Improving mobility and agility in amputees
Human Foot
A powered prosthesis needs to mimic the human foot and ankle, which contain 26 bones, 33 joints, and more than 100 muscles, tendons and ligaments.

Mobility is a key factor to well being, both emotionally and physically. Over a million US citizens are limb amputees, primarily lower-leg amputees.

Powered prostheses have the ability to reduce metabolic cost and increase the preferred speed of gait for below-knee amputees during straight walking by providing sufficient power during push-off. Additionally, they reduce the asymmetrical gait pattern and secondary complications. The current powered prostheses are designed for walking on a straight path; however, studies have shown that turning steps account for 8 to 50 percent of steps in different activities of daily living, and, on average, account for 25 percent of daily steps.

Mo Rastgaar is developing a lightweight, cable-driven, powered ankle-foot prosthesis capable of steering and even traversing slopes. He has received a National Science Foundation grant of nearly $500,000 to make his new artificial-limb design a reality. With this five-year Faculty Early Career Development (CAREER) Award, Rastgaar will further develop his powered ankle-foot prosthesis. His goal: to create an artificial lower leg with the unique ability to restore amputees’ mobility and agility.

To do this, Rastgaar will develop an ankle joint with two controllable degrees of freedom. His research is based on exploring the turning mechanisms in humans, and understanding the contribution of the ankle and steering mechanisms in human gait. Rastgaar’s team of graduate and undergraduate students at the Human-Interactive Robotics Lab (HIRoLab) have developed a prototype of a powered, steerable ankle-foot prosthesis as well as the infrastructure for evaluating this novel prosthetic robot, which features different sensors to detect how an amputee is walking and incorporate realtime force and trajectory feedback control. As the person walks, signals are sent to a microprocessor that adjusts the prosthesis to match the gait of the individual. The additional degrees of freedom provided in this innovative ankle-foot prosthesis will not only improve the gait of amputees as they stride across undulating terrain, but also reduce the likelihood of falling.