Dissertations / Theses on the topic 'Biopolymer Gels'

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2012.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. ).
Three-dimensional biomaterial scaffolds have begun to shown promise for cell delivery for cardiac tissue engineering. Although various polymers and material forms have been explored, there is a need for: injectable gels that meet certain design specifications; a more indepth characterization of the scaffold properties; and a deeper understanding of the relation of select properties to cellular behavior, to provide a rational basis for future in vivo studies. The first objective of this thesis was to develop and characterize novel injectable biopolymer hydrogels capable of safely undergoing covalent cross-linking in vivo to provide a mechanically tunable nanofibrillar scaffold. Soluble type I collagen gels with genipin and transglutaminase cross-linkers, and gelatin-hydroxyphenylpropionic acid (Gtn-HPA) gels, the cross-linking of which are modulated by horse radish peroxidase and hydrogen peroxide, were investigated. The gels were characterized on the basis of rheological properties, resistance to degradation, and effects on stem cell behavior. Another objective was to evaluate the simultaneous differentiation of embryonic carcinoma cells (ECCs) incorporated in the gels into the three cell types in cardiac tissue -- cardiomyocytes, neural cells, and vascular endothelial cells -- and to determine the effects of certain properties of the gels on the differentiation profile, using mesenchymal stem cells as a comparative control. The injectable collagen-genipin and Gtn-HPA gels were found to be mechanically tunable hydrogel systems that supported cell encapsulation and proliferation at safe concentrations of the respective cross-linking agents. ECCs cultured as embryoid bodies (EBs) incorporated in the collagen-genipin and Gtn-HPA gels differentiated into cardiac, neural, and endothelial cells and combinations thereof, demonstrating the capability of EBs to express multiple cell lineages within the same EB. EBs cultured in collagen gels without cross-linkers and collagen gels with 0.25 mM genipin exhibited the highest differentiation efficiency compared to those cultured in monolayer, sponge-like scaffolds, and Gtn-HPA gels. The differentiation medium and culture time also had significant effects on differentiation efficiency. Notable findings included: the increased expression of neural and endothelial markers in EBs cultured in in mixed medium conditions compared to those cultured in neural or endothelial differentiation medium alone, and the correlation between angiogenic and neurogenic differentiation in the EBs in the non-cross-linked collagen gels for all media. Collectively, these findings show promise in using collagen gels cross-linked with 0.25 mM genipin, incorporated with EBs, for cellular therapy in cardiac tissue engineering applications.
by Karen Kailin Ng.
Ph.D.

Les alginates, des polysaccharides produits par les algues brunes, sont des copolymères à blocs linéaires, formés d’unités mannuronate (M) et guluronate (G). En raison de leur abondance naturelle, prix et propriétés physicochimiques avantageuses, les alginates représentent une classe de biopolymères très intéressante et relativement inexplorée pour des applications dans le domaine des matériaux avancés. Dans ce contexte, le présent travail vise à enrichir la gamme des applications des matériaux dérivés d’alginates, en exploitant les propriétés de cette classe de polysaccharides naturels. En particulier, la préparation de matériaux à base d'alginate pour la catalyse, l'adsorption et le domaine biomédical a été étudiée, avec des résultats encourageants dans toutes les applications testées. L'utilisation bénéfique de l'acide alginique en catalyse hétérogène a été démontrée, en tant que promoteur de réaction et support pour l’hétérogénéisation d'un organocatalyseur. L'activité du catalyseur a été trouvée très dépendante de l'accessibilité des groupes fonctionnels, mettant en évidence l’avantage de l’emploi de formulations plus accessibles. La texturation des alginates a été aussi avantageuse dans la préparation de matériaux pour applications en flux. Des mousses d'acide alginique, avec une structure hiérarchique macro-mésoporeuse, ont été développées à cet effet. Une caractérisation précise des matériaux a été réalisée, afin d'optimiser la procédure de préparation et de corréler les propriétés texturales obtenues avec les paramètres utilisés. L'intérêt dans l’utilisation de mousses à base d'acide alginique a été démontré dans une application modèle, l'adsorption de bleu de méthylène à partir de solutions aqueuses, à la fois en batch et en flux. La possibilité de modifier facilement les groupes fonctionnels de l’alginate, couplée avec la nature biocompatible et biodégradable de ces biopolymères, a finalement été exploitée pour le développement de gels auto-réparants, obtenus grâce à la formation de deux types d'interactions covalentes dynamiques : base de Schiff et ester de boronate. Les deux systèmes examinés ont présenté une remarquable habilité à se reconstruire après un dégât, même si l'ampleur de la reconstruction et la stabilité des gels étaient fortement dépendantes des paramètres de préparation des gels et des conditions environnementales utilisées. Les résultats obtenus dans le cadre de cette étude démontrent clairement comment la compréhension et un emploi conscient des propriétés physico-chimiques des alginates peuvent maximiser le potentiel que cette ressource durable dans le domaine de la chimie des matériaux
Alginates, polysaccharides produced by brown algae, are linear block-copolymers formed by mannuronate (M) and guluronate (G) units. Because of their huge natural abundance, cheapness and physicochemical properties, alginates represent a highly attractive and still relatively unexplored class of biopolymers for applications in the field of advanced materials. In this context, the present work aimed to enrich the range of possible applications of alginate-derived materials, making the most of the peculiar features of this class of natural polysaccharides. In particular, the preparation of alginate-based active materials to be employed in the catalysis, adsorption and biomedical field was studied, achieving encouraging results in all the tested applications. The beneficial use of alginic acid in heterogeneous catalysis, both as reaction promoter and as support for the heterogeneization of an organocatalyst, was demonstrated. The activity of the material was found highly dependent on the accessibility of the active functions, highlighting the advantage of employing more accessible alginate formulations. The texturation of alginates was further advantageous for the preparation of materials with improved flowability. Alginic acid foams, bearing a hierarchical macro-mesoporous structure were developed by means of a simple procedure. Accurate characterization was performed to optimize the preparation procedure and to correlate the textural properties of the obtained materials with the parameters used. The interest of the prepared alginic acid foams was demonstrated in a model application, the adsorption of methylene blue from aqueous solutions, both in batch and in flow conditions. The possibility to easily modify alginate functional groups, coupled with the biocompatible and biodegradable nature of alginates, was finally employed for the development of self-healing gels, thanks to the formation of two types of dynamic covalent interactions: Schiff base and boronate ester bonds. Both the examined systems presented a marked ability to recover after damage, even if the extent of the recovery and the stability of the gels was highly dependent on the preparation parameters and environmental conditions used. The results obtained in the course of this study clearly demonstrate how a full comprehension and conscious employment of alginate physicochemical properties can maximize the potential of this sustainable resource in the field of material chemistry

