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This paper highlights the optical coherence elastography (OCE) technique's efficacy in rapidly and non-destructively characterizing biofilm elastic properties. We elucidate critical OCE implementation procedures for accurate measurements and present Young's modulus values for two granular biofilms.
Biofilms are complex biomaterials comprising a well-organized network of microbial cells encased in self-produced extracellular polymeric substances (EPS). This paper presents a detailed account of the implementation of optical coherence elastography (OCE) measurements tailored for the elastic characterization of biofilms. OCE is a non-destructive optical technique that enables the local mapping of the microstructure, morphology, and viscoelastic properties of partially transparent soft materials with high spatial and temporal resolution. We provide a comprehensive guide detailing the essential procedures for the correct implementation of this technique, along with a methodology to estimate the bulk Young's modulus of granular biofilms from the collected measurements. These consist of the system setup, data acquisition, and postprocessing. In the discussion, we delve into the underlying physics of the sensors used in OCE and explore the fundamental limitations regarding the spatial and temporal scales of OCE measurements. We conclude with potential future directions for advancing the OCE technique to facilitate elastic measurements of environmental biofilms.
In wastewater treatment and water resource recovery, beneficial biofilms in attached growth reactors are increasingly employed to enable microbes to convert undesirable pollutants, such as organic matter, nitrogen, and phosphate, into stabilized forms that can be easily removed from the water1. In these systems, the biofilm's emergent function, namely biochemical transformations, is closely associated with the diversity of microbes residing in it and the nutrients these microbes receive2. Accordingly, ongoing biofilm growth can pose a challenge to maintaining consistent reactor functionality because the new biofilm g....
1. System setup
In this study, we used granular biofilms (also known as granular sludge), which were commercially obtained. Granules are spherical biofilms that form through self-aggregation, meaning that they do not require a carrier or surface on which to grow26. Figure 3A shows a representative cross-sectional OCT image that arises due to the spatial variation of the local refractive index in a granular biofilm. The biofilm has a nominal diameter of 3 mm. Some of .......
The attainable imaging depth in the OCT system is determined by the degree of light penetration from the light source, which depends on the wavelength of the source. Moreover, the wavelength determines the axial resolution. Longer wavelengths can penetrate more deeply into the sample but at the expense of reduced axial resolution compared to shorter wavelengths. Transverse resolution, on the other hand, is dependent on both the numerical aperture of the system and the wavelength, with shorter wavelengths delivering .......
The authors thank Aqua-Aerobic Systems, Inc. (Rockford, IL, USA) for providing the granular biofilms studied in this work. The authors also acknowledge the National Science Foundation's support via Award #210047 and #193729.
....Name | Company | Catalog Number | Comments |
3D printed sample holder | |||
3D printed wedge tip | 3 mm width | ||
BNC cables | Any brand | ||
Delay generator | Stanford Research Systems | DG535 | DG535 Digital delay/ Pulse Generator |
Function generator | Agilent Technologies | 33250A 80 MHz Function / Arbitrary Waveform Generator | |
Granular biofilm | Aqua-Aerobic Systems | Obtained from an Aerobic Granular Sludge reactor (Aqua-Aerobic Systems, Inc.) | |
MATLAB | MathWorks | Release 2022a (MATLAB 9.12) | |
Piezoelectric transducer | Thorlabs | PK2JUP1 | Discrete Piezo Stack, 75 V, 30.0 µm Displacement |
SD-OCT System | Thorlabs | Ganymede II, LSM03 scan lens | |
ThorImageOCT | Thorlabs | Version: 5.5.5 |
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