Thèses : « Cellular Ceramics »

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Guzi, De Moraes Elisangela. « Advanced cellular ceramics processed using direct foaming methods ». Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424015.

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The research work presented in this thesis concerns the development of silicon nitride based ceramics with a cellular structure and containing designed interconnected porosity (> 80 vol%) and cell size distribution (10 up to 800 μm) by direct foaming processing routes. Concentrated emulsions (O/W oil-in-water) stabilized by surfactants and gelcasting using environmentally friendly biopolymers as gelling agents, were developed as intermediates in the production of highly porous inorganic materials. Differently from conventional direct foaming methods the evaporation (and expansion) of the alkane droplets affords the foaming during drying of emulsions. Sintering is a critical step in the case of silicon nitride, since high temperatures and increased dwelling time are necessary for sufficient densification to occur, due to a low diffusion in the solid state. In order to overcome this difficulty, we report in this thesis two different strategies by liquid phase sintering with sintering additives: 1) Conventional sintering at 1600 °C and 1700 °C, using N2 flow in order to suppress the dissociation reactions and permit sintering with little weight loss. 2) Sintering by intense thermal radiation, inside a modified SPS set-up, shows to be effective in promote densification of the foam struts and develop of SiC nanowires (increase the fracture toughness of Si3N4 foams) on the cell walls and struts at short times and lower sintering temperatures. Further, the influence of the sintering additives, Y2O3 and MgO, and the effect of the sintering temperature on the formation of rod-like β–Si3N4 grains were also investigated. Highly porous Si3N4 ceramics are promising candidate for various engineering applications such as: gas filtering application (high temperature and harsh environment), heat insulators, catalyst carriers, bioreactors, medical implants, since recent results confirmed the non-cytotoxicity and biocompatibility, owing to remarkable properties as high strength, high stiffness, good toughness, high temperature resistance, high corrosion resistance, good wear resistance and high permeability. During the present research work, the characterization of highly interconnected Si3N4 foams in terms of microstructure (cell size distribution and porosity), mechanical properties and permeability was performed. High compressive strengths (up to 33 MPa) were reported with the increasing of sintering temperature up to 1700 °C (conventional sintering), owing to the development of elongated β–grains, as well a strong packing of particles on cell walls and struts. Permeability evaluation shows that Si3N4 foams are in the range of gelcasting foams (on permeability map) and are suitable for filtering application. The successful combination of colloidal processing, foaming and fast consolidation of foams, and also pressureless sintering at relatively low temperatures applied to produce cellular ceramics based on Si3N4 was also extended to other advanced materials e.g. max-phases belonging to Ti-Al-C system.
Materiali ceramici a base di Si3N4 altamente porosi sono potenziali candidati per varie applicazioni di ingegneria: filtraggio di gas ad alta temperature ed in condizioni critiche, isoltaori termici, trasporto di catalizzatori, bioreattori e impianti biomedici (recenti risultati di letteratura hanno confermato la non citotossicità e la biocompatibilità del Si3N4). L’attività di ricerca della presente tesi riguarda lo sviluppo di materiali ceramici a base di nitruro di silicio caratterizzati da una struttura cellulare, contenenti porosità interconnessa (> 80 vol%) e celle con una distribuzione dimensionale che varia dai 10 μm fino agli 800 μm. La tecnica utilizzata per la produzione dei materiali ceramici cellulari consiste nella schiumatura diretta; sono state sviluppate emulsioni concentrate (O/W olio-in-acqua) stabilizzate da tensioattivi e gelcasting di biopolimeri ecocompatibili, come step intermedi nella produzione di materiali inorganici altamente porosi. Diversamente dai tradizionali metodi di schiumatura diretta, la schiumatura è fornita dall’ evaporazione (ed espansione) delle gocce di alcani durante l'essiccazione delle emulsioni. Mentre nel caso di gelcasting, la capacità dei tensioattivi schiumogeni combinata con la gelificazione termica fornisce la schiumattura. Nel caso della produzione di componenti a base di nitruro di silicio la sinterizzazione rappresenta un punto critico, poiché sono necessarie temperature elevate e prolungato tempo di mantenimento alla T di sinterizzazione al fine di garantire sufficiente densificazione a causa delle basse velocità di diffusione allo stato solido. Al fine di superare queste difficoltà, nella presente tesi sono state sviluppate due strategie: 1) Sinterizzazione convenzionale a 1600 °C e 1700 °C in flusso di N2, al fine di inibire le reazioni di dissociazione e sinterizzare con basse perdite di peso. 2) Sinterizzazione con intensa radiazione termica, attraverso la tecnica dello Spark Plasma Sintering (SPS), la quale si è dimostrata efficace al fine di densificare gli struts della schiuma e sviluppare nanofili di SiC sulle pareti di cella e sugli struts, a temperature più basse e per tempi più brevi rispetto alla sinterizzazione convenzionale. Nanofili di SiC contribuiscono ad aumentare la resistenza alla frattura delle schiume. Inoltre, l’influenza di addittivi di sinterizzazione, Y2O3 e MgO, sulla temperatura di sinterizzazione e sulla formazione di β–Si3N4 grains, sono stati investigati. Le strutture cellulari a base di Si3N4 prodotte con le tecniche sopra descritte sono state caratterizzate in termini di microstruttura (distribuzione della dimensione di celle e porosità), proprietà meccaniche (test di compressione) e permeabilità ai gas. Porosità totale che varia dai ~74 fino agli 89 vol%, e le dimensioni delle celle variano in un ampio range ~20 fino agli 850 μm, in funzione della velocità di emulsione, tipici di biopolimeri. E’ stato trovato che le schiume sinterizzate a 1700 °C (sinterizzazione convenzionale) sono caratterizzate da elevati valori di resistenza a compressione up to 33MPa per effetto dello sviluppo di grani allungati di fase β–Si3N4 e per effetto della notevole densificazione delle particelle in corrispondenza delle pareti di cella e degli struts. Le misure di permeabilità hanno dato valori di costanti di permeabilità nel range delle schiume ottenute con la tecnica del gelcasting e sono pertanto utili per applicazioni di filtraggio. La combinazione di processi colloidali, schiumatura, rapida consolidazione delle schiume e sinterizzazione in assenza di pressione a temperature moderate applicate ai ceramici porosi a base di Si3N4, sono state applicate anche ad altri sistemi come ad esempio al sistema Ti-Al-C (Max-Phases).

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Barg, Suelen [Verfasser]. « Cellular Ceramics via Alkane Phase Emulsified Powder Suspensions / Suelen Barg ». Aachen : Shaker, 2010. http://d-nb.info/1081886919/34.

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Inostroza, Pilar Angelica Sepulveda. « Processing of cellular ceramics synthesised by gel casting of foams ». Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301868.

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Kulkarni, Apoorv Sandeep. « Ceramic Si-C-N-O cellular structures by integrating Fused Filament Fabrication 3-D printing with Polymer Derived Ceramics ». Doctoral thesis, Università degli studi di Trento, 2022. http://hdl.handle.net/11572/349905.

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Ceramic additive manufacturing is gaining popularity with methods like selective laser sintering (SLS), binder jetting, direct ink writing and stereolithography, despite their disadvantages. Laser sintering and binder jetting are too expensive, while direct ink writing lacks resolution and stereolithography lacks scalability. The project aims to combine one of the most versatile, affordable, and readily available 3D printing methods: fused filament fabrication (FFF) with polymer derived ceramics to produce cellular ceramics to overcome the disadvantages posed by the other methods. The process uses a two-step approach. The first step is to 3D print the part using a polymer FFF 3D printer with a thermoplastic polyurethane filament and the second step is to impregnate the part in a polysilazane preceramic polymer and then pyrolyze it in an inert environment up to 1200C. The resulting product is a high-resolution cellular ceramic of the composition SiOC(N). This type of cellular ceramic can find an application in several fields such as scaffolds for bone tissue regeneration, liquid metal filtering, chemical and gas filtering, catalytic converters and electric applications. The process can provide an affordable alternative to the products used in these fields currently.

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Franchin, Giorgia. « Additive Manufacturing of Ceramics. Printing Beyond the Binder ». Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3426205.

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This research project focuses on the production of ceramics via Additive Manufacturing (AM) techniques, with particular focus on extrusion-based technologies. The main advantage of AM is the ability to produce cellular structures with high complexity and controlled porosity, allowing to manufacture light but efficient stretch-dominated structures. The inspiration comes from nature: bone architectures are a great example, consisting of thin, solid skins attached to highly porous, cellular cores. Very few commercially available AM systems are suited for ceramic materials, and most of them use ceramic powders as feedstock. Residual pores and cracks are very hard to avoid and result in low strength, poor reliability and loss of unique material properties such as glass optical transparency. AM technologies employing polymers are at a much more advanced stage of development. The goal has been to exploit such advances and to provide alternatives to the ceramic powder-binder approaches. Three different material families were explored: preceramic polymers, geopolymers, and glass. The same preceramic polymer, a commercial polysilsesquioxane, was employed as a non sacrificial, reactive binder to develop inks for stereolithography (SL) and direct ink writing (DIW). The first technology allowed for production of dense, crack-free SiOC micro-components with strut size down to ~200 μm and optimal surface quality. No shape limitations were experienced, but porous structures or small dense parts are the best options in order to avoid residual pores and cracks. The second approach was employed for the fabrication of complex biosilicate scaffolds for tissue engineering with a rod diameter of 350 µm and unsupported struts. The preceramic polymer had the double role of source of silica and rheology modifier. Ceramic matrix composites (CMCs) were also fabricated; the preceramic polymer developed the ceramic matrix (SiOC) upon pyrolysis in inert atmosphere, whereas reinforcement was given by chopped carbon fibers. Geopolymer components with controlled porosity were designed and produced first by negative replica of PLA sacrificial templates and then by DIW. Highly porous ceramic components with features of ~800 μm and unsupported parts with very limited sagging were produced with the latter approach. A novel extrusion-based AM approach was finally developed for the production of objects starting from molten glass. The system processed glass from the molten state to annealed components of complex, digitally designed forms. Objects possessing draft angles and tight radii were fabricated. Within the design space it was possible to print with high precision and accuracy; parts showed a strong adhesion between layers, and high transparency through the layers.
Questo progetto di ricerca riguarda la produzione di ceramici tramite tecniche di manifattura additiva (AM), con particolare focus su tecnologie estrusive. Il principale vantaggio dell’AM è la possibilità di produrre strutture cellulari ad elevata complessità e porosità controllata, consentendo di produrre reticoli stretch-dominated leggeri ma efficienti. L’ispirazione è offerta dalla natura: le strutture ossee sono un ottimo esempio, in quanto si compongono di un involucro esterno, denso e sottile, e di un cuore a struttura cellulare altamente porosa. I sistemi di AM disponibili in commercio per la produzione di componenti ceramici sono molto pochi, e la maggior parte di essi utilizza polveri ceramiche. È molto difficile evitare porosità residua e cricche, e di conseguenza si ottengono oggetti dalla resistenza limitata e privi delle peculiarità di alcuni materiali, come ad esempio la trasparenza del vetro. Le tecnologie di AM che utilizzano polimeri sono ad uno stadio di sviluppo molto più avanzato. L’obiettivo è di sfruttare tale vantaggio e di fornire alternative agli approcci polvere-legante. Sono stati esplorati tre diversi materiali: polimeri preceramici, geopolimeri, e vetro. Un unico polimero preceramico, un polisilsesquiossano commerciale, è stato utilizzato come legante reattivo, non sacrificale per lo sviluppo di inchiostri per stereolitografia (SL) e direct ink writing (DIW). La prima tecnologia ha consentito di produrre micro-componenti in SiOC densi e privi di cricche, con una dimensione dei pilastri fino a ~200 μm e ottima qualità superficiale. Non ci sono state limitazioni di forma, anche se strutture porose o oggetti densi di piccole dimensioni sono da preferire per evitare porosità residua e cricche. Il secondo approccio ha portato alla fabbricazione di scaffold bioceramici per ingegneria tissutale con filamenti di diametro 350 µm e parti non supportate. Il polimero preceramico ha il doppio ruolo di fonte di silice e di modificatore reologico. Sono stati prodotti anche compositi a matrice ceramica (CMCs); il polimero preceramico sviluppa la matrice (SiOC) tramite pirolisi in atmosfera inerte, mentre il rinforzo è dato da fibre di carbonio macinate. Componenti in geopolimero a porosità controllata sono stati progettati e prodotti prima tramite replica negativa di template sacrificali in PLA, e poi via DIW. Il secondo approccio ha portato alla produzione di reticoli ceramici con filamenti di ~800 μm e parti non supportate con deflessione molto limitata. È stato sviluppato infine un innovativo processo estrusivo a partire da vetro fuso. Un unico sistema è in grado di lavorare il vetro dallo stato fuso fino alla ricottura di componenti complessi progettati digitalmente. Sono stati realizzati oggetti comprendenti sporgenze di diversa entità e piccoli raggi di curvatura. All’interno dello spazio di progettazione è stato possibile stampare con elevata precisione e accuratezza; le parti stampate mostrano una forte adesione tra gli strati e un’elevata trasparenza attraverso di essi.

