Polar jets of swimming bacteria condensed by a patterned liquid crystal

Abstract

Active matter exhibits remarkable collective behavior in which flows, continuously generated by active particles, are intertwined with the orientational order of these particles. The relationship remains poorly understood as the activity and order are difficult to control independently. Here we demonstrate important facets of this interplay by exploring dynamics of swimming bacteria in a liquid crystalline environment with pre-designed periodic splay and bend in molecular orientation. The bacteria are expelled from the bend regions and condense into polar jets that propagate and transport cargo unidirectionally along the splay regions. The bacterial jets remain stable even when the local concentration exceeds the threshold of bending instability in a non-patterned system. Collective polar propulsion and different role of bend and splay are explained by an advection-diffusion model and by numerical simulations that treat the system as a two-phase active nematic. The ability of prepatterned liquid crystalline medium to streamline the chaotic movements of swimming bacteria into polar jets that can carry cargo along a predesigned trajectory opens the door for potential applications in cell sorting, microscale delivery and soft microrobotics.

Surface anchoring controls orientation of a microswimmer in nematic liquid crystal

“…nderstanding self-propulsion in complex and anisotropic fluids is a growing area of research [1][2][3][4][5][6][7][8] . A realization of the experimental system combining motile bacteria with a nematic liquid crystal (LC) was introduced in refs.…”

“…The injection of energy by microswimmers was also shown to result in the creation of moving topological defects (local singularities of molecular orientation) in the LC director field [9][10][11] . Manipulation of bacterial trajectories by the prescribed director patterning suggests novel approaches to control the transport of cargo 8 . Furthermore, many biological fluids, such as mucus, DNA solutions, or suspensions of long viruses exhibit a certain degree of liquid crystallinity [12][13][14][15][16] .…”

Pattern-induced local symmetry breaking in active-matter systems

“…In addition to actomyosin motility assays, patterns with polar and nematic symmetries were commonly suggested in systems of rodlike particles ( 19 – 22 ) and observed in experiments with motile bacteria in liquid crystals ( 51 – 53 ). Moreover, patterns of intertwined symmetries play a prominent role even in equilibrium systems, such as in high-temperature superconductors ( 54 , 55 ).…”

“…This implies a possible relevance of this phenomenon for a broad class of experimental systems beyond the actomyosin motility assay. We hypothesize that pattern-induced symmetry breaking could serve as a useful and general design principle with broad applications to synthetic and living active matter ( 51 – 53 ) as well as other pattern-forming systems with intertwined symmetries ( 54 , 55 ).…”

“…to synthetic and living active matter (51)(52)(53) as well as other pattern-forming systems with intertwined symmetries (54,55).…”