Transport Mechanisms in Porous Media: From Biological Systems to Engineering Materials

Abstract

Flow through porous media governs many natural and engineered systems, from water movement through soils and plant root systems to transport through hydrogel materials. Understanding the mechanisms that control transport in these systems provides opportunities to develop engineering solutions for challenges in agriculture and infrastructure. This dissertation investigates three complementary systems with the shared objective of identifying the mechanisms governing transport and leveraging that knowledge to improve engineered technologies. Alginate seed coatings containing plant growth-promoting-rhizobacteria are widely used in agriculture to improve yields. However, while these coatings often improve plant performance, in some cases they can also reduce germination rates. The origin of these conflicting outcomes remains unknown, limiting progress in seed-coating technologies. In this study, we investigate seed-hydrogel interactions to determine how water and air transport between the gel and the seed influences germination. Analytical modeling together with experiments using artificial seeds, soybean seeds, and transparent substrate demonstrated that delayed germination resulted primarily from restricted oxygen diffusion through the hydrogel coating rather than limitations in water uptake or mechanical confinement. These findings establish mechanistic design principles for improving hydrogel seed coating performance. The second study developed a quantitative methodology to investigate Hydraulic Redistribution (HR), i.e. the ability of plants to move water in soil, in soybean root systems. A fluorescence imaging platform was developed to non-destructively quantify HR in transparent substrate and was integrated with root anatomical characterization and hydraulic transport modeling. We tested three different types of cultivar: explain their characteristics briefly. Hydraulic redistribution differed significantly among soybean genotypes, with the commercial cultivar exhibiting greater nighttime redistribution than both the water saver and water spender lines. Root anatomical analysis further suggested that increased water movement was associated with greater investment in xylem tissue and larger xylem vessels, providing new insight into the structural factors governing hydraulic redistribution. The third study aimed to develop Microbial Induced Calcite Precipitation (MICP) in asphalt. While commonly used with concrete, its application in asphalt technology has been prevented by the high temperatures involved in the asphalt fabrication process. In this project, we identified a bacteria strain, namely Bacillus velezensis AP183, as a biological self-healing agent for asphalt pavements. We found that AP 183 spores survived asphalt production temperatures while remaining viable after incorporation into asphalt. The bacteria retained urease activity and precipitated calcium carbonate under laboratory conditions, demonstrating its potential to support (MICP) following asphalt production. These findings establish an important proof-of-concept for biologically based self-healing asphalt systems. Collectively, this dissertation demonstrates how mechanistic understanding of natural biological processes can guide the development of engineering solutions for improving crop resilience and infrastructure durability. The methodologies and findings presented here provide new experimental frameworks for studying biological transport phenomena while advancing the application of nature-inspired engineering across agricultural and civil infrastructure systems.