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Schultz, Joshua Andrew. « Mathematical modeling and control of a piezoelectric cellular actuator exhibiting quantization and flexibility ». Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45776.

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This thesis presents mathematical modeling and control techniques that can be used to predict and specify performance of biologically inspired actuation systems called cellular actuators. Cellular actuators are modular units designed to be connected in bundles in manner similar to human muscle fibers. They are characterized by inherent compliance and large numbers of on-off discrete control inputs. In this thesis, mathematical tools are developed that connect the performance to the physical manifestation of the device. A camera positioner inspired by the human eye is designed to demonstrate how these tools can be used to create an actuator with a useful force-displacement characteristic. Finally, control architectures are presented that use discrete switching inputs to produce smooth motion of these systems despite an innate tendency toward oscillation. These are demonstrated in simulation and experiment.

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Klang, Katharina [Verfasser]. « The energy dissipation of the sea urchin spine as biomimetic concept generator for cellular ceramics and load-bearing systems / Katharina Klang ». Tübingen : Universitätsbibliothek Tübingen, 2020. http://d-nb.info/1219064521/34.

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Borchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann et Stefan Kaskel. « Preparation and application of cellular and nanoporous carbides ». Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138910.

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A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this review
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

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Borchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann et Stefan Kaskel. « Preparation and application of cellular and nanoporous carbides ». Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27792.

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A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this review.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

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Sridevi, Priya Alexander Hannah Ben-Ze'ev Alexander Stephen. « Regulation of ceramide synthase 1 in cellular stress response ». Diss., Columbia, Mo. : University of Missouri--Columbia, 2008. http://hdl.handle.net/10355/6690.

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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 25, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Stephen Alexander and Dr. Hannah Alexander. Vita. Includes bibliographical references.

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Belaud-Rotureau, Marc-Antoine. « Etude de l'apoptose induite par le ceramide et les anthracyclines dans les cellules leucemiques (doctorat : biologie moleculaire et cellulaire) ». Paris 5, 2000. http://www.theses.fr/2000PA05W066.

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Snelling, Jr Dean Andrew. « A Process for Manufacturing Metal-Ceramic Cellular Materials with Designed Mesostructure ». Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/51606.

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The goal of this work is to develop and characterize a manufacturing process that is able to create metal matrix composites with complex cellular geometries. The novel manufacturing method uses two distinct additive manufacturing processes: i) fabrication of patternless molds for cellular metal castings and ii) printing an advanced cellular ceramic for embedding in a metal matrix. However, while the use of AM greatly improves the freedom in the design of MMCs, it is important to identify the constraints imposed by the process and its process relationships. First, the author investigates potential differences in material properties (microstructure, porosity, mechanical strength) of A356 — T6 castings resulting from two different commercially available Binder Jetting media and traditional 'no-bake' silica sand. It was determined that they yielded statistically equivalent results in four of the seven tests performed: dendrite arm spacing, porosity, surface roughness, and tensile strength. They differed in sand tensile strength, hardness, and density. Additionally, two critical sources of process constraints on part geometry are examined: (i) depowdering unbound material from intricate casting channels and (ii) metal flow and solidification distances through complex mold geometries. A Taguchi Design of Experiments is used to determine the relationships of important independent variables of each constraint. For depowdering, a minimum cleaning diameter of 3 mm was determined along with an equation relating cleaning distance as a function of channel diameter. Furthermore, for metal flow, choke diameter was found to be significantly significant variable. Finally, the author presents methods to process complex ceramic structure from precursor powders via Binder Jetting AM technology to incorporate into a bonded sand mold and the subsequently casted metal matrix. Through sintering experiments, a sintering temperature of 1375 °C was established for the ceramic insert (78% cordierite). Upon printing and sintering the ceramic, three point bend tests showed the MMCs had less strength than the matrix material likely due to the relatively high porosity developed in the body. Additionally, it was found that the ceramic metal interface had minimal mechanical interlocking and chemical bonding limiting the strength of the final MMCs.
Ph. D.

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Nieh, Cuo-Yo. « Priming and temperature loss of steel in a cellular ceramic filter ». Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1054825028.

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Snelling, Dean Andrew Jr. « A Process for Manufacturing Metal-Ceramic Cellular Materials with Designed Mesostructure ». Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51606.

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The goal of this work is to develop and characterize a manufacturing process that is able to create metal matrix composites with complex cellular geometries. The novel manufacturing method uses two distinct additive manufacturing processes: i) fabrication of patternless molds for cellular metal castings and ii) printing an advanced cellular ceramic for embedding in a metal matrix. However, while the use of AM greatly improves the freedom in the design of MMCs, it is important to identify the constraints imposed by the process and its process relationships. First, the author investigates potential differences in material properties (microstructure, porosity, mechanical strength) of A356 — T6 castings resulting from two different commercially available Binder Jetting media and traditional 'no-bake' silica sand. It was determined that they yielded statistically equivalent results in four of the seven tests performed: dendrite arm spacing, porosity, surface roughness, and tensile strength. They differed in sand tensile strength, hardness, and density. Additionally, two critical sources of process constraints on part geometry are examined: (i) depowdering unbound material from intricate casting channels and (ii) metal flow and solidification distances through complex mold geometries. A Taguchi Design of Experiments is used to determine the relationships of important independent variables of each constraint. For depowdering, a minimum cleaning diameter of 3 mm was determined along with an equation relating cleaning distance as a function of channel diameter. Furthermore, for metal flow, choke diameter was found to be significantly significant variable. Finally, the author presents methods to process complex ceramic structure from precursor powders via Binder Jetting AM technology to incorporate into a bonded sand mold and the subsequently casted metal matrix. Through sintering experiments, a sintering temperature of 1375 °C was established for the ceramic insert (78% cordierite). Upon printing and sintering the ceramic, three point bend tests showed the MMCs had less strength than the matrix material likely due to the relatively high porosity developed in the body. Additionally, it was found that the ceramic metal interface had minimal mechanical interlocking and chemical bonding limiting the strength of the final MMCs.
Ph. D.

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Deng, Honghua Materials Science &amp Engineering Faculty of Science UNSW. « Effect of cation addition on cellular response and bone ingrowth into three dimensional porous bioceramics ». Awarded by:University of New South Wales. Materials Science & ; Engineering, 2008. http://handle.unsw.edu.au/1959.4/43733.

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The success of orthopaedic implants fixed in the skeletal system using bone ingrowth into porous surfaces is critically dependent on the extent and quality of the initial bone ingrowth and the subsequent long-term maintenance of the bone within the porous structure. Biologically-significant elements (Ca, Mg, Mn) were incorporated at concentrations up to 5 mol% in solid solution in yttia-stabilised tetragonal zirconia polycrystal (3YTZP), whilst controlling microstructure and phase composition, to investigate the effect of ceramic chemistry on cellular behaviour in vitro and bone ingrowth into porous structures in vivo. Cellular attachment, proliferation, and migration on the ceramics were investigated using in vitro assays using fibroblasts. Cells were able to adhere strongly and proliferate on all ceramic surfaces, exhibiting maximal proliferation and minimal migration on 3YTZP but significantly faster migration on doped-3YTZP. The TZP ceramics were therefore considered to support normal cellular processes and thus were suitable for further study in vivo. A technique based on pressure casting ceramic slurry into a polymer preform of the desire pore structure, followed by polymer burnout and then sintering, was developed for fabricating porous bioceramics containing highly-controlled three-dimensional pore geometries. The ability of a selected pore structure to support bone ingrowth was tested using hydroxyapatite by implanting samples into femoral cortical bone of adult sheep for 4 and 12 weeks. Bone was able to rapidly colonise the porous structure and remodel such that, by 12 weeks implantation time, the majority of the porosity was filled with mature lamellar bone. Porous scaffolds of pure 3YTZP and 3YTZP doped with 1 mol% Mg, 1 mol% Mn, 1 mol% Ca, or 5 mol% Ca were fabricated and tested in the sheep model. Bone ingrowth into the doped compositions was significantly greater than that into pure 3YTZP, and was similar to that into the porous hydroxyapatite, indicating that the dopants significantly promoted osteogenesis within the bioinert scaffolds. This finding has application in clinical applications in that the initial bone ingrowth and, potentially, the long-term maintenance of bone within the porous structure may be improved by the incorporation of small amounts of biologically significant elements.

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Siegkas, Petros. « Static and dynamic performance of Ti foams ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:68938d12-d104-4637-8b08-d1c126ddca84.

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Titanium (Ti) foams of different densities 1622-4100 Kgm-3 made by a powder sintering technique were studied as to their structural and mechanical properties. The foams were tested under static and dynamic loading. The material was tested quasi statically and dynamically under strain rates in the range of 0.001-2500 s-1 and under different loading modes. It was found that strain rate sensitivity is more pronounced in lower density foams. Experiments were complimented by virtual testing. Based on the Voronoi tessellations a computational method was developed to generate stochastic foam geometries. Statistical control was applied to produce geometries with the microstructural characteristics of the tested material. The generated structures were numerically tested under different loading modes and strain rates. Voronoi polyhedrals were used to form the porosity network of the open cell foams. The virtually generated foams replicated the geometrical features of the experimentally tested material. Meshes for finite element simulations were produced. Existing material models were used for the parent material behaviour (sintered Ti) and calibrated to experiments. The virtual foam geometries of different densities were numerically tested quasi statically under uniaxial, biaxial and triaxial loading modes in order to investigate their macroscopic behaviour. Dynamic loading was also applied for compression. Strain rate sensitive and insensitive models were used for the parent material model in order to examine the influence of geometry and material strain rate sensitivity under high rates of deformation. It was found that inertial effects can enhance the strain rate sensitivity for low density foams and numerical predictions for the generated foam geometries were in very good agreement with experimental results. Power laws were established in scaling material properties with density. The study includes: 1. Information on the material behaviour and data for macroscopically modelling this type of foams for a range of densities and under different strain rates. 2. A proposed method for virtually generating foam geometries at a microscopic scale and examine the effect of geometrical characteristics on the macroscopic behaviour of foams.

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Karumuri, Anil Kumar. « Interfacial Modification of Microcellular Carbon : Influence of Ceramic and Carbon Nanotube Coatings ». Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1262043697.

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VAKIFAHMETOGLU, CEKDAR. « FABRICATION AND CHARACTERIZATION OF POROUS CERAMICS WITH HIERARCHICAL POROSITY ». Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3422377.

