Os ingredientes de origem vegetal que compõem as dietas de frangos de corte possuem em suas composições uma fração indigestível, os polissacarídeos não amiláceos (PNAs). Estas macromoléculas poliméricas de açúcares simples (monossacarídeos) são resistentes à hidrólise no trato gastrointestinal dos animais monogástricos, caracterizando-se como fatores antinutricionais. O objetivo deste trabalho foi avaliar o desempenho zootécnico e rendimento de carcaça de frangos de corte criados de 1 a 42 dias de idade, alimentados com dietas à base de milho ou trigo, com ou sem inclusão de xilanase e valorização da matriz energética. No experimento foram utilizados 1.152 frangos de corte machos, da linhagem Cobb 500. Os animais foram distribuídos em blocos casualizados, com os tratamentos em esquema fatorial 2 x 2 x 2 (duas rações : uma com milho e outra com trigo, 2 níveis de xilanase: 0 e 100 g/ton e 2 níveis de energia: de acordo com as recomendações para cada fase e reduzido em 60 kcal/kg em relação às recomendações), totalizando oito tratamentos com 12 repetições de 12 aves por unidade experimental. As dietas experimentais, com milho ou trigo, foram formuladas para atender as exigências nutricionais das aves segundo Rostagno et al. (2011). Os dados de rendimento de carcaça e desempenho de crescimento foram analisados pelo software SAS 9.3, com análise de variância, e as médias comparadas pelo teste de Tukey (P 0,05). Os resultados indicaram melhorias nos parâmetros de desempenho com a adição de enzima em dietas com base de trigo, e melhor conversão alimentar aos 42 dias de idade com o uso da enzima nas dietas com nível de energia padrão / Ingredients of vegetal sources, which compose the diets of broilers, have in its composition an indigestible fraction known as the non-starch polysaccharides (NSP). These polimeric macromolecules of simple sugars (monosaccharides) are resistant to hydrolisis in the gastrointestinal tract of monogastric animals, and are characterized as anti-nutritional factors. The objective of this work was to evaluate the performance and the carcass yield of broilers raised from 1 to 42 days of age, fed with diets based in corn or wheat, with or without inclusion of xylanase and valorization of the energetic matrix. In the experiment it were used 1.152 male broilers, from the Cobb 500 lineage. The animals were distributed in randomized blocks, with treatments in a factorial 2 x 2 x 2 (two feeds: one with corn and the other with wheat, 2 levels of xylanase: 0 and 100 g/ton, and 2 levels of energy: according to recommendations for each phase, and reduced in 60 kcal/kg in relation to the recommendations), completing eight treatments with twelve replications, and twelve birds in each experimental unit. The experimental diets, with corn or wheat, were formulated to supply the nutritional requirements of the birds according to Rostagno et al. (2011). Carcass yield and growth performance data were analyzed by SAS 9.3 software, with analysis of variance, and the means compared by the Tukey test (P 0.05). Results presented improvements in parameters of performance with inclusion of the enzyme in diets based in wheat, and best feed conversion rate for the period of 1 to 42 days of age with the use of enzyme on standard level energy of diet

University of Macau / Institute of Chinese Medical Sciences

Marshmallow é um dos vários tipos de recheio que podem ser produzidos utilizando-se açúcar, açúcar invertido e xarope de glicose adicionado de gomas ou proteínas, como gelatina e albumina, emulsionados em ar. Foram avaliados quatro produtos de mercado quanto à atividade de água, teor de proteína e sua reologia através de ensaios rotacionais, oscilatórios e tixotropia. Os ensaios reológicos foram realizados em conjunto com imagens de microscopia, podendo assim avaliar além do comportamento da espuma também sua estrutura. Produtos com maior teor de proteína e contendo gomas em sua formulação apresentaram valores de atividade de água menores. O uso de proteínas e gomas confere aos produtos estudados características de géis como observado através da reologia. O valor de yield stress determinado pelos ensaios de amplitude mostrou-se coerente com a vida de prateleira dos produtos, sendo que para valores maiores, maior a vida de prateleira, em relação à estabilidade do produto. Os ensaios oscilatórios sob alta frequência foram comparados com os ensaios rotacionais e demonstraram ser de interesse não só para avaliar o comportamento do produto, como também avaliar a recuperação da estrutura da espuma em função do tempo e tensão aplicados. Através