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 191-205).
The cross-linked polymeric microstructures of biological hydrogels (or biogels) give rise to their mechanical properties, which in turn contribute to their proper biological function. For example, cartilage is stiff, elastic, and capable of withstanding substantial compressive forces in the knee, while saliva is thin, highly lubricious, and crucial for the maintenance of oral health. Quantification and modeling of the mechanical properties of these materials can provide insight into their microstructures, which is particularly important when structural changes are associated with impaired biological function. In this thesis, we use a combination of rheological testing and constitutive modeling to study this relationship between microstructure and mechanical properties in three biologically-relevant complex fluid systems. First, we explore the network structure and association dynamics of reconstituted mucin gels using micro- and macrorheology in order to gain insight into how environmental factors, including pathogens and therapeutic agents, alter the mechanical properties of fully-constituted mucus. We find that analyses of thermal fluctuations on the length scale of micron-sized particles are not predictive of the linear viscoelastic response of mucin gels. However, when taken together, the results from both techniques help to provide complementary insight into the structure of the network. For instance, we show that macroscopic stiffening of mucin gels can be brought about in different ways by targeting specific associations within the network using environmental triggers such as modifications to the pH, surfactant, and salt concentration. Additionally, by varying the size of the microrheological probe particles, we show that the disagreement between the rheological techniques on both length scales can be largely attributed to microphase separation and the presence of localized gel regions of varying stiffness. This finding is further supported through imaging techniques and direct visualization of the mucin network. As a second system, we study the temporal stability of saliva and its sensitivity to degradation in order to highlight the importance of considering sample age and enzymatic degradation when reporting extensional rheological measurements of saliva. Measurements show that the shear rheology of salivary mucin solutions (as measured by steady shear viscosity and small amplitude oscillatory shear (SAOS)) is quite insensitive to sample age over a 24 hour period following sample collection. By contrast, the filament thinning dynamics vary dramatically, with the characteristic relaxation time of the saliva and the breakup time of a fluid thread decreasing significantly with sample age. We interpret our results within the framework of a Sticky Finitely Extensible Network (SFEN) model which respects the known physical dimensions and properties of the mucin molecules in saliva, and models them as a network of physically associating and finitely extensible polymer chains. We show that the model can accurately capture the changes observed in the filament thinning dynamics with sample age by incorporating a steady decrease in the molecular weight of the supramolecular aggregates of mucin. As a third and final system, we develop a fractional calculus-based framework for improving the quantification of the mechanical properties of polysaccharide-based food solutions in order to facilitate the development of specific textures for liquid food consumption and for the design of dysphagia products. We demonstrate that fractional rheological models, including the fractional Maxwell model (FMM) and the fractional Jeffreys model (FJM), are able to succinctly and accurately predict the linear and nonlinear viscoelastic response of these food solutions and outperform conventional multi-mode Maxwell models with up to 50 physical elements in terms of the goodness of fit to experimental data. By accurately capturing the shear viscosity of the various liquid food solutions at a shear rate widely deemed relevant for oral evaluation of liquid texture, we show that two of the constitutive parameters of the fractional Maxwell model can be used to construct a state diagram that succinctly characterizes both the viscous and elastic properties of the different fluids. The experimental and theoretical tools employed to interpret the underlying microstructures of the biological fluids considered in these three studies are diverse, ranging from microrheological measurements to the adaptation and development of appropriate nonlinear polymeric constitutive models. As a result, the findings of this thesis should provide a starting point for interpreting the mechanical properties of a variety of complex fluids in a broad range of contexts. In particular, one application for which these techniques have already shown promise is in the emerging use of the material properties of physiological fluids as biomedical diagnostics. By continuing to develop analytical methods for improving the understanding of the relationship between rheology and biological structure, it is expected that these methods will be beneficial in studying the etiology and pathological basis for a number of medical conditions such as preterm birth and cystic fibrosis.
by Caroline Elizabeth Wagner.
Ph. D.

We used sol-gel method for synthesizing nanoclusters of DyBa2Cu3O7-X high TC type II superconductor in presence of biopolymer chitosan. In the first stage, the precursor and biopolymer aggregated into amorphous matrix and hydrogels are then formed by thermogelling. The fibrous nature of the biopolymer chitosan is retained at high temperatures up to 500 °C. After heating to 900 °C, complete decomposition of BaCO3 and formation of the superconductor nanoparticles (with a diameter of 10-20 nm) occurred subsequently. Characterization of specimens was performed using scanning electron microscopy and transmission electron microscopy, supported by other techniques including XRD diffraction, energy dispersive X-ray, FT-IR spectrum and magnetic susceptibility measurements. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34952

Ce travail de thèse vise à explorer des techniques de nanofabrication pour produire des substrats de culture et des matrices de génie tissulaire, basant sur une nouvelle approche biomimétique. Nous avons d’abord développé une nouvelle technique de moulage pour répliquer des nanostructures dans une couche de gélatine. Les motifs micrométriques peuvent être plus facilement obtenus par moulage assisté par aspiration. A plus large échelle, des matrices de trous à travers peuvent être percés dans une couche mince de gélatine en utilisant une machine-outil à commande numérique par ordinateur le tout étant biocompatible pour les études de culture cellulaire. Par la suite, nous avons appliqué une technique électrofilature pour produire des substrats de nanofibres de gélatine pour l'expansion à long terme de cellules souches pluripotentes humaines induites (hiPSCs). Pour montrer l'importance de la morphologie quasi tridimensionnelle des substrats de fibres, les empreintes de fibres en positive et négative ont été obtenus, montrant une corrélation évidente entre la qualité des hiPSCs après l'expansion à long terme et la morphologie de la surface du substrat. Enfin, nous avons fabriqué des nanofibres alignés en PLGA et montré leur supériorité pour la formation de feuille cellulaire en utilisant des cellules cardiaques dérivées d’hiPSCs
This thesis work aimed at exploring nanofabrication techniques to manufacture new types of cell culture substrates and scaffolds for tissue engineering based on a biomimetic approach. Firstly, we demonstrated a gel-embossing technique to replicate nanoscale patterns into gelatin layers. For microscale patterns, aspirationassisted gel-molding could be applied. For patterns of larger feature sizes, through-hole arrays could be punched in thin gelatin layers using a computer-aided mechanical machine, all being biocompatible for cell culture studies. Afterward, we applied an electrospinning technique to produce gelatin nanofibre substrates for long term expansion of human induced pluripotent stem cells (hiPSCs). To show the importance of quasi-three dimensional morphology of the fiber substrates, both positive and negative nanofibres imprints were produced, showing a clear correlation between the quality of the hiPSCs after long-term expansion and the surface morphology of the substrate. Finally, we fabricated PLGA aligned nanofibres and showed their superiority for cell sheet formation using hiPSCs cardiac cells

