Near wall void growth leads to disintegration of colloidal bacterial streamer.

We investigated the failure of thick bacterial floc-mediated streamers in a microfluidic device with micropillars. It was found that streamers could fail due to the growth of voids in the biomass that originate near the pillar walls. The quantification of void growth was made possible by the use of 200 nm fluorescent polystyrene beads. The beads get trapped in the extracellular matrix of the streamer biomass and acted as tracers. Void growth time-scales could be characterized into short-time scales and long time-scales and the crack/void propagation showed several instances of fracture-arrest ultimately leading to a catastrophic failure of the entire streamer structure. This mode of fracture stands in strong contrast to necking-type instability observed before in streamers.