Date of Award

Fall 10-1-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering & Materials Science (ENAS)

First Advisor

Venkadesan, Madhusudhan

Abstract

Striated muscles are actuators of animal bodies. They are responsible for several biomechanical functions critical to survival and these include powering the cardiovascular system and modulating the mechanical interactions the body has with its surroundings. Nearly two centuries of active research on muscle phenomena has led to detailed insights into its microscopic composition, but accurate predictive models of muscle at larger scales remain elusive. This thesis reports on efforts to accurately capture the mechanical properties of striated muscles based on current knowledge of actomyosin dynamics. Specifically, this thesis derives the rheology of striated muscles from the dynamics. Muscle rheology is a characterization of the forces that it develops in resistance to externally imposed changes to its length, i.e. its mechanical behavior as a material. For example, the rheology of elastic solids is stiffness and that of viscous fluids is a damping coefficient. Detailed analyses of actomyosin dynamics suggest that the smallest functional units of striated muscles, half-sarcomeres, are viscoelastic and can function as either a solid-like struct or a fluid-like damper depending on time-durations of interest and neural inputs. Such adaptability may underlie the vastly different biomechanical functions that striated muscles provide to animal bodies. Furthermore, muscles are active structures because their properties require metabolic energy and depend on neural inputs. Striated muscles can therefore exhibit rheologies and functions that elastic springs and viscous fluids cannot. The analysis presented in this thesis may extend beyond muscles and biomedical applications. It may help to engineer muscle-like actuators based on principles of tunable properties and to understand the physics of other materials that can similarly transition between being solid-like and fluid-like.

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