Simultaneous flow stress and strain measurement of bacteria streamer by micro-tensiometer and digital holographic microscopy*

The formation of biofilms allows them to survive environmental insults and colonize various surfaces. Many prior studies have focused on the formation process of biofilm under various conditions, while the understanding of biofilm rheology is less known due to the lack of suitable experiment tools to allow in-situ growth of streamers and measure fluid shear around it. In this study, we present an experimental technique that integrates a micro-pillar microfluidic platform with digital holographic microscopy (DHM) to enable simultaneous measurements of instantaneous streamer strains and flow shear stresses around it. The micro-pillar microfluidic platform allows the in-situ growth of biofilm streamers under various flow conditions, while DHM records the deformation of in-situ biofilm streamers under shear stresses and simultaneously tracks thousands of particles individually in 3D to resolve stresses over deforming streamers during a creep-recovery test. Pseudomonas fluorescens is used as a model in the current experiments. Various flow rates are employed in the current study to investigate the rheology adaptation of biofilm streamers developed to distinct hydrodynamic conditions.