O inchamento de pelotas de minério de ferro, que pode chegar até 400%, é um assunto que desperta interesse da indústria metalúrgica por gerar diversos problemas durante processos de redução. Ele ocorre por dois motivos, a saber, a mudança da estrutura cristalina na transformação da hematita (Fe2O3) para a magnetita (Fe3O4) e o aparecimento de ferro no formato filamentar durante a última etapa de redução. Diversos fatores influenciam o comportamento das pelotas, como a basicidade binária (CaO/SiO2) e o teor de MgO. Foram realizados experimentos para avaliar o efeito destas duas variáveis em suas propriedades físicas, como resistência à compressão e porosidade, e no comportamento das pelotas durante a redução. Os teores de MgO foram de 0%, 1% e 5%, enquanto a basicidade foi de 0,61 a 1,5. Ao adicionar MgO, a porosidade e a redutibilidade aumentam, enquanto o inchamento e a resistência diminuem. Ao adicionar CaO, a porosidade cai por conta da formação de mais fase líquida durante a queima, há diminuição de inchamento. A redutibilidade aumenta até basicidade 1 e depois apresenta uma leve diminuição em basicidade 1,5. / Iron ore pellets swelling, which can reach up to 400%, is a subject that rises concern in metallurgical industry because of the problems it may cause during reduction processes. Several factors can change pellets behavior concerning swelling, such as binary basicity (CaO/SiO2) and the MgO content. Experiments were performed to evaluate the effect of these two variables in the physical properties of the pellets, such as compression strength and porosity, and in their behavior during reduction as well. MgO was added up to 5% and basicity varied in a range from 0.61 to 1.5. Addition of MgO increased porosity and reducibility, while swelling and strength decreased. Addition of CaO caused porosity to decrease because of the formation of more liquid slag during heat treatment. Is also decreased swelling. Reducibility rises when basicity reaches 1.0, but decreases with further increases in CaO content.

Admite-se normalmente na Mecânica dos Solos que os solos que são expansivos em presença d\'água, são contrácteis ao perderem umidade, e vice-versa. Nas regiões tropicais, encontra-se solos, como por exemplo as argilas e solos argilosos sedimentares de baixadas ou ainda argilas e solos argilosos saprolíticos, que assim se comportam quanto às propriedade de expansão e de contração. Graças à atuação do clima quente e úmido das regiões tropicais, os solos se formam e se desenvolvem rápida e intensamente. Os solos tropicais saprolíticos e lateríticos podem apresentar composição mineralógica e estrutura peculiares resultantes destes processos de intemperismo. Dadas estas características, eles podem se comportar de forma particular sob diversos aspectos e, em especial neste trabalho, são abordadas suas \"anomalias\" quanto à expansão e à contração. Há solos tropicais, como as argilas e solos argilosos lateríticos, que são geralmente pouco expansivos, embora contrácteis. De outro lado, existem siltes e solos siltosos micáceos e/ou caulínicos saprolíticos que são frequentemente muito expansivos, apesar de serem pouco ou não contrácteis. Hipóteses sobre os mecanismos envolvidos nos processos de expansão e de contração são feitas na tentativa de compreender o comportamento particular destes solos. Algumas propriedades dos solos de grande interesse à pavimentação, como resistência e perda de resistência em presença d\'água, deformações em geral, fissuras e trincas de contração, entre outras, dependem também do tipo de comportamento do solo à expansão e à contração. Ensaios em amostras compactadas mostram como alguns tipos de comportamento podem ser previstos através da expansão e da contração.Estuda-se os efeitos da secagem dos solos compactados, fenômeno comum nas regiões tropicais, seja logo após a construção. Como já na fase de utilização das rodovias. Constata-se que para solos argilosos e siltosos saprolíticos, como para grande parte dos solos transportados, a secagem é em geral prejudicial, tornando o solo compactado potencialmente mais expansivo e com maior perda de capacidade de suporte em contato com a água. Contrariamente, há alguns tipos de solos lateríticos onde a secagem imprime efeitos benéficos irreversíveis ao solo, gerando uma diminuição na expansão e na perda de resistência quando em presença d\'água. Propõe-se ensaios de reexpansão com medida da capacidade de reabsorção d\'água após secagem de pastilhas moldadas no limite de liquidez e da resistência à penetração do cone para identificar estes solos tropicais lateríticos que possam apresentar melhorias de comportamento pela secagem após compactação. A secagem promove cimentação entre as partículas do solo com a formação de \"agregados\". Utiliza-se ensaios cíclicos de secagem-infiltração em corpos de prova compactados para a verificação da estabilidade destes \"agregados\" em presença d\'água, ou seja, da durabilidade desta transformação. Chamam-se solos \"auto-estabilizantes\" aqueles que por desidratação formam \"agregados\" estáveis e duráveis. Na conclusão do presente trabalho, valendo-se do comportamento diferenciado à expansão e à contração de certos grupos de solos tropicais, novos critérios são estabelecidos como proposta para uma classificação