Nonlinear deformation and localized failure of bacterial streamers in creeping flows

Abstract

We investigate the failure of bacterial floc mediated streamers in a microfluidic device in a creeping flow regime using both experimental observations and analytical modeling. The quantification of streamer deformation and failure behavior is possible due to the use of 200 nm fluorescent polystyrene beads which firmly embed in the extracellular polymeric substance (EPS) and act as tracers. The streamers, which form soon after the commencement of flow begin to deviate from an apparently quiescent fully formed state in spite of steady background flow and limited mass accretion indicating significant mechanical nonlinearity. This nonlinear behavior shows distinct phases of deformation with mutually different characteristic times and comes to an end with a distinct localized failure of the streamer far from the walls. We investigate this deformation and failure behavior for two separate bacterial strains and develop a simplified but nonlinear analytical model describing the experimentally observed instability phenomena assuming a necking route to instability. Our model leads to a power law relation between the critical strain at failure and the fluid velocity scale exhibiting excellent qualitative and quantitative agreeing with the experimental rupture behavior.

Dynamics of bacterial streamers induced clogging in microfluidic devices

“…This is because such sudden changes in deformation characteristics are typically associated with instabilities and phase changes whose consequences are often prominently visible in the structure such as necking failure. 19 However, in the case of stick-slip, we observe no substantial changes in material constitution near the tracking points with the same regularity as the jumps (which appeared at even finer time scales). Thus, we conclude that the sudden changes in deformations (the spurting 'slip' and the sudden arrest of it through 'stick') primarily reflect a more global motion aided by the onset and arrest of sliding at the interfaces, further confirmed through microscopy data.…”

Microfluidic Membrane Filtration Systems to Study Biofouling

“…Streamers form in flowing water and attach to the surface by the upstream "head" while the downstream "tail" can oscillate [6,10,[30][31][32]. Streamers in a microfluidic system are typically tethered at one end to the pillar walls while the rest of the body is suspended in the downstream direction.…”

“…Biswas et al [30] designed a microfluidic membrane mimic by using photolithography technique to investigate the biofouling under different flow condition. The minimum pore size considered was 10 μm and the micropillars were distributed in a staggered pattern.…”

“…The minimum pore size considered was 10 μm and the micropillars were distributed in a staggered pattern. Figure 6 shows the schematic of their microfluidic device with the mimic membrane structure [30]. Transparent PDMS microsystem is used to mimic the membrane to study the bacteria transfer in the porous interface.…”

“…Schematic of microfluidic device with the mimic membrane structure[30]. The dimensions are d = 50 μm, w 1 = 60 μm, w 2 = 104 μm and P = 10 μm.…”