Advances in Biofilm Mechanics

Abstract

A knowledge of the mechanical properties of bacterial biofilms is required to more fully understand how a biofilm will physically respond, and adapt, to the physical forces, such as those caused by fluid flow or particle or bubble impingement, acting upon it. This is particularly important since biofilms are problematic in a wide diversity of scenarios and spatial and temporal scales and many control strategies designed to remove biofilms include a mechanical component such as fluid flow, particle or bubble impingement or a physical contact with the surface generated by scraping or brushing. Knowing when, and how, a biofilm might fail (through adhesive or cohesive failure) will allow better prediction of accumulation and biomass detachment, key processes required in the understanding of the structure and function of biofilm systems. However, the measurements of mechanical properties are challenging. Biofilms are living systems and they readily desiccate if removed from the liquid medium, it is not clear how quickly their mechanical properties might change when removed from their indigenous environment into a testing environment. They are also very thin and are inherently attached to a surface. They cannot be formed into standard test coupons such as plastics or solids, and cannot readily be poured or placed into conventional viscometers or rheometers, such as liquids and gels. Measured parameters such as the elastic and shear modulus, adhesive strength or tensile strength are sparse but are increasingly appearing in the literature. There is a large range of reported values for these properties, although there is general agreement that biofilms are viscoelastic. Biofilms have been assessed with various experimental methods depending on the desired characteristic and available equipment. The aforementioned challenges and lack of standard methods or equipment for testing attached biofilms have led to the development of many creative methods to tease out aspects of biofilm mechanical properties. In this paper, we review some of the more common techniques and highlight some recent results.