geotécnica de solos tropicais para aplicação viária. / In Soil Mechanics it is widely accepted that soils which swell when wet shrink as their water content diminishes and vice versa. In tropical regions there are soils such as sedimentary clay soils or even saprolitic clay soils which conform to this pattern of shrinking and swelling. Because of the hot, wet, tropical climate soil formation and evolution is rapid and intense. These weathering processes may result in saprolitic and lateritic soils having a distinctive mineralogical composition and structure. Given these characteristics they may exhibit unusual behavior patterns in may ways. This paper deals specifically with those anomalies concerning soil shrinkage and swelling. There are some tropical soils, for example lateritic soils, which swell very little and yet can shrink considerably. On the other hand there are various types of micaceous and/or kaolinic saprolitic silt soils which can swell considerably but which shrink very little or not at all. This work contains some hypotheses concerning the mechanisms involved in these swelling and shrinking processes in attempt to understand the special behavior pattern of these soils. Some soil properties which are of great importance to pavement, such as strength and strength loss when contact with water occurs, deformation in general, fissures and cracks due to shrinkage, also depend on the type of soil behavior patterns observed in shrinkage and swelling. Tests on compacted samples have shown how some types of behavior can be predicted through shrinkage and swelling. Studies have been made of the effects of the drying of compacted soils, a common phenomenon in tropical regions, which may occur shortly after construction is completed or when the highways are already operative.These studies show that for both saprolitic silt and clay soils drying has usually a detrimental effect by making the compacted soil more susceptible to swelling and leading to a greater loss of bearing capacity when rewet. However, there are some types of lateritic soils where drying has irreversible beneficial effects on the soil, reducing both swelling and strength loss. As part of my research I used reswelling tests that measure the capacity for water re-absorption of dried soil pats and the fall cone penetration strength after the re-absorption in order to identify those lateritic tropical soils that benefit from drying after compaction. These soils have a self-bonding capacity which facilitates the formation of \"aggregates\". Cycle tests of drying-rewetting were conducted on compacted specimens to verify the stability of the \"aggregates\" when the water content changes or in the other words, the durability of this transformation. Those soils which when dehydrated form stable aggregates are called \"self-stabilizing\". In the final part of my work, new criterias based on the different behavior patterns of certain tropical soils for swelling and shrinkage are established as part of a new geotechnical classification of tropical soils for road construction purposes.

This thesis aims to develop an understanding about swelling and disintegration of multi-component polymeric structures such as pharmaceutical tablets. The thesis presents a model for the diffusion-driven water uptake, swelling deformation and subsequent disintegration of polymer matrix drug-delivery devices. Hygroscopic swelling occurs when a dry tablet enters a humid environment and absorbs water molecules. The modification of tablet structures changes the release profile of the drug in the desired manner. The previous research mostly focused on transport problems related to drug release. This study contributes an understanding of the mechanical behaviour of hydrophilic polymer release matrix materials which are treated as continuum. Modelling of the swelling problem involves concurrent large deformation of the polymer network and diffusion of the solvent through the network. A coupled diffusion-deformation model was created to study the relation between both physics. The coupled diffusion-deformation model was utilised to consider disintegration of polymer matrix through the inclusion of swelling agents. Two cases were presented to illustrate the application of the model: swelling-controlled and immediate-release drug delivery systems. This study used COMSOL Multiphysics®, a finite element commercial software to perform the analysis. Various physical modules: structural mechanics, chemical transport and mathematics were combined for solving coupled diffusion-deformation-damage boundary value problems. The numerical results were validated using existing experimental data from the literature. The model parameters were varied to investigate their sensitivity to the solution. Higher solvent concentration gradient in the matrix produced higher swelling strain, thus increased local stress. Disintegrability was measured by the time taken for the maximum principal stress to reach a given failure. Higher coefficient of water diffusion allows higher amount of water ingression into the matrix. Higher coefficient of hygroscopic swelling generates higher local swelling strain. This study facilitates in understanding the complex phenomena in the application of drug release formulation.

