Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session T03: Biofilms |
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Chair: J Travis Hunsucker, Florida Institute of Technology Room: Ballroom C |
Monday, November 25, 2024 4:45PM - 4:58PM |
T03.00001: Characterizing the mechanical properties of biofilms using Atomic Force Microscopy AFM Kimberly Lopez, Samuel Kok Suen Cheng, Jian Sheng Biofilms are a microbially derived sessile community characterized by cells embedded in a polymer matrix. Measuring the material properties of live biofilms without perturbing them is known to be difficult. Atomic Force Microscopy (AFM) is a great tool for imaging the topology and conducting force-distance-based studies to characterize their mechanical properties. This study uses AFM to characterize the viscoelasticity of biofilms generated by different species: P. aeruginosa, P. fluorescein, and E. coli. Biofilms are first grown on a functionalized glass slide in a microfluidic channel for nanoindentation experiments, and the force-distance curves are obtained. Using the force-distance curves, the contact point is determined to obtain the force-indentation curve. Next, the integration time history is used to model the force curve with Ting's integration and determine the viscoelasticity parameters. The models used for Ting's integral include Hertz, Standard Linear Solid (SLS), Power-law Rheology (PLR), and Maxwellian models. Statistical comparisons of the viscoelastic parameters between species and strains will be conducted. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T03.00002: Motility and nutrient availability modulate biofilm formation in confinement Zehao Chen, Yiran Li, Amir A Pahlavan Biofilms are microbial communities formed when free-swimming bacteria transition to a sessile, surface-attached state. In nature, biofilm colonization is influenced by many environmental factors such as nutrient availability, competition between different species, and chemical and mechanical stresses. Here, using microfluidic experiments and theoretical modeling, we study biofilm formation in confined environments. We show how the interplay between bacterial proliferation, self-generated nutrient gradients, and motility modulates the spatiotemporal evolution of biofilm growth. We discuss the implications of our findings on the evolution of microbial communities in heterogeneous environments. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T03.00003: Measuring drag of dynamically aged marine biofilms treated with ultraviolet light (UVC) J Travis T Hunsucker, Kelli Z Hunsucker The presence of marine biofilms has been shown to cause significant increases in drag on ships and marine vehicles. Previous field experiments have demonstrated the application of ultraviolet light (UVC) results in a considerable reduction in biofilm for both static and dynamic environments. This experiment was designed to address how changes in biofilm treated by UVC modify the drag properties. An epoxy coating was applied to two PVC test plates (10 cm wide x 75 cm long) which were then immersed at Florida Tech’s estuarine field test site. The panels were dynamically aged in the estuarine environment using an open channel flume (10 cm wide x 300 cm long). Panels were immersed for approximately one week to accrue biofilm. A select panel was also exposed to UVC (25W, 254 nm) in the flume over the course of the week. Panels were then removed and the biofilm characteristics (thickness, percent cover, microbial community, chlorophyll content) were determined. Associated drag penalties were measured in a separate field deployed flow channel. Results demonstrate the correct dose of UVC can significantly reduce biofilm formation under flow, which results in lower drag penalties. These reduction in drag penalties are discussed in context of full-scale ships and underwater vehicles. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T03.00004: Understanding the subdiffusive motion of bacteriophages in a mucus layer P Sunthar, Silpa Mariya, J Ravi Prakash, Jeremy Barr Mucosal surfaces are the entry points of pathogens into the animal body and act as the primary sites of defence. Experiments show that viruses called bacteriophages undergo subdiffusive motion within mucus due to their adherence to the mucus network. Understanding this behaviour is important for infection prevention and therapy. Experiments have demonstrated that the motion of a T4 phage exhibit a subdiffusive motion due to the attractive interaction of proteins on the phage to the glycans on the mucin network. This gives it greater residence time and increases its efficiency in infecting its bacterial host. While motion of nano-particles in a polymer network has been studied, the motion of a sticky entity in a network has not been reported. We model the phage as a dendrimer with "sticky" ends that can selectively bind with sites on a network of associative polymers. A multi-particle Brownian Dynamics simulation algorithm based on the GPU-accelerated Python package HOOMD-Blue has been employed. Hydrodynamic and excluded volume interactions are taken into account. The effect of polymer concentration, number of stickers and sticker strength on the dynamics of dendrimers has been analysed. The sticky dendrimers exhibit subdiffusion even when their size is smaller than the "mesh size" of the network, while the non-sticky dendrimers remain diffusive. The origin of subdiffusive behaviour is shown to be related to the time scale of sticker binding, the number of stickers and the radius of gyration of the dendrimer. The diffusion coefficient decreases for both the sticky and non-sticky dendrimers with increasing concentration. This trend is analogous to the observed behaviour of the adherent and non-adherent phages in varying mucin concentrations. