Development and Characterization of Fatty Acid-Coated Microgels Within Microfluidic Systems
Kraft, Mary L.
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https://hdl.handle.net/2142/84124
Description
Title
Development and Characterization of Fatty Acid-Coated Microgels Within Microfluidic Systems
Author(s)
Kraft, Mary L.
Issue Date
2003
Doctoral Committee Chair(s)
Moore, Jeffrey S.
Department of Study
Chemisty
Discipline
Chemisty
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
Fatty acid-coated hydrogel microstructures (mugels) were prepared within microfluidic devices and their properties were investigated. A photopolymerization technique was used to position pH-sensitive mugels within microchannels, and lipophilic acid chlorides were covalently grafted to these objects with an in situ process. The resulting hydrophobic coatings served as selectively permeable barriers that enabled pH-sensitive mugels to remain contracted while bathed by buffered solutions that caused expansion in unmodified samples. Modified mugels were capable of swelling once the fatty acid coating was physically disrupted. Barrier permeability was also chemically induced with buffered detergent solutions, triggering complete hydrogel expansion through an asymmetric process. The influence of the fatty acid chain length on the ion gradient stability in the absence of perturbing additives was investigated. In contrast to solid-supported self-assembled monolayers (SAMs), the ion gradient stability of the modified mugels did not increase with increasing chain length, suggesting the structure of the fatty acid coating was inherently different from that of a SAM. The structure of the fatty acid-modified mugels was elucidated through the characterization of comparable hydrogel substrates. Imaging the microstructures with scanning electron microscopy revealed a rough and irregular hydrogel surface, which indicated structural assessment would be challenging since many surface characterization techniques require smooth substrates to acquire depth profiles. The presence of the fatty acid coating was confirmed through investigation of an analogous model system with X-ray photoelectron spectroscopy and secondary ion mass spectrometry. Laser scanning confocal microscopy and the use of a lipophilic fluorescent dye indicated the coating was confined to the periphery of the mugel. Transmission electron microscopy imaging of modified nonionic hydrogels revealed the mugel matrix was derivatized with fatty acids to a depth of several microns. A straightforward correlation between the structure of the lipophilic acid chloride used to modify the mugel, the depth of ester bond formation, and the permeability of the resulting modified mugels was not identified. The permeability of the fatty acid coating was likely determined by several factors, such as the grafting density, hydrophobicity, total thickness, and fluidity of the fatty acid chains that functionalize the mugel.
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