L'étude des matériaux argileux a de nombreuses applications en génie civil et environnemental. Ces applications, telles que l'enfouissement des déchets nucléaires, les risques naturels liés au gonflement et au retrait des sols, et l'extraction d'hydrocarbures, posent des défis technologiques qui nécessitent de comprendre et de prédire le comportement mécanique des argiles, en particulier sur le long terme. Les argiles gonflantes sont des matériaux complexes, poreux et multi-échelles dont les propriétés sont très sensibles à l'eau. Dans cette thèse, nous cherchons à comprendre l'effet de l'eau sur les propriétés mécaniques à court et long terme des argiles. Notre stratégie est de combiner des simulations numériques à l'échelle du nanomètre et des expériences à l'échelle du micromètre afin de mieux comprendre l'interaction entre ces échelles. Nous avons effectué des simulations moléculaires pour quantifier l'effet de l'eau et du cation interfoliaire sur les propriétés de gonflement, élastiques et de fluage des feuillets d'argile, qui à cette échelle sont inaccessibles à l'expérience. Nous avons également effectué une étude comparative de différents modèles de feuillets d'argile de complexité croissante afin de mieux comprendre les interactions qui régissent la cohésion entre les feuillets d'argile. Nous avons mesuré expérimentalement les propriétés de films d'argile autoporteurs bien ordonnés. Nous avons montré l'effet de l'humidité relative et de la nature du cation interfoliaire sur les déformations de ces films d'argile. En particulier, nous avons quantifié le gonflement de ces films induit par l'humidité en combinant microscopie électronique à balayage environnementale et corrélation d'images numériques. Nous avons également effectué des essais de traction et de fluage sur ces films à humidité contrôlée. Nous avons comparé les données obtenues par nos expériences aux résultats des simulations moléculaires. Cette comparaison permet de discuter les mécanismes élémentaires de déformation et les échelles pertinentes pour la compréhension du comportement hydromécanique des argiles / The study of clay-based materials has many applications in civil and environmental engineering. These applications include underground nuclear waste disposal, the natural risks associated to the swelling and shrinkage of soils, and the extraction of hydrocarbons. They pose significant technological challenges that require to understand and to predict the mechanical behavior of clays, in particular on the long term. Swelling clays are complex porous multi-scale materials and their properties are very sensitive to water. In this thesis, we aim at understanding the impact of water on the short-term and long-term mechanical properties of clays. Our strategy was to combine numerical simulations at the scale of the nanometer and experiments at the scale of the micrometer to have a better insight of the interplay between these scales. We performed molecular simulations to estimate the effect of water and of the interlayer cation on the swelling, elastic and creep properties of clay layers, which are inaccessible to experiments at this scale. We also carried out a comparative study of various numerical models of increasing complexity in order to better understand the interactions that governs the cohesion between the clay layers. We measured experimentally the properties of well-ordered self-supporting clay films. We investigated the impact of relative humidity and of the nature of the interlayer cation on the mechanical properties of these clay films. In particular, we quantified the humidity-induced swelling of these films by using a combination of environmental scanning electron microscopy and digital image correlation. We also performed tensile tests and creep tests on these films at controlled relative humidity. We compared the data obtained by our experiments to the results of the molecular simulations. This comparison makes it possible to discuss the elementary deformation mechanisms and the scales relevant to the understanding of the hydromechanical behavior of clays

