Biological contaminants and biomolecules play a major role in disease etiology and pathogenesis. In the context of disease prevention and management, removal of biological contaminants and biomolecules often relies on separations performed in fluidic systems. The design and operation of such systems relies fundamentally on understanding how fluidic transport phenomena are governed by material properties and effects such as sorption. This thesis focuses on understanding transport phenomena in two novel fluidic systems and leverages the insights to develop devices for water filtration and blood purification. In the first section, we focus on the characterization and engineering of gymnosperm xylem for developing water filters. The xylem tissue, which transports water and nutrients in plants, has nanoscale pores that can remove contaminants from water. However, xylem’s functional attributes as a water filter, such as flow rate, filtration capacity, rejection performance, susceptibility to foulants in water, etc., are not well-understood. Additionally, methods that can help tailor these attributes to suit practical needs have not been developed. We generate new insights into the mechanisms that govern the transport of water through xylem. These include the non-linear dependence of resistance to fluid flow on filter thickness explained using a percolation-based model, ‘self-blocking’ behavior governed by the dissolution and convective re-deposition of hemicellulose within the xylem conduits, and elevated propensity for fouling in the presence of large organic molecules and dust. We use these insights to develop methods for fabrication of practically useful xylem filters. We demonstrate that these filters have shelf-life >2 years and can provide >3 log removal of E. coli, MS-2 phage, and rotavirus from synthetic test waters and coliform bacteria from natural water sources. To show how xylem could be incorporated in filtration devices, we develop a gravity-operated functional device prototype for household drinking water treatment using user-centered design approaches. The findings related to the characterization, modeling, and engineering of xylem reported in the thesis fundamentally advance the state of knowledge about xylem tissue and lay the groundwork for the design and development of a wide variety of xylem-based devices in the future. In the second section, we focus on modeling cytokine transport in an extracorporeal blood purification (EBP) device for managing hypercytokinemia. Traditional EBP methods, which focus on non-specific removal of broad-spectrum cytokines to regulate host immune response, have many disadvantages, such as potential immuno-suppression and elimination of desirable molecules. A cytokine-specific EBP method can overcome these drawbacks. We study the cytokine binding and transport characteristics in a device, where selective cytokine removal is achieved by pumping the blood through tubes coated with antibodies. Analogous to the Lévêque problem, we develop a mass transport model which can predict the rate of cytokine removal and volumetric clearance as a function of device geometry, operational conditions, and surface properties. These predictions matched in vitro experimental results. In the future, such devices could be used for creating flexible and highly selective blood-filtering platforms for elimination of individual, harmful cytokines as they are expressed, facilitating the development of personalized treatment strategies.Ph.D.