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T03.00005: The drag of artificial biofilm-like surfaces in a turbulent channel flow Elizabeth G Callison, Mohammad Elsouht, Harish Ganesh, Steven Louis Ceccio Drag penalties and performance degradation are some of the adverse effects induced by soft and hard biofouling in a marine environment. Understanding the mechanisms by which the compliance, effective roughness, and morphology of soft biofouling streamers interact with the flow is essential. However, studying soft biofilms in a laboratory setting is challenging due to sloughing and growth non-uniformities. In this study, two commercial fur surfaces are used as models to understand the interaction between streamers and the flow. The two Faux-Fur surfaces are studied in a turbulent channel flow and their coefficient of friction subjected to flow is determined and compared to their time averaged rigid replicas produced from profile scans. Spectral modal analysis is performed on high-speed videos of fur motion to extract relevant spatial and temporal scales of the studied surfaces, and compared to the characteristic scales of the flow. Furthermore, 2D planar PIV is performed at a downstream location to highlight the effect of streamer morphology (mainly height) on the skin-friction profile across a wide range of friction based Reynolds number. Additionally, a compliant scientific-fur of known material properties is manufactured and studied to isolate the effect of fur morphological and mechanical parameters. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T03.00006: Influence of shear and turbulence fluctuations on biofilm growth: A key issue for ocean microplastics Federico Pizzi, Mona Rahmani, Elena Sorribes Sigales, Joan Grau Barcelo, Cristina Romera-Castillo, Francesc Peters, Lluis Jofre, Francesco Capuano This study investigates biofilm growth under turbulent flows with the aim of understanding biofouling on microplastics (MPs) in oceanic environments. By increasing particle stickiness, biofilms promote MP aggregation and sinking; therefore, a thorough understanding of this multi-scale process is crucial to improve predictions of the MPs fate. We conducted a series of laboratory experiments using an oscillating-grid system to promote biofilm growth under homogeneous-isotropic turbulence with a grid Reynolds number between 305 and 2220. Biofilm formed in all cases in a days-scale then the biomass on the pieces was carefully measured and interpreted using a one-dimensional model, coupling the biofilm metabolism (Michaelis-Menten kinetics) with the turbulent diffusion of the surrounding bulk liquid. The biomass initially grows with turbulence intensity following an increase of the Sherwood number (i.e., enhanced availability of nutrients); then, the growth rate saturates due to: (i) uptake-limited kinetics; (ii) biofilm erosion due to shear forces. Furthermore, a subset of plastic pieces were analyzed with a scanning electron microscope, revealing that turbulence also affects the microscopic configuration of biofilm clusters, increasing their compactness with the turbulent fluctuations. These results contribute not only to our fundamental understanding of biofilms under flow, but can also inform global models of MP transport in marine environments. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T03.00007: Investigating Citrobacter sp. MICI21 Biofilm Growth on Patterned 2D Graphene, hBN, and Diamond Surfaces Niaz Faysal, Joseph Thalakkottor Biofouling, the accumulation of microorganisms, plants, and algae on wet surfaces, poses significant challenges to the freshwater and marine industries. In pursuit of eco-friendly mitigation strategies, we investigate the attachment and biofilm growth of Citrobacter sp. MICI21 on patterned 2D surfaces. The study focused on 2D surfaces composed of Graphene, hexagonal Boron Nitride (hBN), and/or Diamond on an underlying Copper substrate. The study aims to determine the degree of preferential growth on these different 2D patterned materials and to understand how it changes the effective surface chemistry of the substrate. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T03.00008: Adsorption and Aggregation Dynamics of Bovine Serum Albumin at the Air-Water Interface Peyman Dastyar, Arezoo M Ardekani Protein denaturation and aggregation present significant challenges in the development and stability of biological and pharmaceutical products. Due to the presence of amino acids and their amphiphilic nature, proteins exhibit a propensity to interact and aggregate. These molecules experience pronounced conformational changes at fluid-fluid interfaces, leading to aggregate formation that affects their properties and functionality. Interfacial rheology is a valuable technique to probe these intermolecular interactions, providing insights into the strength and temporal evolution of molecular networks. In this study, we investigated the interfacial properties of Bovine Serum Albumin (BSA) at the air-water interface across various concentrations using a rotational rheometer equipped with double-wall ring (DWR) geometry. This setup effectively differentiates interfacial stresses from bulk stresses. Our findings demonstrate that the interfacial viscoelasticity of BSA solutions increases over time, which indicates the development of a molecular network and progressively stronger interactions at the interface. Moreover, a comparative analysis of the time-dependent viscoelasticity of BSA solutions across different concentrations revealed that the elastic modulus rises up to a certain concentration, beyond which it does not exhibit significant change. Additionally, we observed that while viscoelasticity reaches equilibrium over extended periods, at higher concentrations, it decreases after an initial stabilization phase. |
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