Soft mechanism design for effective force transduction from living muscle

We present a versatile and efficient bio-actuator which integrates the nonlinearities inherent to living muscle in order to bolster maturation and amplify output displacements. Skeletal muscle has benefits over synthetic actuators at the micrometer to centimeter scale due to its ability to self-assemble in situ from liquid mixtures of ECM and myoblasts and due to its propensity to draw energy from its surrounding media environment. Our muscle-powered bio-actuators consist of an engineered skeletal muscle derived from C2C12 myoblasts interfacing with a soft PDMS scaffold. Our design incorporates constraints on the contractility of muscle imposed by its anatomy and the dynamics of excitation-contraction coupling. A compliant scaffold mechanism which provides force-resistant attachment for the muscle is designed using an analytical model of large angular beam bending to generate large amplitude rotations of a pair of thin filaments. An elastohydrodynamic low Reynolds number model of the scaffold is used to predict and optimize the swimming speed of the bio-actuator. We present an experimental implementation of the bio-actuator performing two types of untethered locomotion, walking and swimming, progressing at 1.6 and 0.4 body lengths per minute, respectively.