Biofilm viscoelasticity and nutrient source location control biofilm growth rate, migration rate, and morphology in shear flow*

Our numerical model to simulate the growth and deformation of a viscoelastic biofilm in shear flow under different nutrient conditions uses the Immersed Boundary Method with viscoelastic parameters determined a priori from measurements reported in the literature. Biofilm growth occurs at the biofilm-fluid interface by a stochastic rule that depends on the local nutrient concentration. We compare the growth, migration, and morphology of viscoelastic biofilms with a common relaxation time of 18 min over the range of elastic moduli 10-1000 Pa in different nearby nutrient source configurations. Our results agree with the biophysical principle that biofilms can adapt to their mechanical and chemical environment by modulating their viscoelastic properties. Furthermore, by comparing the behavior of a purely elastic biofilm to a viscoelastic biofilm with the same elastic modulus, we find that the elastic biofilm underestimates growth rates and downstream migration rates if the nutrient source is downstream, and it overestimates growth rates and upstream migration rates if the nutrient source is upstream. Future modeling can use our comparison to identify errors that can occur by simulating biofilms as purely elastic structures.