Researchers at the University of Pittsburgh have received an award from the National Science Foundation’s Cyber-Physical Systems program to enable the development of an ultrasound sensor system at the heart of a hybrid exoskeleton that uses both electrical nerve stimulation and external motors. Kang Kim (left) with Nitin Sharma and a hybrid exoskeleton prototype in the Neuromuscular Control and Robotics Laboratory in the Swanson School of Engineering. Courtesy of Swanson School of Engineering. Principal investigator of the three-year, $400,000 award is Nitin Sharma, assistant professor of mechanical engineering and materials science at Pitt's Swanson School of Engineering. Co-principal investigator is Kang Kim, associate professor of medicine and bioengineering. The Pitt team is collaborating with researchers led by Siddhartha Sikdar, associate professor of bioengineering and electrical and computer engineering at George Mason University, who also received a $400,000 award. The latest funding furthers Sharma's development of hybrid exoskeletons that combine functional electrical stimulation, which uses low-level electrical currents to activate leg muscles, with powered exoskeletons, which use electric motors mounted on an external frame to move the wearer's joints. "An exoskeleton biosensor needs to be noninvasive, but systems like electromyography aren't sensitive enough to distinguish signals in complex muscle groups," Kim said. "Ultrasound provides image-based, real-time sensing of complex physical phenomena like neuromuscular activity and fatigue. This allows Nitin's hybrid exoskeleton to switch between joint actuators and functional electrical stimulation, depending upon the patient's muscle fatigue." In addition to mating Sharma's hybrid exoskeleton to Kim's ultrasound sensors, the research group will develop computational algorithms for real-time sensing of muscle function and fatigue. Human subjects using a leg-extension machine will enable detailed measurement of strain rates, transition to fatigue and full fatigue to create a novel muscle-fatigue prediction model. Future phases will allow the Pitt and George Mason researchers to develop a wearable device for patients with motor impairment. "Right now an exoskeleton combined with ultrasound sensors is just a big machine, and you don't want to weigh down a patient with a backpack of computer systems and batteries," Sharma said. "The translational research with George Mason will enable us to integrate a wearable ultrasound sensor with a hybrid exoskeleton and develop a fully functional system that will aid in rehabilitation and mobility for individuals who have suffered spinal cord injuries or strokes."