Physically assembled gels are widely applicable in the food industry, biomedical devices, drug delivery, and soft robotics due to their tunable mechanical properties and thermoreversibility. The mechanical responses of these gels originate from their microstructure. Therefore, factors affecting the gel microstructure like polymer molecular weight, solvent quality, and polymer concentration play a significant role in determining their mechanical behavior. Gel microstructure also changes during the deformations resulting in a deviation from the structure-property relationship established for the low deformations. During large deformations, other factors like stress relaxation, poroelasticity, and polymer chain entanglement contribute significantly to the gel response. This complexity extends to the understanding of their failure behavior that occurs at large deformations. The low strain mechanical behavior of gels is governed by load-bearing chain density. They are often represented with non-linear elastic models, which ignore the contribution from viscous dissipation, polymer entanglements, surface tension, and bond dissociation. In addition, the available theoretical models cannot capture the experimental conditions like boundary confinement, therefore, numerical simulations are useful to test the developed model by comparing with experimental observations. With this objective, the present dissertation is focused on understanding the failure of physically assembled gels that consists of an ABA-type triblock copolymer dissolved in a B-block (midblock) selective solvent. Here, gelation occurs as a result of relative difference in the solubility of A-blocks (endblocks) and B-blocks (midblocks) with solvent. The thermo-mechanical characterization of these gels was performed using rheology, cavitation rheology, and DSC. A custom-built experimental set-up was developed to conduct large deformation experiments like tensile tests, creep failure experiments, and fracture experiments with a predefined crack. To characterize the gel microstructure, small-angle x-ray/neutron techniques were used. A change in the gel microstructure during deformation was also captured. The microstructure of gels was tuned by varying temperature, polymer volume fraction, midblock length, and by addition of midblock homopolymer. Finite element simulations have been used to understand the effect of boundary confinement, surface tension, and viscous dissipation. The present work provides a better understanding of failure behavior in physically assembled gels through the polymer dynamics at nano-scale level.

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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23926号 / 工博第5013号 / 新制||工||1782(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 古川 修平, 教授 生越 友樹, 教授 浜地 格 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Phase transitions of the gelatin – water and agaroza - water systems have been studied using the cloud-point method. Phase diagrams of these systems are constructed at different values of pH of medium. It is shown that pH of medium influences on the melting temperature of gelatin and agaroza gels. / Методом точек помутнения изучены фазовые переходы в системах желатин – вода и агароза – вода. Построены фазовые диаграммы систем при разных pH среды в магнитном поле и вне поля. Установлено, что pH среды влияет на температуру плавления гелей желатина и агарозы.

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Metal-organic frameworks (MOFs) are a class of hybrid materials that offer a promising platform for a range of catalytic reactions. Due to their complex structure, MOFs offer unique opportunities to serve as novel catalysts, or as host to improve the properties of previously studied species. However, while other catalytic approaches have been studied for many decades, the recency of their discovery means that significant work is still needed to develop MOFs as a viable option for large scale application. Herein, we aimed to advance the field of MOFs as both novel catalysts, and as host platforms for other catalytic species. To this end, we studied synthetic pathways to produce favorable MOF properties such as higher porosity and active site concentration through introduction of defects and macromorphological control, as well as utilization of molecular catalysts imbedded in the MOF structure for multicomponent, light driven reactivity. Chapter 1 introduces the history MOFs and the pursuit of the stable structures commonly associated with MOF chemistry. The synthesis process for zirconium-based MOFs will be discussed, with specific attention given to the modulated synthesis process which can harnessed to change MOF properties and improve catalysis. Two specific reactions will be introduced which serve as a basis for study in this work. First, the hydrolysis of organophosphate nerve agents by MOFs acting as novel catalysts will be introduced. The mechanism of reaction, as well as previous work in this field will be discussed. Finally, water oxidation as part of artificial photosynthesis through incorporated molecular catalysts will be introduced. Chapter 2 presents a modulator screening study on a zirconium-based MOF, UiO-66. One of the most commonly studied MOFs, UiO-66 provides an excellent platform for synthetic modulation. Particle size and defect level were measured of 26 synthetic variations and synthetic conditions were found to isolate changes in defect level and particle size, which typically change coincident with each other. Hydrolysis of the organophosphate compound dimethyl 4-nitrophenylphosphate (DMNP) was used to study the impact of particle size and defect level on reactivity. The reaction was found to be surface limited, even at high levels of missing linker defects. In Chapter 3, the macromorphology of three zirconium-based MOFs were tuned through synthesis modification. MOF powders and xerogels were prepared and characterized to highlight the desirable properties obtained through the gelation process. The materials were compared in the hydrolysis of DMNP and significant enhancement was observed for UiO-66 and NU-1000 xerogels. This was largely attributed to the introduction of mesoporosity and nanocrystalline particle sizes, which significantly increase the number of reactive sites easily accessible for catalysis. In Chapter 4 the authors examine MOFs as a host for molecular catalysts for use in photoelectrochemical water oxidation. A ruthenium-based catalyst [Ru(tpy)(dcbpy)]2+ was incorporated into UiO-67 through a mixed linker synthesis and grown on a WO3 substrate (Ru-UiO-67/WO3). Previous work from our group demonstrated Ru-UiO-67 retained the catalytic activity as the molecular species, while improving the recyclability of the material. In this work, addition of WO3 as a light harvester allowed for the reaction to be driven at a photoelectrochemical underpotential, a first for MOF-based water oxidation. Finally, Chapter 5 offers a perspective of the field of MOF-based artificial photosynthesis. Particular attention is given to issues of diffusion, selectivity, stability, and moving towards integration of multiple components rather than the study of half-reactions. / Doctor of Philosophy / Catalysts are a key component of chemistry that has a major impact on everyday life. From biological examples to industrial settings, catalysts are used to facilitate chemical conversions to new products and compounds. Because of the high demand, development of new catalysts with improved reactivity is a significant scientific challenge. A new class of materials known as metal-organic frameworks (MOFs) have been recently shown to acts as new catalysts or improve the properties of existing catalysts. Herein, we discuss the use of MOFs as catalysts for both development of new catalysts and improving known species. MOF-based catalysts have been used in a range of reactions from destruction of toxic chemical weapons to the production of renewable energy through artificial photosynthesis. This work is intended to highlight the potential for MOF-based catalysts and the next steps to further realize their potential.