Os Vertissolos apresentam alto potencial para a produção agrícola e para estocar carbono. No entanto, diversos aspectos sobre sua gênese, fundamentais para qualidade e sustentabilidade do solo, permanecem incompreendidos. As várias lacunas sobre suas características particulares estão relacionadas ao incomum teor de alumínio trocável; a manifestação de feições morfológicas e vérticas em uma matriz inorgânica dominada por fases cauliníticas; e a preservação e estoque de carbono em condições climáticas de semiárido e temperado. Dessa forma, os objetivos deste estudo foram (i) investigar a gênese de um Vertissolo ácido, bem como os fatores e mecanismos da geração dessa acidez, (ii) compreender o papel dos interestratificados no desenvolvimento das feições vérticas em Vertissolo com predomínio de caulinita na fração argila, e (iii) investigar os fatores e mecanismos que promovem a gênese de Vertissolos Ebânicos sob diferentes condições climáticas no Brasil. Amostras de seis perfis de Vertissolos foram utilizadas, sendo quatro Ebânicos e dois Háplicos, ambos localizados entre as regiões nordeste, sudeste e sul do Brasil. Análises morfológica, físicas, químicas, mineralógicas e isotópicas foram realizadas. Na modelagem dos difratogramas foi utilizado o programa Newmod. Para identificação dos grupos funcionais orgânicos do solo realizou-se a ressonância magnética nuclear da fração ácido húmico, e a subtração espectral. Todos os Vertissolos apresentaram textura de argilosa a muito argilosa, consistência seca variando de dura a extremante dura e consistência molhada entre muito plástica e muito pegajosa. Os valores de pH variaram entre ácido e alcalino. Foram eutróficos, com predomínio de cálcio no complexo de troca na maioria dos perfis. O teor de carbono reduziu em profundidade, não mascarou o potencial de contração e expansão, e promoveu melhorias na agregação, principalmente nos horizontes superficiais. Houve autigênese de minerais, os minerais primários predominaram nas frações areia e silte, e na fração argila espécies de esmectitas dioctaedrais. Independente da espécie esmectítica e do tipo de vegetação (plantas C3 e/ou C4) houve maior diversidade de grupos funcionais nos horizontes superficiais. O mecanismo de estabilização do carbono nos Vertissolos Ebânicos ocorreu por meio da interação entre as fases inorgânicas e orgânicas, mediada por pontes de cátions polivalentes não metálicos e metálicos, e também por interação eletrostática entre os constituintes inorgânicos e orgânicos. A manifestação das feições morfológicas e vérticas no Vertissolo com predomínio de caulinita na fração argila foi gerada pelos interestratificados caulinita-montmorilonita resultantes da perda da lâmina tetraedral das esmectitas via transformações no estado sólido. A acidez no Vertissolo ácido foi gerada pela hidrólise e dissolução das fases minerais mediados por um clima passado mais úmido e continuado pelo clima atual úmido, sendo os teores de alumínio trocável naturais. Nesse contexto, esse estudo contribui com avanços na gênese, mineralogia e mecanismos de estabilização do carbono no solo, os quais são temáticas relevantes desse milênio e contribui a outras áreas cientificas. / Vertisols have high potential for agricultural production and for carbon stocking. However, several aspects about its genesis, fundamental to soil quality and sustainability, remain misunderstood. The various gaps on its particular characteristics are related to the unusual exchangeable aluminum content; the manifestation of morphological and vertic features in an inorganic matrix dominated by kaolinitic phases; and the preservation and stocking of carbon in semi-arid and temperate climatic conditions. Thus, the aims in this study were to (i) investigate the genesis of an acidic Vertisol, as well as the factors and mechanisms of the acidity generation, (ii) understand the role of the interstratified clay minerals in the development of vertic features in a kaolinitic Vertisol, and iii) investigate the factors and mechanisms that promote the genesis of Pellic Vertisols under different climatic conditions in Brazil. Samples of six profiles of Vertisols were used, being four Pellic and two Haplic, both located between the northeast and southern regions of Brazil. Morphological, physical, chemical, mineralogical and isotopic analyzes were performed. In the modeling of the diffractograms, the Newmod program was used. For the identification of the organic functional groups of the soil, the nuclear magnetic resonance of the humic acid fraction and the spectral subtraction were performed. All the Vertisols presented a texture of clayey to