Growth dynamics and morphology of bacterial biofilms under laminar shear flows
Time: Wed 2026-06-10 10.00
Location: F3, Lindstedtvägen 26
Language: English
Subject area: Engineering Mechanics
Doctoral student: Cornelius Wittig , Strömningsmekanik, Fluids and Surfaces Group
Opponent: Associate Professor Roberto Rusconi, Humanitas Unversity and Research Hospital
Supervisor: Professor Shervin Bagheri, Strömningsmekanik; Thomas Crouzier, Glykovetenskap; Professor Wouter van der Wijngaart, Mikro- och nanosystem
QC260519
Abstract
Any surface that is exposed to a biological fluid is likely to be contaminated by bacterial biofilms. These biofilms, consisting of cells that are embedded inside a protective matrix made from extracellular polymeric substances, can significantly increase drag, decrease thermal transport, or cause persistent infections. It has long been understood that there is a complex interplay between the near-wall flow field and the resulting biofilm formation. A wealth of experimental methods has been developed to grow biofilms under controlled conditions. However, these methods must necessarily find a compromise between the level of control (biochemical and physical), and the complexity found in realistic systems.
This thesis presents a series of experimental millifluidic biofilm studies in laminar shear flows using automated growth and data-acquisition setups. Biofilms were grown in canonical channel flows under varying levels of shear and on smooth and structured surfaces. The accumulation of biofilm was monitored using optical coherence tomography. On flat surfaces, the biofilm growth was found to be limited by shear-driven erosion, resulting in a linear accumulation in time that is inversely proportional to the wall shear stress. Additionally, the biofilm microcolonies were shown to form geometric defects that serve as nucleation sites for the formation of streamers, thin biofilm filaments that can extend far downstream. Finally, surface structures, specifically rectangular grooves larger than individual bacteria, enable the contamination of areas that would otherwise remain clean by providing local shelter from whic h thebiofilm can then expand in a multi-step process. The steps of this process are characterised by different interactions of physics and biology, from Lagrangian particle dynamics determining the initial colonisation to non-Newtonian material properties that allow the expansion into high-shear regions.
These results highlight the importance of the physical conditions under which a biofilm forms. Using a combination of experimental studies, numerical modelling, and theory, this thesis contributes to the field of biofilm research, providing insight into the mechanical processes that shape biofilm development.