Bacterial Streamer Formation in Porous Media

  • Author / Creator
    Hassanpourfard, Mahtab
  • One of the central puzzles concerning the interaction of low Reynolds number (Re<<1) fluid transport with bacterial biomass is the formation of filamentous structures called bacterial streamer. Bacterial streamers can be tethered at one or both ends to solid surfaces, while the rest of the structure is suspended in liquid. Bacterial streamer formation in low Re fluid transport is of significant technological and biomedical interest due to relevance to a wide variety of critical operating scenarios including clogging of biomedical devices such as heart stents, catheters, porous media, and water filtration systems. In the present study, we investigate formation and temporal evolution of biofilm-mediated streamers. These streamers form from deformation of pre-formed biofilm on a surface after several hours of injecting bacterial solution into the microfluidic device. Once the streamers form, they accelerate the clogging by accruing more biomass from the injected flow. Our experiments, carried out in a microfluidic device, rely on fluorescence microscopy techniques. Our microfluidic device consists of an array of micro-posts, which was fabricated using soft-lithography. Detailed procedures for experimentation with the microfluidic device are also presented in this study. We report our discovery of a new kind of low Re bacterial streamers, which appear from pre-formed bacterial flocs. In sharp contrast to the biofilm-mediated streamers, these streamers form over extremely small timescales (less than a second). We demonstrate that floc-mediated streamers form when a freely-moving floc adheres to the micropillar’s wall and gets rapidly sheared by the background flow. We also show that, at their inception, the deformation of the flocs is dominated by recoverable large strains indicating significant elasticity. These strains subsequently increase tremendously to produce filamentous streamers. Interestingly, we find that these fully formed streamers are not static structures and show viscous response at time scales larger than their formation time scales. We also show that such novel streamer formation can lead to rapid clogging of microfluidic devices. Thereafter, the clogging dynamics of bacterial biomass that accumulated in the device due to the formation of bacterial streamers is investigated. Particularly, we find the existence of a distinct clogging front which advances via pronounced ‘stick-slip’ of the viscoelastic bacterial biomass over the solid surface of the micro pillar. Thus, the streamer, the solid surface, and the background fluidic media define a clear three-phase front influencing these advancing dynamics. Interestingly, we also find that once the clogging becomes substantial, contrary to a static homogenous saturation state, the clogged mimic exhibits an instability phenomena marked by localized streamer breakage and failure leading to extended water channels throughout the mimic. These findings have implications for design and fabrication of biomedical devices, and membrane-type systems such as porous balloon catheters, porous stents, and filtration membranes prone to bacteria induced clogging as well as understanding bacterial growth and proliferation in natural porous media such as soil and rocks. Finally, we study the impact of nanoparticles as antibacterial agents to combat biofilm formation. In our work, we use Mg(OH)2 nano-platelets to inhibit the growth of planktonic bacteria, and consequently biofilm and bacterial streamer formation. The results demonstrate that depending on the concentration of Mg(OH)2 nano-platelets in the solution they can act as an antibacterial or a bacteriostatic agent for Pseudomonas fluorescens as a model organism for biofilm formation. Furthermore, they can inhibit streamer formation in the microfluidic devices.

  • Subjects / Keywords
  • Graduation date
    Spring 2017
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.