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 μm to 50 μm 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 (η) 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.

Keywords:

• biofilm
• Burger model
• creep
• mechanical properties
• rheometry
• viscoelasticity

Acknowledgements

This work was funded by the National Institutes of Health RO1 grant GM60052-02 and in part by the co-operative agreement EEC-8907039 between the National Science Foundation and Montana State University, Bozeman and the W M Keck Foundation. For their technical advice and contributions we thank Ladean McKittrick, Department of Civil Engineering, Alexandra Vinogradov, Department of Mechanical Engineering, Isaac Klapper, Department of Mathematics and Ryan Cargo, the Center for Biofilm Engineering at Montana State University, Bozeman, Montana.