Why a microfluidic approach for continuous measurements of biofilm viscosity

A microfluidic method combining video tracking with a semi-empirical viscous flow model provides continuous, non-intrusive measurements of time-varying viscosity in biofilms from Pseudomonas sp. bacteria. The approach uses measured velocity and height of tracked biofilm segments, which move under the low shear force imposed by flowing nutrient solutions.

The initial measured viscosities for the first 24 hours after inoculation were among the lowest reported to date. Following a low viscosity growth stage, sudden thickening was observed. During this stage, viscosity increased by over an order of magnitude in less than ten hours. The technique was also demonstrated as a promising platform for parallel experiments by subjecting multiple biofilm-laden microchannels to nutrient solutions containing NaCl in the range of 0 mM to 34 mM. Even in this narrow range of ionic strengths, preliminary data suggest a strong relationship between ionic strength and biofilm properties, such as average viscosity and time of onset of rapid thickening. The technique opens the way for a combinatorial approach to study the response of biofilm viscosity under well-controlled physical, chemical and biological growth conditions.