Modeling biofilm streamer formation: Regulation by pulsatile flow dynamics and mechanical interactions

Biofilm streamers in microchannels cause severe blockages and microbial contamination, leading to membrane fouling in wastewater treatment, microfluidic sensor performance degradation, and elevated infection risks in biomedical implants, with their formation tightly regulated by flow field dynamics. This study employs a two-dimensional immersed boundary method (IB2d) to investigate the early-stage mechanical formation mechanism of biofilm streamers under pulsatile flow. The IB2d framework accurately captures dynamic fracture and reconnection of inter-particle elastic connections, core processes governing streamer formation. A morphology-based inverse calibration method was developed using straight-channel detachment experimental data, determining the effective spring stiffness range of Bacillus subtilis biofilms to be 6.8 × 105–1.05 × 106 N/m. Under steady-state flow, low velocities promoted large-scale continuous streamers via front-to-rear aggregate migration, while high velocities only supported small stable tail streamers, governed by a two-stage micro-mechanical chain of reversible elastic stretching and irreversible shear-induced fracture. In pulsatile flow, increasing amplitude uniformly inhibited streamer formation by intensifying elastic connection breakage. Notably, frequency exerted a distinct non-monotonic effect, with the strongest inhibition at 0.5 Hz within a narrow 0.4–0.6 Hz band, arising from unfavorable synchronization between the flow cycle and aggregate migration/connection repair processes. These findings provide a green chemical-free flow regulation idea for early-stage biofilm control.