(623d) Colloidal Microstructure and Mechanics of Artificial and Naturally Occurring Staphylococcal Biofilms

Biofilm-like bacterial constructs consisting of sub-micron bacterial cells and chitosan are tuned to create materials with distinct microstructural and mechanical features.  While it is known that biofilms are viscoelastic in nature and the colloidal microstructure of biofilms can vary depending on their growth environment, little is known about the contributions of individual biofilm components to biofilm mechanics.  Bacterial biofilms can be thought of as composite materials that contain bacterial cells surrounded by matrix materials, such as polysaccharides, proteins and DNA.  Here, we use bacteria cells and chitosan—a polysaccharide with physical chemistry similar to a naturally occurring polysaccharide—as building blocks to create biofilm-like composites and probe the contributions of individual components to biofilm structure and mechanics.  Using confocal laser scanning microscopy coupled with bacteria identification and dynamic bacteria tracking tools, we characterize the microstructure, mobility, and creep compliance of the biofilm-like composites.  We find biofilm constructs with microstructures similar to those of naturally occurring biofilms, as characterized through the local number densities and radial distribution functions.  We also find concentration dependent dynamic phases of the bacterial constructs, including a mobile bacteria phase, a bacterial cluster gel phase, and an arrested bacterial gel phase.  We discuss the similarities and differences between the microstructure and mechanics of these synthetic bacterial-constructs and naturally occurring Staphylococcal biofilms.  Through this work, we create structurally and mechanically similar biofilm-like constructs, we reveal physical interactions that may contribute to biofilm mechanical behavior, and we utilize principles from colloidal science to advance the understanding of bacterial biofilm behavior.