Figure 7

Comparison of growth and migration rate of viscoelastic biofilms in different nutrient source configurations and at a shear flow value \(u_\text {max} = 5\times 10^{-6}\) m/s over a range of elastic moduli. (a) Ratio of the biomass of the biofilms at 2.5 h to their initial biomass. Below \(E\approx 80\) Pa biofilms grow more in a downstream configuration relative to an upstream configuration. Above \(E\approx 80\) Pa biofilms grow more in an upstream configuration relative to a downstream configuration. In the symmetric full-stream and no-concentration configurations, biofilm growth is independent of the elastic modulus. (b) Horizontal migration rate. The nearly constant offset between the downstream and upstream configurations provides a measure of the migration rate toward the nutrient source. The full-stream configuration provides a measure of the migration rate in response to shear flow. In the limit of large elastic modulus, the strain rate becomes negligible and the migration rate is due primarily to growth toward the nutrient source. (c) Vertical migration rate. Soft biofilms in the downstream and the full-stream configurations have similar migration rates. Stiff biofilms in downstream and upstream configurations have similar migration rates.