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A two-fluid model for locomotion under self-confinement

Accepted version
Peer-reviewed

Type

Article

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Authors

Reigh, S 

Abstract

The bacterium Helicobacter pylori causes ulcers in the stomach of humans by invading mucus layers protecting epithelial cells. It does so by chemically changing the rheological properties of the mucus from a high-viscosity gel to a low-viscosity solution in which it may self-propel. We develop a two-fluid model for this process of swimming under self-generated confinement. We solve exactly for the flow and the locomotion speed of a spherical swimmer located in a spherically symmetric system of two Newtonian fluids whose boundary moves with the swimmer. We also treat separately the special case of an immobile outer fluid. In all cases, we characterize the flow fields, their spatial decay, and the impact of both the viscosity ratio and the degree of confinement on the locomotion speed of the model swimmer. The spatial decay of the flow retains the same power-law decay as for locomotion in a single fluid but with a decreased magnitude. Independent of the assumption chosen to characterize the impact of confinement on the actuation applied by the swimmer, its locomotion speed always decreases with an increase in the degree of confinement. Our modeling results suggest that a low-viscosity region of at least six times the effective swimmer size is required to lead to swimming with speeds similar to locomotion in an infinite fluid, corresponding to a region of size above ≈25μm for Helicobacter pylori.

Description

Keywords

4012 Fluid Mechanics and Thermal Engineering, 40 Engineering, Infectious Diseases

Journal Title

Physical Review Fluids

Conference Name

Journal ISSN

2469-990X
2469-990X

Volume Title

2

Publisher

American Physical Society
Sponsorship
European Commission (618323)
European Research Council (682754)
This work was funded in part by the Isaac Newton Trust, Cambridge, and by the European Union through a Marie Curie CIG Grant and a ERC Consolidator Grant.