Viscoelastic Properties of a Mixed Culture Biofilm from Rheometer Creep Analysis

Abstract

The mechanical properties of mixed culture biofilms were determined by creep analysis using an AR1000 rotating disk rheometer. The biofilms were grown directly on the rheometer disks which were rotated in a chemostat for 12 d. The resulting biofilms were heterogeneous and ranged from 35 microns to 50 microns in thickness. The creep curves were all viscoelastic in nature. The close agreement between stress and strain ratio of a sample tested at 0.1 and 0.5 Pa suggested that the biofilms were tested in the linear viscoelastic range and supported the use of linear viscoelastic theory in the development of a constitutive law. The experimental data was fit to a 4-element Burger spring and dashpot model. The shear modulus (G) ranged from 0.2 to 24 Pa and the viscous coefficient (eta) from 10 to 3000 Pa. These values were in the same range as those previously estimated from fluid shear deformation of biofilms in flow cells. A viscoelastic biofilm model will help to predict shear related biofilm phenomena such as elevated pressure drop, detachment, and the flow of biofilms over solid surfaces.

Exopolysaccharides of the Biofilm Matrix: A Complex Biophysical World

“…This has been previously observed with purified polysaccharides like cellulose [73]. Moreover, bending of biofilm structures in the shear direction during the application of shear stress has been mentioned to explain the viscoelastic response of a mixed culture biofilm [72]. NF biofilms have been submitted to oscillation analysis with a cone-plate rheometer [66].…”

“…Previous work has suggested that laboratorygrown and some natural biofilms are viscoelastic in nature [3,8,72]. During rotation analysis, a rheofluidification behaviour is observed for NF biofilms [66].…”

“…Viscoelasticity is thought to be a general mechanical property of biofilms. A very wide range of elasticity and viscosity values has been previously observed for a wide sample of biofilms formed artificially in laboratory experiments or coming from natural aquatic environments [4,72,76]. Thus, it wasn't surprising to observe that the rheological properties of NF biofilms are different from the ones of natural biofilms from different aquatic environments like Nymph Creek (Yellowstone National Park) and Chico Hot springs (Montana) algal biofilms [4].…”

Modelling mechanical characteristics of microbial biofilms by network theory

“…The simplest modelling approaches for biofilms make use of empirical elastic or shear moduli to express a linear relationship between scalar stress and strain measures as in earlier studies [13][14][15][16][17]. The viscoelastic response has classically been interpreted in terms of linear spring-dashpot analogies such as the standard linear solid, the generalized Maxwell or Burgers model [18][19][20][21][22][23][24]. Expressing the relaxation function in terms of a Prony series, Towler et al [25] used the latter model within a commercial finite element program to perform two-dimensional simulations.…”

Viscoelasticity in Biological Systems: A Special Focus on Microbes

“…Biofilms, all of which exhibit classic viscoelastic behaviours [109,115,116,118,119], can grow in a wide variety of environments including laboratory conditions, under flow and even in hot springs, demonstrating their ability to absorb elevated changes in shear stresses. Biofilms are elastic for shorter periods, can resist shear stresses and detachment, and over longer periods of time they flow as viscous fluids and become streamlined [109,112,114].…”