Dynamics of Straight and Helical Flagella in Active Matter

The behavior of stiff, straight rods at thermodynamic equilibrium has a well-established theoretical background. Reptation theory can be used to predict the properties of these stiff polymer suspensions at the semi-dilute and entangled states. While stiff polymers of shapes other than straight pose problems for analytic derivations of these material properties, experimental evidence shows that reptation can still be used to understand the emergence of the suspension's material properties. Active matter is constantly driven out of thermodynamic equilibrium by the injection of energy at the sub-unit level, which can lead to dynamics of the filaments beyond the simple Brownian motion within its caged volume, and consequently, a difference in the properties of such suspension. We explore the dynamics of bacterial flagella suspended at high concentrations in a microtubule-based active gel. We explore how the concentration and shape of the flagella affect their response to the active flows, and how the length and time scale of the active flows are, in turn, affected by the presence of the passive filaments. The dynamics of single flagella are also tracked in three dimensions to measure the filaments' orientation and position response to the active flows, and determine the scaling of their displacement in the comoving frame.