Figure 2.

Indentation test principle. A sphere probe with the diameter of 20 µm was used in the indentation measurement. When the probe was indented into the biofilm surface, the deflection of the probe cantilever was monitored, and the applied force was calculated with the measured vertical deflection and the spring constant of the cantilever. The force as a function of indentation depth was then plotted, and the biofilm outer layer Young’s modulus and thickness was determined accordingly.