Orientador: Cesar Costapinto Santana
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: biopolímero denominado quitosana vem sendo reconhecido como uma importante fonte de matrizes para adsorventes em processos de recuperação e purificação de bioprodutos, com novas aplicações em várias áreas do conhecimento como a biotecnologia. Uma importante vantagem nessa utilização é a disponibilidade da quitina na natureza, podendo ser encontrada facilmente na carapaça de crustáceos. A flexibilidade apresentada por essas matrizes se deve principalmente à compatibilidade adsorbato/adsorvente e à possibilidade de modificações estruturais de modo a atender a características diversificadas de interação química e de resistência mecânica. No presente trabalho foi realizada a caracterização reológica de soluções e géis de quitosana, com a determinação das propriedades viscosas e viscoelásticas. As soluções concentradas foram obtidas por dissolução da quitosana em solução de ácido acético e os géis foram obtidos através de modificações da quitosana com a utilização do glutaraldeído, nas concentrações de 2,5g/100ml, 3,Og/100ml e 3,5g/100ml e nas temperaturas de 10°C, 30°C e 50°C. As propriedades viscosas e viscoelásticas das amostras de quitosana foram obtidas com a utilização do reômetro Haake CV20. Esse equipamento pode ser programado para trabalhar em dois métodos de obtenção de dados experimentais. No método de cisalhamento permanente, as propriedades obtidas são representativas do comportamento viscoso das amostras, através da obtenção das seguintes variáveis: tensão de cisalhamento, taxa de cisalhamento e viscosidade de cisalhamento. No método de cisalhamento oscilatório, as propriedades determinadas são representativas do comportamento viscoelástico das amostras, através da obtenção das seguintes variáveis: módulo de rigidez, módulo de dissipação e viscosidade complexa. Foi realizada a interpretação da correlação estrutura - propriedade apresentada pela quitosana e pelos géis modificados através da reticulação com glutaraldeído. Foram atribuídos modelos específicos para o comportamento reológico das soluções e géis de quitosana. A determinação dos parâmetros nas diversas faixas estudadas permite concluir que é possível preparar e caracterizar a quitosana na forma de soluções concentradas e na forma de géis de acordo com a concentração e ° grau de reticulação das amostras analisadas
Abstract: The chitosan biopolymer has recently being appointed as an important source of matrices used as adsorbents in processes for the recovery and purification of bioproducts, with new applications in areas such as biotechnology. An important advantage is that chitin occurs naturally and is commonly found in crustacean shells. The flexibility exhibited by these matrices became from the compatibility adsorbate/adsorbent and the possibility of structural modifications to satisfy diversified characteristics of chemical interaction and mechanical strength. In this work, the rheological characterization of chitosan solutions and gels was carried out in order to investigate viscosity and viscoelasticity properties. The concentrated solutions were prepared by dissolving chitosan with acid acetic solution and the gels were prepared by adding glutaraldehyde, solutions at different concentrations of 2,5g/100ml, 3,Og/100ml and 3,5g/100ml and temperatures of 10°C, 30°C and 50°C. The viscosity and viscoelasticity properties of chitosan samples were measured with a rheometer (model Haake CV20). The equipment can be operated in two different ways in order to obtain the experimental data. The first one is the steady shear rheological measurement, where the viscosity properties are described through values for shear stress, shear rate and shear viscosity. The second is the oscillatory shear rheological measurement, where the viscoelasticity properties are described through values for storage modulus, 1055 modulus and complex viscosity. The correlation between structure and properties exhibited by chitosan samples and gels modified by crosslinking with glutaraldehyde were studied. Rheological specific models were adjusted to the experimental data in order to describe the behavior of chitosan solutions and gels. The parameter determinations allow concluding that is possible to prepare and characterize chitosan samples as concentrated solutions and gels depending only on the concentration and the degree of crosslinking of the sample studied.
Mestrado
Desenvolvimento de Processos Biotecnologicos
Mestre em Engenharia Química

Ce travail a été réalisé dans le cadre d'une convention avec la société Elf Aquitaine. L'analyse a porté sur six extractions d'os chaule, et a consisté à caractériser ces différentes extractions par la détermination des paramètres rhéologiques (modules d'élasticité et de perte, complaisance et gonflement) en fonction de divers paramètres tels que la température, la concentration et le temps de murissement du gel, en utilisant d'une part la modélisation statistique pour les mesures cinétiques et les distributions de temps caractéristiques pour les mesures de fluage. Il résulte de cette étude que seules les chaines alpha, beta et gamma participent à l'élasticité du gel

Orientador: Rosiane Lopes da Cunha
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: A avaliação do processo de gelificação ácida de caseinato de sódio (CS) induzida por glucona-d-lactona (GDL) foi realizada em diferentes taxas e com ampla faixa de concentração de proteína (2-6% p/p). A cinética de acidificação e gelificação foi avaliada desde o pH 6,7 até o ponto isoelétrico das caseínas através da medida de pH e de propriedades mecânicas obtidas em compressão uniaxial (tensão e deformação na ruptura). A formação da rede do gel foi mais influenciada pelas interações eletrostáticas do que pelas diferentes taxas de acidificação, principalmente em pH próximo ao pI das caseínas. Além disso, interações hidrofóbicas e ligações de hidrogênio também estiveram envolvidas na estabilização da estrutura da rede, promovendo géis mais fortes. Também foi avaliado o processo de gelificação de proteínas do leite em pH 6,7 em sistemas contendo carragena. Neste caso, a ?-carragena foi adicionada em concentração de 0,3 a 0,8% (p/p) em misturas contendo caseinato de sódio (2 a 8% p/p), isolado protéico de soro (0,5 a 7% p/p) ou sacarose (5 a 30% p/p). Estes sistemas foram estudados a partir de ensaios reológicos em cisalhamento oscilatório, propriedades mecânicas e microestrutura. A temperatura de início da gelificação ou do desenvolvimento de estrutura (Ts) aumentou com a concentração de carragena em sistemas puros, enquanto que a presença de sacarose ou isolado protéico de soro promoveu um aumento da Ts e a adição de caseinato de sódio não modificou esta temperatura, em relação aos géis puros. Após a fomação do gel, um aumento da concentração de carragena levou a géis mais elásticos, rígidos, deformáveis e firmes, sendo que a adição de sacarose exerceu pouco efeito nas propriedades reológicas destes sistemas. A adição de isolado protéico de soro enfraqueceu a rede do gel em baixas concentrações (até 3%), mas houve formação de uma rede mista em maiores concentrações, sem demonstração de sinergismo entre os biopolímeros. A mistura de carragena e caseinato de sódio mostrou sinergia até 5% (p/p) desta proteína e para maiores concentrações, ocorreu o enfraquecimento da rede, diminuição da rigidez e firmeza do gel, provavelmente relacionada à micro-separação de fases, observada por microscopia confocal. Os espectros mecânicos mostraram que a maioria destes sistemas mistos apresentou comportamento de gel fraco, devido ao efeito simultâneo das interações físicas e incompatibilidade termodinâmica. No entanto, géis fortes foram observados na maior e menor concentração de carragena e caseinato de sódio, respectivamente, indicando a importância da interação eletrostática entre estes dois biopolímeros. O aumento da concentração de carragena e de proteínas promoveu um aumento da heterogeneidade da microestrutura do gel e a intensidade de interações repulsivas entre os biopolímeros e a formação da rede do gel, dominado pela carragena, afetou de maneira complexa as propriedades físicas destes sistemas
Abstract: Evaluation of acid-induced sodium caseinate (CS) gelation promoted by glucono-d- lactone (GDL) was performed at different acidification rates with several protein concentrations (2-6% w/w). The kinetics of acidification and gelation were followed from pH 6.7 to the isoelectric point of casein by evaluation of the pH and mechanical properties using uniaxial compression measurements (stress and strain at rupture). Gel network formation was more influenced by electrostatic interactions than different acidification rates, showing the contribution of rearrangements of bonds to strengthening the network, mainly at steady-state pH close to pI of caseins. Besides the hydrophobic interactions and hydrogen bonds were also important forces involved in structure stabilization, leading to stronger gels. Moreover, evaluation of gelation process of milk proteins at pH 6.7 in systems containing ?-carrageenan. In this study, the ?-carrageenan was added at concentration from 0.3 to 0.8% (w/w) into mixtures containing sodium caseinate (2 a 8% w/w), whey protein isolate (0.5 a 7% w/w) or sucrose (5 a 30% w/w). This systems was analysed using rheological measurements under oscillatory shear, mechanical properties and microstructure. The temperature at which structure development began or initial of gelation (Ts) augmented with increasing carrageenan concentration for pure systems, but sucrose or whey protein isolate addition promoted an increase of Ts and sodium caseinate did not affect this temperature, in relation to pure gel. After gel formation, increasing carrageenan concentration promoted more elastic, stronger, deformable and firmer, as well as sucrose addition showed a little effect to decrease elastic character of gel. Whey protein addition weakened gel network at lower concentrations (up to 3% w/w), but at higher concentration was observed a mixed gel network entanglement of carrageenan and whey protein, without sinergism between this biopolymers. Mixed gels of carrageenan and sodium caseinate showed synergism up to 5% (w/w/) of this protein and increasing concentration led to weaken the gel network, decreasing the rigidity and the firmness of gel, probably related to micro-phase separation, observed by confocal microscopy. Mechanical spectra showed that most of mixed systems presented weak gel behaviour, due to simultaneous effect of physical interactions and thermodynamic interactions. However, stronger gels were formed at higher and lower concentration of carrageenan and sodium caseinate, respectively, which indicate the relevance of electrostatic interactions between these biopolymers. Increasing carrageenan and proteins concentrations led to greater microstructure heterogeneity and increased repulsive interactions between biopolymers and thus gel formation, dominated by carrageenan, affected in a complex way the physical properties of these systems
Doutorado
Doutor em Engenharia de Alimentos