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The research work presented in this thesis is concerned with the production of porous components by using preceramic polymers as a starting precursor. During the preliminary studies on which the production of polymer derived cellular ceramics was based; various compositions have been investigated. Cellular SiOC ceramics having a complex morphology were produced using three different types of polysiloxane precursors. Pore formation was attributed to the different polymer architecture which resulted in a different behavior (larger weight loss, shrinkage and gas evolution) upon pyrolysis. In this context; polysiloxane precursors were crosslinked, crushed, sieved and pressed to form compacts yielding with porous SiOC monoliths by pyrolysis. The resulted ceramic bodies showed compressive strength values reaching to 37.4MPa (~53vol% porosity). Hot-isostatic pressing enabled the formation of SiOC(N) tablets having extremely high piezoresistivity in between 100-1700 at high temperatures (700-1000°C). By using a polysilazane precursor microcellular SiOCN and macrocellular SiCN foams were produced via sacrificial templating or a physical blowing agent. Foams had mostly interconnected porosity ranging from ~60 to 80 vol% and possessing a compressive strength in the range ~1 to 11 MPa. By following the similar strategies boron including porous (70 vol%) PDC monoliths have also been produced. In the direction to produce high specific surface area (SSA) hierarchically porous PDC components; Periodic Mesoporous Organosilica (PMO) particles were embedded into a foamed polysiloxane polymer, and by pyrolysis, permeable SiOC monoliths having SSA of 137 m2/g were obtained. In the method; catalyst assisted pyrolysis (CAP), silicon nitride, silicon oxynitride or silicon carbide nanowires were formed directly during the pyrolysis of highly porous monoliths. Increasing the pyrolysis temperature caused an increase in the length and the amount of nanostructures produced. The growth mechanisms for the nanowires depended on the pyrolysis conditions and catalyst type. The presence of the nanowires afforded high SSA values to the macro-porous ceramics, ranging from 10 to 110 m2/g. The differences were explained in terms of the morphology and amount of the nanowires that were produced using the two different catalysts (Co or Fe). High temperature etching of SiCN ceramics yielded with disordered or graphitic carbon materials possessing a hierarchical bi-modal pore structure (micro-mesopores with mean pore size, 3-11 nm) and large SSA, up to 2400 m2/g. The resulting porosity (pore size, PSD, and SSA) strongly depended on nanostructural phase evolution of the PDC material, as well as on etching conditions. The mean pore size increased with increasing pyrolysis temperature.
Il lavoro di ricerca esposto nella presente tesi riguarda la produzione di componenti porosi mediante l’uso di polimeri preceramici quali precursori iniziali. Durante una fase preliminare del lavoro di ricerca, sulla quale si è basata la produzione di ceramici cellulari derivati da polimeri, sono state studiate varie composizioni. Ceramici cellulari di SiOC aventi una morfologia complessa sono stati realizzati usando tre diversi tipi di precursori polisilossanici. La formazione di pori è stata attribuita alle differenti strutture dei polimeri, che hanno comportato differenti comportamenti durante la pirolisi (maggiore perdita in peso, diminuzione del volume e sviluppo di gas). In tale contesto, precursori polisilossanici sono stati reticolati, ridotti in polvere, setacciati e pressati al fine di ottenere campioni risultanti in monoliti di SiOC poroso, mediante pirolisi. I campioni ceramici cosí ottenuti esibivano valori di resistenza a compressione fino a 37,4 MPa (con una porosità pari a circa il 53% in volume). La pressatura isostatica a caldo ha consentito la formazione di campioni di SiOC(N) aventi piezoresistivitá estremamente elevata, compresa tra 100 e 1700 ad alte temperature (700-1000°C). Utilizzando un precursore polisilazanico, sono state prodotte schiume microcellulari di SiOCN e macrocellulari di SiCN, mediante l’impiego di fillers sacrificali o di un agente schiumante fisico. Le schiume presentavano una porosità prevalentemente interconnessa compresa tra ~60 e 80 vol% ed una resistenza a compressione compresa tra ~1 e 11 MPa. Utilizzando procedimenti simili, sono stati inoltre prodotti campioni monolitici porosi (70 vol%) di PDC contenenti boro. Al fine di produrre componenti ceramici derivati da polimeri, dotati di porosità gerarchica e di elevata area superficiale specifica (SSA), particelle di PMO (Periodic Mesoporous Organosilica) sono state immerse in un polimero polisilossanico schiumato e, mediante pirolisi, sono stati ottenuti campioni monolitici di SiOC permeabili dotati di una elevata SSA, pari a 137 m2/g. Mediante tale metodo, pirolisi catalizzata assistita (CAP), nanofili di nitruro di silicio, di ossinitruro di silicio o di carburo di silicio sono stati formati direttamente durante la pirolisi di campioni monolitici altamente porosi. L’aumento della temperatura di pirolisi ha provocato un aumento nella lunghezza e nella quantità di nanostrutture prodotte. Il meccanismo di crescita dei nanofili dipende dalle condizioni di pirolisi e dal tipo di catalizzatore. La presenza dei nanofili ha permesso di raggiugere elevati valori di SSA nei ceramici macroporosi, compresa tra 10 e 110 m2/g. Le diversità in tali valori sono state spiegate in termini di morfologia e quantità dei nanofili prodotti impiegando due diversi catalizzatori (Co e Fe). L’ablazione superficiale (etching) ad elevate temperature di ceramici di SiCN ha condotto a materiali contenenti carbonio amorfo o grafitico dotati di una struttura gerarchica bimodale dei pori (micro-mesopori con dimensione media dei pori di 3-11 nm) ed elevata SSA, fino a 2400 m2/g. La porosità risultante (dimensione dei pori, PSD e SSA) dipendeva fortemente dall’evoluzione della fase nanostrutturale del materiale PDC, nonché dalle condizioni di etching. La dimensione media dei pori aumentava all’aumentare della temperatura di pirolisi.

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Parker, Jeffery Todd. « Bartonella Henselae Inhibits Cellular Apoptotic Regulators to Ensure Survival ». Digital Archive @ GSU, 2009. http://digitalarchive.gsu.edu/biology_diss/68.

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Human pathogens survive anti-pathogen host immune assault by either circumventing or evading the host immune response. Bartonella henselae, an intracellular pathogen previously shown to disrupt intrinsic apoptotic messengers to enhance its survival, exploits multiple facets of the cellular apoptotic mechanisms. Cellular pathways affected by apoptotic processes were assessed using real-time reverse-transcriptase-polymerase-chain-reaction (rRT-PCR) to measure the effect of B. henselae on cell regulator gene expression (TRADD, FADD, caspase-8 and caspase-3), caspase activity, DNA cell cycle analysis, cell regulator protein expression and overall cell viability and morphology. The presence of B. henselae suppresses overall gene expression for TRADD and FADD and it dramatically suppresses ceramide-induced TRADD and FADD gene expression. The presence of B. henselae has a noticeable effect on ceramide-induced caspase-8 and caspase-3 gene expression. Only caspase-3 enzymatic activity was ceramide-induced and likewise supressed by the presence of B. henselae, whereas caspase-6 and caspase-8 were unaffected and equivalent to controls. The presence of B. henselae inhibits ceramide-induced DNA fragmentation, maintains overall cell morphology and enhances host cell viability. Lastly, B. henselae inhibits the time-dependant ceramide-induction of TRADD protein and suppresses ubiquitous FADD protein expression. We demonstrated that B. henselae inhibits apoptotic induction in a systematic manner following exogenous apoptotic induction. B. henselae protection of microvascular endothelial cells from apoptosis induction begins at the modulation of cell surface receptor-dependent signaling. B. henselae minimizes, but does not completely abrogate, the cytotoxic effect of the apoptogenic shingolipid ceramide on human microvascular endothelial cells (CDC.EU.HMEC-1). Broadening our understanding of the sequence of cell regulator suppression events by intracellular pathogens will provide insight into disease manifestation. Further, understanding how infected cells initiate and conclude apoptosis will open new avenues into the study of disease treatment.

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LAMBENG, NATHALIE. « Differenciation des cellules pc12 et mort cellulaire : role de la voie apoptogene dependante du ceramide et de son inhibition par le ngf et l'amp cyclique ». Paris 7, 1999. http://www.theses.fr/1999PA077132.

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L'objectif de ce travail, realise sur des cellules pc12 a l'aide de techniques de pharmacologie, d'immunocytochimie, de videomicroscopie a fluorescence et de microscopie electronique, etait de determiner si l'etat de differenciation neuronale pourrait constituer un facteur de vulnerabilite chez l'adulte. Les cellules pc12 differenciees de maniere terminale par le ngf et l'amp cyclique degenerent en effet de maniere programmee lors du retrait des facteurs differenciateurs. Trois mecanismes d'inhibition, exerces independamment par un facteur serique, le ngf et l'ampc, previennent la mort de ces cellules. La differenciation terminale conduit a la perte de l'inhibition serique. De plus, le degre de differenciation des cellules pc12 determine leur vulnerabilite au retrait des facteurs trophiques. Ce lien entre differenciation et mort cellulaire met en jeu des regulateurs du cycle cellulaire, sans qu'une synthese d'adn prealable a une mitose n'intervienne. Ces cellules meurent grace a l'activation d'une cascade de signalisation dependante du ceramide. La levee de l'inhibition serique provoque en effet une synthese de ceramides, une augmentation des taux de calcium libre et d'especes radicalaires oxygenees dans les mitochondries. Des alterations morphologiques du reticulum endoplasmique et des mitochondries sont observees en meme temps que les modifications de l'homeostasie calcique et la production de radicaux libres mitochondriaux. Le ngf et l'ampc inhibent la voie de signalisation en aval de ces deux etapes. Le programme de mort dans les cellules differenciees de maniere terminale debute a ce niveau. Par ailleurs, le ngf previent les modifications (gonflement, rupture de la membrane externe) des mitochondries. Ces alterations, ainsi que celles du noyau (desintegration de la membrane nucleaire, aucune condensation de la chromatine), se distinguent de l'apoptose classique.

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Šenk, Vít. « Keramické porézní materiály - příprava, struktura a vlastnosti ». Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229407.

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The thesis targets to preparation a foam ceramics suitable for supporting, catalytic and biological applications. Theoretical part deals with methods of preparation, properties and applications of foam ceramics. Experimental part of work is focused on preparation foams by template method using polymer foam. Properties of ceramic slurry were evaluated according to discharge time of Ford cup. Foam structure is assessed using images and mechanical properties are judged by compressive tests.

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MacKnight, Patrick. « The interaction between ceramide-1-phosphate and Group IVA cytosolic phospholipase A2 and its role in wound healing ». VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5633.

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The sphingolipid, ceramide-1-phosphate (C1P), directly binds and activates Group IVA cytosolic phospholipase A2 (cPLA2a) to generate eicosanoids. Due to the role of eicosanoids in wound healing, we choose to use our novel genetic mouse model expressing cPLA2a with an ablated C1P interaction site (KI) to examine the cPLA2a/C1P interaction in wound healing. Wound closure rate was not affected, but wound maturation was dramatically enhanced by loss of the C1P/cPLA2α interaction based on the following findings. Wounds in KI mice displayed: i) increased infiltration of dermal fibroblasts into the wound environment; ii) increased wound tensile strength; and iii) higher Type I/Type III collagen ratios. These findings were recapitulated in vitro as primary dermal fibroblasts (pDFs) from KI mice showed significantly increased collagen deposition and migration velocity compared to WT and KO pDFs. Additionally, the KI showed an altered eicosanoid profile of reduced pro-inflammatory prostaglandins (e.g., PGE2) and increased levels of specific HETE species (e.g., 5-HETE). Elevated 5-HETE levels promoted increased dermal fibroblast migration and collagen deposition. This “gain of function” role for the mutant cPLA2a was also linked to differential cellular localization of cPLA2α and 5-HETE biosynthetic factors. These studies demonstrate regulation of key in vivo biological mechanisms by a defined protein:lipid interaction and provide new insights into cPLA2a function.

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BUISSON, LEGENDRE NATHALIE. « Controle de la proliferation des keratinocytes humains en culture par les ceramides et les metalloproteinases matricielles (doctorat : biologie cellulaire) ». Reims, 2000. http://www.theses.fr/2000REIMM202.

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Schneider, Christophe. « Mise en evidence et role du systeme sphingomyeline/ceramide dans les cellules thyroidiennes porcines en culture ». Reims, 2000. http://www.theses.fr/2000REIMS003.

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La thyroide est une glande endocrine dont le principal regulateur est la tsh. Sa fonction majeure est la synthese et la secretion des hormones thyroidiennes t 3 et t 4. Ces dernieres annees ont vu l'apparition d'une nouvelle voie de signalisation impliquant les sphingolipides et notamment les ceramides. Ces derniers, outre leur role de constituant de la membrane cellulaire, interviennent dans de nombreuses fonctions biologiques importantes telles que la proliferation cellulaire, la differenciation, l'inflammation ou l'apoptose. L'objectif de nos travaux a ete de montrer l'existence de la voie ceramide dans les thyrocytes porcins en culture, de mettre en evidence la presence de cibles directes des ceramides et d'etudier leur interaction avec les autres voies de signalisation. La premiere partie de nos travaux a montre l'existence d'activite sphingomyelinase neutre et acide modulees par l'etat de differenciation de nos cellules. L'il1, au meme titre que la sphingomyelinase exogene est capable d'activer cette voie ceramide. La seconde partie de notre travail a permis de montrer une inhibition dose-dependante par les ceramides et l'il1 de la production d'ampc induite par la tsh et impliquant la sous-unite inhibitrice g i du systeme adenylate cyclase. Par contre, ni les ceramides, ni l'il1 n'ont d'influence sur la fonctionnalite des thyrocytes porcins en culture. Enfin, l'etude de la signalisation cellulaire en aval des ceramides nous a permis de mettre en evidence un effet direct de ces derniers sur une pkc atypique, la pkc. D'autre part, un effet de l'il1 a egalement ete observe sur la pkc. Les ceramides et l'il1 modulent egalement l'expression des kinases erk1/2 et l'activite du facteur de transcription nfkb. La connaissance des processus de regulation regissant la voie sphingomyeline/ceramide apparait donc essentielle dans la comprehension des mecanismes aboutissant a l'apoptose ou la differenciation cellulaire et au controle de l'invasion tumorale.

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Jefferson, Grace Elizabeth. « Calcitriol Increases Ceramide, Diacylglycerol, and Expression of Genes Involved in Lipid Packaging in Skeletal Muscle ». UKnowledge, 2016. http://uknowledge.uky.edu/khp_etds/31.

