A marine biofilm flow cell for in situ determination of drag and biofilm structure

It is not straightforward to link biofilm parameters to frictional drag, because of the heterogeneous distribution and viscoelasticity of the produced matrix. Here we present the design and calibration of a flow cell in which marine biofilms can be cultured under flow and then assessed for drag, structural and mechanical properties. The flow cell test section comprised a rectangular channel constructed by sandwiching together rigid PVC panels and side panels of clear acrylic, which allow natural light to enter. The Fanning friction factor (Cf) of the flow cell was found by measuring the pressure drop (ΔP) at various flow velocities (u). Flow cell calibration was carried out using a clean inert marine coating, and various roughness grades of sandpaper sheets to find Cf for each rigid roughness. ΔP was proportional to u2, indicating flow was turbulent (R2 = 0.99). The top panel of the flow cell can be substituted with a clear acrylic lid to allow simultaneous measurement of Cf and biofilm physico-mechanical properties by optical coherence tomography (OCT). Here, we demonstrated that the flow cell can be used to image microbial fouling using OCT. Future experiments will assess physico-mechanical and drag properties of marine fouling biofilms under flow.