The role of surface adhesion on the macroscopic wrinkling of biofilms

Biofilms, bacterial communities of cells encased by a self-produced
matrix, exhibit a variety of three-dimensional structures. Specifically,
channel networks formed within the bulk of the biofilm have been
identified to play an important role in the colonies viability by
promoting the transport of nutrients and chemicals. Here, we study channel
formation and focus on the role of the adhesion of the biofilm matrix to
the substrate in Pseudomonas aeruginosa biofilms grown under constant flow
in microfluidic channels. We perform phase contrast and confocal laser
scanning microscopy to examine the development of the biofilm structure as
a function of the substrates surface energy. The formation of the wrinkles
and folds is triggered by a mechanical buckling instability, controlled by
biofilm growth rate and the film's adhesion to the substrate. The
three-dimensional folding gives rise to hollow channels that rapidly
increase the overall volume occupied by the biofilm and facilitate
bacterial movement inside them. The experiments and analysis on mechanical
instabilities for the relevant case of a bacterial biofilm grown during
flow enable us to predict and control the biofilm morphology.