Fig. 2.

Schematic of the different mechanical methods that can be used to analyze biofilms. Mechanical methods to analyze biofilms can be divided into indentation (application of a normal force) or shear (application of a shear force). (A) For indentation, a probe or indenter is brought into contact with the biofilm, and the mechanical properties analyzed using either compression (pushing), tension (pulling) or dynamic (cycling of compression and tension) modes. For analysis under shear, there are two main ways that shear forces can be applied to a biofilm, (B) using spinning disc rheometry (spinning) or (C) using fluid shear (flow). (B) For spinning disc rheometry, a parallel plate probe is brought into contact with the biofilm, and changes in stress or strain measured under different modes of analysis. This can be either constant, where a constant stress (creep) or constant strain (relaxation) is applied; ramp, where an increasing stress or strain (stress-strain curve) is applied; or dynamic oscillation, where the probe is oscillated at either increasing stress, strain or frequency (frequency sweep, stress sweep, strain sweep). (C) When grown under fluid shear, time-lapse microscopy can be used to visualize and measure the deflection of biofilm structures in response to changes in the fluid flow rate. Alternatively, fluorescent beads can be incorporated into the system and their movement tracked through the biofilm.