da análise reológica da formulação e da interface, bem como análises da tensão interfacial e microscopia, foram avaliadas as diferentes gomas, em pH 4 e 7,5, determinando assim que a goma κ-carragena em pH 4 foi a que apresentou melhores resultados para a estabilidade da espuma. A formulação escolhida com base nos ensaios reológicos de interface e tensão interfacial foi avaliada quanto a sua estabilidade por 60 dias através de ensaios reológicos oscilatórios e microscopia, apresentando estabilidade pelo período estudado. Foi avaliado ainda o tempo de processo necessário para obtenção de um produto estável com melhor capacidade de aeração, levando a um tempo de processo de 15 minutos. / Marshmallow is a kind of aerated filling made from sugar, inverted sugar, glucose syrup, added by polysaccharide and proteins, like gelatin and albumin. Four market products were evaluated regarding water activity, protein content and through dynamic and rotational, besides thixotropy evaluation. Rheological tests were done together with image rheology, evaluating not only product behavior but also the product structure. High protein content product formulated with polysaccharides presented lower water activity values, the use of protein and polysaccharides in the formulations produce gel like products, as can be seeing through rheology. Amplitude sweep determine the yield stress, and it was coherent with the shelf life indicated by each product, higher yield stress raises the product shelf life. Dynamic oscillatory tests under high frequency were compared to rotational tests, and showed to be of interest to evaluate foam behavior and structure recovery as a function of time and stress applied. Interfacial rheology were performed to evaluate different polysaccharides under pH 4 and 7,5, determining that κ- carragena at pH presented better results for foam stability. The chosen formulation after rheological tests of interface and surface tension was evaluated for 60 days through dynamic oscillatory tests and microscopy, showing stability for all studied period. Processing time of aeration was also evaluated, and a time of 15 minutes was the processing time with better stability.

Photobacterium profundum SS9 is a γ-proteobacterium which grows optimally at 15°C and 28 MPa (a psychrophilic piezophile) and can grow over a range of temperatures (2-20oC) and pressures (0.1-90 MPa). Previous research had demonstrated that P. profundum SS9 adapts its membrane proteins and phospholipids in response to growth conditions. In this study, methodology was developed for growing P. profundum SS9 under cold temperatures and high pressures in both liquid and solid cultures. The effect of changing growth conditions on cell envelope polysaccharides was then investigated. The lipopolysaccharide (LPS) profile of a rifampicin resistant P. profundum SS9 derivative, SS9R, was shown to change at 0.1 MPa with respect to temperature and at 15°C with respect to pressure. Compositional analysis showed that the LPS was almost entirely composed of glucose. This provides evidence that, under these conditions, the major polysaccharide produced by P. profundum SS9 is a glucan. Two putative polysaccharide mutants, FL26 & FL9, were previously isolated from a screen for cold-sensitive mutants of P. profundum SS9R. Both mutants displayed an increased sensitivity to cold temperatures on solid medium and were unaffected in their growth at high pressure. FL26 was found to exhibit an LPS alteration similar to previously published O-antigen ligase mutants, providing evidence that this mutant is likely to lack O-antigen ligase. Interestingly, FL26 was also shown to have a reduced ability to form biofilms and had increased swimming motility. This suggests that there are a number of changes which occur in FL26 in the absence of O-antigen. FL9 was found to have an altered LPS and capsular polysaccharide (CPS), similar to an E. coli wzc mutant. In E. coli, Wzc is involved in the polymerisation and transport of CPS, disruption of which can also lead to LPS alterations. The LPS and CPS alterations may lead to the cold-sensitivity phenotype, either individually or in combination. In conclusion, alterations in the cell envelope polysaccharides were shown to affect cold temperature sensitivity on solid agar. Cold-sensitivity is most likely directly related to the LPS alterations and stability of the membrane under cold temperatures. Exopolysaccharides (EPS) have previously been shown to affect desiccation and freezethaw resistance, making it is possible that the CPS plays a similar role in this case.

