Type of Document Dissertation Author Campbell, Tedric Dewayne Author's Email Address email@example.com URN etd-07022007-182226 Title Synthesis and Physical Characterization of Biocompatible Hydrogels Degree Doctor of Philosophy Department Chemistry and Biochemistry, Department of Advisory Committee
Advisor Name Title Oliver Steinbock Committee Chair Albert Stiegman Committee Member Paul Q. Trombley Committee Member Robert L. Fulton Committee Member Keywords
- Spinal Cord
- Nerve Conduits
Date of Defense 2007-04-23 Availability unrestricted AbstractPolymers are a group of materials composed of molecules which have long sequences of atoms linked to each other by covalent bonds. They have existed in natural forms since life began; however, in 1910 Leo Baekeland produced bakelite, a phenolformaldehyde resin, which became the first commercialized fully-synthetic polymer. Nevertheless, it took another decade for scientists to truly accept the unusual properties of polymers as well as the forces that accompany them.
The attractive forces between polymer chains play a large part in determining the polymer's properties. Because polymer chains are so long, these inter-chain forces are amplified far beyond the attractions between conventional molecules. In addition, the more entangled and elongated the chains are, the more amorphous is the polymer. Polymer chain length can be attributed to the monomer content within its structure. If the monomer is able to polymerize with a crosslinking agent, then this new macromolecule can be referred to as a gel.
The gel is a semi-rigid mass of a lyophilic sol in which all the dispersion medium has penetrated into the sol particles. A particular class of gels, hydrogels, are hydrophilic polymer networks, which can take up large volumes of water and swell while retaining their shape. These materials are usually formed by radical polymerization of hydrophilic monomers and cross-linkers that dissolve in aqueous medium. The cross-linker can be a bifunctional monomer forming a network during polymerization. Depending on the particular chemical structure, these swollen networks display different properties due to external stimulation.
The goal of this dissertation is the preparation of poly [N-(2-hydroxypropyl) methacrylamide] (PHPMA) hydrogels in which the typically random polymer network is altered to arrays of parallel channels. One particular application is to use the PHPMA hydrogels as templates for nerve cells. Ideally, the diameter of these channels should match the archetypal diameter of neuronal cell bodies or axons in order to provide a maximal internal surface area. With that aim in mind, we devised and optimized an experimental technique in which a modified HPMA-pregel solution is polymerized and cross-linked in the presence of an externally applied electric field. In addition, the effects of the porogen, polyethylene glycol, on the efficacy of channel formation, swelling dynamics, and the mechanical and structural characteristics of the resulting material are investigated.
In conjunction with the aforementioned goal, we also functionalized the PHPMA hydrogels by incorporating Poly-L-Lysine into the polymer matrix. Poly-L-Lysine, a highly positively charged amino acid chain, is commonly used as a coating agent to promote cell adhesion in culture. Poly-L-Lysine will be used as a subbing solution in the biocompatible scaffolds that will serve as a host for mammalian olfactory bulb neurons.
The research outlined above represents the major focus of this dissertation. The long-term goal was to enhance prosthetics in the area of biomedical engineering. Moreover, the dissertation is complemented by the description of two minor projects that (a) describe the creation of a mesoporous silica monolith containing oriented macroporous channels and (b) document light-scattering measurements of Belousov-Zhabotinsky(BZ) solutions in sodium bis (2-ethylhexyl) sulfosuccinate(AOT) water-in-oil microemulsions. The latter data should be helpful for understanding non-equilibrium Turing patterns in BZ-AOT systems.
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