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Background: Vitamin D is crucial for skeletal muscle function. 25-hidroxyvitamin D (25(OH)D) has been correlated with skeletal muscle mass and intramyocellular lipid (IMCL) content. The purpose of this study was to understand how calcitriol, the active vitamin D metabolite, directly affects myocellular size and lipid partitioning. Methods: C2C12 myotubes were treated with calcitriol (100nM) or vehicle control for 24 or 96 h. Myotube diameter and protein synthesis rate were measured to determine effects of calcitriol on myocellular size. Intramyocellular triacylglycerol (IMTG), diacylglycerol (DAG), and ceramide content were measured by LC/MS. Expression of genes involved in lipid packaging and lipolysis were measured by RT-PCR. Insulin-stimulated phosphorylated Akt (Thr 308) was determined by western blot. Results: Calcitriol did not affect myocellular size or protein synthesis rate. Calcitriol increased total DAG and ceramides in a sub-species specific manner. Calcitriol increased IMTG area, but did not affect total IMTG content. Calcitriol reduced mRNA content of diglyceride acyltransferase and increased mRNA content of lipid packaging genes. Calcitriol did not negatively affect insulin-stimulated pAkt. Conclusions: These results suggest calcitriol directly alters lipid content and packaging in skeletal muscle cells. Altering the expression of lipid packaging genes and increasing IMCL subspecies content may be mechanisms by which vitamin D improves skeletal muscle function in vivo.

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Bezombes, Christine. « Implication de la voie sphingomyeline-ceramide dans la reponse des cellules de leucemies aigues myeloides aux agents cytotoxiques ». Toulouse 3, 1999. http://www.theses.fr/1999TOU30206.

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Dans les cellules myeloides, nous avons mis en evidence la voie sphingomyeline-ceramide induite par la daunorubicine (dnr), une anthracycline largement utilisee dans le traitement des leucemies aigues myeloides. Cette voie de signalisation consiste en l'activation d'une sphingomyelinase (smase) neutre, responsable de l'hydrolyse de la sphingomyeline et de la generation de ceramide ; celui-ci etant le mediateur directement mis en cause dans la signalisation apoptotique. L'enzyme cle de cette signalisation est bien la smase neutre puisque nous avons montre que des cellules deficientes en smase acide (issues de patients atteints de la maladie de niemman-pick) ainsi que des cellules deficientes en ceramidase acide (issues de patients atteints de la maladie de farber) sont tout aussi sensibles que les cellules normales a divers agents cytotoxiques. Par ailleurs, la smase neutre apparait etre hautement regulee. En effet, il a ete montre dans le laboratoire l'implication de proteases et de la proteine kinase c dans la regulation de cette enzyme. De plus, nous avons mis en evidence le role important joue par les radicaux libres oxygenes (rlo) ainsi que p53/p56 lyn, une src kinase, dans la stimulation de la smase neutre. Au cours de ce travail, nous avons donc identifie et caracterise certains parametres regulateurs de la smase neutre, enzyme cle dans la signalisation apoptotique induite par de nombreux agents cytotoxiques. Cette etude nous a permis de definir une cascade d'evenements moleculaires conduisant in fine a la mort par apoptose des cellules de leucemies aigues myeloides.

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Batocchi, Pierre. « Pile à combustible à céramique conductrice protonique : développement, optimisation des matériaux, réalisation de cellules élémentaires PCFC opérant dans le domaine de température 400-600 °C ». Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20022.

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Ce travail s'inscrit dans le cadre du développement des piles à combustible à céramique conductrice protonique (PCFC) opérant dans le domaine de température 400 – 600 °C et concerne l'optimisation des composants de la cellule élémentaire. L'optimisation du matériau électrolytique consiste à rechercher le meilleur compromis entre stabilité chimique et conductivité élevée. Le matériau BaCe0.9Y0.1O2.95, synthétisé par la voie flash combustion, présente la conductivité protonique la plus élevée (10-2 S.cm-1 à 600 °C) mais réagit fortement avec le CO2. La substitution partielle du cérium par le zirconium (BCZY) et le niobium (BCYN30) a conduit à une amélioration significative de la stabilité chimique tout en conservant une conductivité de l'ordre de 5 × 10-3 S.cm-1 à 600 °C. En ce qui concerne les électrodes, l'enjeu est de développer des matériaux présentant une conductivité électronique élevée, une porosité suffisamment importante et une bonne tenue mécanique. L'approche a consisté en la mise au point de stratégies d'élaboration (synthèse en une étape, utilisation de porogène) permettant le contrôle de la microstructure des matériaux anodiques afin de minimiser les résistances spécifiques surfaciques (ASR). Comme dans le cas des SOFC, les matériaux cathodiques sont conducteurs mixtes ionique-électronique (MIEC). Le développement de cathodes composites MIEC-électrolyte a permis de réduire significativement les ASR. Les tests en pile de cellules élémentaires PCFC ont révélé que les performances dépendaient essentiellement de la nature et de l'épaisseur du matériau électrolytique et de la mise en œuvre de matériaux d'électrode de morphologie contrôlée et architecturée. L'optimisation des assemblages a permis d'accroître sensiblement les performances (156 mW.cm-2 à 600 °C)
Materials components for a Proton Conducting Fuel Cell (PCFC) operating in the 400 – 600 °C temperature range have been optimised. Electrolyte material optimisation involved finding the best compromise between chemical stability and conductivity. BaCe0.9Y0.1O2.95, synthesised by flash combustion, exhibits the highest protonic conductivity (10-2 S.cm-1 at 600 °C) but reacts strongly with CO2. Partial substitution of cerium by zirconium (BCZY) and niobium (BCYN30) led to a significant improvement of the chemical stability without drastic effect on the conductivity (5 × 10-3 S.cm-1 at 600 °C). The aim for the electrodes is to develop materials which exhibit high electronic conductivity, sufficient degree of porosity and good mechanical properties. The approach comprised the development of elaboration strategies (one-step synthesis, use of porogen) that allow the control of microstructure in order to minimize area specific resistances (ASR) at the anode. As in the case of SOFCs, cathodic materials are mixed ionic-electronic conductors (MIEC). Development of composite cathodes MIEC-electrolyte led to a significant reduction of ASR. PCFC single cell tests showed that performance was mostly dependent on electrolyte thickness and composition, and on the characteristics of nanostructured electrodes with controlled architecture and porosity. Optimisation of assemblies led to fuel cells performances of 156 mW.cm-2 at 600 °C

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Stanciuc, Ana-Maria. « In vitro evaluation of cell-material interactions on bioinert ceramics with novel surface modifications for enhanced osseointegration ». Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI053/document.

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Cette thèse porte sur l'évaluation de la réponse cellulaire in vitro vis-à-vis de différentes stratégies de modification de surface pour améliorer la capacité d’ostéointégration de céramiques bioinertes pour implants orthopédiques et dentaires. Premièrement des surfaces l'alumine-zircone avec différentes micro-rugosités obtenues par moulage par injection ont été étudiées. Le comportement d'ostéoblastes primaires humains (obtenus à partir de têtes de fémurs soumis à arthroplastie) a été étudié sur les surfaces telles quelles ou modifiées par traitement avec acide hydrofluorique. La micro-rugosité a eu seulement un effet mineur sur la réponse ostéoblastique tandis que la combinaison de micro- et nano-rugosité a eu un effet synergique sur la maturation ostéoblastique. Cette stratégie de modification de surface ouvre la voie vers des cupules acétabulaires céramiques monoblocs directement ostéo-intégrées. Deuxièmement, le robocasting (une technique d’impression 3D) a été exploré pour la production de structures macroporeuses en alumine-zircone avec une haute reproductibilité et contrôle architectural. Les structures imprimées ont présentées une topographie aux multiples niveaux grâce au design et les conditions de frittage. Les ostéoblastes ont pu s'attacher sur les structures 3D mais la préservation des cellules à l’intérieur des scaffolds sur le long terme reste à améliorer. Des techniques de sélection rapide de modifications de surface ont fait l'objet de la dernière partie de cette thèse. Deux différentes stratégies ont été utilisées sur la zircone: laser femtoseconde pour la production de multiples motifs sur un échantillon unique et échantillons avec un gradient de rugosité via le contrôle du temps d’attaque chimique. La morphologie des cellules souches humaines a permis d'avoir un indicateur précoce de la lignée de différentiation cellulaire. En conclusion, les différentes techniques de modification de surface de zircone et alumine-zircone utilisées à travers la thèse peuvent moduler l’interaction cellule-matériau en stimulant la différentiation ostéoblastique de cellules souches et la maturation des ostéoblastes
The focus of this PhD thesis is the in vitro evaluation of cell-material interactions on bioinert ceramics with novel surface modifications for enhanced osseointegration of orthopaedic and dental implants. Firstly, alumina-zirconia surfaces with different micro-roughnesses obtained by injection moulding were studied. The behaviour of human primary osteoblasts (hObs) obtained from patients undergoing total hip replacements was studied on the different micro-rough ZTA surfaces and on combined micro-/nano-rough surfaces modified by hydrofluoric acid treatment. Micro-roughness alone had minor effects on hOb response while the combination micro-/nano-roughness induced a synergic effect on hOb maturation. This latter surface modification technique opens the way to the fabrication of ceramic acetabular cups with direct implantation capabilities. Secondly, robocasting (a 3D printing technique) was explored for the fabrication of a alumina-zirconia macroporous structures with high reproducibility and control of the architecture. Roughness at different scales was observed for the 3D structures due to the scaffold design and to the low temperature sintering conditions. Osteoblasts were able to attach on the 3D structures but cell retention at long term needs further optimization. Rapid screening of cell-material interactions was the subject of the last part of the thesis. Two different strategies were tested on zirconia: femtosecond laser to produce multiple patterns on a single sample and samples with a roughness gradient by the control of chemical etching time. Stem cell morphology was used as an early marker of cell differentiation lineage. In conclusion, the different surface modification techniques of zirconia and alumina-zirconia surfaces used in the thesis allow the modulation of cell-material interactions by stimulating stem cells osteogenesis and osteoblast maturation

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Mahfouz, Rana. « Insulinorésistance musculaire induite par les céramides : étude des mécanismes d'action et de l'implication du transporteur CERT ». Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066012/document.

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L'obésité et le diabète de type 2 sont associés à la sédentarité et à une alimentation riche en graisses. En effet, les acides gras saturés s'accumulent dans les tissus non adipeux, comme les muscles squelettiques pour générer des lipides appelés céramides (CER). Mon projet de thèse s'est articulé en deux parties dont l'objectif est d'empêcher les CER d'agir. Nous avons montré que, selon la structure de la membrane plasmique, les CER altèrent la voie de signalisation insulinique en ciblant la PKB, protéine clef de la voie insulinique, via la voie PKC? dans les myotubes L6 et la voie PP2A dans les myotubes C2C12. Nous avons aussi mis en évidence que les CER altèrent la sensibilité à l'insuline via la voie PKC? dans les cellules musculaires humaines. Une fois les CER produits au niveau du réticulum endoplasmique (RE), ils sont transportés au Golgi par un transporteur CERT pour y être métabolisés en sphingomyéline (SM) et des études ont montré que la transformation des CER en SM pouvait être une étape cruciale pour empêcher les CER d'agir. Dans plusieurs modèles d'insulino-résistance musculaire, l'expression de CERT est diminuée et nous avons démontré l'importance du transport des céramides du RE vers le Golgi en inhibant artificiellement l'activité ou l'expression de CERT. A l'opposé, la surexpression de CERT améliore la sensibilité à l'insuline dans les cellules musculaires dans des conditions lipotoxiques. Nos résultats montrent que CERT joue un rôle crucial dans les mécanismes conduisant au développement de l'insulinorésistance musculaire puisque sa présence est essentielle pour le maintien d'un trafic normal des CER entre le RE et le golgi
Obesity and type 2 diabetes are associated with a sedentary lifestyle and a diet rich in fat. Indeed, saturated fatty acids accumulate in non-adipose tissue such as skeletal muscle to generate lipids called ceramides (CER). My thesis project was divided into two parts with the objective to prevent CER to act. We have shown that, depending on the structure of the plasma membrane, CER alter the insulin signaling pathway by targeting PKB, a key insulin signalling protein, via a PKCζ pathway in L6 myotubes and a PP2A pathway in C2C12 myotubes. We also demonstrated that CER affect insulin sensitivity via the PKCζ pathway in human muscle cells. Once CER generated in the endoplasmic reticulum (ER), they are transported to the Golgi by a carrier called CERT to be metabolized into sphingomyelin (SM). Studies have shown that the transformation of CER into SM could be a crucial step to prevent CER to act. In several muscle insulin resistance models, expression of CERT is decreased and we demonstrated the importance of the transport of ceramide from the ER to the Golgi by inhibiting artificially the activity or the expression of CERT. In contrast, overexpression of CERT enhances insulin sensitivity in muscle cells in lipotoxiques conditions. Our results show that CERT plays a crucial role in mechanisms leading to the development of muscle insulin resistance since its presence is essential for maintaining normal traffic of CER between the ER and the Golgi

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Mamode, Cassim Adiilah. « Role of the most abundant plant sphingolipids, Glycosyl Inositol Phosphoryl Ceramides GIPCs, in membrane structure and host/pathogen interactions ». Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0413.