In this work, thermosensitive hydrogels having tunable thermo-mechanical properties were synthesized. Generally the thermal transition of thermosensitive hydrogels is based on either a lower critical solution temperature (LCST) or critical micelle concentration/ temperature (CMC/ CMT). The temperature dependent transition from sol to gel with large volume change may be seen in the former type of thermosensitive hydrogels and is negligible in CMC/ CMT dependent systems. The change in volume leads to exclusion of water molecules, resulting in shrinking and stiffening of system above the transition temperature. The volume change can be undesired when cells are to be incorporated in the system. The gelation in the latter case is mainly driven by micelle formation above the transition temperature and further colloidal packing of micelles around the gelation temperature. As the gelation mainly depends on concentration of polymer, such a system could undergo fast dissolution upon addition of solvent. Here, it was envisioned to realize a thermosensitive gel based on two components, one responsible for a change in mechanical properties by formation of reversible netpoints upon heating without volume change, and second component conferring degradability on demand. As first component, an ABA triblockcopolymer (here: Poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEPE) with thermosensitive properties, whose sol-gel transition on the molecular level is based on micellization and colloidal jamming of the formed micelles was chosen, while for the additional macromolecular component crosslinking the formed micelles biopolymers were employed. The synthesis of the hydrogels was performed in two ways, either by physical mixing of compounds showing electrostatic interactions, or by covalent coupling of the components. Biopolymers (here: the polysaccharides hyaluronic acid, chondroitin sulphate, or pectin, as well as the protein gelatin) were employed as additional macromolecular crosslinker to simultaneously incorporate an enzyme responsiveness into the systems. In order to have strong ionic/electrostatic interactions between PEPE and polysaccharides, PEPE was aminated to yield predominantly mono- or di-substituted PEPEs. The systems based on aminated PEPE physically mixed with HA showed an enhancement in the mechanical properties such as, elastic modulus (G′) and viscous modulus (G′′) and a decrease of the gelation temperature (Tgel) compared to the PEPE at same concentration. Furthermore, by varying the amount of aminated PEPE in the composition, the Tgel of the system could be tailored to 27-36 °C. The physical mixtures of HA with di-amino PEPE (HA·di-PEPE) showed higher elastic moduli G′ and stability towards dissolution compared to the physical mixtures of HA with mono-amino PEPE (HA·mono-PEPE). This indicates a strong influence of electrostatic interaction between –COOH groups of HA and –NH2 groups of PEPE. The physical properties of HA with di-amino PEPE (HA·di-PEPE) compare beneficially with the physical properties of the human vitreous body, the systems are highly transparent, and have a comparable refractive index and viscosity. Therefore,this material was tested for a potential biological application and was shown to be non-cytotoxic in eluate and direct contact tests. The materials will in the future be investigated in further studies as vitreous body substitutes. In addition, enzymatic degradation of these hydrogels was performed using hyaluronidase to specifically degrade the HA. During the degradation of these hydrogels, increase in the Tgel was observed along with decrease in the mechanical properties. The aminated PEPE were further utilised in the covalent coupling to Pectin and chondroitin sulphate by using EDC as a coupling agent. Here, it was possible to adjust the Tgel (28-33 °C) by varying the grafting density of PEPE to the biopolymer. The grafting of PEPE to Pectin enhanced the thermal stability of the hydrogel. The Pec-g-PEPE hydrogels were degradable by enzymes with slight increase in Tgel and decrease in G′ during the degradation time. The covalent coupling of aminated PEPE to HA was performed by DMTMM as a coupling agent. This method of coupling was observed to be more efficient compared to EDC mediated coupling. Moreover, the purification of the final product was performed by ultrafiltration technique, which efficiently removed the unreacted PEPE from the final product, which was not sufficiently achieved by dialysis. Interestingly, the final products of these reaction were in a gel state and showed enhancement in the mechanical properties at very low concentrations (2.5 wt%) near body temperature. In these hydrogels the resulting increase in mechanical properties was due to the combined effect of micelle packing (physical interactions) by PEPE and covalent netpoints between PEPE and HA. PEPE alone or the physical mixtures of the same components were not able to show thermosensitive behavior at concentrations below 16 wt%. These thermosensitive hydrogels also showed on demand solubilisation by enzymatic degradation. The concept of thermosensitivity was introduced to 3D architectured porous hydrogels, by covalently grafting the PEPE to gelatin and crosslinking with LDI as a crosslinker. Here, the grafted PEPE resulted in a decrease in the helix formation in gelatin chains and after fixing the gelatin chains by crosslinking, the system showed an enhancement in the mechanical properties upon heating (34-42 °C) which was reversible upon cooling. A possible explanation of the reversible changes in mechanical properties is the strong physical interactions between micelles formed by PEPE being covalently linked to gelatin. Above the transition temperature, the local properties were evaluated by AFM indentation of pore walls in which an increase in elastic modulus (E) at higher temperature (37 °C) was observed. The water uptake of these thermosensitive architectured porous hydrogels was also influenced by PEPE and temperature (25 °C and 37 °C), showing lower water up take at higher temperature and vice versa. In addition, due to the lower water uptake at high temperature, the rate of hydrolytic degradation of these systems was found to be decreased when compared to pure gelatin architectured porous hydrogels. Such temperature sensitive architectured porous hydrogels could be important for e.g. stem cell culturing, cell differentiation and guided cell migration, etc. Altogether, it was possible to demonstrate that the crosslinking of micelles by a macromolecular crosslinker increased the shear moduli, viscosity, and stability towards dissolution of CMC-based gels. This effect could be likewise be realized by covalent or non-covalent mechanisms such as, micelle interactions, physical interactions of gelatin chains and physical interactions between gelatin chains and micelles. Moreover, the covalent grafting of PEPE will create additional net-points which also influence the mechanical properties of thermosensitive architectured porous hydrogels. Overall, the physical and chemical interactions and reversible physical interactions in such thermosensitive architectured porous hydrogels gave a control over the mechanical properties of such complex system. The hydrogels showing change of mechanical properties without a sol-gel transition or volume change are especially interesting for further study with cell proliferation and differentiation.
In der vorliegenden Arbeit wurden thermosensitive Hydrogele mit einstellbaren thermo-mechanischen Eigenschaften synthetisiert. Im Allgemeinen basiert der thermische Übergang thermosensitiver Gele auf einer niedrigsten kritischen Löslichkeitstemperatur (LCST) oder kritischer Mizellkonzentration bzw. –temperatur(CMC/ CMT). Der temperaturabhängige Übergang von Sol zu Gel mit großer Volumenänderung wurde im ersten Fall bei thermosensitiven Hydrogelen beobachtet und ist vernachlässigbar für CMC/ CMT abhängige Systeme. Die Änderung des Volumens führt zum Ausschluss von Wassermolekülen, was zum Schrumpfen und Versteifen des Systems oberhalb der Übergangstemperatur führt. Die Volumenänderung kann unerwünscht sein, wenn Zellen in das Gel eingeschlossen werden sollen. Die Gelierung im zweiten Fall beruht hauptsächlich auf der Mizellbildung oberhalb der Übergangstemperatur und weiterem kolloidalem Packen von Mizellen im Bereich der Gelierungstemperatur. Weil die Gelierung hauptsächlich von der Polymerkonzentration abhängt, kann sich das Gel bei Zugabe von Lösungsmittel leicht wieder lösen. Hier sollten thermosensitive Gele entwickelt werden, die auf zwei Komponenten beruhen. Eine Komponente sollte aus einem ABA-Triblockcopolymer mit thermosensitiven Eigenschaften bestehen, dem Poly(ethylen glycol)-b-Poly(propylenglycol)-b-Poly(ethylen glycol) (PEPE), dessen Sol-Gel-Übergang auf Mizellierung und kolloidalem Jamming der gebildeten Mizellen basiert, und einer weiteren makromolekularen Komponente, einem Biopolymer, dass die Mizellen vernetzt. Auf diese Weise sollten thermosensitive Gele realisiert werden, die keine oder nur eine kleine Volumenänderung während der Änderung der mechanischen Eigenschaften zeigen, die stabiler gegenüber Verdünnung sein sollten als klassische Hydrogele mit einem CMC-basierten Übergang und die jedoch gezielt abgebaut werden können. Die Hydrogele wurden auf zwei Arten vernetzt, entweder durch physikalisches Vermischen, bei dem die Vernetzung durch elektrostatische Wechselwirkungen erfolgte, oder durch kovalente Kopplung der beiden Komponenten. Als makromolekulare Komponente zur Vernetzung der Mizellen wurden Biopolymere (hier: die Polysaccharide Hyaluronsäure (HA), Chondroitinsulfat oder Pektin oder das Protein Gelatin) verwendet, um die Hydrogele enzymatisch abbaubar zu gestalten. Um eine starke ionische/elektrostatische Wechselwirkung zwischen dem PEPE und den Polysachariden zu erzielen, wurde PEPE aminiert, um hauptsächlich monoaminiertes bzw. diaminiertes PEPE einsetzen zu können. Die Gele, die auf der physikalischen Mischung von aminierten PEPE mit HA bestehen, zeigten im Vergleich zu PEPE bei gleicher Konzentration eine Zunahme der mechanischen Eigenschaften, wie beispielsweise dem elastischem Modulus (G′) und dem Viskositätsmodulus (G′′) bei gleichzeitiger Abnahme der Gelierungstemperatur (Tgel). Durch Variation des Gehalts an aminierten PEPE-, konnte die Tgel in einem Bereich von 27-36 °C eingestellt werden. Interessanterweise zeigten die physikalischen Mischungen mit diaminierten PEPE (HA·di-PEPE) höhere mechanische Eigenschaften (elastischer Modulus G′) und eine höhere Stabilität gegenüber Verdünnungseffekten als Mischungen mit monoaminiertem PEPE (HA·mono-PEPE). Dies zeigt den starken Einfluss der elektrostatischen Wechselwirkungen zwischen der Carboxylgruppe der HA und der Amingruppe von PEPE. Die physikalischen Eigenschaften HA·di-PEPE sind vergleichbar mit den physikalischen Eigenschaften des Glaskörpers im Auge hinsichtlich Transparenz, Brechungsindex und Viskosität. Deswegen wurde das Material hinsichtlich seiner biologischen Anwendung getestet und zeigte sich sowohl im Überstand als auch im direkten Kontakt als nichtzytotoxisch. Zukünftig wird dieses Material in weiteren Untersuchungen bezüglich seiner Eignung als Glaskörperersatz geprüft werden. Zusätzlich konnte der enzymatische Abbau der Hydrogele mit Hyaluronidase gezeigt werden, die spezifisch HA abbaut. Beim Abbau der Hydrogele stieg Tgel bei gleichzeitiger Abnahme der mechanischen Eigenschaften. Aminiertes PEPE wurde zusätzlich zur kovalenten Bindung unter Verwendung von EDC als Aktivator an Pektin und Chondroitinsulfat eingesetzt. Tgel konnte auf 28 – 33 °C eingestellt werden durch Variation der Pfropfungsdichte am Biopolymer bei gleichzeitiger Zunahme der thermischen Stabilität. Die Pec-g-PEPE Hydrogele waren enzymatisch abbaubar, was zu einer leichten Erhöhung von Tgel und zu einer Abnahme von G′ führte. Die kovalente Bindung der aminierten PEPE an HA erfolgte unter Verwendung von DMTMM als Aktivator, der sich in diesem Fall als effektiver als EDC herausstellte. Die Reinigung mittels Ultrafiltration führte zu einer deutlich besseren Aufreinigung des Produkts als mittels Dialyse. Die gegrafteten Systeme waren in Nähe der Körpertemperatur bereits im Gelstadium und zeigten eine Erhöhung der mechanischen Eigenschaften bereits bei sehr geringen Konzentrationen von 2.5Gew.%. Die höheren mechanischen Eigenschaften dieser Hydrogele erklären sich durch die Kombination der Mizellbildung (physikalische Wechselwirkung) des PEPE und der Bildung kovalenter Netzpunkte zwischen PEPE und HA. PEPE bzw. entsprechende physikalische Mischungen derselben Komponenten zeigten kein thermosensitives Verhalten bei einer Konzentration unterhalb von 16 Gew%. Diese thermosensitiven Hydrogele zeigten auch eine Löslichkeit auf Abruf durch enzymatischen Abbau. Das Konzept der Thermosensitivität wurde in 3D strukturierte, poröse Hydrogele (TArcGel)eingeführt, bei dem PEPE kovalent an Gelatin gebunden wurde und mit LDI vernetzt wurde. Das gepfropfte PEPE führte zu einer Erniedrigung der Helixbildung der Gelatinketten. Nach Fixierung der Gelatinketten durch Vernetzung zeigte das System eine Erhöhung der mechanischen Eigenschaften bei Erwärmung (34-42 °C). Dieses Phänomen war reversibel beim Abkühlen. Eine mögliche Erklärung der reversiblen Änderungen bezüglich der mechanischen Eigenschaften sind die starken physikalischen Wechselwirkungen zwischen den Mizellen des PEPE, die kovalent an Gelatin gebunden wurden. Ferner wurde durch AFM Untersuchungen festgestellt, dass bei Temperaturerhöhung (37 °C) die örtlichen elastischen Moduli (E) der Zellwände zugenommen haben. Zusätzlich wurde die Wasseraufnahme der TArcGele durch PEPE und die Temperatur (25 °C und 37 °C) beeinflusst und zeigte eine niedrigere Wasseraufnahme bei höherer Temperatur und umgekehrt. Durch die niedrigere Wasseraufnahme bei hohen Temperaturen erniedrigte sich die Geschwindigkeit des hydrolytischen Abbaus im Vergleich zu dem strukturierten Hydrogel aus reiner Gelatin. Diese temperatursensitiven ArcGele könnten bedeutsam sein für Anwendungen im Bereich Stammzellkultivierung, Zelldifferenzierung und gerichteter Zellmigration. Zusammenfassend konnte bei den thermosensitiven Hydrogelen gezeigt werden, dass die Vernetzung von Mizellen mit einem makromolekularen Vernetzer die Schermoduli, Viskosität und Löslichkeitsstabilität im Vergleich zu reinen ABATriblockcopolymeren mit CMC-Übergang erhöht. Dieser Effekt konnte durch kovalente und nichtkovalente Mechanismen, wie beispielsweise Mizell- Wechselwirkungen, physikalische Interaktionen von Gelatinketten und physikalische Interaktionen von Gelatinketten und Mizellen, realisiert werden. Das Pfropfen von PEPE führte zu zusätzlichen Netzpunkten, die die mechanischen Eigenschaften der thermosensitiven architekturisierten, porösen Hydrogele beeinflussten. Insgesamt ermöglichten die physikalischen und chemischen Bindungen und die reversiblen physikalischen Wechselwirkungen in den strukturierten, porösen Hydrogelen eine Kontrolle der mechanischen Eigenschaften in diesem sehr komplexen System. Die Hydrogele, die eine Veränderung ihrer mechanischen Eigenschaften ohne Volumenänderung oder Sol-Gel-Übergang zeigen sind besonders interessant für Untersuchungen bezüglich Zellproliferation und –differenzierung.

