Live in-situ Biofilm Micro-rheology Experimental Study with Simultaneous Flow Shear and Stain Measurement using Digital Holographic Microscopy

Recent studies reveal the elasticity of a live biofilm can be regulated by flow shear. Despite much research, the viscoelasticity of a live biofilm under shear is less understood due to lack of experimental tools. We present an experimental technique that combines a creep-recovery microfluidics platform, enabling the in-situ growth of bacteria biofilms and Digital Holographic Microscopy (DHM) to provide simultaneous strain and flow stress measurement. Live biofilms are grown in-situ within microfluidics under varying flow conditions. During experiments, 1 μm particle suspension replaces the culture to perform the creep-recovery cycle. High-speed holograms of tracer particles and live biofilms are recorded simultaneously. A correlation-based algorithm is applied to separate biofilm and particle phases, which enables the measurement of strain deformation of the biofilm by Digital Image Correlation (DIC) and 3D flow around it by DHM simultaneously. From stress-strain measurement, the viscoelasticity is computed directly. The system has been applied to measure viscoelasticity of Pseudomonas fluorescens and P. aeruginosa biofilms grown at three flow conditions (e.g., 2, 10, and 20 mm/s) and creeping speed of 2X, 5X, and 10X. The experiments will also resolve break-off shear.