Viscoelasticity of the Biofilm Matrix

Biofilms are communities of interacting microbes embedded in a matrix of polymers, proteins, ions, and water. Most studies of biofilms have focused on the biological characteristics of biofilm microbes and the biochemical properties of components of the biofilm matrix. However, the presence of the matrix confers on the system of microbes a set of mechanical properties that do not exist for bacteria suspended or swimming in liquid. Thus, the mechanics of biofilms are both an emergent property and a phenotypic signature of the biofilm state. They are also much less studied than the biological and biochemical properties of biofilms. Here, we review the foundational concepts of viscoelasticity, which is the class of both solid and fluid mechanics into which biofilm properties fall. Next, we present approaches that have been used to do rheological studies on biofilms; rheology is the study of how matter changes shape and moves under force. Finally, we survey what is known about biofilm viscoelasticity and how different components can contribute. We end with suggestions for future work to understand how viscoelasticity could be linked to biofilm survival.