Fig. 6: Biofilm growth at the top and bottom walls for different flow conditions.

a The top row displays 3D reconstructions obtained in Paraview from z-stack images of the biofilm grown at various investigated shear rates (\({\dot{\gamma }}_{w}\) 1.67 was omitted), colorimetric scale bar depicting biofilm thickness in μm was reported on the left. In the second raw images of a single field of view depicting the biofilm growth on the top surface. In the third row, images of biofilm growth at the bottom surface. b Biovolume (μm³/μm²) of the biofilm measured at the top (in blue) and bottom (in red) walls as a function of shear rate (\({\dot{\gamma }}_{w}\), s⁻¹). Box plots illustrate the statistical distribution of biovolume values, showing an increase in biofilm growth with shear rate up to \({\dot{\gamma }}_{w}\) 10 s⁻¹, followed by a decrease at higher shear rates. Biofilm growth is more pronounced on the bottom wall compared to the top. c Substratum coverage (A.U.) at the top (in blue) and bottom (in red) walls as a function of shear rate (\({\dot{\gamma }}_{w}\), s⁻¹). Substratum coverage follows a similar trend to biovolume, increasing with shear rate up to \({\dot{\gamma }}_{w}\) 1 s⁻¹ before decreasing. The bottom surface exhibits a higher biofilm coverage than the top surface, indicating an asymmetrical biofilm development influenced by gravity.