Most people probably do not spend much time contemplating the mechanics of walking, likely unaware of their ankle’s crucial role.
The human ankle supplies considerably more energy than both the hip and knee, making it a critical part of walking. Unfortunately, the standard below-knee prosthesis does not produce enough power to support an amputee’s walk.
Instead, most prostheses only dissipate energy, or store and reuse energy in walking. This requires the amputee’s other joints to work harder, causing the amputee to expend more energy and resulting in an often unnatural and asymmetric gait.
Dr. Xiangrong Shen, assistant professor of mechanical engineering at The University of Alabama, hopes to develop a solution to this problem. After receiving a grant of about $564,000 from The Eunice Kennedy Shriver National Institute of Child Health and Human Development, he launched a four-year project with researchers from UA, Vanderbilt University and the Georgia Institute of Technology to produce alternative below-knee prosthesis capable of actively powering the ankle joint in use.
According to Shen, there are two key components in the new prosthesis. The first is a special type of liquid fuel called monopropellant. Monopropellant works as an energy-storing medium and decomposes upon contact with certain catalysts. The use of this fuel allows for a light-weight prosthesis that stores enough energy to operate for daily use.
The second component is a sleeve muscle actuator, an artificial muscle that replaces the motor used in some alternative prosthesis as the prosthetic actuator. The sleeve muscle is more powerful, with a lighter weight and more compact profile, and its elastic properties are similar to a biological skeletal muscle.
Shen has successfully demonstrated the basic concept of the actuator and how to use it to drive a robotic joint.
“The idea is to benefit those amputees to live a higher quality life. That’s the motivation for all these works,” Shen said.
To better guarantee the safety and reliability of the prosthesis, Shen plans to explore new approaches in fuel storage, exhaust management, thermal insulation and heat management.
“This is a relatively new system,” Shen said. “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.”
After the research element of the project is completed, Shen and his team will test the device at Georgia Tech where he will use their multi-camera motion capturing system to measure his subject’s gait. He will also use a force plate to assess the kinetics in the walking as well.
At UA, Shen will work with Dr. John Baker, professor in mechanical engineering, and Dr. Samit Roy, the William D. Jordan professor of aerospace engineering and mechanics. Shen expects the project to be completed by 2016.