Individual behavior and pairwise interactions between microswimmers in anisotropic liquid

Abstract

A motile bacterium swims by generating flow in its surrounding liquid. Anisotropy of the suspending liquid significantly modifies the swimming dynamics and corresponding flow signatures of an individual bacterium and impacts collective behavior. We study the interactions between swimming bacteria in an anisotropic environment exemplified by lyotropic chromonic liquid crystal. Our analysis reveals a significant localization of the bacteria-induced flow along a line coaxial with the bacterial body, which is due to strong viscosity anisotropy of the liquid crystal. Despite the fact that the average viscosity of the liquid crystal is two to three orders of magnitude higher than the viscosity of pure water, the speed of bacteria in the liquid crystal is of the same order of magnitude as in water. We show that bacteria can transport a cargo (a fluorescent particle) along a predetermined trajectory defined by the direction of molecular orientation of the liquid crystal. We demonstrate that while the hydrodynamic interaction between flagella of two close-by bacteria is negligible, the observed convergence of the swimming speeds as well as flagella waves' phase velocities may occur due to viscoelastic interaction between the bacterial bodies.

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

“…Furthermore, these defects can be guided by applied electric or magnetic fields, surface anchoring, light, or chemical and temperature gradients. These findings extend our scope of tools to control and manipulate microscopic objects in active matter [33,36,50,51]. Moreover, with the recent progress in the lithographic design of light-sensitive surface anchoring patterns, topological defects can be created on demand and guided by light [52].…”

“…Previous experiments with bacteria suspended in liquid crystals were performed either in thin closed glass cells or in pendant drops [32][33][34][35][36]. The freestanding geometry was necessary to minimize the effect of in-plane surface anchoring.…”

“…[32][33][34][35][36]. The material exhibits unique optical and mechanical properties, including guidance of bacteria along the nematic director, visualization of nanometer-thick bacterial flagella [32], transport of cargo along bacterial trajectories [33], and dynamic self-assembly of bacterial clusters [35].…”

Geometry of thresholdless active flow in nematic microfluidics

“…This may be of practical importance, since controlling boundaries and boundary conditions for liquid crystals is a highly developed technology that has long been used for the construction of liquid crystal displays. Efforts are under way to extend such control to the active regime [13,45,46]. Consider nonplanar alignment of the director to the walls of a three-dimensional channel with torsional symmetry [by which we mean equivalently that the sample is bounded by a surface of revolution about the z axis as shown in Fig.…”

Elementary Flow Field Profiles of Micro-Swimmers in Weakly Anisotropic Nematic Fluids: Stokeslet, Stresslet, Rotlet and Source Flows

“…Furthermore, many biomaterials can form a nematic phase [14]. To investigate the influence of anisotropic background on swimming bacteria, studies of bacterial solutions in lyotropic liquid crystals were conducted, investigating the behavior of single bacteria [15][16][17], their pairwise interaction [18] or their collective motion [19,20]. Bacterial suspensions in liquid crystals can be used for transport of microcargo [21].…”