A video imaging method for time-dependent measurements of molecular mass transfer and biofilm dynamics in microchannels
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A video imaging method for time-dependent measurements of molecular mass transfer and biofilm dynamics in microchannels M. Parvinzadeh Gashti, M. Zarabadi, J. Greener Département de Chimie, Université Laval, Québec, QC, G1V 0A6, Canada Corresponding email: [email protected] ABSTRACT The biomass accumulation and movement of biofilms in a microchannel is monitored by optical microscopy. First, the average optical density of the biofilm is monitored in time as a measure of biofilm thickness and structural heterogeneity. These results are used as inputs to calculate changing flow velocities due to resulting excluded volume. Next the displacement velocity of moving biofilm segments was recorded in different places in the microchannel. Quantitative analysis by a particle tracking routine showed differences in displacement velocity near and far from the microchannel corner, which is believed to be related to the local shear forces which vary depending on the height of the biofilm segment and its position in the microchannel. The effect of changing biofilm thickness and different hydrodynamic environments in the microchannel are then discussed in terms of their effects on molecular loading rates. Finally, a demonstration of a flowtemplated growth approach as a means to homogenize the growth environment. INTRODUCTION Biofilms are natural viscoelastic substances consisting of bacteria and a surrounding extracellular polymeric substance (EPS).[1,2] This is a broad class of biomaterials that is wellrepresented in nature, ranging from coatings on aquatic surfaces to dental plaque. From a biotech perspective biofilms are interesting an ambient condition catalytic materials, which can self-repair and even adapt to changing reaction conditions.[3,4] As the biofilm EPS is an effective shield against antibiotics and can resist various components of the immune system, biofilm-based infections can be chronic or even become terminal. For example, cystic fibrosis is a well-known disease resulting from polysaccharide alginate-producing Pseudomonas aeruginosa which must be treated before the EPS has fully-formed and matured.[5] Great advances have been made in understanding the molecular biology of biofilms in the last 10 years, yet there remains a strong need for quantitative physical characterization. However, biofilms are highly complex, heterogeneous materials, with properties that change in space and time. Therefore, the challenge for analytical scientist has been to develop and adapt techniques to better understand these materials. However, at the same time, facile methods for wideuse should also be developed. Biofilms are known to be extremely responsive to their hydrodynamic environment both for their development and for molecular penetration of antibiotics and other foreign species. Most biofilms require at least some tangential flow against their surface to facilitate mass-transport through the biofilm-liquid interface, whilst the EPS helps to prevent detachment. A previous study applied known shear stresses against se
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