very clayey, dry consistency ranging from hard to extremely hard and wet consistency between very plastic and very sticky. The pH values varied between acid and alkaline. They exhibit high base saturation, with the predominance of calcium in the exchangeable complex in most of the profiles. The carbon content reduced in depth; did not overlap the shrinking-swelling potential; and promoted improvements in aggregation, especially in the upper horizons. There was autigenesis of minerals, primary minerals predominated in the sand and silt fractions, and in the clay fraction species of dioctahedral smectites. Regardless of the smectic species and the type of vegetation (C3 and/or C4 plants), there was a greater diversity of functional groups in the superficial horizons. The mechanism of carbon stabilization in the Pellic Vertisols occurred through the interaction between inorganic and organic phases, mediated by bridges of non-metallic and metallic polyvalent cations, and by electrostatic interaction between inorganic and organic constituents. The manifestation of the morphological and vertic features in the kaolinitic Vertisol was generated by the interstratified kaolinite-montmorillonite resulting from the loss of the tetrahedral sheet of smectites by solid-state transformations. The acidity in the acid Vertisols was generated by the hydrolysis and dissolution of the mineral phases mediated by a humid past climate and continued by the current humid climate, being the exchangeable aluminum contents natural. In this context, this study contributes to advances in the genesis, mineralogy, and mechanisms of soil carbon stabilization, which are relevant themes of this millennium and contribute to other scientific areas.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-07-21T19:09:46Z No. of bitstreams: 1 CiceroAgostinho.pdf: 718364 bytes, checksum: 5b373c12916005349c74311789694b95 (MD5) / Made available in DSpace on 2017-07-21T19:09:46Z (GMT). No. of bitstreams: 1 CiceroAgostinho.pdf: 718364 bytes, checksum: 5b373c12916005349c74311789694b95 (MD5) Previous issue date: 2011-03-31 / The aim of this study was to evaluate the effect of two different concentrations (4 mg and 12 mg) of dexamethasone to control pain, swelling and trismus after third molar surgery inclusos. This clinical study was conducted with 16 adult patients of both sex, displaying mandibular third molar in the same position bilaterally, with an indication for surgical removal. Patients were treated with 4 mg or 12 mg of dexamethasone 1 hour before surgery on the first or second surgery. The choice of which side was operated first and which dose of dexamethasone would be taken first was performed randomly and double blind. The trismus was assessed by measuring the distance interincisal. Pain was assessed by the amount of tablets (paracetamol 750mg) taken after the surgery and the visual analogue pain scale (VAS). These data were obtained before surgery, 24 and 48 hours after surgery. Based on statistical analysis (Student's t test, Wilcoxon and Friedman), the results showed no differences in variables (swelling, pain and trismus) between the two doses of dexamethasone (4mg and 12mg). / O objetivo deste trabalho foi avaliar o efeito de duas concentrações diferentes (4mg e 12mg) de dexametasona no controle da dor, edema e trismo após a cirurgia de terceiros molares inferiores inclusos. Este estudo clínico foi realizado com 27 pacientes adultos, de ambos os sexos, que apresentavam terceiros molares inferiores inclusos na mesma posição bilateralmente, com indicação para remoção cirúrgica. Os pacientes foram medicados com 4mg ou 12mg de dexametasona uma hora antes do procedimento cirúrgico na primeira ou na segunda cirurgia. A escolha de qual lado foi operado primeiro e qual dose de dexametasona seria empregada inicialmente era realizada de forma randomizada e duplo-cega. O trismo foi avaliado pela medida da distância interincisal. A dor foi avaliada mediante a contagem da quantidade de comprimidos (paracetamol 750mg) ingerida após a cirurgia e da Escala Visual Analógica da dor (VAS). Esses dados foram obtidos antes da cirurgia, 24 horas e 48 horas depois do procedimento cirúrgico. Com base na análise estatística (teste t-student, Wilcoxon e Friedman), os resultados não mostraram diferença nas variáveis (edema, dor e trismo) entre as duas doses de dexametasona.