Le diabète de type 1 est un dysfonctionnement du système immunitaire qui provoque l’attaque des cellules insulino-sécrétrices du pancréas. Cette affection du système immunitaire fait l’objet de nombreuses recherches scientifiques en raison de son important impact négatif sur la santé de la population mondiale. Les groupes de recherche des professeurs Bégin-Drolet, Ruel et Hoesli utilisent la technologie d’impression tridimensionnelle d’encres fugitives pour vasculariser des matrices d’hydrogel ensemencées de cellules insulino-sécrétrices. L’encapsulation de ces cellules dans l’hydrogel permet de les isoler du système immunitaire et leur fournit une structure de support semblable à celle de la matrice extracellulaire naturelle. La vascularisation de l’hydrogel par le moulage d’encres sacrificielles est en mesure d’apporter, via la perfusion, les nutriments aux cellules réparties dans le gel. Elle permet aussi de retirer les déchets métaboliques et l’insuline produits par les cellules. Le projet présenté dans ce mémoire consiste en la conception d’un dispositif pour la mise à l’essai de cette approche par des expérimentations ex vivo et in vitro. Le dispositif constitue une preuve de concept quant à l’efficacité de la méthode pour l’obtention d’un pancréas bioartificiel vascularisé et actif. / Type 1 diabetes, an immune system dysfunction that causes the attack of insulin secretory cells, is the subject of many scientific researches because of its significant negative impact on the world’s population health. Bégin- Drolet, Ruel and Hoesli research groups use the 3D printing technology of sugar fugitive ink to build embedded vascular networks in hydrogel scaffolds seeded with insulin secretory cells. Cells encapsulation in hydrogel allows them to be isolated from the immune system and provides a tridimensional support structure that mimic the natural extracellular matrix. Vascular channels resulting from the rapid casting of fugitive inks, allows adequate perfusion of nutrients supply to encapsulated cells, and transportation of metabolic wastes and secreted insulin they produce. The aim of this project, presented in this thesis, consists in designing a device to test this approach by ex vivo and in vitro experiments. The device is the proof of concept that the method of sacrificial ink molding of cell seeded hydrogel scaffolds is effective and promising for the construction of a vascularized bioartificial pancreas.

Ces travaux de recherche ont permis d ' élaborer une méthode de gélification 'à froid ' induite par l'addition de sels de calcium à des protéines de soya thermiquement dénaturées, le but ultime étant d'utiliser ces hydrogels dans le développement de nouveaux aliments fonctionnels et comprimés nutraceutiques ayant des effets bénéfiques sur la santé. Les résultats obtenus démontrent la formation de deux types d 'hydrogels distincts selon la teneur en sels de calcium utilisés. À faible teneur en sels de calcium, des hydrogels filamenteux caractérisés par une microstructure ordonnée et une bonne capacité de rétention d'eau sont obtenus, alors que des hydrogels poreux, agrégés et ayant une faible capacité de rétention d'eau sont identifiés lorsqu'une haute teneur en sels de calcium est utilisée. Ces deux types d 'hydrogels démontrent des propriétés rhéologiques distinctes, utilisées pour quantifier leur dimension fractale respective. Il a été démontré par cette étude que les hydrogels de type filamenteux sont sujet à un mécanisme de formation lent selon un patron dicté par l'encombrement stérique des agrégats primaires, tandis que les hydrogels agrégés sont formés rapidement de façon totalement aléatoire, créant une microstructure désordonnée. Des études in vitro en conditions gastro-intestinales montrent clairement la capacité des hydrogels filamenteux et agrégés à protéger des molécules de vitamine B2, emprisonnées dans leur structure, contre les conditions gastriques (enzymes digestives, pH acide) et à les libérer en conditions intestinales. Les hydrogels filamenteux montrent des profils de libération de la vitamine B2 plus constants que ceux agrégés dû à leur structure moins poreuse. Des comprimés formés à partir des hydrogels lyophilisés et compressés ont également été conçus. Les études in vitro effectuées sur ces comprimés démontrent, comme les études menées sur les hydrogels, une bonne protection de la vitamine B2 en présence de conditions gastriques et une libération accrue lorsque soumis aux conditions intestinales. D'intéressantes perspectives dans le développement de véhicules (hydratés ou comprimés) pour la protection de molécules nutraceutiques et leur libération intestinale sont donc envisageables à partir des hydrogels développés dans le cadre de cette étude.