Abstract

Biofilm formation impacts many fields, from medical technologies, e.g. catheter design, to infrastructure development, e.g. water supply pipes. For the case of motile micro-swimmers, the early stages of biofilm behaviour are dependent on the physical properties of swimmers and their ambient flow environments as these affect the likelihood of surface interactions and surface colonisation.

We study the initial stages of biofilm formation for dilute suspensions of micro-swimmers in two-dimensional pressure-driven flows. We highlight the effects of swimmer geometry and linearly varying shear flow on swimmer trajectories and how the history of bulk-flow dynamics affects swimmer-wall interactions. Continuum modelling, using a two-dimensional Smoluchowski equation, allows us to obtain population-level features of the equilibrium problem, while the use of stochastic individual-based models allows us to analyse the observed features, explore cell behaviours throughout the bulk flow, and highlight the roles of rotational and translational diffusion on the resulting swimmer orientation distributions at the channel walls. We further quantify the role of the purely deterministic aspects of bulk-flow swimming on swimmer distributions at the channel wall via a novel accumulation index.

Finally, we also study the interplay between the choice of boundary conditions in continuum modelling and the observed bulk-flow dynamics. These insights highlight the importance of shape and shear effects on swimmer-wall interactions and the non-triviality of the choice of boundary conditions when developing continuum models for swimmer suspensions.