In their natural environments microorganisms exist predominantly in aggregates and biofilms. The ability of bacteria to form aggregates is associated with the biosynthesis of polymers such as polysaccharides. In this study the physical mechanisms underlying bacterial aggregation by extracellular polysaccharides are investigated by utilising the bacterium Sinorhizobium meliloti. S. meliloti biosynthesises an extracellular polysaccharide called succinoglycan, which is well characterised in terms of its structure and biosynthesis. A range of previously constructed succinoglycan biosynthesis mutants were screened for altered aggregation. An S. meliloti exoS mutant (a gain of function mutation that results in a constitutively active two component regulator called ExoS) overproduces succinoglycan and has enhanced aggregation compared to the parent strain, Rm1021. The aggregates settle to the bottom of the culture vessel resulting in loss of turbidity of the cultures and phase separation. Microscopic observation showed that succinoglycan did not appear to be attached to the aggregates, which formed ordered structures of laterally aligned cells. By addition of purified succinoglycan it was found that the critical concentration of polymer required to induce aggregation and phase separation of the cultures decreased with increasing cell concentration. These observations suggest that aggregation of S. meliloti cultures in the presence of succinoglycan is driven by macromolecular crowding, otherwise known as depletion attraction. Depletion attraction can drive the ordered arrangement and aggregation of colloidal particles in the presence of polymers. Aggregation of the particles increases the volume available to the polymers, maximising their entropy and the entropy of the system. Addition of succinoglycan to stationary phase Escherichia coli cultures and polystyrene colloids also resulted in aggregation consistent with depletion attraction. Furthermore alternative polymers such as the bacterial extracellular polysaccharide xanthan produced by Xanthomonas campestris can result in aggregation of bacteria by depletion attraction. Depletion attraction may therefore be a ubiquitous force driving aggregation of crowded dispersions of bacteria and polymers. The second part of the thesis focuses on how depletion driven aggregation can lead to surface-associated biofilm formation. Imaging of the sediment formed by the exoS mutant showed that the structure formed at the base of the culture vessel leads to development of an ordered structure composed of interlinked aggregates. The role of succinoglycan in surface attachment is complex and varies with culture conditions. Depletion attraction may facilitate interaction with a surface but alternative factors may then play a role in anchoring the cells to the surface. Under certain conditions the cells may produce factors which allow binding of the cells to a surface independently of succinoglycan. This study has demonstrated for the first time that an extracellular polysaccharide produced by bacteria can result in aggregation via depletion attraction which may be an under explored mechanism by which aggregation of bacteria can occur.

Burkholderia pseudomallei is the aetiological agent of melioidosis and a potential bioterror threat. Infections are difficult to treat due to extensive antibiotic resistance and there is no prophylactic vaccine available. Studies have shown that the capsular polysaccharide (CPS) of B. pseudomallei is a virulence factor, immunogen and candidate antigen for a glycoconjugate vaccine. However, polysaccharides are complex to synthesise. One approach is to genetically engineer Escherichia coli to express the CPS; however, previous attempts at cloning the CPS coding locus from B. pseudomallei into E. coli were unsuccessful. This project proposes to clone only the essential genes from B. pseudomallei and to use native E. coli mechanisms to complete CPS synthesis. This would contribute to development of a new platform for the expression of any bespoke polysaccharide in E. coli. Six biosynthetic genes for the nucleotide sugar precursor were successfully expressed in E. coli. The structure of the precursor was verified by mass spectrometry. Precursor synthesis was also performed in an in vitro microfluidics system. This minimised the quantity of substrates and enzymes required, in preparation for the characterisation of glycosyltransferases required for CPS assembly. A novel assay for characterising glycosyltransferase activity was also developed, as current available options are prohibitively expensive and require significant quantities of glycosyltransferase which are difficult to purify. Finally, plasmids for the expression of additional glycosyltransferases to link the nascent B. pseudomallei CPS to truncated polysaccharides in E. coli were constructed. The aim of this project was to contribute to the development of a platform for the expression of bespoke polysaccharides in E. coli. The CPS of B. pseudomallei was chosen as the model polysaccharide as it has a simple structure and its manufacture is desirable for use in a vaccine against melioidosis.