Macromolécules formées par la répétition de nombreuses sous-unités appelées monomères, les biopolymères sont des polymères issus de la biomasse constituant une classe de matériaux utilisée dans des domaines très divers : industrie pharmaceutique et cosmétique, génie tissulaire, agroalimentaire et médical. Leur disponibilité, leur prix, leur non toxicité et leur biodégradabilité font de ces matériaux un sujet d’intérêt croissant pour la communauté. L’assemblage des biopolymères en gels induit par un facteur externe (cations métalliques, pH, agents réticulants organiques) est une de leurs propriétés les plus intéressantes. Une bonne compréhension de ces assemblages en vue d’optimiser les propriétés physico-chimiques, micro- et macroscopiques des gels passe nécessairement par une modélisation des biopolymères et de leurs interactions inter- et intramoléculaires. Cette modélisation doit être capable de fournir des descriptions précises de la réactivité des molécules et donc des interactions à courtes et longues distances telles que les interactions covalentes, électrostatiques et les liaisons de Van der Waals ou hydrogène. Mais l’effet de la température et du solvant exigent aussi des simulations sur des échelles de temps et d’espace étendues. En ce sens, une approche computationnelle joue le rôle de « microscope numérique ».Dans le cadre de cette thèse, une approche multi-échelle a été élaborée pour l’étude d’un groupe de polysaccharides : les alginates. La formation de complexes alginate/cation multivalent (Alg/Mn+) est une étape déterminante de tout le processus de gélification. L’étude suivant la théorie de la fonctionnelle de la densité avec correction de dispersion (DFT-D) de modèles d’alginates complexant des cations divalents (Mn2+, Co2+, Cu2+ et Zn2+ ) et trivalents (Al3+, Cr3+, Ga3+, Fe3+, La3+ et Sc3+) nous a mené aux conclusions suivantes. La tendance de l’énergie de liaison est indépendante de : la longueur et le nombre des chaines d’alginates, la présence d’eau dans la première sphère de coordination et la spéciation du métal. Dans toutes les structures hydratées, une liaison monodentate entre le cation et les groupements carboxylates est établie. Ainsi, l’interaction entre les cations et l’alginate ne dépend que de paramètres locaux que l’on peut expliquer par une contribution covalente significative provenant de la donation de charges des oxygènes ligands carboxyliques vers Mn+. L’importance de la force de liaison pour la complexation a été confirmée par l’étude DFT-D d’échanges cationiques. Les simulations Born-Oppenheimer Molecular Dynamics (BOMD)/Molecular Dynamics (MD) de dimannuronates dans l’eau et de complexes de lanthane et d’aluminium ont montré que l’eau prévient la formation de liaisons hydrogène intra-chaine en solvatant les groupements fonctionnels polaires. Dans les complexes de dimannuronate de lanthane et de dimannuronate d’aluminium, les fonctions de distribution radiale des atomes d’oxygène carboxyliques confirment l’établissement d’un mode de liaison monodentate. Dans tous les complexes simulés, aucune molécule d’eau ne sépare l’ion métallique et le ligand. Ceux-ci forment donc un complexe à sphère interne. Comme alternative aux simulations MD, une méthode de recuit parallèle Monte Carlo a été implémentée dans le code deMon2k. Les méthodes QM/MM et QM/MC permettront aussi d’examiner l’effet de chaines plus longues sur la complexation de cations de métaux de transition en considérant la température et le solvant aqueux explicite. Ces outils computationnels pourront être utilisés directement pour l’étude de différents polysaccharides et biopolymères
Biopolymers are macromolecules formed by the repetition of numerous subunits called monomers and derived from biomass. They constitute a class of materials used in various fields: pharmaceutical and cosmetic industry, tissue engineering, agro-alimentary and medicine. Their availability, price, non-toxicity and biodegradability make these materials a growing topic of interest to the community. The assembly of biopolymers in gels induced by an external factor (metal cations, pH and organic crosslinking agents) is one of their most interesting properties. The optimization of the physico-chemical, micro- and macroscopic properties of the gels necessitates understanding of factors that influence the gel equilibrium structures. Molecular modeling tools applied to study the inter- and intra-molecular interactions in biopolymer assemblies at short and long distances, such as covalent, electrostatic and the Van der Waals interactions or hydrogen bonds, can provide valuable information The effect of temperature and solvent also requires simulations on extended time and space scales. In this sense, a computational approach plays the role of "digital microscope".In this thesis, a multi-scale approach has been developed for the study of a group of polysaccharides: alginates. The formation of alginate/multivalent cation complexes (Alg/Mn+) is a determining step in the entire gelation process. The Density Functional Theory augmented with an empirical London dispersion term (DFT-D) applied to study various models of alginate complexes with divalent (Mn2+, Co2+, Cu2+ and Zn2+) and trivalent (Al3+, Cr3+, Ga3+, Fe3+, La3+ and Sc3+) metal cations led to the following conclusions. The tendency of binding energy of metal cations is independent on : the length and number of alginate chains, the presence of water in the first coordination sphere and the speciation of the metal. In all the hydrated structures, a monodentate mode of binding is established between the cation and the carboxylate groups. Thus, the interaction between cations and alginate depends only on local parameters which can be explained by a significant covalent contribution from the charge donation of carboxylic oxygen ligand atoms to Mn+. The importance of the binding strength for the complexation was confirmed by the DFT-D study of ion exchange using mixed La3+/Cu2+ alginate complexes. The Born-Oppenheimer Molecular Dynamics (BOMD) / Molecular Dynamics (MD) simulations of dimannuronates in water and lanthanum, and aluminum complexes revealed that water prevents the formation of intra-chain hydrogen bonds by solvating the functional groups. In the complexes of lanthanum dimannuronate and aluminum dimannuronate, the radial distribution functions of the carboxylic oxygen atoms confirm the establishment of a monodentate bonding mode. In all simulated complexes, no water molecule separates the metal ion from the ligand, thus forming inner sphere complex.As an alternative to MD simulations, a Monte Carlo parallel tempering method has been implemented in the deMon2k code. The QM/MM and QM/MC methods will also allow the examination of longer chains effect on the transition metal cations complexation by considering the temperature and the explicit aqueous solvent. These computational tools can be used straightforwardly for the study of other polysaccharides and biopolymers