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Les Glycosyl-Inositol Phosphoryl Céramides (GIPCs) sont les sphingolipides majeurs de la biosphère. Ils représentent jusqu’à 40%mol des membranes plasmiques (MP) des plantes et des champignons. Les GIPCs sont cependant restés presque totalement ignorés depuis leur découverte il y a plus de 50 ans. Aucune donnée n’est disponible sur leurs rôles dans la structuration des membranes biologiques, leur organisation en nanodomaines membranaires et leurs interactions avec les autres lipides et les protéines. De nombreuses questions à propos des GIPCs de plantes restent encore sans réponse, telles que la structure chimique exacte de la tête polaire dont le nombre de sucres ; l’influence de ces molécules sur l’épaisseur de la membrane ou encore sur la structuration des nanodomaines ; et enfin l’implication des GIPC dans les relations hôte-pathogène chez les plantes. Le but de ce projet est de purifier et caractériser les différentes classes de GIPCs de plantes, afin d’étudier leurs rôles structurants avec les phytostérols et les phospholipides par des méthodes de biophysique et de biochimie structurale. Ce projet multidisciplinaire permettra l’émergence d’une nouvelle thématique et procurera une base de données indispensable pour comprendre la structure des MP végétales et entre autres, leurs rôles dans la réponse contre les pathogènes
Glycosyl Inositol Phosphoryl Ceramides (GIPCs) are the major sphingolipids of the biosphere. They account for up to 40 mol% of the plasma membranes (PM) of plants and fungi. Since their discovery over 50 years ago, GIPCs remained however almost completely ignored. No data are available on their roles in the structure of biological membranes, on their organization in membrane nanodomains and their interactions with other lipids and proteins. Many questions about plant GIPCs remain unanswered, such as the exact chemical structure of the polar as well as the number sugars grafted; their influence on the thickness of the membrane or on the structure of nanodomains; and also their involvement in host-pathogen interactions in plants. The purpose of this project is to purify and characterize the different classes of plant GIPCs to study their structural roles with phytosterols and phospholipids by biophysical and structural biochemistry methods. This multidisciplinary project will enable the emergence of a new theme and will provide an essential database for understanding the structure of plant PM and among others, their roles in the response against pathogens

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Korolkov, Ilia. « Propriétés photoélectriques de vitrocéramiques et cristaux de chalcogénures ». Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S145/document.

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La crise de l’énergie ainsi que les problèmes écologiques sont considérés comme les défis les plus importants de demain. Cependant, les sources d’énergies renouvelables et respectueuses de l’environnement ne sont pas suffisamment développées, ce qui entraîne une contribution faible à la production d’énergie. Les cellules solaires font partie des sources d’énergies renouvelables les plus attractives et prometteuses. Cependant, les panneaux solaires existants ont toujours un facteur de qualité négatif, c’est-à-dire que leur production et leur entretien demandent plus d’énergie qu’ils ne sont capables de produire pendant leur cycle de fonctionnement. Malgré la réduction exponentielle du prix des panneaux solaires, leur efficacité de conversion n’est pas suffisante. Les succès récents dans la science des matériaux ont beaucoup contribué à son amélioration, néanmoins des études sur les nouveaux matériaux photovoltaïques sont nécessaires. Les travaux de recherche présentés dans ce manuscrit concernent les vitrocéramiques de chalcogénures dans le système GeSe2-Sb2Se3-CuI. De nombreuses compositions chimiques différentes ont été préparées et analysées du point de vue structural et électrique dans le cadre de ce système. Il a été démontré que la phase Sb2Se3, responsable des propriétés photoélectriques dans les vitrocéramiques, possède un grand potentiel pour les applications photovoltaïques grâce à ses propriétés optiques bien adaptées. L’influence des modifications de la composition des cristaux de Sb2Se3 sur la structure et les propriétés électriques a été étudiée. La flexibilité du type de conductivité et la résistivité des cristaux massifs de Sb2Se3 ont été montrées. Enfin, les couches minces à base de vitrocéramiques et cristaux massifs étudiés ont été préparées par la pulvérisation cathodique RF magnétron. Leur structure et les propriétés électriques sont également décrites dans cette thèse. Une cellule solaire complètement fonctionnelle, basée sur Sb2Se3 dopé iode et sur la vitrocéramique de 40GeSe2-40Sb2Se3-20CuI, a été préparée et caractérisée
Energy crisis and global ecological problems are considered as important challenges of nearest future. Eco-friendly and renewable sources of energy are still severely undeveloped and contribute weakly to the energy production. One of the most attractive and promising domains of renewable energy is a solar light harvesting. However, existing solar panels still possess negative quality factor, i.e. their fabrication and maintenance require more energy that they are capable to produce during their life cycle. Despite exponential reduction of the price, solar cells are not efficient enough in terms of light to energy conversion. Recent breakthroughs in material science contributed a lot to the increase of efficiency, however further investigation of novel materials are needed. Here, chalcogenide glassceramics of GeSe2-Sb2Se3-CuI system were studied in details. Within this system various chemical compositions were prepared and analyzed for their structure and photoelectric properties. We found that Sb2Se3 phase, responsible for the appearance of photoelectric effect in glass-ceramics, have a great potential for light harvesting due to its suitable optical properties. In the present work we demonstrated the influence of various dopants on photoelectric properties of Sb2Se3 crystals. We showed a possibility of conductivity type and resistivity tuning of bulk Sb2Se3 crystals in a wide range of values. Thin film devices based on studied bulk compositions were prepared by RF sputtering and characterized structurally and electrically as well. We demonstrated a fully functional thin film solar device based on iodine doped Sb2Se3 and 40GeSe2-40Sb2Se3-20CuI glass-ceramic

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Loricourt, Johan. « Réalisation de liaisons céramique-métal par brasage dans une cellule prototype d’électrolyse de la vapeur d’eau à haute température pour la production d’hydrogène ». Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20037.

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L'électrolyse de la vapeur d'eau à haute température et sous pression avec des électrolytes à conduction protonique est un moyen envisagé pour produire massivement de l'hydrogène à un coût compétitif. Pour être fonctionnelle, une cellule d'électrolyse doit être hermétique vis-à-vis de l'extérieur et entre le compartiment anodique (O2 et H2O) et le compartiment cathodique (H2). Ainsi, la réalisation de liaisons céramique-métal est nécessaire, soit pour l'intégration de l'électrolyte (liaison perovskite-métal), soit pour l'intégration d'alimentations électriques (liaison alumine-métal). Compte-tenu des conditions de fonctionnement de la cellule (600°C, 50 bars, vapeur d'eau), seul un procédé de brasage est envisageable pour réaliser des jonctions résistantes mécaniquement et hermétiques. L'expertise des processus de corrosion sous vapeur d'eau a permis de définir la partie métallique et la brasure pour cette application et a montré que des alliages spécifiques étaient requis. L'étude de métallisation des céramiques par PVD pour permettre le mouillage de la brasure au moment du brasage a montré que la présence d'une barrière de diffusion était nécessaire, pour éviter la dissolution du dépôt lors du passage à l'état liquide de la brasure. Après une étude de mouillabilité à chaud de la brasure sélectionnée sur les céramiques métallisées et les substrats métalliques, les liaisons ont été optimisées en appliquant la méthodologie des plans d'expériences sur des éprouvettes normalisées. L'ensemble des résultats a ainsi conduit au développement de liaisons céramique-métal possédant de bonnes propriétés mécaniques (Rm = 60 MPa à 20°C) et hermétiques
Steam electrolysis at high temperature and under pressure with protonic conduction electrolyte is a way to produce hydrogen massively at low cost. To operate, an electrolysis cell must be hermetic especially between the anodic compartment (O2 and H2O) and the cathodic one (H2). Thus, ceramic to metal assemblies are needed, either to insert the electrolyte (perovskite-metal junction) or to realize power supply (alumina-metal junction).Considering the operating conditions (873°K, 725 PSI, steam), only a brazing process is possible to realize strong and hermetic junctions.The evaluation of corrosion process under steam pressure has enabled to select a metallic component and a brazing alloy for this application, and has shown that specific alloys are needed.The studies of ceramics metallization by PVD to assure the brazing alloy wetting throughout the brazing process have shown that a barrier diffusion was necessary to avoid the dissolution of coatings when the brazing alloy become liquid.After wetting experimentations of the chosen brazing alloy over the metalized ceramics and the metallic substrate, ceramic to metal assemblies have been optimized in applying the experimental design methodology on standard samples (ASTM).The whole results have enabled to develop hermetic ceramic to metal assemblies having good mechanical properties (Rm = 8700 PSI at 300°K)

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Santos, Cécile. « Conception, synthèse et évaluation de nouveaux inhibiteurs du transport de céramide : vers de nouveaux agents de sensibilisation des cellules cancéreuses chimiorésistantes ». Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30238/document.

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Au cours de leur métabolisme, les céramides, produits de novo au niveau du réticulum endoplasmique, sont transportés vers l'appareil de Golgi pour être convertis en sphingomyéline. Le mode principal de ce transport implique la protéine cytosolique CERT (CERamide Transfer). La surexpression de CERT, responsable d'un abaissement du taux intracellulaire en céramide pro-apoptotique, a été associée au phénomène de résistance aux agents chimiothérapeutiques de plusieurs lignées de cellules tumorales. L'inhibition de CERT permet de resensibiliser ces lignées cellulaires aux agents anti-cancéreux. Cependant, une seule famille d'inhibiteurs de CERT est connue à ce jour : les HPAs. A l'extrémité C-terminale de la protéine, le domaine START contient le site de liaison du céramide nécessaire à l'activité de transport de CERT. A partir de structures cristallographiques, une méthode d'identification de nouveaux ligands, combinant des outils in silico et in vitro, a été développée. La jaspine B, des analogues HPAs et des iminosucres ont été mis à jour en tant qu'antagonistes potentiels de CERT par cette méthode. Certains des composés identifiés ont été synthétisés et évalués in vitro. Des sondes fluorescentes de la jaspine B ont été conçues afin d'approfondir la compréhension de son mécanisme d'inhibition. En parallèle, un test de liaison in vitro HTR-FRET a été développé, permettant le criblage haut-débit de la Chimiothèque Nationale Essentielle
During its metabolism, ceramides, produced de novo in the endoplasmic reticulum, are transported to the Golgi complex to be converted into sphingomyelin. The main way of this transport involves the cytosolic CERT protein (Ceramide Transfer). Overexpression of CERT, responsible for a diminution of intracellular level of proapoptotic ceramide, is associated with the phenomenon of resistance to chemotherapeutic agents in several tumor cell lines. The CERT inhibition allows to resensitize these cell lines to anticancer drugs. Yet, only a single family of inhibitors is known to date: HPAs. Located at the C-terminal region of the protein, the START domain contains the binding site of ceramide necessary for the transport activity of CERT. Based on crystallographic structures, a method for the identification of new CERT ligands, combining in silico and in vitro tools, was developed. Jaspine B, HPAs analogs and iminosugars were identified as potential antagonists using this method. Some of these compounds were synthesized and evaluated in vitro. Fluorescent probes of jaspine B were designed for a better understanding of it mechanism of action. In parallel, an in vitro HTR-FRET binding assay was developed, allowing the high-throughput screening of the National Essential Compound Library

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Ponsot, Inès. « Glasses and Glass-Ceramic Components from Inorganic Waste and Novel Processing ». Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424636.

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Thanks to European environmental rules and regulations establishment, waste recycling has become a more and more relevant problematic. For manufacturing plants, especially those producing hazardous wastes, expenses linked to waste production have drastically increased over the last decades. In the proposed work, various hazardous and non-hazardous wastes, among: soda-lime and borosilicate glass cullet, cathode ray tubes glass, exhausted lime from fume abatement systems residues, sludge and slags from ferrous and non-ferrous metallurgy, and pre-stabilized municipal solid waste incinerators ashes are used to elaborate several compositions of glass-ceramics. High-temperature treatment (minimum 800 °C) associated to a Direct Sintering process (30 min) was an efficient way to stabilize chemically the final products. The impact of each waste on the final product’s mechanical properties was studied, but also their synergies between each other, when mixed together. Statistic mixture designs enabled to develop interesting products for modern building applications, such as porous tiles and lightweight panels destined to insulation, with a purpose of fulfilling multifunctional properties.
Grazie alle regole e normative ambientali europee istituite, il riciclaggio dei rifiuti è diventato una problematica sempre più rilevante. Per gli impianti di produzione, in particolare quelli che producono rifiuti pericolosi, le spese connesse allo smaltimento sono drasticamente aumentate negli ultimi decenni. Nel lavoro proposto, vari rifiuti, pericolosi o no, vengono utilizzati per elaborare diverse composizioni di vetroceramiche. Si distinguono rottami di vetro della produzione di finestre, di contenitori farmaceutici e di tubi catodici. I rifiuti non vetrosi invece sono calce esausta da residui di sistemi di filtrazione di fumi, scorie metallurgiche da leghe ferrose e non e ceneri da inceneritori. E' presentata nel presente lavoro la ricerca di un metodo di trattamento ad alta temperatura (minima 800 ° C) efficace per stabilizzare chimicamente il prodotto finale, tramite i diversi processi di sinterizzazione diretta, sinter-cristallizzazione e vetrificazione. Sono stati studiati gli effetti di ogni rifiuto sulle proprietà meccaniche del prodotto finale, ma anche le nuove funzionalità ottenute attraverso le sinergie risultanti dalla loro miscela. Miscele calibrate hanno permesso di sviluppare prodotti interessanti per applicazioni edilizie moderne, come le piastrelle porose e pannelli leggeri destinati all’isolamento.