Orientador: Fauze Ahmad Aouada / Resumo: O objetivo do trabalho foi realizar a síntese dos bionanocompósitos constituídos de carboximetilcelulose (CMC), poliacrilamida (PAAm) e diferentes concentrações de nanoargila laponita RDS (0 % referência, 1 %, 2%, 4% e 5 %), com possibilidades de aplicação em sistemas de remoção/liberação controlada de pesticida paraquat. Foi possível confirmar a formação dos bionanocompósitos constituídos de CMC/PAAm/nanoargila utilizando as técnicas de espectroscopia de absorção no infravermelho (FTIR) e microscopia eletrônica de varredura (MEV). A disposição das plaquetas de nanoargila na matriz polimérica foi avaliada pela técnica de difração de raios-X (DRX), em que resultou na possibilidade das plaquetas estarem intercaladas, além de possivelmente estarem esfoliadas. O comportamento térmico dos hidrogéis foi avaliado pelas análises termogravimétrica (TG) e calorimetria exploratória diferencial (DSC). Os bionanocompósitos se mostraram estáveis termicamente até aproximadamente 200 °C. Foi realizada a caracterização dos bionanocompósitos, determinando o grau de intumescimento (Q) em água destilada, diferentes soluções salinas (NaCl, CaCl2 e AlCl3) e soluções com diversos pH (1, 2, 4, 5, 6, 8 e 10). Observou-se uma redução nos valores de Q em baixas concentrações de nanoargila para água destilada (Q0% = 33,7 g/g para Q2% = 23,8 g/g), seguida de um acréscimo com o aumento do teor de nanoargila (Q4% = 28,4 g/g e Q5% = 33,01 g/g) em relação aos hidrogéis com 1 e 2 % de nanoargila. Foi também c... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The objective of this research was to study the bionanocomposites synthesis constituted of carboxymethylcellulose (CMC), polyacrylamide (PAAm) and different contents of nanoclay laponite RDS (0% as reference, 1%, 2%, 4% and 5%), with possibility application in systems of removal/release paraquat pesticide. The confirmation of bionanocomposites formation constituted of CMC/PAAm/nanoclay was verified by the Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (MEV) techniques. It was possible to evaluate the platelets configuration of nanoclay in the polymeric matrix by X-ray diffraction (DRX), which resulted in the possibility of platelets be intercalated, and possibly exfoliated. The thermal stability of the hydrogels was investigated by analysis thermogravimetric (TG) and differential exploratory calorimetry (DSC). The results confirmed that the bionanocomposites are thermal stability until amount 200 °C. It was also realized the characterization of bionanocomposites, obtaining the swelling degree (Q) in distilled water, different saline solutions (NaCl, CaCl2 and AlCl3) and solutions with various values of pH (1, 2, 4, 5, 6, 8 and 10). It was observed a reduction in values of Q in low concentration of nanoclay to distilled water (Q0% = 33.7 g/g to Q2% = 23.8 g/g), followed of increase with additions of nanoclay content (Q4 = 28.4 g/g and Q5% = 33.0 g/g). It was also verified strong influence (reduction) in the values of Q in solutions saline which... (Complete abstract click electronic access below) / Mestre

Jusqu'à aujourd'hui, le traitement des maladies oculaires postérieures, telles que la dégénérescence maculaire liée à l'âge, la rétinopathie diabétique et l'uvéite, reste difficile. L'œil avec ses différentes barrières oculaires est bien protégé des agressions extérieures. Ces barrières réduisent également la biodisponibilité des médicaments pour le vitré. Après une administration topique, seule une quantité limitée (0,001 - 0,0004 %) permet d'atteindre le vitreux. Ceci est causé par exemple par une dilution des larmes et une faible perméabilité cornéenne du médicament. Après une administration systémique ou orale, les barrières hémato-oculaires empêchent le médicament d'entrer et seulement environ 2 % du médicament administré se trouve dans le vitré. Afin d'atteindre des concentrations thérapeutiques, une dose élevée doit être administrée, ce qui augmente le risque d'effets secondaires. La façon la plus efficace de traiter les maladies postérieures restent l'injection intravitréenne. Cependant, de petites molécules lipophiles comme la dexaméthasone peuvent facilement se diffuser à travers la rétine et les barrières oculaires et ont donc une demi-vie limitée de quelques heures seulement. Étant donné que de nombreuses maladies postérieures sont chroniques, une injection intravitréenne fréquente serait nécessaire. Chaque injection comporte des risques de décollement de la