碩士
國立中興大學
化學工程學系
88
The gel point of complex biopolymer solutions was studies by rheometers (SR5 and RFS), and the effect of physical attractive interactions and composition (or stoichiometry) to the network structure of mixed gels was explored. The attractive forces include electrostatic interaction and synergism. Electrostatic interaction takes place between two polymers with opposite charges. Synergistic interaction is often found in mixed solutions of plant galactomannans (locust bean gum or guar gum) and galactans (carrageenan or agar). According to the definition of gel point defined by Winter, when the system reaches the sol-gel transition, tand does not vary with frequency and remains constant (tand = tan(np/2), n is a critical exponent). Fractal dimension, df, can be obtained by theoretical formula of Muthukumar. The larger of the fractal dimension is, the tighter is the network formed by the mixed gels. The mixed gels with larger df generally exhibit better mechanical properties. In food science, the larger df may imply firmer texture. Among the mixed gel systems in electrostatic interaction that we studied, the gel point can only be found in chitosan-gelatin mixed system. In other systems, insoluble coacervates generally formed so the gel point cannot be detected by a rheometer. In the chitosan-gelatin mixed system, the relationship between mixing ratio and n is similar to that in traditional chemical cross-linking systems. This may imply that the network structure is independent of the forming mechanism (i.e. chemical binding or physical interaction). In the synergistic interaction systems, owing to less solubility of galactomannan and konjac glucomannan, the mixed gel solutions show high degree of heterogeneity, making the exact gel point be screened. In that case, only "pseudo" gel-ponits were found.

