(245f) Using Freely Suspended Biofilms to Study Interactions Among Bacterial Cells: Mechanical and Transport Properties

Biofilms - communities of bacterial cells encased in their extracellular polymeric matrix - are relevant materials in both medicine and engineering: the same features of a biofilm that often pose challenges to its eradication in a medical setting (three dimensional structure, cohesiveness, and resilience in the face of environmental changes) can be beneficial to a deliberately designed structural material.

In either case, there is a need to measure the physical properties of biofilms at a practically relevant (bulk) scale. However, measuring bulk scale features is complicated by the fact that biofilms are inherently heterogeneous materials, and their mechanical behavior is also closely linked to microscopic features: the chemistry of cell-cell interactions, local composition, and structural heterogeneity. Existing methods to probe biofilms at a bulk scale do not always take these different length scales into account, sometimes using a local section of biofilm as a proxy for the behavior of the whole film, or neglecting structural heterogeneity by pooling many plates’ worth of material for a single measurement.

We try to address these limitations by making custom millifluidic devices that suspend a three millimeter biofilm sample across a support, and impose tunable hydrostatic pressure drops in the Pa-kPa range across the film. The resulting deformation of the film through an aperture is visualized with optical coherence tomography and used to estimate bulk mechanical properties of the film. Our method requires only microliters of material, causes minimal disruption to the film structure, allows for measurement of both average properties as well as local heterogeneity, and is compatible with other types of measurements as well (e.g. confocal microscopy, perfusion, or optical properties).

We pair our device with a model system: E. coli K-12 DH10B, an inherently poor biofilm former, engineered to surface display membrane-tethered elastin like polypeptides (ELPs) with various repeat lengths. These precisely tailored building blocks then grow and assemble into bulk materials, which we test. We investigate the effects of varying ELP repeats and presence or absence of a disulfide bond-forming cysteine on the bulk mechanical properties of the biofilms.