Through the actuation of elastic filaments, microorganisms can move through a viscous fluid or generate a flow within a complex environment. In this talk, we will focus on simple models of two such systems. First, as a step towards understanding the chemotactic behavior of bacteria within micropores, we consider a single elastic helical flagellum confined in a cylindrical tube. We will examine its swimming performance when it is driven by an applied torque, balanced by an opposite torque on a virtual cell body. In particular, we will demonstrate some interesting dynamics when the axis of the helical swimmer is initially not parallel to the axis of the cylinder. Second, we will examine the hydrodynamic synchronization of cilia. Minimal models of colloidal particles driven by optical traps have been used to shed light on synchronization. Here we extend the minimal model that represents a cilium by a bead to one that represents the cilium as an elastic filament. The beat angle of this filament switches between two ‘traps’, driving the motion of the power and recovery strokes. We will contrast the behavior of this simple model with a more detailed model of a cilium that tracks individual dynein molecular motors that are themselves driven by a geometric switch. While each model of a single cilium captures a realistic beat form, the emergent behavior of pairs of cilia are surprisingly different.

Lisa Fauci