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Ehret, Christophe. « Synthèse de nouveaux ligands du récepteur CD1d : applications à la vaccination anti-tumorale ». Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00767140.

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L'objectif de cette thèse a été d'optimiser la réponse immunitaire anti-tumorale induite par les cellules dendritiques (DC) et les cellules iNKTs, en réponse à la prise en charge du KRN7000 (a-galactosyl-céramide) par la molécule CD1d située sur les DCs. Le premier axe de travail visait à synthétiser de nouveaux analogues du KRN7000, en fonctionnalisant la position C6 du sucre et en greffant un groupement phényl sur l'une des chaînes grasses. Les études in vitro ont montré que les modifications apportées par rapport au KRN7000 n'ont pas altéré la prise en charge des molécules obtenues par les DCs. Dans tous les cas, une sécrétion de cytokines a pu être observée. Des études complémentaires visant à décrire le profil cytokinique in vivo sont en cours. Le second axe a consisté en la mise au point d'une stratégie de vectorisation du KRN7000 afin de favoriser sa présentation aux DCs, en l'associant à des molécules d'intérêt comme un peptide spécifique d'une tumeur, une molécule de ciblage des DCs ou des ligands des TLRs. Dans les conditions utilisées, le phénomène d'anergie induit classiquement par l'administration répétée du KRN7000 n'a pas pu être levé. Cependant, nous avons montré d'une part que le KRN7000 vectorisé dans les liposomes est toujours pris en charge par les cellules dendritiques, et d'autre part qu'une réponse immunitaire se traduisant par la production de cytokines par les cellules iNKTs est induite.

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Petit, Clémence. « Etude des propriétés mécaniques de matériaux cellulaires par la tomographie aux rayons X et par modélisation par éléments finis ». Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0130/document.

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Les matériaux cellulaires sont des échantillons à très forte porosité qui peuvent être décrits à deux échelles : la mésostructure et la microstructure. Le lien entre l'architecture des matériaux et les propriétés mécaniques a été largement étudié dans la littérature. Les caractéristiques microstructurales peuvent avoir une influence importante sur les propriétés macroscopiques. Le but de ce travail est de relier les caractéristiques architecturales et microstructurales des matériaux cellulaires à leurs propriétés mécaniques grâce notamment à la tomographie aux rayons X. Une nouvelle approche combinant l'imagerie 3D à plusieurs résolutions, le traitement d'images et la modélisation éléments finis a permis de prendre en compte la microstructure de la phase solide. Quatre matériaux cellulaires modèles ont ainsi été étudiés : des mousses d'aluminium, des structures cellulaires périodiques en alliage de cobalt-chrome, des échantillons de β-TCP et des composites hydroxyapatite/β-TCP. Les matériaux métalliques ont été fournis par des collègues d'autres laboratoires, tandis que les matériaux céramiques ont été fabriqués dans le cadre de cette étude. Pour chaque type de matériaux (métaux et céramiques), une structure régulière et une stochastique ont été comparées. Pour utiliser la méthode multi-échelle développée dans ce travail, les échantillons ont d'abord été scannés grâce à la tomographie locale dans laquelle l'échantillon est placé près de la source de rayons X. La tomographie locale permet de scanner la petite partie irradiée de l'échantillon et d'obtenir une image agrandie par rapport aux images à plus basse résolution. Ces images permettent d'observer certains détails de la phase solide non visibles à plus basse résolution. Différentes étapes de traitement d'images ont ensuite été mises en œuvre pour obtenir une image à basse résolution incluant les informations provenant des images à haute résolution. Ceci a été réalisé grâce à une série d'opération de seuillage et sous-résolution des images à haute résolution. Le résultat de ces différentes étapes de traitement d'images donne une image de l'échantillon initial à basse résolution mais qui inclut l'information supplémentaire décelée à haute résolution. Ensuite, des essais mécaniques in situ ont été réalisés dans le tomographe pour suivre à basse résolution l'évolution des échantillons pendant la déformation. Les images initiales citées plus haut ont été utilisées pour produire des maillages éléments finis. Des programmes Java ont été adaptés pour créer des fichiers d'entrée pour les modèles éléments finis à partir des images initiales et des maillages. Les images initiales contenant les informations à propos de la phase solide, les images des essais mécaniques et les modèles éléments finis ont permis d'expliquer le comportement mécanique des échantillons en reliant les sites d'endommagement expérimentaux et les lieux de concentrations de contraintes calculés
Cellular materials are highly porous systems for which two scales are mainly important: the mesostructure and the microstructure. The mesostructure corresponds to the architecture of the materials: distribution of solid phase “walls” and macroporosity and can be characterized by X-ray tomographic low resolution images. The link between the architecture of the materials and the mechanical properties has been frequently studied. The microstructure refers to the characteristics of the solid phase. Its microstructural features (presence of a secondary phase or of defects due to the sintering) can have a strong influence on the macroscopic properties. The aim of this work is to link the morphological and microstructural features of metallic and ceramic based cellular materials and their mechanical properties thanks to X-ray tomography and finite element modelling. A new method combining X-ray tomography at different resolutions, image processing and creation of finite element modelling enabled to take into account some microstuctural features of the cellular samples. Four different cellular materials were studied as model materials: aluminium foam fabricated by a liquid state process, cobalt periodic structures made by additive manufacturing, β-TCP porous samples fabricated by conventional sacrificial template processing route and hydroxyapatite/β-TCP composites made by additive manufacturing (robocasting). The metal based materials were provided by colleagues while the ceramic based porous materials were fabricated in the frame of the current study. For each type (metals or ceramics), a stochastic and a regular structure have been compared. For implementing the multiscale method developed in this work, the samples were firstly scanned in a so called “local” tomography mode, in which the specimen is placed close to the X-ray source. This allowed to reconstruct only the small irradiated part of the sample and to obtain a magnified image of a subregion. These images enable to observe some details which are not visible in lower resolution. Different image processing steps were performed to generate low resolution images including microstructural features imaged at high resolution. This was done by a series of thresholding and scaling of the high resolution images. The result of these processing steps was an image of the initial sample. Then, in situ mechanical tests were performed in the tomograph to follow the deformation of the sample at low resolution. The above mentioned initial images were used to produce finite element meshes. Special Java programs were adapted to create finite element input files from initial images and meshes. The initial images containing information about the solid phase, the images from the mechanical tests and the finite element models were combined to explain the mechanical behaviour of the sample by linking the experimental damage locations in the sample and the simulated stress concentration sites

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ESPINOSA, DE LOS MONTEROS MARIA DOLORES ARACELI. « Contribution a l'etude des oligodendrocytes in vitro ». Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13008.

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Une technique permettant d'obtenir des oligodendrocytes en culture homogene a ete mise au point. Il s'agit de sous-cultures de cellules provenant de cultures primaires agees de 20 jours, derivees de cerveau de rat nouveau-ne. L'analyse de ces cultures primaires, aux premiers jours, a revele la presence de precurseurs d'oligodendrocytes; leur transformation en oligodendrocytes differencies a ete suivie par immunohistochimie. Dans les sous-cultures, les oligodendrocytes se multiplient activement, deviennent matures et sont capables de former des figures myeliniques, malgre l'absence de neurones. Ces structures ont ete caracterisees morphologiquement et biochimiquement

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Ricard, Jérôme. « Etude du développement des kystes de Toxoplasma gondii in vitro : rôle de la voie de signalisation du TNF-[alpha] de la cellule hôte : rôle de la phospholipase C-spécifique de la phosphatidylcholine du parasite ». Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10196.

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Toxoplasma gondii est responsable d'atteintes cliniques graves chez les immunodeprimes, a cause de la reactivation de kystes quiescents. Les mecanismes presidant a l'interconversion entre les differentes formes parasitaires sont tres peu connus. Nous avons etudie l'effet du tnf- sur la kystogenese du parasite in vitro dans des fibroblastes humains mrc5 et avons montre qu'il induisait une augmentation du nombre de kystes formes. Cet effet a pu etre mime par du ceramide, second messager du tnf-, impliquant vraisemblablement la voie des sphingomyelinases dans le processus. L'action du tnf et du ceramide n'a pas ete le resultat d'une modification de la multiplication du parasite. Divers inhibiteurs et activateurs des voies des sphingomyelinases ont ete utilises. Parmi eux, l'ester de phorbol pma a eu un effet similaire a celui du tnf-. Le d609, inhibiteur specifique de la phospholipase c specifique de la phosphatidylcholine (pc-plc) localisee en amont de la sphingomyelinase acide, a inhibe la multiplication du parasite et a induit la formation de kystes apparemment plus differencies, comme l'ont montre les marquages avec l'anticorps monoclonal cc2 et les observations en microscopie electronique. Il a egalement eu pour effet d'inhiber l'invasion parasitaire dans le cas d'un traitement des parasites avant infection, ou d'induire une augmentation de la multiplication parasitaire dans le cas d'un pretraitement des fibroblastes. La presence d'une pc-plc supposee chez le parasite a ete mise en evidence par western-blot. Nous avons montre un role pour le tnf-, probablement relaye par la voie du ceramide, dans l'induction de la kystogenese de t. Gondii. Nous avons identifie la pc-plc comme une enzyme importante pour le cycle de developpement du parasite et qui semble impliquee dans l'invasion, la multiplication et l'enkystement. Une meilleure comprehension des relations existant entre l'hote et le parasite lors de la formation des kystes pourrait permettre a terme de prevenir les reactivations toxoplasmiques.

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Fayeulle, Dominique. « Elaboration et étude de révêtements céramiques à sous-couche d'accrochage cellulaire pour la protection chimique et thermique de composants de turbomachines ». Paris, ENMP, 1989. http://www.theses.fr/1989ENMP0149.

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Etude d'un nouveau procédé de fabrication des barrières thermiques fondé sur le dépôt électrophorétique d'une couche métallique (nicraly+ta) pour obtenir des sous-couches d'accrochage par aluminisation en phase vapeur avant la réalisation des barrières thermiques par projection plasma de zircone partiellement stabilisée. On analyse les propriétés des produits réalisés par ce procédé et leur potentiel d'application pour la protection des composants de turbomachines

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Bakar, Joudi. « Etude de la biosynthèse lipidique au cours de la différentiation kératinocytaire en lien avec l’intégrité de la fonction barrière cutanée Comprehensive characterization and simultaneous analysis of overall lipids in reconstructed human epidermis using NPLC/HR-MS n : 1-O-E (EO) Cer, a new ceramide subclass Biomolecular modifications during keratinocyte differentiation : Raman spectroscopy and chromatographic techniques ». Thesis, université Paris-Saclay, 2021. http://www.theses.fr/2021UPASF018.