rétine, d'hémorragie et d'autres effets secondaires. Les implants biodégradables pour administration intravitréenne peuvent prolonger la libération du médicament et en diminuer les effets secondaires. PLGA est un polymère largement utilisé qui est biocompatible et biodégradable. Il peut également soutenir la libération du médicament de quelques jours à plusieurs mois. Dans cette étude, les implants de formation in situ (ISFI) et les implants préformés préparés par extrusion à chaude ont été étudié en profondeur. L'objectif de ce travail était (i) d'étudier l'impact du volume du rejet (ii) évaluer le comportement de libération, de gonflement et de dégradation des implants préformés préparés avec différentes charges de médicament et différents types de polymères, (iii) visualiser la libération de médicament et l'absorption d'eau des implants préformés et de l'ISFI en utilisant des médicaments modèles colorés et (iv) étudier l'effet des quantités variables des différents additifs sur les caractéristiques essentielles de l'ISFI. Ces informations peuvent aider à fabriquer des implants avec différents profils de libération. Nos études montrent que l'ISFI est assez robuste en ce qui concerne les différents volumes de l'humeur vitreuse que l'on peut rencontrer in vivo. Cependant, le poids moléculaire et la concentration du polymère ont une forte influence sur la morphologie et le gonflement de l'implant. Par conséquent, la dégradation et la libération du médicament sont affectées. Pour les implants préformés, le gonflement "orchestre" la libération du médicament. Au début, seule une quantité limitée d'eau peut se diffuser dans les implants. Ainsi, seules des quantités insignifiantes du médicament sont dissoutes et peuvent être libérées. Lorsque le PLGA commence à se dégrader, le polymère devient plus hydrophile et de plus grandes quantités d'eau peuvent pénétrer. Ce gonflement du polymère facilite la dissolution et la diffusion du médicament et déclenche la libération du médicament. Les études utilisant des médicaments modèles colorés corroborent le rôle de la pénétration de l'eau et de la dissolution du médicament pour les implants préformés. En ce qui concerne l'ISFI, il a visualisé l'importance de la concentration du polymère sur la structure interne de l'implant qui en résulte et par conséquent l'absorption d'eau et la libération du médicament. Le comportement de gonflement et la morphologie de l'ISFI pourraient également être modifiés de manière significative en utilisant différents additifs. L'effet global sur la libération du médicament a été limité. / Until today, the treatment of posterior eye diseases, such as age-related macular degeneration, diabetic retinopathy and uveitis, remains challenging. The eye with its different ocular barriers is well protected from external factors. Those barriers also reduce the bioavailability of drugs to the vitreous. After a topical administration, only a limited amount (0.001 – 0.0004 %) reaches the vitreous. This is caused by for example reflexive blinking, tear dilution and a low corneal permeability of the drug. After a systemic or oral administration, the blood-aqueous and the blood-retinal barrier hinder the drug from entering and only around 2 % of the administered drug is found in the vitreous. In order to reach therapeutic concentrations, a high dose has to be given which in turn increases the risk for systemic side effects. The most efficient way to treat posterior diseases remains the intravitreal injection. However, small lipophilic molecules like dexamethasone can easily diffuse through the retina and the blood-ocular barriers and, thus, have a limited half-life of just a few hours. Since many of the posterior diseases are chronic, a frequent intravitreal injection would be necessary. Every intravitreal injection bears the risks for retinal detachment, hemorrhage, and other side effects. Biodegradable implants for intravi-treal administration can prolong the drug release and in turn decrease the side effects. Poly(lac-tic-co-glycolic acid) (PLGA) is a widely used polymer that is biocompatible and biodegrada-ble. It can also sustain the drug release from a few days up to several months. In this study, in-situ forming implants (ISFI) and pre-formed implants prepared via hot melt extrusion were studied in depth. The aim of this work was (i) to study the impact of the volume of the release medium, polymer type and concentration as well as drug content of different ISFI, (ii) to eval-uate the drug release, swelling