Researchers at the University of Pittsburgh (Pitt) were awarded a $400,000 grant to develop an ultrasound sensor system for a hybrid exoskeleton. The exoskeleton system will use electrical nerve stimulation and external motors to help people with motor impairments walk without causing muscle fatigue and potential injury. The grant was awarded by the National Science Foundation’s Cyber-Physical Systems (CPS) program. The Pitt team is collaborating with researchers at George Mason University who also received a $400,000 CPS award for its research proposal about ultrasound sensors for exoskeletons.
From left, Kim and Sharma stand with the hybrid exoskeleton prototype. Photograph courtesy of the Swanson School of Engineering.
Nitin Sharma, PhD, is the principal investigator of the three-year award and an assistant professor of mechanical engineering and materials science at Pitt’s Swanson School of Engineering. The grant will further Sharma’s development of hybrid exoskeletons that combine functional electrical stimulation (FES) and powered exoskeletons.
“One of the most serious impediments to developing a human exoskeleton is determining how a person who has lost gait function knows whether his or her muscles are fatigued. An exoskeleton has no interface with a human neuromuscular system, and the patient doesn’t necessarily know if the leg muscles are tired, and that can lead to injury,” said Sharma. “Electromyography (EMG), the current method to measure muscle fatigue, is not reliable because there is a great deal of electrical ‘cross-talk’ between muscles, and so differentiating signals in the forearm or thigh is a challenge.”
To overcome the low signal-to-noise ratio of traditional EMG, Sharma partnered with co-principal investigator Kang Kim, PhD, associate professor of medicine and bioengineering at Pitt, whose research in ultrasound focuses on analyzing muscle fatigue.
“An exoskeleton biosensor needs to be noninvasive, but systems like EMG 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 FES, depending upon the patient’s muscle fatigue.”
In addition to combining a hybrid exoskeleton with 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 researchers to develop a wearable device for patients with motor impairments.
Editor’s note: This story was adapted from materials provided by Pitt.
