A pliable exoskeleton made of plastics and composite materials were designed by scientists at Carnegie Mellon University, with Harvard University, University of Southern California, MIT, and BioSensics, to help people with ankle-foot weakness from neuromuscular diseases. The device is best suited for people with gait disorders, such as foot drop (forefoot drops because of muscle or nerve weakness) and equinus (limited upper bending motion of ankle), derived from cerebral palsy, stroke, multiple sclerosis, and amyotrophic lateral sclerosis (better known as Lou Gehrig’s disease). Traditional ankle braces exist to help support the ankle and can improve range of motion but wearer is in danger of muscle atrophy from disuse.
The robotic device imitates the muscles, tendons, and ligaments of the lower leg and allows the wearer to produce natural ankle motion, with the help of soft materials, lightweight sensors, and advanced control software. The artificial tendons on orthotic device are secured to four pneumatic artificial muscles (PAMs), which correlate to four muscles that control ankle motion: the peroneus longus, peroneus brevis, anterior tibialis, and posterior tibialis muscles. The pliable exoskeleton generated an ankle range of sagittal motion of 27 degrees—a normal walking gait.
Exoskeletons, in general, are rigid and allow for a very limited range of motion; they only have a single pivot point. However, a pliable exoskeleton is more difficult to control compared to its inflexible counterpart. In the original prototype, the sensors had difficulty tracking ankle and foot motion and the scheme for controlling foot motion had to be adjusted. Improvements, such as utilizing touch-sensitive artificial skin made of thin rubber sheets that contain liquid metal alloy, have already been installed to increase the device’s potential usability.
A pliable exoskeleton can help strengthen the walking muscles in the ankle and foot weakened by neuromuscular diseases. The researchers are hoping this robotic orthotic device will help reeducate the neuromuscular system and improve lower leg function while restoring the natural gait.