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La différenciation des kératinocytes s'accompagne de profondes modifications de la composition lipidique du contenu cellulaire pour former à la fin le ciment intercornéocytaire responsable de la fonction de la barrière cutanée. Les céramides forment la classe lipidique majeure de l’épiderme. Cette classe est très complexe, elle-même se divise en sous-classes qui diffèrent par leur microhétérogénéité structurale. Le but de ce travail a été de développer une méthodologie analytique permettant d’étudier la biosynthèse ces lipides épidermiques au cours de la différenciation kératinocytaire. A ce sujet, deux techniques analytiques ont été utilisés :1) La Chromatographie Liquide à Haute Performance en phase normale couplée à la Spectrométrie de Masse à Haute Résolution NP-HPLC/HR-MSⁿ. Une méthode a été développée afin de séparer les classes lipides de différente polarité en une seule analyse et de caractériser les structures fines des lipides et notamment la micro-hétérogénéité structurale des céramides. 2) La Microspectroscopie Raman qui offre des informations à l’échelle moléculaire et « tissulaire ». Les images spectrales en pseudo-couleurs ont la capacité de mieux suivre l’évolution des lipides au cours de la différenciation et de renseigner sur l’organisation lipidique du Stratum Corneum. Trois modèles cellulaires ont été utilisés pour répondre aux objectifs fixés : 1) Un modèle cellulaire en 2D : pour le suivi de la différenciation dès les étapes précoces (couche basale). Ce modèle a permis de fournir des informations au niveau cellulaire par imagerie Raman. Il a également été utilisé pour mettre en place les premiers développements en NP-HPLC/ HR-MSⁿ. 2) Un modèle d’épiderme reconstruit humain (en 3D) sain, mimant mieux l’environnement in vivo : pour le suivi de la différenciation à partir de Stratum Granulosum (SG) et jusqu’à la formation des multicouches de Stratum Corneum (SC). Ce modèle a permis de fournir des informations au niveau tissulaire (couches épidermiques) et de réaliser toute la caractérisation approfondie des céramides, en tenant compte de l’ensemble des micro-hétérogénéités structurales. 3) Un modèle d’épiderme reconstruit humain (en 3D) altéré : pour illustrer l’adéquation de la méthode en NP-HPLC/HR-MSⁿ afin de mettre en évidence l’impact sur le profil lipidique d’un déficit enzymatique ciblé et d’appréhender l’effet potentiel d’une molécule active. Les résultats majeurs obtenus à partir des travaux expérimentaux sont les suivants : 1) Le développement d’outils analytiques pertinents dans l’élucidation de mélanges lipidiques complexes et leur évolution au niveau cellulaire ou tissulaire. 2) L’application innovante de la Microspectroscopie Raman au niveau de la cellule de kératinocyte (modèle cellulaire en 2D) : plusieurs modifications moléculaires au sein de la cellule ont été observées et notamment entre les jours 9 et 13 de la différenciation indiquant le passage entre SG et SC. 3) L’identification pour la première fois dans la littérature de deux nouvelles sous-classes de céramides (1-O-E (EO) Cer et A-1-O (EO) Cer) dans le modèle d’épiderme reconstruit humain sain mais également dans le SC humain, à partir des données fournies par la méthode développée en NP-HPLC/HR-MSⁿ. 4) La mise en évidence d’une perturbation du profil lipidique à maturation sur un modèle d’épiderme reconstruit humain altéré. L’ensemble de ces résultats a pu offrir une meilleure compréhension du métabolisme lipidique lors de la maturation des kératinocytes, de façon très détaillée au niveau moléculaire, qui permettrait d'appréhender de façon plus raisonnée les perturbations de la fonction barrière cutanée, physiologiques ou pathologiques
The keratinocytes differentiation is accompanied by profound modifications of the lipid composition of the cell contents to form at the terminal differentiation stage the intercorneocyte cement (lipid matrix) responsible for the skin barrier function. Ceramides are the major lipid class of the epidermis. This class is very complex, it self is divided into subclasses which differ in their structural micro-heterogeneity. The aim of this work was to develop an analytical methodology to study the biosynthesis of these epidermal lipids during keratinocyte differentiation. On this subject, two analytical techniques were used: 1) Normal Phase-High Performance Liquid Chromatography coupled with High Resolution Mass Spectrometry NP-HPLC/HR-MSⁿ. A method has been developed in order to separate the lipid classes of different polarity in a one single run and to characterize the fine structures of lipids in particular the structural micro-heterogeneity of ceramides. 2) Raman Microspectroscopy, which provides information at levels of molecules and of tissues. Pseudo-color spectral images have the ability to better follow the evolution of lipids during differentiation and to provide information on the lipid organization of the Stratum Corneum. Three cellular models were used to achieve our objectives: 1) A 2D cell model: for monitoring the differentiation from the early stages (basal layer). This model made it possible to provide information at the cellular level by Raman imaging. It was also used to establish the first developments in NP-HPLC/HR-MSⁿ. 2) A healthy 3D reconstructed human model of epidermis, better mimicking the environment in vivo: for monitoring differentiation from Stratum Granulosum (SG) and up to the formation of Stratum Corneum (SC) multilayers. This model allowed to provide information at the tissue level (epidermal layers). In addition, it is on this model that all the in-depth characterization of ceramides was carried out, taking into account all the structural heterogeneities. 3) An altered 3D human reconstructed epidermis model: to illustrate the suitability of the NP-HPLC/HR-MSⁿ method in order to highlight the impact on the lipid profile of a targeted enzymatic deficit and to understand the potential effect of an active molecule. The major results obtained from the experimental work are as follows: 1) The development of relevant analytical tools in the elucidation of complex lipid mixtures and their evolution at the cellular or tissue level. 2) The innovative application of Raman Microspectroscopy at the level of the keratinocyte cell (2D cell model): several molecular modifications within the cell were observed and in particular between days 9 and 13 of differentiation indicating the passage between SG and SC. 3) The identification for the first time in the literature of two new subclasses of ceramides (1-OE (EO) Cer and A-1-O (EO) Cer) in the healthy human reconstructed epidermis model but also in the human SC, from data provided by the developed method in NP-HPLC/HR-MSⁿ. 4) Demonstration of a disruption of the lipid profile at maturation on an altered reconstructed human epidermis model. All of these results have been able to provide a better understanding of lipid metabolism during keratinocyte maturation, in very detail at the molecular level, which would allow a more reasoned understanding of the physiological or pathological disturbances of the skin barrier function

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Monge, Madeleine. « Séquence d'apparition du galactosylcéramide, de la protéine de Wolfram, de la protéine basique encéphalitogène et du protéolipide de Folch dans l'oligodendrocyte et dans la myéline au cours de la myélinisation chez la souris : étude comparative de la différenciation de l'oligodendrocyte in vivo and in vitro ». Paris 6, 1986. http://www.theses.fr/1986PA066245.

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Storm, Johannes. « Entwicklung und Bewertung von effizienten Berechnungskonzepten für keramische Filter ». Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-218483.

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Die vorliegende Dissertation beschäftigt sich mit der thermo-mechanischen Beschreibung und Bewertung von keramischen Filtern für die Metallschmelze-Filtration mithilfe der Finiten-Elemente-Methode. Infolge des zellularen Aufbaus des Werkstoffs handelt es sich um ein Mehrskalenproblem. Grundlegende Aufgaben der Arbeit waren deshalb die geometrische und mechanische Modellbildung sowie die Untersuchung verschiedener effizienzsteigernder Methoden zur Gewinnung einer akkuraten numerischen Lösung. Dabei wurden sowohl verschiedene Verfahren aus der Fachliteratur implementiert und kritisch bewertet, als auch neue Ansätze verfolgt. Die Untersuchungen konzentrierten sich auf das effektive elastische und elastisch-plastische Verhalten von Kelvin-, Weaire-Phelan- und Voronoi-Strukturen. Insbesondere die entwickelten Methoden und Werkzeuge zur automatisierten Modellbildung gestatten in einfacher Weise die Umsetzung von Parameterstudien und Optimierungsaufgaben. Aus darauf aufbauenden Sensitivitätsstudien wurden Empfehlungen hinsichtlich der geometrischen und mechanischen Modellbildung für zellulare Werkstoffe abgeleitet. Diese betreffen auch vielfach eingesetzte Methoden zur Modellreduktion für diese Werkstoffe und tragen somit zukünftig zu einer effizienteren Bewertung von Filterstrukturen bei.

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Rozié, Alexandrine. « Criblage de petites molécules d'intérêt thérapeutique et recherche de leur mécanisme d'action ». Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30246.

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L'identification du mécanisme d'action de petites molécules bioactives permet i) de révéler des cibles pharmacologiques inattendues, contre lesquelles pourront être développées de nouvelles molécules thérapeutiques, ii) de découvrir des modes d'actions originaux qui pourront inspirer le développement de nouveaux médicaments et iii) de développer des biomarqueurs de la réponse à ces traitements. L'objectif de ma thèse était d'appliquer plusieurs approches d'identification de cibles à des petites molécules, soit nouvelles, issues d'un crible phénotypique, soit déjà connues mais dont le mécanisme d'action n'était pas identifié. Dans un premier volet de mes travaux, un crible phénotypique a été développé afin d'identifier dans la Chimiothèque Nationale Essentielle de nouveaux sensibilisateurs au prototype d'une famille d'agent anticancéreux endommageant l'ADN, la camptothécine (CPT). La CPT est un poison de la topoisomérase I, inducteur d'un type particulier de cassures double-brin de l'ADN (CDB) associées aux fourches de réplication. Ce crible a conduit à l'identification d'un nouveau sensibilisateur que nous avons nommé Shuri1. Nous avons établi que Shuri1 induit en soi des CDB sélectivement dans les cellules en réplication. Nous avons démontré que Shuri1 se comporte comme un inhibiteur de la protéine kinase CHK1 impliquée dans la signalisation des dommages de l'ADN. De fait, certaines mutations conférant la résistance à un inhibiteur spécifique de CHK1 confèrent également la résistance à Shuri1. Dans un deuxième volet de cette thèse, nous avons étudié le mécanisme d'action de la Jaspine B, une molécule naturelle issue d'éponges marines et qui présente une forte cytotoxicité contre différentes lignées cellulaires tumorales solides humaines. Précédemment, plusieurs mécanismes ont été proposés pour la Jaspine B, mais aucun ne rend compte de l'ensemble des effets cellulaires de cette molécule. En collaboration avec l'équipe d'Yves Génisson du SPCMIB de Toulouse, un analogue "clickable" de la Jaspine B a été synthétisé et a permis de la localiser par microscopie dans la cellule sous la forme d'agrégats au niveau du réticulum endoplasmique (RE). En utilisant la lipidomique, la génomique fonctionnelle et l'imagerie en temps réel, nous avons établi un modèle du mécanisme d'action de la Jaspine B dans des cellules cancéreuses. Nos travaux montrent que la Jaspine B se comporte comme une prodrogue qui est bioactivée par une des céramides synthases, enzymes impliquées dans la biosynthèse des céramides. La Jaspine B N-Acylée ainsi produite au niveau du RE s'accumule sous forme d'agrégats responsables de la perméabilisation du RE et de la cellule qui conduit à la mort cellulaire. Nous avons montré que ce mécanisme explique également les effets cytotoxiques d'un autre lipide issu des éponges marines
The identification of the mechanism of action of small bioactive molecules allows (i) to reveal unexpected pharmacological targets against which new therapeutic molecules that can be developed, (ii) to discover original modes of action that can inspire the development of new drugs, and (iii) to develop biomarkers of response to these treatments. The objective of my thesis was to apply several target identification approaches to small molecules, either new, from a phenotypic screen, or already known but the mechanism of action of which was not identified. In a first part of my work, a phenotypic screen was developed in order to identify in the " Chimiothèque Nationale Essentielle ", new sensitizers to the prototype of a family of DNA-damaging anti-cancer agents, camptothecin (CPT). CPT is a poison of topoisomerase I, inducing a particular type of double-strand DNA breaks (DSB) associated with replication forks. This screen led to the identification of a new sensitizer that we named Shuri1. We have established that Shuri1 induces DSB selectively in replicating cells. We demonstrated that Shuri1 behaves as an inhibitor of the CHK1 protein kinase involved in the signaling of DNA damage. Accordingly, some mutations conferring resistance to a specific CHK1 inhibitor also confer resistance to Shuri1. In a second part of my thesis, I studied the mechanism of action of Jaspine B, a natural molecule derived from marine sponges that exhibits strong cytotoxicity against different human solid tumor cell lines. Previously, several mechanisms have been proposed for Jaspine B, but none accounts for the cellular effects of this molecule. In collaboration with Yves Génisson's team at the SPCMIB in Toulouse, a clickable analogue of jaspine B was synthesized and was localized by cell microscopy as aggregates at the endoplasmic reticulum (ER). Using lipidomics, functional genomics and real-time imaging, we have established a model of the Jaspine B mechanism of action in cancer cells. My work supports that Jaspine B behaves as a prodrug that is bioactivated by one of the ceramide synthases, enzymes involved in ceramide biosynthesis. The N-Acylated Jaspine B thus produced at the ER accumulates as aggregates responsible for the permeabilization of the ER and of the cell leading to cell death. We further established that this mechanism also explains the cytotoxic effects of another lipid produced by marine sponges

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Cree, Duncan. « Production and characterization of three-dimensional, cellular, Metal-filled ceramics ». Thesis, 2009. http://spectrum.library.concordia.ca/976524/1/NR63360.pdf.

