A Benchtop biorobotic platform for in vitro observation of muscle-tendon dynamics with parallel mechanical assistance from an elastic exoskeleton

Publication date: Available online 21 March 2017
Source:Journal of Biomechanics
Author(s): Benjamin D. Robertson, Siddarth Vadakkeveedu, Gregory S. Sawicki
We present a novel biorobotic framework consisting of a biological muscle-tendon unit (MTU) mechanically coupled to a feedback controlled robotic environment simulation system that mimics in-vivo inertial/gravitational loading and mechanical assistance from a parallel elastic exoskeleton. We demonstrate that this biorobotic system can effectively mimic the human neuromechanical response to a passive elastic exoskeleton (Exo) during vertical hopping making it a useful tool for directly observing how biological muscle dynamics change in the context of exoskeleton assistance. Based on predictions from our previous modeling studies, we applied combinations of biological stiffness by modulating muscle activation using rate-coding and exoskeleton stiffness by dialing in a desired virtual spring constant that would result in human-like behavior. These conditions resulted in system-level force-length dynamics (i.e., stiffness), reduced biological loads, increased muscle excursion, and constant muscle average positive power output—all consistent with laboratory experiments on intact humans during hopping. Exoskeleton mechanical assistance led to reduced estimated metabolic cost and MTU apparent efficiency, as well as increased apparent efficiency for the MTU+Exo system as a whole. Findings from this study suggest that the increased natural resonant frequency of the artificially stiffened MTU+Exo system, along with invariant movement frequencies, may underlie observed limits on the benefits of exoskeleton assistance. Our novel approach demonstrates that it is possible to capture the salient features of human locomotion with exoskeletons in an isolated muscle-tendon preparation and provides a powerful new tool for detailed, direct examination of the effects of assistive devices on muscle-tendon neuromechanics and energetics.



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