FucoPol is a high molecular weight exopolysaccharide (EPS) secreted by the bacterium Enterobacter A47 that is composed of the neutral sugars fucose, galactose and glucose, and the acidic sugar glucuronic acid. It also has substituent acyl groups (acetyl, succinyl and pyruvyl). The presence of glucuronic acid, together with succinyl and pyruvyl, confer the polymer an ani-onic character. The main goal of this thesis was to develop polymeric structures based on FucoPol. First-ly, FucoPol was produced using glycerol as the sole carbon source for the cultivation of Entero-bacter A47. A production of 7.74 g L-1 was reached at the end of 96 h of cultivation. The overall volumetric productivity was 1.97 g L−1 day−1 and the net yield of FucoPol on glycerol was 0.085 g g-1. The produced polymer was extracted from the broth and used to test different gelling pro-cedures. Based on the anionic character of the polymer, different salts of mono-, di- and triva-lent cations were tested (KCl, KNO3, NaCl, NaH2PO4, CaCl2, CaSO4, MgCl2, MgSO4, CuSO4, CuCl2, ZnSO4, ZnCl2, FeSO4, FeCl2, FeCl3) to evaluate the gelling capacity of FucoPol. The gelation of FucoPol occurred in the presence of divalent cations tested excepting calcium salts, at room temperature (25 ºC) in alkaline media (NaOH 2M), while for FeCl3, gels formed only by mixing FucoPol solution with salt aqueous solution at room temperature (25 ºC), with a low pH. Release of copper and/or iron from FucoPol gel beads (FeCl3, CuSO4,) was evaluated in different biological solutions (NaCl (0.9%), SGF, SIF, PBS and DMEM). FucoPol beads tested maintained their shape in NaCl and disintegrated in SGF. CuSO4/FucoPol beads maintained their shape during the assay in PBS, and disintegrated in DMEM and SIF. FeCl3/FucoPol beads became more faint and translucent in DMEM, SIF and PBS while CuSO4/FeCl3/FucoPol beads maintained their shape in these media. The cytotoxicity of FucoPol in different human cell lines (fibroblasts, A2780, A549, HCT116, MCF7) was assessed by MTS assay and results shown that FucoPol was not cytotoxic. Cytotoxicity of FucoPol beads was assessed by Trypan Blue method for K562 cells and results suggest that Fe/FucoPol beads were not cytotoxic, and FucoPol beads prepared with copper af-fect the viability of K562 cells.

