SCH: Wearable Multi-Modal Sensing and Stimulation Arrays for Muscle-Aware Exoskeleton Control

Functional electrical stimulation (FES) and powered exoskeletons are promising rehabilitation interventions to promote the independence and recovery of persons with neurological injury. These interventions aim to encourage active participation of a user’s weak muscles to bring about substantial gains in recovery. A wearable sensor that measures the paralyzed muscle’s force can potentially inform the user’s participation levels, allowing personalization of FES or exoskeleton assistance.

Current muscle sensors such as electromyography create poor representations of muscle force, mainly due to noise interference and incompatibility with FES. Instead, recent evidence suggests that ultrasound (US) enables high fidelity measurements of muscle strength due to its ability to visualize muscle activity directly. However, conventional US probes are hardly wearable, and their clinical deployment in FES systems and exoskeletons is nearly impossible.

We plan a US-based sensing array technology to help devise new rehabilitation strategies that lead to faster recovery and smart health monitoring of muscles post a neurological injury such as spinal cord injury, stroke, multiple sclerosis, etc. The technology would be widely applicable in several medical problems that involve a human in the loop, including upper and lower extremity prostheses and exoskeletons, rehabilitation, and surgical robots.

The research integrates outreach programs targeting K-12 students, talks and demos at a planetarium, and an annual summer program.

The overall project objective is to create a new muscle-machine interface technology that combines dynamic in vivo ultrasound (US) imaging with electromyographic (EMG) signals for monitoring voluntary and FES-induced muscle activity. The individual objectives of the project are to 1) develop of a sensing array composed of EMG electrodes and ultrasound transducers, 2) use the feedback from the sensing arrays to synchronize exoskeleton assistance with a user’s impaired motor intent, and 3) validate the sensing array to measure muscle force changes due to FES, and 4) use the feedback from the sensing array to coordinate FES with an exoskeleton.

Once successfully translated to practice, an ultrasound-based sensing array would help visualize muscle fibers’ contractile behavior and muscle force production, potentially in more than one imaging plane. Potentially, the array would facilitate symbiotic adjustment of the exoskeleton and FES assistance when integrated with the modeling and control framework.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.