Date of Award
Doctor of Philosophy in Chemistry (PhD)
College, School or Department Name
Department of Chemistry
Patricia A. Heiden
This research has three parts. Two parts deal with novel nanoparticle assemblies for drug delivery, and are described in Part A, while the third part looks at properties of fish scales, an abundant and little-used waste resource, that can be modified to have value in medical and other areas.
Part A describes fundamental research into the affects of block sequence of amphiphilic block copolymers prepared from on a new and versatile class of monomers, oligo(ethylene glycol) methyl ether acrylate (OEGA) and the more hydrophobic di(ethylene glycol) methyl ether methacrylate (DEGMA). Polymers from these monomers are biologically safe and give polymers with thermoresponsive properties that can be manipulated over a broader temperature range than the more researched Nisopropylacrylamide polymers. Using RAFT polymerization and different Chain Transfer Agents (CTAs) amphiphilic block copolymers were prepared to study the effect of block sequence (hydrophilic OEGA and more hydrophobic DEGMA) on their thermoresponsive properties. Pairing hydrophilic chain ends to a hydrophobic DEGMA block and hydrophobic chain ends to hydrophilic blocks (“mis-matched polarity”) significantly affected thermoresponsive properties for linear and star diblock copolymers, but little affected symmetric triblock copolymers. Specifically matching polarity in diblock copolymers yielded nanoparticles with higher cloud points (CP), narrow temperature ranges for coil collapse above CP, and smaller hydrodynamic diameter than mis-matched polarity. Using this knowledge two linear OEGA/DEGMA diblock copolymers were prepared with thiol end groups and assembled into hybrid nanoparticles with a gold nanoparticle core (GNP-polymer hybrids). This design was made using the hypothesis that a hybrid polymer drug carrier with a high CP (50-60 °C) and a diblock structure could be designed with low levels of drug release below 37 °C (body temperature) allowing the drug carrier to reach a target (tumor) site with minimal drug loss and accompanying side effects, to healthy tissue. Once at a tumor site safe wavelengths of light could heat the gold core and polymer domain to above the CP releasing the bulk of the drug where it is needed. The results were promising but suggested additional modification of the copolymer is required to further reduce release low temperature drug release. The second half of Part A addressed multi-drug controlled release from tissue scaffolds prepared from “nanoparticle fibers”. Tissue scaffolding for cell regeneration requires the ability to both physically support cells and promote their growth. This may require a drug “cocktail” of low or high molecular weight drugs to be released at different rates depending on the therapeutic levels needed for each drug. This work succeeded in producing a novel, flexible, and robust system of assembled fibers of nanoparticles that could independently control the release of multiple drugs.
Fish scale is an abundant and growing waste resource, with supplies far exceeding current uses, which have focused on harvesting the components of scales (hydroxyapatite and collagen) and ignored the scale itself. No studies have looked at the chemical modification of the intact scales, but such modifications may make scales suitable and even desirable additives into polymers for new composites with useful applications. Part B of this research investigated chemical modification of fish scales, characterized the changes to the upper biomineral layer and inner collagen layer, and the effects of these modifications on nanomechanical properties and moisture uptake. We described some possible uses for modified scales.
Xiang, Xu, "BIOLOGICAL MATERIALS: PART A. TEMPERATURE-RESPONSIVE POLYMERS AND DRUG DELIVERY AND PART B. POLYMER MODIFICATION OF FISH SCALE AND THEIR NANO-MECHANICAL PROPERTIES", Dissertation, Michigan Technological University, 2015.