O Streptococcus pneumoniae, também conhecido como pneumococo, é um importante agente etiológico causador de pneumonia, bacteremia, meningite e otite aguda do ouvido médio, acometendo especialmente crianças e idosos. A cápsula polissacarídica (PS) é o fator de virulência mais importante e localiza-se na superfície do microrganismo e tem ação anti-fagocítica in vivo. O pneumococo expressa pelo menos 91 cápsulas diferentes, que são química e sorologicamente distintas. Usualmente, a cápsula é o antígeno das vacinas anti-pneumocócicas, tanto como polissacarídeo livre ou conjugado a proteínas. O sorotipo 6B acomete principalmente crianças e é o segundo mais prevalente no Brasil, e a otimização das condições de cultivo buscando maior produtividade em PS é o alvo desta tese. Simultaneamente, também foi investigada a influência do inóculo e da glicose residual no instante do pulso ou do início da alimentação em cultivos descontínuos alimentados. Nos cultivos descontínuos alimentados foi observado que quanto menor a densidade óptica da cultura do inóculo, maior a concentração de PS obtida. A concentração da glicose residual no momento do pulso provavelmente influenciou a produção de PS: a produção foi maior quando o pulso foi dado ainda em altas concentrações de substrato. Por isso, obteve-se uma produção de PS ~390 mg/L em cultivo descontínuo alimentado com pulso, quando DO 600 nm da cultura do inóculo ~1,6 e o pulso de glicose e acetato de amônio ~15 g/L. Observou-se também que, mesmo com DO do inóculo ~1,65, a produção de PS foi somente 248 mg/L, devido à aplicação do pulso quando a concentração de glicose residual era ~4,5 g/L. A menor produção de PS foi obtida quando a DO da cultura do inóculo foi ~2,6 e a concentração de glicose residual ~3,4 g/L, gerando somente 194 mg/L de PS. Assim, cultivos descontínuos alimentados com pulso renderam melhores resultados que os cultivos descontínuos alimentados. A alimentação constante rendeu maior quantidade de PS quando comparada à alimentação exponencial. E tanto os ensaios descontínuos com ou sem pulso e os descontínuos alimentados foram melhores do que os cultivos contínuos, principalmente se considerarmos a facilidade de operação. O efeito da concentração residual da glicose no instante da alimentação na produção de PS é provavelmente influenciado pela presença de outros componentes do meio, devido aos requerimentos nutricionais do pneumococo. O estado fisiológico do inóculo determinou uma importante correlação entre a produção de PS nos cultivos descontínuos alimentados do sorotipo 6B: cultura do inóculo no meio da fase exponencial rendeu maior produção de PS. Esta correlação poderia ser conseqüência do perfil de crescimento do microrganismo in vitro e da ação de enzimas líticas após a fase exponencial. Foi observado, portanto, um efeito sinérgico entre a DO da cultura do inóculo, a concentração de glicose residual no momento de alimentação e produção de PS nos cultivos descontínuos alimentados. / Streptococcus pneumoniae is a major pathogen commonly responsible for pneumonia, bacteraemia, meningitis and otitis media, especially among young children and older adults. The most prominent pneumococcal virulence factor is the capsular polysaccharide (PS), which coats the surface of the bacterium and acts as an antiphagocytic factor in vivo. S. pneumoniae express at least 91 distinct capsules which are chemically and serologically distinct. The capsule is currently used as antigen in pneumococcal vaccines, either as free polysaccharide or conjugated to proteins. Pneumococcal serotype 6B is the second most prevalent in Brazil and the optimization of cultivation conditions is part of this study. Simultaneously we investigated the influence of the growth phase of the inoculum and the residual glucose concentration at the instant of the pulse or the start of feeding on PS production in batch and fed-batch cultivation. Streptococcus pneumoniae serotype 6B strain ST 433/03 was used. Bench scale experiments were carried out using a variant of the Hoeprich medium, containing glucose, acid-hydrolyzed casein, dialyzed yeast extract, L-glutamine and asparagine as nitrogen sources, choline as a growth factor and salts. The experiments were conducted in bioreactors monitored by the LabView 7.1program. It was observed in fed-batch cultivation, that the lower was the OD of the starter culture, the higher was the PS concentration obtained. The residual glucose concentration at the moment of the pulse also influenced the PS production: the PS production was higher when the pulse was given at higher residual glucose concentration. Hence, in fed-batch culture the highest PS production (387 mg/L) was obtained using an OD=1.6 of the starter culture and giving the pulse when the residual glucose was ~15 g/L. Using a similar inoculum (OD=1.65), the PS concentration reached 248 mg/L after giving the pulse when the residual glucose was 4.5 g/L. The lowest PS production was obtained when a culture with an OD=2.6 was inoculated into the reactor and the pulse was given when the residual glucose was 3.4 g/L (PS=194 mg/L). The effect of the residual glucose concentration at the instant of the start of feeding on PS production was probably influenced by the presence of other components in the concentrated feeding medium, which could better fit the nutritional requirements of the microorganism. The physiological state of the inoculum showed an important correlation to the PS production in batch and fed-batch cultivation of S. pneumoniae serotype 6B: mid-log phase inocula yielded high PS production. This correlation is consequence of the in vitro growth profile, the action of lytic enzymes after the log phase. In fed-batch cultivation, it was also observed a synergic effect of the inoculum OD and the residual glucose concentration in the moment of the pulse on PS production.

