The viscoelastic properties of microbial biofilms have attracted great interests in recent years due to the ubiquity of biofilms and their wide range of industrial and municipal applications causing tremendous societal impacts. Biofilms are predominantly architected by extracellular polymeric substances (EPS) matrices composed of bacterial cells and biopolymers secreted by the cells. EPS matrices bridge the gene expression from bacterial cells and important explicit characteristics of biofilms (morphology, biological function, and physical robustness). It is believed that the viscoelastic properties of EPS play an important role to affect biofilms’ characteristics, but these biofilm properties are understudied. The challenges of viscoelastic characterization in biofilms are due to their irregular geometry, spatially heterogeneous properties, and their delicate nature. In addition, most of existing tools are only suitable for rheological measurements at macro- or micro-scales, but not for mesoscale where numerous key features of biofilms directly link to. In this study, a novel framework of viscoelastic characterization for biofilms at mesoscale is developed. The framework combines Optical Coherence Elastography (OCE) technique and a theoretical acoustic wave model, where the former measures frequency-dependent phase velocity of elastic waves propagating in biofilms, and the latter predicts dispersion curves based on given material properties, geometry, and boundary conditions. The viscoelastic properties of biofilms are determined through inverse modeling, calculating the dispersion curve that has the best curve-fitting result to the experimental data. This framework considers both a plate structure and a curved structure and are validated against soft hydrogel plates and spheres by obtaining their viscoelastic properties. Then, the framework is applied to estimate the shear modulus and viscosity of a lab-developed mixed-culture planar biofilm and a practical granular biofilm acquired directly from a full-scale wastewater processing reactor. This work represents the first attempt to explore elastic waves for quantitative mechanical characterization of biofilms in mesoscale. It provides a powerful tool that can facilitate the study of the relationships between biofilms’ morphology, function, and mechanical properties.

Creator

• Liou, Hong-Cin

DOI

• https://doi.org/10.21985/n2-trxh-ws42

Subject

• Environmental engineering
• Mechanical engineering
• Acoustics

Language

• en

Alternate Identifier

• etdadmin_upload_714259
• http://dissertations.umi.com/northwestern:14970

Keyword

• Rheology
• Optical coherence elastography (OCE)
• Nondestructive testing
• Viscoelastic properties
• Biofilms
• Wave propagation

Date created

• 2019-01-01

Resource type

• Dissertation

Rights statement

• In Copyright