Microscale locomotion in a nematic liquid crystal

Krieger, Madison S.; Spagnolie, Saverio E.

doi:10.1039/c5sm02194d

Cited by 36 publications

(42 citation statements)

References 47 publications

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“…In the continuum description, the distribution of force dipoles results in an active stress σ act . In a dilute limit, the active stress σ act can be written as [13,41] …”

Section: Modelmentioning

confidence: 99%

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

et al. 2017

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Active matter exemplified by suspensions of motile bacteria or synthetic self-propelled particles exhibits a remarkable propensity to self-organization and collective motion. The local input of energy and simple particle interactions often lead to complex emergent behavior manifested by the formation of macroscopic vortices and coherent structures with long-range order. A realization of an active system has been conceived by combining swimming bacteria and a lyotropic liquid crystal. Here, by coupling the well-established and validated model of nematic liquid crystals with the bacterial dynamics, we develop a computational model describing intricate properties of such a living nematic. In faithful agreement with the experiment, the model reproduces the onset of periodic undulation of the director and consequent proliferation of topological defects with the increase in bacterial concentration. It yields a testable prediction on the accumulation of bacteria in the cores of þ1=2 topological defects and depletion of bacteria in the cores of −1=2 defects. Our dedicated experiment on motile bacteria suspended in a freestanding liquid crystalline film fully confirms this prediction. Our findings suggest novel approaches for trapping and transport of bacteria and synthetic swimmers in anisotropic liquids and extend a scope of tools to control and manipulate microscopic objects in active matter.

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“…In the continuum description, the distribution of force dipoles results in an active stress σ act . In a dilute limit, the active stress σ act can be written as [13,41] …”

Section: Modelmentioning

confidence: 99%

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

et al. 2017

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“…The effects of thermal fluctuations of the nematic director on the dynamics of a model active particle moving in a LC have further been considered theoretically and by means of computer simulations 123,124 . Meanwhile, the effect of liquid-crystalline anisotropy on the behavior of a classical Taylor swimming sheet 125 undulating with small-amplitude traveling waves has been examined [126][127][128][129] .…”

mentioning

confidence: 99%

Dynamics of a simple model microswimmer in an anisotropic fluid: Implications for alignment behavior and active transport in a nematic liquid crystal

Daddi-Moussa-Ider

Menzel

2018

Phys. Rev. Fluids

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Several recent experiments investigate the orientational and transport behavior of self-driven bacteria and colloidal particles in nematic liquid crystals. Correspondingly, we study theoretically the dynamics of a minimal model microswimmer in a uniaxially anisotropic fluid. As a first step, the hydrodynamic Green's function providing the resulting fluid flow in response to a localized force acting on the anisotropic fluid is derived analytically. On this basis, the behavior of both puller-and pusher-type microswimmers in the anisotropic fluid is analyzed. Depending on the propulsion mechanism and the relative magnitude of different involved viscosities, we find alignment of the swimmers parallel or perpendicular to the anisotropy axis. Particularly, also an oblique alignment is identified under certain circumstances. The observed swimmer reorientation results from the hydrodynamic coupling between the self-induced fluid flow and the anisotropy of the surrounding fluid, which distorts the self-generated flow field. We support parts of our results by a simplified linear stability analysis. Our theoretical predictions are in qualitative agreement with recent experimental observations on swimming bacteria in nematic liquid crystals. They support the objective of utilizing the, possibly switchable, anisotropy of a host fluid to guide individual microswimmers and active particles along a requested path, enabling controlled active transport. I. INTRODUCTIONActive particles have the ability to move autonomously in a surrounding fluid by converting energy into directed motion. Artificial self-propelled nano-and microscale machines hold great promise for future medical research to reach otherwise inaccessible areas of the body to perform delicate and precise tasks. Prospective biomedical applications are precision nanosurgery, biopsy, and transport of radioactive substances to tumor areas and inflammation sites 1-3 . Over the last few decades, significant research efforts have been devoted to investigate the behavior of self-propelling active particles due to their importance and relevance as model systems for transport and locomotion in the micro-and nano-scale world; for recent reviews see Refs. 4-12. Unusual macroscopic signatures and intriguing spatiotemporal patterns emerge from the interaction between several active particles. For instance, the onset of collective motion 13-19 , formation of dynamic clusters 20-26 , wave patterns 27-30 , laning 31-35 , motility-induced phase separation 36-41 , swarming 42-44 , and active turbulence 45-52 are observed. In many cases, artificial self-driven particles and swimming microorganisms have to propel through complex fluids, such as polymer gels and viscoelastic microemulsions [53][54][55][56][57][58][59][60][61][62][63] . Notable examples include sperm navigation through the mammalian female reproductive tract 64,65 , bacteria locomotion in biofilm matrices composed of extracellular polymeric substances 66,67 , nematode movement in soil 68,69 , and the motion of synthetic mic...

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“…Bacterial suspensions in liquid crystals can be used for transport of microcargo [21]. While investigating swimming bacteria in liquid crystals is particularly challenging due to high toxicity of many nematics, this problem is avoided by studying artificial active particles in liquid crystals [22], or, for example, properties of a Taylor's swimming sheet [23,24]. Even passive systems, such as sedimentation of spheres shows an intertwined behavior of fluid velocity and internal structure of nematics.…”

Section: Introductionmentioning

confidence: 99%

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

Kos

Ravnik

2018

Fluids

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Analytic formulations of elementary flow field profiles in weakly anisotropic nematic fluid are determined, which can be attributed to biological or artificial micro-swimmers, including Stokeslet, stresslet, rotlet and source flows. Stokes equation for a nematic stress tensor is written with the Green function and solved in the k-space for anisotropic Leslie viscosity coefficients under the limit of leading isotropic viscosity coefficient. Analytical expressions for the Green function are obtained that are used to compute the flow of monopole or dipole swimmers at various alignments of the swimmers with respect to the homogeneous director field. Flow profile is also solved for the flow sources/sinks and source dipoles showing clear emergence of anisotropy in the magnitude of flow profile as the result of fluid anisotropic viscosity. The range of validity of the presented analytical solutions is explored, as compared to exact numerical solutions of the Stokes equation. This work is a contribution towards understanding elementary flow motifs and profiles in fluid environments that are distinctly affected by anisotropic viscosity, offering analytic insight, which could be of relevance to a range of systems from microswimmers, active matter to microfluidics.

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Microscale locomotion in a nematic liquid crystal

Cited by 36 publications

References 47 publications

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

Dynamics of a simple model microswimmer in an anisotropic fluid: Implications for alignment behavior and active transport in a nematic liquid crystal

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

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