Mannans are highly water-soluble mannose heteropolymers produced by a number of organisms, including yeasts. Polyhydroxyalkanoates (PHAs) are aliphatic polyesters produced by numerous bacteria as a carbon and energy source, with interesting thermal and mechanical properties. The main objective of this thesis was to prepare different polymeric structures base on mannans and PHAs for use in the pharmaceutical and biomedical areas. Mannans were produced by Komagataella pastoris using glycerol as carbon source, extracted with a heat-alkali treatment and purified using dialysis. PHAs were produced by mixed cultures using fermented fruit pulp waste, extracted using chloroform or hypochlorite and purified in ethanol. A successful deproteinization and an unsuccessful phosphorylation procedure was performed in mannans. The results show a decrease in protein content of 69.49 ± 0.44 % and a decrease in phosphate content of 60.45 ± 1.23 %, respectively. Mannans were tested in normal fibroblasts, HCT116 and A2780 cell lines for their cytotoxicity, by MTS assay, and no cytotoxicity was discovered. They were then used to prepare gel structures, and gelled using di- and tri-valent cations of iron and copper at low temperature (4 ⁰C) and alkaline pH. Gel particles were obtained in the above conditions and tested for their stability in water. Particles made using tri-valent iron were found the most stable. Mannans were also used to produce films. Films were obtained from i) mannans in water dried at 30 ⁰C or freeze dried, ii) from the previously produced films (30 ⁰C) and then coated with iron, at neutral pH or followed by immersion in an alkaline solution and, iii) from gel beads dried at 30 ⁰C or freeze dried. Films were tested for cell adhesion in vitro using normal fibroblasts, but no positive results were found. PHAs with different HV ratios were used to produce films, pure and blended with mannans, using chloroform as solvent by a solvent casting method. The produced films were tested for cell adhesion in vitro, using fibroblasts and MCF7-GFP. Pure PHA films were deemed good matrices for this application with cells adherent to their surface, whereas blend matrices failed in this regard. Some pure PHA matrices were then tested for their cytotoxicity using MCF7-GFP, and with the exception of co-polymer PHBHV with HV content of 18 % (extracted with hypochlorite), they were found to be non-cytotoxic, rendering them useful for biomedical applications such as wound dressing or drug delivery.

Questo lavoro riguarda dispersioni di nanotubi di carbonio in surfattanti e biopolimeri in soluzione acquosa. Il principale obiettivo è determinare i parametri critici che governano le dispersioni in sistemi concentrati. L'uso di matrici acquose complesse è pensato essere rilevante nella futura preparazione di biomateriali. Per questo scopi, matrici con interessanti capacità orientazionali e/o proprietà meccaniche notevoli sono considerate. I nanotubi di carbonio sono stati dispersi in sistemi micellari e nematici di sodio dodecil solfato e biopolimeri concentrati (DNA, Lisozima). I sistemi sono stati caratterizzati con reologia, microscopie, scattering dinamico della luce, mobilità elettroforetica e NMR.
This work focuses on the dispersions of carbon nanotubes in surfactants and biopolymers water-based matrices. The main objective is to determine the critical parameters govering the dispersions in concentrated systems. The use of complex aqueous matrices is thought to be relevant in the future design of improved biomaterials. For these purposes, matrices with interesting orienting capabilites and/or mechanical properties are taken into account. Carbon nanotubes were dispersed in micellar and micellar nematic surfactant (sodium dodecyl-sulfate, triton-X-100) systems and concentrated biopolymer (DNA, lysozyme) solutions. The systems were characterized with rheology, microscopies, dynamic light scattering, electrophoretic mobilities measurements and NMR spectroscopy.

Dissertação de Mestrado Integrado em Engenharia Química apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Este trabalho tem como principal objetivo o desenvolvimento de géis injetáveis para libertação controlada e localizada de fármacos em feridas. Desta forma, prepararam-se nanopartículas para encapsular o fármaco em estudo que foram posteriormente incorporadas num gel, que pode ser injetado no local pretendido. Estes sistemas de libertação controlada de fármacos (SLCs) foram produzidos a partir de polímeros de base natural, biodegradáveis e biocompatíveis, como o quitosano e o k-carragenano e usando um fármaco também de origem natural, o naringin. O encapsulamento do naringin, um flavonóide com diversas propriedades terapêuticas, entre elas anti-inflamatórias e anti ulcerosa, foi efetuado em nanopartículas de quitosano preparadas através do método de gelificação iónica. As nanopartículas foram formadas por reticulação com tripolifosfato de sódio (TPP), usando um método já reportado na literatura, e pela primeira vez com o citrato de dihidrogenado de colina (CD), um líquido iónico que revelou ser um bom reticulante alternativo ao TPP. A distribuição de tamanhos das nanopartículas, assim como a estabilidade ao longo do tempo, foi estudada com recurso à técnica de Dispersão Dinâmica da Luz (Dynamic Light Scattering – DLS) que revelou tamanhos médios próximos de 180 nm para o caso das nanopartículas reticuladas com TPP e 330 nm para as nanopartículas reticuladas com CD, apresentando ambas uma boa estabilidade durante as 72 horas do estudo. A morfologia das nanopartículas foi ainda avaliada por Microscopia Eletrónica de Varrimento (SEM). No decorrer do trabalho, foram estudados diferentes sistemas de libertação de naringin nomeadamente nanopartículas de quitosano reticuladas com TPP ou com CD, géis de kcarragenano com e sem reticulante iónico (KCl) e sistemas combinados de nanopartículas de quitosano incorporadas nos géis de k-carragenano, por forma a concluir sobre a eficiência de cada sistema na libertação controlada do fármaco. Os perfis de libertação foram estudados em solução fosfato salina a pH 7 e a 37 ºC para todos os SLCs preparados. Os resultados obtidos mostram que os sistemas compostos apenas pelas nanopartículas apresentaram perfis de libertação do naringin mais rápidos, com 60 % do naringin libertado ao fim de 1 h e a quase totalidade ao fim de 4 h de monitorização. A libertação do naringin a partir dos géis de k-carragenano revelou ser mais controlada, embora o fármaco também se tenha libertado quase na sua totalidade ao fim de cerca de 6 h de monitorização. Finalmente, verificou-se que a libertação do naringin através dos géis de k-carragenano reticulados com KCl, com e sem nanopartículas incorporadas, é uma alternativa eficaz para garantir uma libertação do fármaco mais controlada, uma vez que, com este sistema, apenas cerca de 30 % de naringin foi libertado ao fim de 1 h de monitorização. Estes dois sistemas (com e sem nanopartículas de quitosano) apresentaram perfis de libertação muito semelhantes, verificando-se a libertação de apenas cerca de metade da quantidade total de fármaco durante 10 dias de monitorização. Os perfis de libertação medidos foram correlacionados com um modelo matemático semi-empírico baseado na resolução simplificada da segunda lei de difusão de Fick (equação de Peppas). A partir do modelo foram calculados parâmetros cinéticos que facilitam a comparação entre os diferentes perfis de libertação medidos e permitem inferir sobre os mecanismos que controlam a libertação do fármaco a partir dos diferentes SLCs estudados.