Design and Synthesis of Nitric Oxide Releasing Polymers for Biomedical Applications Public Deposited

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  • March 20, 2019
Creator
  • Coneski, Peter N.
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Poor biocompatibility is an ongoing problem for almost all types of implanted medical devices. The adhesion of cells and proteins at implant surfaces often results in serious complications such as infection, scar tissue formation, and thrombosis. The mediation of these effects by the endogenously produced free radical nitric oxide (NO) support its use a biocompatibility agent for many types of implantable materials. My dissertation research has focused on the development of materials capable of controllably releasing NO to facilitate implant compatibility. To examine the influence of N-diazeniumdiolate structure on NO release characteristics and their physical retention within polymeric matrices, various dialkyl diamines were synthesized and covalently modified to store NO. Diazeniumdiolation reactions of the synthesized diamines however resulted in the competitive formation of both N-diazeniumdiolates and potentially carcinogenic N-nitrosamines. Amine spacing and total alkyl content of these polymer additives were investigated as a means to control the efficiency of the diazeniumdiolation reaction. The ability of these amine compounds to form stabilizing hydrogen bonds to a nitrosamine intermediate species controlled the overall efficiency of diazeniumdiolation, with compounds more capable of forming intermolecular hydrogen bonds resulting in greater nitrosamine content. Monoamine compounds were shown to predominantly form diazeniumdiolated products due to their inability to form stabilizing intermolecular hydrogen bonds. As the characteristics of biomedical implants are closely selected based on their intended application, supplementing material properties is not a universal task. To extend the therapeutic benefits of NO release to degradable materials, a group of absorbable NO-releasing polyesters was synthesized. Highly crosslinked polyesters were formed by the thermal polycondensation and curing of polyols with diacid compounds, followed by a thiol functionalization step. Thiol-modified polymers could then be modified to store and controllably release NO via S-nitrosothiol functionalities. The ability of these materials to store and release NO was dependent on the selection of starting materials, curing temperatures, and the material's glass transition temperature. Reduced bacterial adhesion was observed for all NO-releasing polyesters over controls, with materials capable of releasing higher amounts of NO providing greater antibacterial character. Synthesizing these polymers from metabolic intermediates and non-toxic compounds resulted in products with minimal toxicity to healthy mammalian cells. Further diversification of NO-releasing materials was provided by the synthesis and characterization of S-nitrosothiol-modified polyurethanes. The modification of both hard and soft segment domains of polyurethanes was shown to result in the formation of NO-releasing polyurethane species. The extent and characteristics of NO release were shown to be highly dependent on NO donor position along the polymer backbone, with more substantial NO release resulting from soft segment modified materials. Increased phase miscibilities were shown to occur as a result of specific hard segment modifications, which in turn influenced the extent of NO release. Finally, the fabrication of electrospun polymer microfibers with NO release capabilities is reported. The physical dispersion of various NO donating materials such as nanoparticles and low molecular weight compounds was investigated as a means to controllably deliver NO to physiological environments. The release of NO from these scaffolds was shown to be diffusion mediated both in terms of solution uptake into the fibers and diffusion of NO out of the fiber. Hydrophobic microfibers exhibited prolonged NO release durations compared to hydrophilic materials as they inhibited solution uptake into fibers regulating the rate of diazeniumdiolate decomposition. As a result, microfiber diameter also influenced the rate of NO release from fibers due to greater diffusion pathways required to trigger NO release via diazeniumdiolate protonation.
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  • In Copyright
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  • "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry (Polymer Chemistry)."
Advisor
  • Schoenfisch, Mark H.
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  • Chapel Hill, NC
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  • Open access
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