京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21190号 / エネ博第364号 / 新制||エネ||71(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 佐川 尚, 教授 森井 孝, 教授 松田 一成 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

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A polyelectrolyte complex is formed by mixing two oppositely charged polyelectrolytes in a solution. The electrostatic interactions between partially charged polymeric chains lead to the formation of a stable complex while avoiding the use of covalent cross linkers. Since complex formation can improve the stability of polyelectrolyte and metal ions in polyelectrolyte can provide various functionalities, PECs incorporated with metal ions are promising candidates for manufacturing stable and multifunctional structures. While the coordination of metal ions and polyelectrolytes has been extensively investigated in solutions and multilayer films, to our knowledge, no research has been performed to study the effect of metal ion/polyelectrolyte interactions on PECs structures and properties. The following research demonstrates the impact of different metal ions in controlling PEC structure morphology and applications. These discoveries indicate great potential of metal ions in PECs to fabricate functional PEC nanostructures. The research investigates the effect of the interactions between different metal ions and polyelectrolytes on the morphology and properties of PECs, explore the fabrication of different structures using embedded metal ions and understand the impact of metal ion/polyelectrolyte interactions on the nanoparticle structures. The research concludes: 1) incorporating metal ions of different valence into PECs introduces metal ion/polyelectrolyte interactions that can tune the morphology of PECs; 2) metal ion/polyelectrolyte interactions can be used to control the PECs swelling properties and stability in aqueous solutions; 3) the release of embedded metal ions from PECs to aqueous solutions is affected by metal ion/polyelectrolyte interactions; and 4) the embedded metal ions function as a reagent reservoir for various applications to produce functional structures.

Polymer-derived Ceramics (PDCs) represent a unique class of high-temperature stable materials synthesized directly by the thermal decomposition of polymers. This research first focuses on the fabrication of high temperature stable siliconcarbonitride (SiCN) fibers by electrospinning for ceramic matrix composite (CMC) applications. Ceraset™ VL20, a commercially available liquid cyclosilazane, was functionalized with aluminum sec-butoxide in order to be electrospinnable. The surface morphology of the electrospun fibers was investigated using the fibers produced from solvents. The electrospun fibers produced from the chloroform/N,N-dimethylformamide solutions had hierarchical structures that led to superhydrophobic surfaces. A “dry skin” model was proposed to explain the formation of micro/- and nanostructures. The second objective of the research is to align the multiwalled carbon nanotubes (MWCNTs) in PDC fibers. For this purpose, a non-invasive approach to disperse carbon nanotubes in polyaluminasilazane chloroform solutions was developed using a conjugated block copolymer synthesized by ATRP. The effect of the polymer and CNT concentration on the fiber structure and morphology was also examined. Detailed characterization using SEM and TEM was performed to demonstrate the orientation of CNTs inside the ceramic fibers. Additionally, the electrical properties of the ceramic fibers were investigated. Finally, the structural evolution of polymer-derived amorphous siliconborocarbonitride (SiBCN) ceramics with pyrolysis temperatures was studied by solid-state NMR, Raman and EPR spectroscopy. Results suggested the presence of three major components: (i) hexagonal boron nitride (h-BN), (ii) turbostratic boron nitride (t-BN), and (iii) BN2C groups in the final ceramic. iv The pyrolysis at higher temperature generated boron nitride (BN3) with a simultaneous decomposition of BN2C groups. A thermodynamic model was proposed to quantitatively explain the conversion of BN2C groups into BN3 and “free” carbon. Such structure evolution is believed to be the reason that the crystallization of Si4.0B1.0 ceramics starts at 1500 ° C, whereas Si2.0B1.0 ceramics is stable upto 1600 ° C.

“Blood vessel mimics” (BVMs) are tissue-engineered constructs that serve as in vitro preclinical testing models for intravascular devices. The Cal Poly Tissue Engineering lab specifically uses BVMs to test the cellular response to stent implantation. PLGA scaffolds are electrospun in-house using the current “Standard Protocol” and used as the framework for these constructs. The performance of BVMs greatly depends on material and mechanical properties of the scaffolds. It is desirable to create BVMs with reproducible properties so that they can be consistent models that ultimately generate more reliable results for intravascular device testing. Reproducibility stems from the consistency of the scaffolds. Thus, scaffolds with consistent material and mechanical properties are necessary for creating reproducible BVMs. The aim of this thesis was to characterize the reproducibility of the electrospun PLGA scaffolds using fiber diameter measurements and compliance testing. Initial work in this investigation involved designing and testing several experimental electrospinning protocols to obtain smaller fiber diameters, which have been shown to elicit more ideal cellular responses. The most successful protocol in that regard was then analyzed for the reproducibility of fiber diameters and compared to the reproducibility of the Standard Protocol. After determining that the Standard Protocol produced scaffolds with more consistent fibers, a large-scale reproducibility study was performed using this protocol. In this expanded study, both fiber diameter and compliance were analyzed and used to characterize the scaffolds. It was established that the scaffolds demonstrated inconsistent mean fiber diameter and mean compliance. The current standard electrospinning protocol therefore does not create PLGA scaffolds with statistically reproducible properties. Future modifications should be made to the electrospinning parameters in order to reduce variability between the scaffolds and future studies should be performed to determine the acceptable range of properties.