Chemical and Biomolecular Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2751
Browse
2 results
Search Results
Item Bio-Derived Microscale Containers for Disease Treatment and Diagnostics(2017) Liu, James; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Micro-erythrosomes (mERs) are microscale containers (3 to 5 µm in diameter) derived from red blood cells (RBCs, also called erythrocytes). They are prepared by removing hemoglobin from RBCs and resuspending the empty structures in buffer. In this work, we focus on adding new functionalities to mERs, with both therapeutics and diagnostics in mind. In our main study, we demonstrate the use of mERs as “Killer Cells” to attack cancer. mERs are loaded with the enzyme glucose oxidase (GOx) and then incubated in vitro with a strain of head and neck cancer cells (15B). In the presence of glucose from external media, the Killer Cells generate hydrogen peroxide (H2O2). H2O2 is a reactive oxygen species (ROS) which induces the cancer cells to undergo apoptosis (programmed cell death). We find a reduction in 15B cell viability of over 80%. In ancillary studies, we explore strategies for the long-term retention of solutes in mERS. Specifically, the cationic biopolymer chitosan is adsorbed to the surfaces of mERs, and the anionic biopolymer alginate is encapsulated in their cores. Both strategies are able to extend the diffusion time for loaded solutes. Additionally, we have attempted to adapt mERs for use as MRI contrast agents by incorporating lipids containing gadolinium into the membrane. These studies lay the foundation for many mER applications and demonstrate their versatility.Item New Concepts for Gelation of Alginate and its Derivatives(2013) Javvaji, Vishal; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioengineering applications require materials that offer tunable and precise control over material properties. In particular, hydrogels of the polysaccharide, alginate have been widely studied for applications such as drug-delivery vehicles, matrices for encapsulation of cells, and scaffolds for tissue engineering. The ability of alginate to form a physically cross-linked hydrogel under mild conditions is a key factor for many applications. Traditionally, alginate gelation has been induced by the addition of divalent ions like calcium (Ca2+). In this work, we explore new ways to induce gelation of alginate or its derivatives. These new routes are of interest because they can allow researchers to circumvent current limitations and moreover they can also enable new applications. Three new concepts are explored: (1) ionic gelation activated by light; (2) ionic gelation activated by an enzyme and its substrate; (3) gelation of hydrophobically modified alginate mediated by biological cells. In our first study, we demonstrate a concept for ionic gelation of alginate in response to light, which enables us to create chemically erasable and spatially selective patterns of alginate gels. We impart light responsiveness by combining alginate, an insoluble calcium vector (e.g., CaCO3) and a light responsive component, viz. a photoacid generator (PAG). Upon UV irradiation, the PAG dissociates to release H+ ions, which react with the CaCO3 to generate free Ca2+ in-situ. In turn, the Ca2+ ions cross-link the alginate to form a gel. We show photopatterning of alginate gels, which are used to entrap contents (e.g., microparticles) and subsequently release them by a Ca2+ chelator. In our second study, we demonstrate enzymatic gelation of alginate. Here, we use an enzyme/substrate reaction to generate H+ ions. The components of our system are glucose oxidase (GOx, enzyme), glucose (substrate), alginate and CaCO3. First, GOx catalyzes oxidation of glucose to generate H+ ions. These H+ ions solubilize CaCO3 and release free Ca2+ ions in-situ. In turn, Ca2+ ions cross-link alginate chains into a gel. A sol-gel transition is observed only when GOx senses and catalyzes glucose. By exploiting the specificity of the enzyme for its substrate, we use this concept to build a visual test for the presence of glucose in an unknown product. In our final study, we induce gels by combining a hydrophobically modified (hm) derivative of alginate with biological cells. Gelation occurs due to hydrophobic interactions between the grafted hydrophobes and the bilayers of biological cells. The polymer chains thus get attached to the cells and bridge the cells into a three-dimensional network. This gelation can also be reversed (to release the cells) by addition of a supramolecule, α-cyclodextrin, which has a hydrophobic binding pocket that binds to the hydrophobes. Cell gelation by hm-alginate may be useful in cell culture and tissue engineering applications. As a step towards these potential applications, we show that the process of gelation by hm-alginate is benign to the cells.