An official website of the United States government
The encapsulation of active particles, such as bacteria or active colloids, inside a droplet gives rise to a non-trivial shape dynamics and droplet displacement. To understand this behaviour, we derive an asymptotic solution for the fluid flow about a deformable droplet containing an active particle, modelled as a Stokes-flow singularity, in the case of small shape distortions. We develop a general solution for any Stokes singularity and apply it to compute the flows and resulting droplet velocity due to common singularity representations of active particles, such as Stokeslets, rotlets and stresslets. The results show that offsetting of the active particle from the centre of the drop breaks symmetry and excites a large number of generally non-axisymmetric shape modes as well as particle and droplet motion. In the case of a swimming stresslet singularity, a run-and-tumble locomotion results in superdiffusive droplet displacement. The effect of interfacial properties is also investigated. Surfactants adsorbed at the droplet interface counteract the internal flow and arrest the droplet motion for all Stokes singularities except the Stokeslet. Our results highlight strategies to steer the flows of active particles and create autonomously navigating containers.
more »
« less
Rhagovelia Uses Interfacial Run-and-Tumble Locomotion to Improve Food Capture in Flowing Environments
Synopsis Rhagovelia oriander is a freshwater water strider native to the rivers and streams of North and South America, known for its distinctive skating movement on the water’s surface. This movement resembles the correlated random-walk pattern seen in microorganisms such as Escherichia coli. Previous studies have primarily focused on limb adaptations and biomechanics, leaving the ecological significance inadequately addressed. We combine field observations with controlled laboratory experiments using a flow mill to investigate the dynamics of R. oriander under typical flow conditions. Our findings indicate that this insect exhibits a two-dimensional run-and-tumble motion, often incorporating lateral tumbles following straight runs (run distance: $$30.7\pm 9.3$$ mm). We find that this behavior is resilient to changes in flow speed. In-silico simulations of particle interception demonstrated that this locomotion method enhances encounter rates compared to linear movement, particularly when the simulated food particle is following a rapid flow field. Our results document run-and-tumble locomotion in a millimeter-scale organism, showcasing a unique example of convergent behavior across diverse taxonomic groups and providing valuable insights into locomotion ecology while serving as a source of inspiration for bioinspired robotics and environmental exploration algorithms.
more »
« less
- PAR ID:
- 10617987
- Publisher / Repository:
- ICB
- Date Published:
- Journal Name:
- Integrative And Comparative Biology
- ISSN:
- 1540-7063
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
In unconfined environments, bacterial motility patterns are an explicit expression of the internal states of the cell. Bacteria operating a run-and-tumble behavioral program swim forward when in a ‘run’ state, and are stalled in place when in a reorienting ‘tumble’ state. However, in natural environments, motility dynamics often represent a convolution of bacterial behavior and environmental constraints. Recent investigations showed thatEscherichia coliswimming through highly confined porous media exhibit extended periods of ‘trapping’ punctuated by forward ‘hops’, a seemingly drastic restructuring of run-and-tumble behavior. We introduce a microfluidic device to systematically explore bacterial movement in a range of spatially structured environments, bridging the extremes of unconfined and highly confined conditions. We observe that trajectories reflecting unconstrained expression of run-and-tumble behavior and those reflecting ‘hop-and-trap’ dynamics coexist in all structured environments considered, with ensemble dynamics transitioning smoothly between these two extremes. We present a unifying ‘swim-and-stall’ framework to characterize this continuum of observed motility patterns and demonstrate that bacteria employing a consistent set of behavioral rules can present motility patterns that smoothly transition between the two extremes. Our results indicate that the control program underlying run-and-tumble motility is robust to changes in the environment, allowing flagellated bacteria to navigate and adapt to a diverse range of complex, dynamic habitats using the same set of behavioral rules.more » « less
-
We present an in silico microswimmer motivated by peritrichous bacteria, E. coli, which can run and tumble by spinning their flagellar motors counterclockwise (CCW) or clockwise (CW). Runs are the directed movement driven by a flagellar bundle, and tumbles are reorientations of cells caused by some motors' reversals from CCW to CW. In a viscous fluid without obstacles, our simulations reveal that material properties of the hook and the counterrotation of the cell body are important factors for efficient flagellar bundling and that longer hooks in mutant cell models create an instability and disrupt the bundling process, resulting in a limited range of movement. In the presence of a planar wall, we demonstrate that microswimmers can explore environment near surface by making various types of tumble events as they swim close to the surface. In particular, the variation of tumble duration can lead the microswimmer to run in a wide range of direction. However, we find that cells near surface stay close to the surface even after tumbles, which suggests that the tumble motion may not promote cells' escape from the confinement but promote biofilm formation.more » « less
-
ABSTRACT Drosophila’s innate response to gravity, geotaxis, has been used to assess the impact of aging and disease on motor performance. Despite its rich history, fly geotaxis continues to be largely measured manually and assessed through simplistic metrics, limiting analytic insights into the behavior. Here, we have constructed a fully programmable apparatus and developed a multi-object tracking software capable of following sub-second movements of individual flies, thus allowing quantitative analysis of geotaxis. The apparatus monitors 10 fly cohorts simultaneously, with each cohort consisting of up to 7 flies. The software tracks single flies during the entire run with ∼97% accuracy, yielding detailed climbing curve, speed and movement direction with 1/30 s resolution. Our tracking permits the construction of multi-variable metrics and the detection of transitory movement phenotypes, such as slips and falls. The platform is therefore poised to advance Drosophila geotaxis assay into a comprehensive assessment of locomotor behavior.more » « less
-
Abstract Despite centuries of investigation, bubbles continue to unveil intriguing dynamics relevant to a multitude of practical applications, including industrial, biological, geophysical, and medical settings. Here we introduce bubbles that spontaneously start to ‘gallop’ along horizontal surfaces inside a vertically-vibrated fluid chamber, self-propelled by a resonant interaction between their shape oscillation modes. These active bubbles exhibit distinct trajectory regimes, including rectilinear, orbital, and run-and-tumble motions, which can be tuned dynamically via the external forcing. Through periodic body deformations, galloping bubbles swim leveraging inertial forces rather than vortex shedding, enabling them to maneuver even when viscous traction is not viable. The galloping symmetry breaking provides a robust self-propulsion mechanism, arising in bubbles whether separated from the wall by a liquid film or directly attached to it, and is captured by a minimal oscillator model, highlighting its universality. Through proof-of-concept demonstrations, we showcase the technological potential of the galloping locomotion for applications involving bubble generation and removal, transport and sorting, navigating complex fluid networks, and surface cleaning. The rich dynamics of galloping bubbles suggest exciting opportunities in heat transfer, microfluidic transport, probing and cleaning, bubble-based computing, soft robotics, and active matter.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1093/icb/icaf110
