A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Lateral Capsule Migration in Microfluidic Channels(2017) Wang, Yiyang; Dimitrakopoulos, Panagiotis; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A capsule motion inside a microfluidic channel has attracted a lot of attention in recent decades owing to its important applications in industrial, pharmaceutical and physiological systems such as in cell sorting, targeted drug delivery and blood flow. In this dissertation, we computationally investigate an elastic capsule's lateral migration inside a constricted microfluidic device under Stokes flow conditions. We use the Membrane Spectral Boundary Element (MSBE) method to determine the capsule dynamics due to its high computational accuracy and versatility in dealing with complex solid geometries. In the bounded Poiseuille flow of the microfluidic constriction, a capsule, placed initially off-centered will migrate away from the wall and move toward the channel centerline. The capsule's lateral migration behavior is caused by the combination of the wall effects due to the existence of the channel boundary, the shear gradient generated by the non-linear velocity distribution of the flow, and the lift force created by the capsule deformation. We use a constricted device instead of a straight channel to do the simulations, because the capsule's lateral migration in a straight channel is too slow to be observed easily, while the existence of the converging connection of the constricted device increases the capsule's lateral velocity and thus facilitates its migration. The main goal of our research is to investigate the effects of the capsule's physical properties on its lateral migration behavior. We released various deformable capsules at different initial positions, membrane hardness, viscosity ratios, and capsule volumes inside the constricted channel and computed their deformation behavior and migration trajectories. Our results show that changing a capsule's viscosity ratio or the membrane hardness does not strongly affect the capsule's lateral migration due to the capsule's weak inner circulation. On the other hand, changing the capsule's initial position and capsule volume strongly affect its migration trajectories. Thus soft particles with different sizes can be separated and identified.Item Bio-Inspired Polymer Microparticles for Targeted Recognition and Response(2014) Arya, Chandamany; Raghavan, Srinivasa R.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microbeads and microcapsules are container structures that are frequently used in biomedical applications. In this dissertation, we have sought to impart new functionalities to these particles, inspired by phenomena observed with biological cells. We have engineered polymer microparticles that recognize and respond to specific species from the surroundings (e.g. cells, polymer chains, metal ions). Three classes of new microparticles are reported, which are each reminiscent of a different type of biological cell in terms of recognition capabilities and response. In the first part of this dissertation, we create functionalized microbeads from the biopolymer, chitosan, and use these to selectively recognize and capture Circulating Tumor Cells (CTCs) from blood. The microbeads are functionalized with a protein (streptavidin) and packed into an array within a microfluidic device. Blood samples with biotin-labeled CTCs are flowed over the packed bed of chitosan beads. Similar to how macrophages adhere to foreign bacteria (i.e. antibody-antigen interactions), the streptavidin-labeled chitosan beads can selectively recognize and adhere to the biotin-labeled CTCs. We show that such a packed bed of chitosan beads could serve as an inexpensive platform for customized capture of different rare cells (cancer cells, stem cells etc) from blood. In the next study, we develop a class of microbeads that undergo clustering (aggregation) in the presence of specific polymers. The inspiration for this comes from the cells (e.g., platelets) and polymers involved during the formation of blood clots. Our system consists of chitosan microbeads coated with cyclodextrins (sugar molecules with a hydrophobic binding pocket), which are then exposed to a polymer that is decorated with hydrophobic units. The particles bind to the polymer chains via hydrophobic interactions and in turn, the particles are induced to form clusters. Subsequently, the polymer precipitates and forms a matrix around the particle clusters, leading to a structure that is reminiscent of a blood clot (platelets enveloped by a mesh of fibrin chains). Lastly, we develop a class of microparticles that have the ability to selectively destroy other microparticles. The inspiration here is from the body's immune system, where cells like the killer T cells selectively destroy cancer and virus infected cells without harming healthy cells. Towards this end, we synthesize two types of microparticles: chitosan capsules that contain the enzyme glucose oxidase (GOx), and beads of a different biopolymer, alginate that are crosslinked with copper (Cu2+) ions. The chitosan capsules enzymatically convert glucose from the surroundings into gluconate ions. When these capsules approach the alginate/copper beads, the gluconate ions chelate the copper ions, leading to the disintegration of the alginate beads. Other beads that do not contain Cu2+ are not affected in this process.