Effect of microfluidic channel geometry on Bacillus subtilis biofilm formation

Biofilms are microbial colonies encased in an extracellular polymer matrix self-secreted through bacterial proliferation and differentiation. Biofilms exist almost everywhere such as sewers, rivers and oceans. In the fluid environment, the formation of biofilms is closely related to the relevant parameters of the flow field, such as the shear stress, the secondary flow, and the Reynolds number. In this paper, we use microfluidic channels made of polydimethylsiloxane to study the channel-geometry effect on Bacillus subtilis biofilms formation, such as the biofilm adhesion and structure. Our study shows that both the shear stress and the secondary flow play roles in the biofilm adhesion at the initial stage, the shear stress decides whether the biofilm adheres, if yes, then the secondary flow determines the adhesion rate. Our study further shows that after the biofilm forms, its structure evolves from loose to dense, with a concomitant 20-times rise in adhesion. Our study provides new insights into the adhesion of biofilms in natural and industrial fluid environments and helps understand the growth of biofilms.