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Elongated microswimmers such as E. coli exhibit run-and-tumble dynamics that bias motion in response to chemical gradients. In confined pressure-driven flows, elongated swimmers also reorient along Jeffery orbits, spending extended periods oriented near the upstream or downstream direction. Near boundaries, this alignment leads to upstream swimming, contributing to contamination and surface colonisation [1,2].
In this work, we investigate the competition between shear-induced reorientation and finite memory chemotactic responses in confined flows. We show that strong chemotactic sensitivity amplifies temporal comparisons in chemical signalling, fundamentally altering the orientation phase space associated with shear-induced dynamics of near-wall swimmers. In particular, strong chemorepulsive cues at channel surfaces lead to the loss of longer upstream trajectories, inducing a transition from positive rheotaxis to downstreamdominated transport.
Chemotactic memory, when coupled with chemorepulsive surface cues, inhibits upstream contamination by progressively reducing the number of swimmers occupying upstream-oriented states. These results identify a general mechanism by which memory-driven chemotactic responses can be used to control microswimmer transport in flow, offering new design principles for limiting surface colonisation in microfluidic and biomedical environments, complementing existing studies of microswimmer–surface interactions and suspension dynamics [3,4,5].
[1] Rachel N. Bearon and Andrew L. Hazel. “The trapping in high-shear regions of slender bacteria undergoing chemotaxis in a channel.” Journal of Fluid Mechanics 771 (2015): R3.
[2] Tolga Kaya and Hur Koser. “Direct upstream motility in Escherichia coli.” Biophysical Journal 102.7 (2012): 1514-1523.
[3] Smitha Maretvadakethope, et al. “The interplay between bulk flow and boundary conditions on the distribution of microswimmers in channel flow.” Journal of Fluid Mechanics 976 (2023): A13.
[4] Roberto Rusconi, Jeffrey S. Guasto, and Roman Stocker. “Bacterial transport suppressed by fluid shear.” Nature Physics 10.3 (2014): 212-217.
[5] Barath Ezhilan and David Saintillan. “Transport of a dilute active suspension in pressure-driven channel f low.” Journal of Fluid Mechanics 777 (2015): 482-522.