The plasma membrane is one of the most thoroughly studied and at the same time most complex, diverse, and least understood cellular structures. Its function is determined by the molecular composition as well as the spatial arrangement of its components. Even after decades of extensive membrane research and the proposal of dozens of models and theories, the structural organization of plasma membranes remains largely unknown. Modern imaging tools such as super-resolution fluorescence microscopy are one of the most efficient techniques in life sciences and are widely used to study the spatial arrangement and quantitative behavior of biomolecules in fixed and living cells. In this work, direct stochastic optical reconstruction microscopy (dSTORM) was used to investigate the structural distribution of mem-brane components with virtually molecular resolution. Key issues are different preparation and staining strategies for membrane imaging as well as localization-based quantitative analyses of membrane molecules. An essential precondition for the spatial and quantitative analysis of membrane components is the prevention of photoswitching artifacts in reconstructed localization microscopy images. Therefore, the impact of irradiation intensity, label density and photoswitching behavior on the distribution of plasma membrane and mitochondrial membrane proteins in dSTORM images was investigated. It is demonstrated that the combination of densely labeled plasma membranes and inappropriate photoswitching rates induces artificial membrane clusters. Moreover, inhomogeneous localization distributions induced by projections of three-dimensional membrane structures such as microvilli and vesicles are prone to generate artifacts in images of biological membranes. Alternative imaging techniques and ways to prevent artifacts in single-molecule localization microscopy are presented and extensively discussed. Another central topic addresses the spatial organization of glycosylated components covering the cell membrane. It is shown that a bioorthogonal chemical reporter system consisting of modified monosaccharide precursors and organic fluorophores can be used for specific labeling of membrane-associated glycoproteins and –lipids. The distribution of glycans was visualized by dSTORM showing a homogeneous molecule distribution on different mammalian cell lines without the presence of clusters. An absolute number of around five million glycans per cell was estimated and the results show that the combination of metabolic labeling, click chemistry, and single-molecule localization microscopy can be efficiently used to study cell surface glycoconjugates. In a third project, dSTORM was performed to investigate low-expressing receptors on cancer cells which can act as targets in personalized immunotherapy. Primary multiple myeloma cells derived from the bone marrow of several patients were analyzed for CD19 expression as potential target for chimeric antigen receptor (CAR)-modified T cells. Depending on the patient, 60–1,600 CD19 molecules per cell were quantified and functional in vitro tests demonstrate that the threshold for CD19 CAR T recognition is below 100 CD19 molecules per target cell. Results are compared with flow cytometry data, and the important roles of efficient labeling and appropriate control experiments are discussed. / Die Plasmamembran gehört zu den am meisten untersuchten, gleichzeitig aber auch zu den komplexesten, vielfältigsten und am wenigsten verstandenen biologischen Strukturen. Ihre Funktion wird nicht nur durch die molekulare Zusammensetzung bestimmt, sondern auch durch die räumliche Anordnung ihrer Bestandteile. Selbst nach Jahrzehnten intensiver Forschung und der