days of power from one canister of fuel.
A monopropellant, the fuel used in the prosthesis, has several advantages over traditional propellants. Unlike traditional propellants, a monopropellant doesn’t have to be mixed with a variety of other gases to be used as a fuel source. Instead, only a small amount of a certain catalyst will need to be used.
In addition, the new propellant-powered prosthesis includes a sleeve muscle actuator. The actuator performs the same function as a traditional electric motor. With a monopropellant sleeve muscle actuator, it’s possible to achieve higher performance, lower weight, and higher efficiency than with a traditional electric motor.
“This is a relatively new system,” remarks Xiangrong Shen, assistant professor of mechanical engineering at the University of Alabama. “There are some problems in putting the prosthesis into clinical use because the components of the prosthesis are still being developed. In our research, the long-term goal is to develop powered prostheses with comparable appearance and functionality as human limbs.”