and degradation behavior of pre-formed implants prepared with different drug loadings and polymer types, (iii) to visualize the drug release and water uptake of ISFI and pre-formed implants using colored model drugs and (iv) to investigate the effect of varying amounts of different additives on key features of ISFI. This knowledge can help to manufacture implants with different release profiles. Our studies show that ISFI are rather ro-bust regarding different volumes of the vitreous humor that could be encountered in vivo. How-ever, the polymer molecular weight and polymer concentration have a strong influence on the morphology and swelling behavior of the implants. Consequently, the degradation and drug release are affected. For pre-formed implants the swelling “orchestrates” the drug release. In the beginning only limited amounts of water can diffuse into the implants. Thus, only insignif-icant amounts of the drug are dissolved and can be released. When the PLGA starts to degrade, the polymer becomes more hydrophilic and bigger amounts of water can penetrate. This poly-mer swelling facilitates drug dissolution and diffusion and initiates the drug release. The studies using colored model drugs corroborate the role of water penetration and drug dissolution for pre-formed implants. Concerning ISFI, it visualized the importance of the polymer concentra-tion on the resulting inner implant structure and consequently the water uptake and drug release. The swelling behavior and morphology of ISFI could also be significantly altered using differ-ent additives. The overall effect on the drug release was limited.

<p><font face="Tahoma"> <p align="left">The purpose of this study is to evaluate the need for prophylactic antibiotic treatment in third molar surgery and to establish specific guidelines for antibiotic prophylaxis in the department of Maxillo-Facial and Oral Surgery (MFOS) at Tygerberg Academic, Groote Schuur and Mitchells Plain Hospitals.</p> </font></p>

Processing of nanostructured WC-Co and W-Co powders,modelling of Fe-Mn-Si alloy, swelling of Fe-Cu alloy, andmechanical properties and sintering of Fe-Mn-Si steels havebeen studied in the present thesis. W-Co precursors made by chemical synthesis were used toproduce nanostructured WCCo and W-Co powders by calcination,reduction and carburization. The phase constituents in thecalcined powders depend on temperature and atmospheres. Cobaltcan accelerate the reduction rate of the W-Co precursors as acatalyst, and cobalt influences the formation of intermediatephases during the reduction of the precursors. The ratio of carbon monoxide to carbon dioxide controlscarburization process, gives different intermediate phases andcarburization rates. There exist several intermediate phases: W6Co6C, W3Co3C, W2C due to varying carbon monoxide content in thecarburization gases. Nanostructured WC-Co powders with aparticle size of 20-50 nm have been obtained. The effect of silicon content on the particle sizedistribution of milled Fe-Mn-Si master alloy powders is muchmore significant than that of manganese content. A finer finalparticle size can be obtained in the alloy powders with highersilicon compositions. Long time milling results in theagglomeration of small particles. The grinding process can bedescribed using classic batch grinding equation based on thepopulation balance model. A swelling model for Fe-Cu alloyssintered at the temperatures above the melting point of copperhas been established based on the penetration mechanism. In themodel, the particle coordination number and heating rate wereused to express the porosity and the thickness of the diffusionlayers between iron and copper particles respectively. The effects of sintering temperature and time on theproperties of sintered steels have been studied. Fe-Mn-Simaster alloys made by cast-milling, atomizing, and acombination of atomization and milling have been covered. Themilled, and atomizationmilled alloy steels showed goodmechanical properties with small dimensional change. Transientliquid phase of the Fe-Mn-Si alloys accelerates densification,and offer fast diffusion of alloying elements. The addition ofa small amount of Fe-Mn-Si master alloy to Astaloy 85Mo powdercan lead to high strength with zero dimensional change. <b>Key words:</b>Processing; Modelling; Nanostructured powder;WC-Co; W-Co; Calcination; Reduction; Carburization; Particlesize; Sintered steel; Fe-Cu alloy; Swelling; Fe-Mn-Si masteralloy; Mechanical properties; Sintering parameters.