Sprecher
Beschreibung
Bacteria invade surfaces by forming dense colonies encased in a polymer matrix. Successful settle-
ment of founder bacteria, early microcolony development and later macroscopic spreading of these
biofilms on surfaces rely on complex physical mechanisms. Recent data show that on soft hydrogels,
substrate rigidity is an important determinant for biofilm initiation and spreading, through mostly
unknown mechanisms. Using a thermodynamically consistent thin-film approach for suspensions on
soft elastic surfaces supplemented with biomass production and an imposed osmotic pressure we
investigate in silico the role of substrate softness in the osmotic spreading of biofilms. We show that
spreading is considerably slowed down on soft substrates and may be completely halted depending
on the biomass production rate. We find, that the critical slowing down of biofilm spreading on
soft surfaces is caused by a reduced osmotic influx of solvent into the biofilm at the edges, which
results from the thermodynamic coupling between substrate deformation and interfacial forces. By
linking substrate osmotic pressure and mechanical softness through scaling laws, our simple model
semi-quantitatively captures a range of experimentally observed biofilm spreading dynamics on hy-
drogels with different architectures, underscoring the importance of inherent substrate properties in
the spreading process.