A Musculoskeletal Simulation Framework for In Silico Design and Optimization of a Soft Exosuit for Children with Muscular Dystrophy

PROJECT SUMMARY/ABSTRACT Muscular dystrophies (MD), such as Duchenne MD and Becker MD, are rare genetic diseases that cause progressive muscle degeneration in approximately 14 in 100,000 males ages 5-24. Currently there is no known treatment that can stop or reverse the damage caused by MD. Dystrophic muscle is especially susceptible to damage during eccentric contraction. Soft exosuits are an emerging class of wearable device that may be able to reduce eccentric contraction during functional movements such as downhill walking, which requires substantial eccentric knee extensor contraction. Exosuits utilize compliant textile-based actuators to inherently provide safety and comfort to the user, which is highly desirable for avoiding excessive muscle injury in boys with MD. However, one potential barrier to development of exosuits for boys with MD is the risk of injury during human subjects testing of new prototypes. Musculoskeletal simulations are an ideal tool for early-stage design of exosuits for children with MD because simulations provide characterization of muscle eccentric contraction, which is difficult to observe experimentally, and avoid risk of injury to human subjects when testing prototypes. Thus, the overall objective of this project is to develop a musculoskeletal simulation framework for in silico design and optimization of a soft exosuit for children with MD. First, existing simulations of healthy adults walking downhill will be modified to include a simulated soft exosuit. The initial exosuit design will be based on existing physical prototypes. A novel optimization framework will be used to optimize the exosuit to minimize eccentric contraction in the rectus femoris (a knee extensor) during downhill walking. Statistical analysis will be performed to test the hypotheses that (1) simulated eccentric contraction (i.e., net negative work) in the rectus femoris is significantly reduced by the exosuit and (2) eccentric contraction is further reduced following optimization. In addition, changes in joint reaction forces and eccentric contraction in other muscles will be quantified to investigate potential adverse side effects. After establishing potential benefits of the exosuit using the adult model, a musculoskeletal model of a child will be developed. A simulated isometric task will be used to calibrate maximum isometric muscle force in a typically developing and MD child model to match published strength data. Preliminary simulations of a child walking downhill with the exosuit will be generated by scaling the adult movement data using a retargeting algorithm. The exosuit optimization framework will be applied to both the typically developing child and child with MD models to determine whether the optimized exosuit provided a sufficient reduction in rectus femoris eccentric contraction to be statistically significant in future human subjects experiments. The proposed research aims to establish a foundation for design of an exosuit that can substantially improve quality of life for children with MD in the near term. In addition, the musculoskeletal simulation-based design optimization framework will facilitate rapid in silico design and testing of assistive devices, such as soft exosuits, without risk to human subjects.PROJECT NARRATIVE Assistive devices such as soft exosuits have the potential to provide substantial increase in quality of life for children with muscular dystrophy. This project aims to develop a simulation-based design optimization framework for quickly, safely, and effectively designing exosuits for these children. Ultimately, this work will spur innovation in design of exosuits for children with muscular dystrophy.