Using Active Materials at Liquid Interfaces to Regulate Bacterial Biofilm Mechanical Properties

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Bacteria can grow on liquid/air interfaces by attaching to the interface, excreting proteins, and reproducing. This creates a slimy, elastic sheet called a pellicle (a biofilm grown at an air/water interface). Pellicles occur in the lungs of cystic fibrosis patients, where they allow infection to spread, or in oil spill cleanup where they enable oil-degrading bacteria access to crude. To reduce infection, pellicles should be made less stable; to enhance oil cleanup, pellicles should be made more stable. The stability of pellicles depends in part on the bacteria type, which in real-world applications cannot be changed. Therefore, to alter pellicle properties, the local environment needs to be changed to affect bacteria behavior. The PI will alter pellicle properties by adding materials directly to liquid interfaces. For instance, adding soap to an interface weakens biofilms, whereas adding small particles strengthens them. This research will study a range of materials that can modify interfaces and determine how and why the properties of interfaces can be used to control pellicle mechanical strength. An interesting 'super Saturday' science club for elementary students will be supported. 'Science it's a girl thing' for 5th and 11th grade students will also be created. The PI teaches fluids and also serves to promote graduate school to undergraduates. He is part of a formal program in mechanical engineering to enhance diversity and women participation which is low in engineering in particular for mechanical engineering. He will teach a new course and solidly integrates research and educational plans.When surface active materials adsorb to an change the properties of a liquid interface, it is known to affect the viscoelasticity of a pellicle. However, there is little study of this phenomenon and still confusion as to what mechanisms cause observed changes. This research will determine how mechanical and chemical properties of an interface such as viscoelasticity, charge, and wettability affect interfacial viscoelasticity of P. aeruginosa pellicles. This will be done by using specific adsorbed particles, proteins, and surfactants to systematically control interfacial properties. A custom-built rheometer will be employed to characterize interfacial viscoelastic storage and loss moduli and simultaneously monitor bacteria movement within the biofilm. This will allow discernment of the impacts of interface properties on pellicle formation and correlation of biological behavior to interfacial mechanics in a way that has not been previously accomplished. The conclusions drawn about the role of interface properties on pellicle formation will be broadly applicable to all pellicle-forming bacteria due to the focus on mechanistic processes. The resulting data will provide a unique understanding of pellicle formation and a new means to change ultimate mechanical properties of pellicles.