Veröffentlichung dutzender Membranmodelle und Theorien bleibt die genaue strukturelle Organisation der Plasmamembran ein Rätsel. Moderne Bildgebungsverfahren wie etwa die hochauflösende Fluoreszenzmikroskopie gehören mittlerweile zu den effizientesten Techniken der Lebenswissenschaften und werden immer öfter verwendet, um die räumliche Anordnung als auch die Anzahl von Biomolekülen in fixierten und lebenden Zellen zu studieren. Im Rahmen dieser Arbeit wurde die hochauflösende Mikroskopie-Methode dSTORM (direct stochastic optical reconstruction microscopy) angewendet, um die räumliche Verteilung von Membranmolekülen mit annähernd molekularer Auflösung zu untersuchen. Schwerpunkte dieser Arbeit sind dabei verschiedene Präparations- und Färbemethoden für die mikroskopische Untersuchung von Zellmembranen sowie lokalisationsbasierte quantitative Analysemethoden von Membranmolekülen. Eine Voraussetzung für die räumliche als auch quantitative Analyse von Membranmolekülen ist die Vermeidung von Photoschalt-Artefakten in rekonstruierten Lokalisationsmikroskopie-Bildern. Um dies genauer zu demonstrieren, wurden die Auswirkungen von Anregungsintensität, Markierungsdichte und verändertem Photoschalten auf die räumliche Verteilung von Proteinen der Plasma- und Mitochondrienmembran in dSTORM-Bildern analysiert. Es wird gezeigt, dass eine dicht markierte Plasmamembran in Kombination mit ungeeigneten Photoschaltraten zu artifiziellen Clustern in der Membran führt. Es sind vor Allem oft die Projektionen dreidimensionaler Membranstrukturen wie etwa Mikrovilli und Vesikel dafür verantwortlich, dass lokale Unterschiede in der Lokalisationsdichte entstehen, wodurch unter Umständen Bildartefakte generiert werden können. Darüber hinaus werden alternative Mikroskopie-Methoden und Möglichkeiten, Artefakte in Einzelmolekül-Lokalisationsmikroskopie-Bildern zu verhindern, präsentiert und ausführlich diskutiert. Ein weiteres zentrales Thema dieser Arbeit ist die räumliche Anordnung von glykosylierten Membranmolekülen. Es wird demonstriert, wie ein bioorthogonales chemisches Reportersystem bestehend aus modifizierten Monosacchariden und organischen Fluorophoren für die spezifische Markierung von Membran-assoziierten Glykoproteinen und –lipiden eingesetzt werden kann. Mittels dSTORM wird gezeigt, dass die Verteilung von Glykanen in der Plasmamembran unterschiedlicher Zelllinien homogen und frei von Clustern ist. Des Weiteren zeigt eine quantitative Analyse, dass sich in etwa fünf Millionen Glykane auf einer einzigen Zelle befinden. Die Ergebnisse demonstrieren, dass die Kombination aus metabolisch markierten Zielmolekülen, Click-Chemie und Einzelmolekül-Lokalisationsmikroskopie effizient genutzt werden kann, um Glykokonjugate auf Zelloberflächen zu untersuchen. In einem dritten Projekt wurde dSTORM zur Untersuchung von Rezeptormolekülen auf Krebszellen verwendet. Die Expression dieser Oberflächenproteine ist so gering, dass sich nur wenige Moleküle auf einer Zelle befinden, die jedoch als Zielmoleküle in der personalisierten Immuntherapie dienen könnten. Dafür wurden primäre Tumorzellen aus dem Knochenmark von Patienten, die am Multiplen Myelom erkrankt sind, auf die Expression des CD19-Oberflächenproteins als potentielles Ziel für CAR-modifizierte T-Zellen (chimeric antigen receptor) untersucht. Es wird gezeigt, dass sich, abhängig vom untersuchten Patienten, auf einer Zelle 60 bis 1600 CD19-Moleküle befinden. Funktionale in-vitro-Experimente demonstrieren, dass weniger als 100 CD19 Moleküle ausreichen, um CD19-CAR-T-Zellen zu aktivieren. Diese Ergebnisse werden mit Durchflusszytometrie-Daten verglichen und die wichtige Rolle von Lebendzellfärbung und geeigneten Kontrollexperimenten wird diskutiert.

