Low Reynolds number biohybrid swimming

Biohybrid robotics are a new class of mechanical systems which use biological cells as machine components in microscale to mesoscale actuators and motile structures. Eukaryotic cells come pre-programmed to accomplish a wide range of functionalities, from sensing environmental factors to providing contractile forces. Current laboratory techniques permit control over the expression of specific biological mechanisms in a cell as well as the addition of new ones. Biological cells can be cultured on biocompatible, elastomeric, soft robotics chassis, which are cheap, robust, and easy to fabricate. The replacement of classical machine components with biological cells enables the extension of robotics to smaller size scales at low cost and with the potential for mass production. Here, we present the design and fabrication of a biohybrid flagellum, using a single cluster of one to several cardiomyocytes to generate a bending force on a microscale filament. A slender body elastohydrodynamic model is used to provide design criteria for the system, ensuring that the actuation of a single cell cluster will produce time irreversible deformation and net propulsion at low Reynolds number. Microscale polydimethylsiloxane filaments are fabricated by etching channels into silicon wafers and filling those channels with uncured elastomer by capillary draw. Cell adhesion location is controlled by selective functionalization of the filament. Functional instances are presented in one- and two-tailed forms, powered by the spontaneous, periodic contraction of cardiac myocytes. In a biocompatible environment, these swimmers are self-powered and self-controlled, relying on no external stimulation. Together with the model, the system represents a characterized machine component capable of generating propulsion that can be readily assembled into more complex configurations to design a motile swimmer with specific functionality. Additional work to extend the utility of the swimmer is presented, including a microfluidic templating platform, consisting of a removable microfluidic ``stamp'' with multiple inlets and channels intersecting the filament. Individual channels can be used to place unique cell types on different regions of the swimmer. In this manner, we hope to be able to engineer multicellular biohybrid systems. We show an extended slender body elastohydrodynamic model with coupled, synchronizable actuators capable of generating more complex filament deformations and scaled up swimming performance by, for example, synchronization by mechanical strain coupling. To characterize the ability of strain coupled cardiomyocytes to synchronize, an experimental platform is constructed to produce high speed sinusoidal substrate deformation of a 2D cell culture on a microscope. We find that cardiac contractile dynamics do respond to cyclical strain, including the ability to synchronize to frequency shifts within a limited range. We present a relaxation oscillator model with nonlinear strain dependence that exhibits similar oscillator dynamics to the experimentally studied sinusoidal substrate perturbation