title: A hydrodynamic mechanism for attraction of undulatory microswimmers to surfaces (bordertaxis).
abstract: Although small nematodes significantly impact human and animal health, agriculture, and ecology, little is known about the role of hydrodynamics in their life cycles. Using the nematode Caenorhabditis elegans as a model undulatory microswimmer, we have observed that animals are attracted to and swim along surfaces. The attraction to surfaces does not require mechanosensory neuron function. In dilute swarms, swimmers aggregate near surfaces. Using resistive force-based theory, symmetry arguments, and direct hydrodynamic simulations, we demonstrate that forces resulting from the interaction between the swimmer-induced flow field and a nearby surface cause a short-range hydrodynamic torque that stirs the swimmers towards the surface. When combined with steric forces, this causes locomotion along the surface. This surface attraction may affect nematode mate and food finding behaviour and, in the case of parasitic nematodes, may facilitate host penetration. Surface attraction must be accounted for when studying animals' responses to various stimuli, and suggests means of controlling undulatory microswimmers.
authors.affiliation: Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, 220 South 33rd Street, USA.
authors.forename: Jinzhou
authors.initials: J
authors.lastname: Yuan
authors.affiliation: Department of Neurology, Perelman School of Medicine, University of Pennsylvania, 415 Curie Boulevard, Philadelphia, PA 19104, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Raizen
authors.affiliation: Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, 220 South 33rd Street, USA bau@seas.upenn.edu.
authors.forename: Haim H
authors.initials: HH
authors.lastname: Bau
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000502:physiology*; D006801:Humans; D057446:Hydrodynamics; D008954:Models, Biological; D013550:Swimming / Q000502:physiology*
keywords: aggregation; high throughput; hydrodynamic; short range; sorting; surface