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Aybar, M., Perez-Calleja, P., Li, M., Pavissich, J. P., & Nerenberg, R. (2019). Predation creates unique void layer in membrane-aerated biofilms. Water Res., 149, 232–242.
Abstract: The membrane-aerated biofilm reactor (MABR) is a novel wastewater treatment technology based on oxygen-supplying membranes. The counter diffusion of oxygen and electron donors in MABRs leads to unique behavior, and we hypothesized it also could impact predation. We used optical coherence tomography (OCT), microsensor analyses, and mathematical modeling to investigate predation in membrane-aerated biofilms (MABs). When protozoa were excluded from the inoculum, the MAB's OCT-observable void fraction was around 5%. When protozoa were included, the void fraction grew to nearly 50%, with large, continuous voids at the base of the biofilm. Real-time OCT imaging showed highly motile protozoa in the voids. MABs with protozoa and a high bulk COD (270 mg/L) only had 4% void fraction. DNA sequencing revealed a high relative abundance of amoeba in both high and low-COD MABs. Flagellates were only abundant in the low-COD MAB. Modeling also suggested a relationship between substrate concentrations, diffusion mode (co- or counter-diffusion), and bioflim void fraction. Results suggest that amoeba proliferate in the bioflim interior, especially in the aerobic zones. Voids form once COD limitation at the base of MABs allows predation rates to exceed microbial growth rates. Once formed, the voids provide a niche for motile protozoa, which expand the voids into a large, continuous gap. This increases the potential for biofilm sloughing, and may have detrimental effects on slow-growing, aerobic microorganisms such as nitrifying bacteria. (C)2018 Elsevier Ltd. All rights reserved.
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Baler, R. V., Wijnhoven, I. B., del Valle, V. I., Giovanetti, C. M., & Vivanco, J. F. (2019). Microporosity Clustering Assessment in Calcium Phosphate Bioceramic Particles. Front. Bioeng. Biotechnol., 7(281), 7 pp.
Abstract: There has been an increase in the application of different biomaterials to repair hard tissues. Within these biomaterials, calcium phosphate (CaP) bioceramics are suitable candidates, since they can be biocompatible, biodegradable, osteoinductive, and osteoconductive. Moreover, during sintering, bioceramic materials are prone to form micropores and undergo changes in their surface topographical features, which influence cellular physiology and bone ingrowth. In this study, five geometrical properties from the surface of CaP bioceramic particles and their micropores were analyzed by data mining techniques, driven by the research question: what are the geometrical properties of individual micropores in a CaP bioceramic, and how do they relate to each other? The analysis not only shows that it is feasible to determine the existence of micropore clusters, but also to quantify their geometrical properties. As a result, these CaP bioceramic particles present three groups of micropore clusters distinctive by their geometrical properties. Consequently, this new methodological clustering assessment can be applied to advance the knowledge about CaP bioceramics and their role in bone tissue engineering.
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Contreras-Raggio, J. I., Arancibia, C. T., Millan, C., Ploeg, H. L., Aiyangar, A., & Vivanco, J. F. (2022). Height-to-Diameter Ratio and Porosity Strongly Influence Bulk Compressive Mechanical Properties of 3D-Printed Polymer Scaffolds. Polymers, 14(22), 5017.
Abstract: Although the architectural design parameters of 3D-printed polymer-based scaffolds-porosity, height-to-diameter (H/D) ratio and pore size-are significant determinants of their mechanical integrity, their impact has not been explicitly discussed when reporting bulk mechanical properties. Controlled architectures were designed by systematically varying porosity (30-75%, H/D ratio (0.5-2.0) and pore size (0.25-1.0 mm) and fabricated using fused filament fabrication technique. The influence of the three parameters on compressive mechanical properties-apparent elastic modulus E-app, bulk yield stress sigma(y) and yield strain epsilon(y)-were investigated through a multiple linear regression analysis. H/D ratio and porosity exhibited strong influence on the mechanical behavior, resulting in variations in mean E-app of 60% and 95%, respectively. sigma(y) was comparatively less sensitive to H/D ratio over the range investigated in this study, with 15% variation in mean values. In contrast, porosity resulted in almost 100% variation in mean sigma(y) values. Pore size was not a significant factor for mechanical behavior, although it is a critical factor in the biological behavior of the scaffolds. Quantifying the influence of porosity, H/D ratio and pore size on bench-top tested bulk mechanical properties can help optimize the development of bone scaffolds from a biomechanical perspective.
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