Bacterial communities attached to surfaces form biofilms which are important in both engineered bioreactors and natural environments. Despite the importance of biofilm structure as an essential mediator of biofilm growth and activity, little is known about the relationship between biofilm structure and mechanical properties that control retention of biomass in biofilms. To address this knowledge gap, the PIs propose to develop a novel methodology, termed Optical Coherence Elastography, for rapid quantitative 3D mapping of mechanical properties in biofilms.
The project team will develop the Optical Coherence Elastography method and use it to assay properties and dynamics of mixed-culture biofilms representative of those employed for biological nitrogen (N) removal. Efforts will be organized around two specific objectives: 1) Develop a dynamic Optical Coherence Elastography method for mesoscale nondestructive mapping of elastic moduli in environmental biofilms; and, 2) Employ Optical Coherence Elastography to quantify the relationship between mesoscale biofilm mechanical properties, morphology, and performance in mixed culture N-cycling biofilms. Initial applications of Optical Coherence Elastography will relate mesoscale gradients in Young's and Shear moduli to variation in biofilm roughness, internal porosity and thickness. Nondestructive elastography will enable time-series measurement of mesoscale structural and mechanical features during development of these essential environmental biofilms. Thus, this project advances understanding of critical yet poorly understood interrelationships between physical structure and mechanical properties in environmental biofilms. Macroscale biofilm characteristics such as biomass accumulation and chemical transformation rates are known to be linked to mesoscale biofilm structure and mechanical properties, yet the vast majority of work on biofilm structure has focused on the microscale. Optical Coherence Elastography will enable, for the first time, co-located, real-time, non-invasive, in situ mapping of biofilm morphology and mechanical properties at the mesoscale. The proposed Optical Coherence Elastography methodology employs a shear wave transducer to propagate localized deformations in biofilms. Deformations are then continuously imaged via phase sensitive optical coherence tomography. The spatially resolved mesoscale biofilm mechanical property distribution is obtained by relating the speed of propagation of deformations to local density and elastic or viscoelastic properties. Optical Coherence Elastography has recently been applied for biomedical research, but is an entirely new approach to biofilm characterization. Results of the proposed work will open new possibilities to elucidate the interplay between mesoscale biofilm properties, microscale biofilm composition, and emergent system function in environmental biofilms. This project will support one Ph.D. student and as undergraduate student. Project experimental systems will be used to design experiments for a core laboratory course at Northwestern and demonstrations for outreach to K-12 students and community groups.