La cellulose, polymère naturel appartenant à la famille des polysaccharides, est non fusible. Pour la mettre en forme, il est donc nécessaire soit de la dériver, soit de la solubiliser. L'objectif de notre travail est de préciser les mécanismes qui conduisent à la dissolution de la cellulose native. Cinq mécanismes sont observés lors de cette étude, basée sur des fibres de cellulose native d'origine diverse (coton, bois, ramie, jute, lin, chanvre, sisal et abaca). Chaque échantillon est observé dans une large gamme de systèmes aqueux (NMMO - eau à différentes teneurs en eau ou hydroxyde de sodium - eau - additif) et des liquides ioniques. Des données recueillies sur des échantillons dépourvus de leurs parois externes suite à un traitement enzymatique, ainsi que des dérivés cellulosiques, viennent compléter cette étude. Nous avons identifié cinq mécanismes de gonflement et de dissolution de fibres de cellulose native : Mode 1: dissolution rapide par désintégration de la fibre en fragments Mode 2: gonflement par ballonnement, dissolution de toute la fibre Mode 3: gonflement par ballonnement, dissolution partielle de la fibre Mode 4: gonflement homogène, non dissolution de la fibre Mode 5: pas de gonflement ni de dissolution (cas d'un système non solvant) Malgré les différences morphologiques entre toutes les fibres de cellulose testées et les dérivés cellulosiques, les mécanismes de gonflement et de dissolution restent similaires. Trois zones le long des fibres de cellulose sont définis lors d'un mécanisme impliquant un gonflement par ballonnement: les ballons, la membrane des ballons, les sections non gonflées (zones situées entre les ballons). Chacune de ces zones présentent un mécanisme de dissolution particulier. Le mode 2 est donc détaillé en 4 étapes. Les ballons sont des entités constituées d'une membrane (paroi primaire, plus une partie de la paroi secondaire), caractérisée par une structure hélicoïdale. La membrane est la partie de la fibre la plus difficile à dissoudre. Il est important de noter que la cellulose à l'intérieur des ballons est dissoute. Les mécanismes de gonflement et de dissolution ne sont pas liés à la nature chimique des agents solvants. La qualité du solvant influe évidemment sur le mode de dissolution induit, mais le facteur clé des mécanismes est la structure morphologique de la fibre.

Chitosan films are an excellent media for binding metal ions due to the electrostatic nature of the chitosan molecules. Addition of cross-linking or plasticizing agents alters texture of the films, but their effect on metal-binding capacity has not been fully characterized. The objective of this research was to determine effects of plasticizers and cross-linkers on physical and metal-binding properties of chitosan films and coatings prepared by casting and by spincoating. Chitosan films were prepared using 1% w/w chitosan in 1% acetic acid with or without (control) additives. Plasticizing agents were tetraethylene glycol (TEG) and glycerol while citric acid, ethylenediamine tetraacetic acid (EDTA), and tetraethylene glycol diacrylate (TEGDA) were used as cross-linkers. The additives were applied in concentrations of 0.10%, 0.25%, and 0.50% w/w of film-forming solution. The films were prepared by casting and by spincoating. Films were cast at ambient conditions for tests within one week (fresh films) and eight weeks (aged) after casting. The cast films were evaluated for thickness, residual moisture (by the Karl Fischer method), Cr(VI) binding capacity, puncture strength, and puncture deformation while the chitosan coatings were tested for thickness, Cr(VI) binding capacity, solubility in aqueous solution, and surface morphology (using atomic force microscopy). Cast films with cross-linkers showed an increase in resistance to puncture while plasticized films become more elastomeric. Control films bound 97.2% Cr(VI) ions from solution (0.56 mg Cr(VI)/g film), and addition of plasticizers did not affect chromium binding, tying up to 96.7% Cr(VI) ions from solution (0.56 mg Cr(VI)/g film). Films containing cross-linkers yielded binding capabilities ranging from 42.3% to 94.3% bound Cr(VI) ions (0.26-0.52 mg Cr(VI)/g film). Ultrathin coatings also possess the ability to bind Cr(VI) from solution, though only a maximum of 7.4% of Cr(VI) ions could be bound from solution, the thin films had the ability to bind up to 224 mg Cr(VI)/g ultrathin film. These coatings use less chitosan, but they display greater binding per mass. Overall, plasticizers do not alter, while cross-linkers may reduce, the binding capacity of chitosan films, but physical properties of the films can be controlled by inclusion of additives.