Micro-Mechanical Measurement of the Cohesive Strength of Biofilms
Graduate student Eric Poppele was partially supported by a U.S. Department of Education GAANN Fellowship
Our long-range goal is to develop control strategies for biofilm reactors based on an improved understanding of the factors affecting biofilm cohesive strength. Quantifying the relationship between strength and environmental conditions will aid efforts to model biofilm growth and development, and may reveal new strategies for the control of biofilm properties. For example, reactor start-up conditions may be better optimized by providing conditions that increase cohesive strength and therefore decrease start-up times. Alternatively, detachment of excess or undesirable biofilm may be promoted by applying conditions that decrease the cohesive strength of a biofilm, making it more susceptible to removal. These are just a few examples of the way in which an improved understanding of the factors controlling biofilm cohesive strength could be used to improve the operation of engineered systems.
Previous attempts at measuring biofilm cohesive stength were problematic for several reasons: (1) the geometry of the detached particle (i.e. contact area) and/or the applied force were not well defined; (2) the biofilm had to be grown on a specific testing platform, precluding the analysis of “real world” samples; and (3) cohesive strength was not measured at the scale at which detachment typically occurs. Therefore, we developed a micro-mechanical technique for directly measuring the cohesive strength of biofilms and other microbial aggregates at an appropriate scale (<100 microns). The method is based on the observed deflection of a cantilevered glass micro-pipette as it separates a particle from the intact biofilm, or separates a biofilm fragment captured between two pipettes (Figure 1). The main objective of this research was to correlate the cohesive strength of pure and mixed-culture biofilms with changes in environmental conditions, including nutrient levels and fluid shear stress.
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