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This research focuses on the infiltration of two porous structures. In the first, two different silicon sources were used to infiltrate structures derived from different Canadian pine, beech and maple species for the production of silicon carbide (SiC). This allows the use of a precursor structure that is already available, thus saving time, energy and cost of manufacturing. Carbonized wood species measuring 15 mm x 11 mm x 13 mm were used as precursors for the production of silicon carbide (SiC) using two silicon sources (sol and powder) in order to produce a porous SiC structure mimicking that of wood. The liquid sol was vacuum infiltrated into the pyrolyzed wood species, dried and reacted at 1575 °C under a 70 L/h flow of argon. Scanning electron microscopy (SEM) showed SiC grains formed on the interior of the tracheid walls and a high density of SiC whiskers were discovered in certain tracheids of pine and vessels of beech and maple. Both cyclic and repeated infiltration processes were undertaken. In addition, infiltration of carbonized pine wood with molten silicon was carried out in order to obtain a porous SiC structure. Infiltration was based on capillary forces within the preform and the infiltration depth was measured. Optical microscope, SEM, EDS and XRD were used for microstructure characterization and phase identification. In the second part of this work, a liquid A356 aluminum alloy was infiltrated into a porous silicon carbide foam structure. Three dimensional silicon carbide (SiC) ceramic foams were employed as reinforcement for producing an aluminum alloy metal matrix composite with potential as a base plate material in electronic packaging. These are commonly manufactured with aluminum/silicon carbide (Al/SiC) particulate materials, nickel-iron and copper alloys. A base plate provides mechanical strength to the integrated circuit design, as well as aids in transfering the heat from the chip to the heat sink. Packaging base plate materials are required to have low coefficient of thermal expansion (CTE), high thermal conductivity, and low density. A356 aluminum alloy was vacuum infiltrated into a 100 PPI (pores per inch), silicon carbide (SiC) foam network, at 775°C using an in-house built apparatus. It has been shown that this metal matrix composite has similar properties to traditional packaging materials with the added benefit of a lower density. CTE and thermal conductivity are within the range of commercially available materials, with porosity levels of 7%, using this method. Flexural strength and Young's modulus of the composite provide reasonable values as a result of the low reinforcement concentration employed. Secondary Electron Microscopy (SEM) was used to investigate the fractured surfaces of the Charpy, flexural strength and compression tests. In the Charpy and flexural strength samples, the A356 aluminum-silicon alloy matrix shows signs of mixed fracture; cleavage regions and some dimpling. In the network structure, the majority of the failure is from SiC layers debonding from the aluminum matrix with some SiC layer peeling (inter-delamination). Compressive loading showed internal damage in the form of failed SiC struts. X-ray Diffraction (XRD) analysis did not detect any brittle aluminum carbide at the Al/SiC interface. The Rule of Mixtures (ROM) is used for a first rough estimate of certain mechanical and thermal properties

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Desai, Dhanashri Tejpal. « 3D-Printing of Lunar Soil Simulant by Direct-Extrusion method ». Thesis, 2023. https://etd.iisc.ac.in/handle/2005/6172.

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The extrusion-based additive manufacturing (EAM) technique is recently being widely employed for the 3D printing of complex-shaped components made of ceramic powder (containing irregular-shaped particles) when it is cast in the form of a slurry/ink. In this work, we utilize a direct extrusion method for printing structures from extra-terrestrial soil simulants using a piston-based extruder. Printing is demonstrated using a slurry composed of lunar soil simulant (LSS) variant ISAC-1 (avg. particle size ~ 90µm) mixed with biopolymer guar gum as a sustainable binding agent and DI water as a solvent. Parts were printed using a 2 mm diameter nozzle by optimizing print speed, nozzle height, inter-layer drying time, and build temperature, to ensure shape retention post-printing. The final green parts were dried in a hot air oven (50°C) for 48hrs, followed by sandpaper polishing. The strengths of the printed specimens were evaluated using compression and flexure tests and were found to be comparable to that of bio-consolidated structures. Unlike solid geometries, the well-known shell-infill type area-filling strategy generated several travels and re-tracings in the toolpath for cellular geometries. Owing to the yield stress of slurry, the travels and re-tracings resulted in discontinuous print and poor dimensional accuracy respectively. This necessitated a toolpath with increased continuity in the extrusion path. The customized toolpath is generated by defining a continuous nodal path over a lattice structure corresponding to the cellular frame. The extrusion flow rate is tuned according to the nodal path and the requirement of material deposition. Qualitatively the increased extrusion continuity in the customized toolpath resulted in continuous print with improved dimensional accuracy, whereas quantitatively a significant (~ 60%) reduction in print time is observed. These results show the potential for using the direct extrusion 3D printing method in remote extra-terrestrial environments to obtain lightweight load-bearing structures like cellular frames.

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Wronowska, Weronika. « Computational models of response to cellular stress factors ». Doctoral thesis, 2019. https://depotuw.ceon.pl/handle/item/3595.

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This doctoral dissertation concerns the subject of formal modeling of biological processes in response to stress conditions. In particular, disturbances of these mechanisms play an important role in the etiology of neu- rodegenerative and neoplastic diseases. In the dissertation I present two formal models describing molecular processes corresponding to selected levels of cell function. The metabolic level is represented by the model of sphingolipid metabolism, while the model of Heat shock response is an example of a formal model for gene expression regulation loop.In addition, in the dissertation I proposed an innovative calculation method that allows estimating the number of subpopulations of cells that differ in transcriptomic response to a stress factor. This method also allows to infer the activation of various signaling pathways in response to the extracellular stress factors. Proposed formal model of sphingolipid metabolism is the first model described in the literatur containing all key elements for the metabolism of these bioactive lipids in human cells. In addition, the model allows to track their behavior depending on the cellular organelle being analyzed. Indeed, the described model can be used to study metabolic changes associated with neurodegenerative diseases. In this context, model elements were used to develop a quantitative systemic pharmacological model for Alzheimer's disease by pharmacological company CERTARA. Then in the dissertation I describe a series wet lab experiments performed to validate the sphingolipid metabolism model. The results of these studies, in particular the analysis of the effects of ceramide (bioactive sphingolipid) on neoplastic nerve cells (neuroblastoma) have enabled the development of an innovative method to study the heterogeneity of cellular response to stress factor. The use of this new computational approach, called MPH (Molecular Process Heterogeneity), allows the decomposition of the expression matrix in a way that provides information about (i) the proportions of the studied subpopulations in a given sample and (ii) the transcription patterns specific for each subpopulation. The proposed method allowed to verify hypotheses regarding the cytoprotective role of PJ34, i.e. an inhibitor of poly (ADP-ribose) polymerase - PARP for ceramide treated neuroblastoma SH-SY5Y line cells. The second formal model described in this dissertation is the Heat Shock Response (HSR) model in HeLa cells. It allows to study the mechanism of gene expression regulation in particular it focuses on HSP70 from the HSP family. HSP70 is a key chaperonin for the cells protection against the effects of thermal denaturation of proteins.In the model I presented a regulatory loop working on the principle of negative feedback including all the interactions critical for the cellular heat shock response. The biochemical scheme of the model consists of twelve reactions that have been transformed into a system of ordinary differential equations. I tested the model's behavior, among others, by performing model's sensitivity analysis, which allowed me to identify reactions key for the models stability and the noise propagation within the model. The name HSR suggests that the cell response is caused by heat stress, however HSP proteins are involved in the reaction to various stress factors. Their participation is crucial for the development of both cancer and neurodegenerative diseases, moreover, there are numerous reports on links between HSP70 activity and sphingolipid metabolism pathways. Due to the complexity and multidimensionality of cellular stress response mechanisms, the use of a systemic approach seems to be the only way that can bring us closer to understanding and describing the principles of molecular response to stress. The use of computational models and computer simulations allows an insight into the nature of these complex systems.
Niniejsza rozprawa doktorska dotyczy tematyki formalnego modelowania procesów biologicznych stanowiących elementy odpowiedzi na warunki stresowe. Zaburzenia tych mechanizmów często leżą u podłoża rozwoju chorób nowotworowych i neurodegeneracyjnych. W rozprawie prezentuję dwa formalne modele opisujące procesy molekularne odpowiadające wybranym poziomom funkcjonowania komórek. Poziom metaboliczny reprezentuje model komórkowego metabolizmu sfingolipidów, z kolei model odpowiedzi komórki na warunki stresu termicznego, stanowi przykład formalnego modelu regulacji ekspresji genów. Ponadto w rozprawie zaproponowałam metodę obliczeniową pozwalająca szacować liczność podpopulacji komórek różniących się odpowiedzią transkryptomiczną na czynnik stresowy. Metoda ta pozwala również wnioskować na temat aktywacji różnorodnych ścieżek sygnałowych w odpowiedzi na czynniki stresu komórkowego. Opracowany przeze mnie formalny model metabolizmu sfingolipidów jest pierwszym w literaturze modelem zawierającym wszystkie elementy kluczowe dla metabolizmu tych bioaktywnych lipidów w komórkach ludzkich. Ponad to model umożliwia śledzenie ich zachowania w zależności od analizowanego organellum komórkowego. Co istotnie opisywany model może być wykorzystywany do badania zmian metabolicznych towarzyszących chorobom neurodegeneracyjnym. W tym kontekście elementy modelu zostały wykorzystane do opracowania ilościowego systemowego modelu farmakologicznego dla choroby Alzheimera przez firmę CERTARA. Następnie w rozprawie opisuję badania laboratoryjne wykonane w celu walidacji modelu metabolizmu sfingolipidów. Wyniki tych badań, w szczególności analiza wpływu ceramidu (bioaktywnego sfingolipidu) na nowotworowe komórki nerwowe (neuroblastoma) pozwoliły na opracowania innowacyjnej metody badania heterogeniczności reakcji komórek na czynnik stresowy. Metoda ta, nazwana MPH (ang.Molecular Process Heterogeneity), pozwala na rozłożenie macierzy ekspresji w taki sposób, że otrzymujemy informację o (i) proporcjach badanych subpopulacji w danej próbce oraz (ii) wzorcach transkrypcji specyficznych dla każdej subpopulacji. Zaproponowana metoda pozwoliła na weryfikację hipotez dotyczących cytoprotekcyjnej roli PJ34, czyli inhibitora polimerazy poli (ADP-rybozy) – PARP na komórki nerwiaka zarodkowego linii linii SH-SY5Y traktowane ceramidem. Drugim formalnym modelem, opisanym w niniejszej rozprawie jest model szoku termicznego (ang.Heat Shock Response; HSR) w komórkach HeLa. Pozwala on na badanie mechanizmu regulacji ekspresji genów kodujących białka z rodziny HSP w szczególności HSP70, będącego chaperoniną kluczową dla ochrony komórek przed efektami cieplnej denaturacji białek. W modelu przedstawiłam pętlę regulatorową działającą na zasadzie ujemnego sprzężenia zwrotnego obejmującą interakcje krytyczne dla odpowiedzi komórki na szok termiczny. Schemat biochemiczny modelu składa się z dwunastu reakcji, które zostały przekształcone w układ równań różniczkowych zwyczajnych. Zachowania modelu badałam między innymi metodą analizy wrażliwości modelu co pozwoliło na wskazanie kluczowych reakcji, których zaburzenie propaguje szum na pozostałe interakcje. Nazwa HSR sugeruje, że odpowiedź komórki wywołana jest stresem cieplnym, jednakże białka z grupy HSP uczestniczą w reakcji na najrozmaitsze czynniki stresowe. Ich udział jest kluczowy dla rozwoju zarówno chorób nowotworowych jak i neurodegeneracyjnych, co więcej raportowano istnienie powiązań między aktywnością HSP70, a ścieżkami metabolizmu sfingolipidów. Z uwagi na ogromną złożoność i wielowymiarowość mechanizmów komórkowej reakcji na stres, zastosowanie podejścia systemowego wydaje się być jedyną drogą mogącą przybliżyć nas do zrozumienia i opisania zasad molekularnej reakcji na stres. Wykorzystanie modeli obliczeniowych i symulacji komputerowych pozwala na wgląd w naturę tych złożonych systemów.

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Yu, Hiu Ming (Bosco). « The Architectural Optimization of Stretch-formed Ceramic-aluminum Microtruss Composites ». Thesis, 2012. http://hdl.handle.net/1807/33600.

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Microtruss cellular materials have large internal surface areas and small cross-sectional strut dimensions, permitting surface modification to substantially enhance their mechanical performance. For instance, a ~400% increase in compressive strength with virtually no weight penalty can be induced by a hard anodized Al2O3 ceramic coating of only ~50 µm thickness. The present study seeks the optimal architecture of these composites by exploring three research challenges: architecture and degree of forming are interdependent due to stretch-forming, architecture and the material properties are interdependent due to work-hardening, and ceramic structural coatings add design complexity. Theoretical predictions and architectural optimizations demonstrated a potential weight reduction of ~3% to ~60% through the increase of internal truss angle for both annealed and work-hardened microtruss cores. While further validation is needed, experimental evidence in this study suggested the collapse in ceramic-aluminum microtruss composites could be considered as a mixture of composite strut global buckling and oxide local shell buckling mechanisms.

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Yang, Cheng-Lin, et 楊承琳. « Trivalent Chromium Induces Autophagy by Activating Sphingomyelin Phosphodiesterase 2 and Increasing Cellular Ceramide Levels in Renal HK2 Cells ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/92502930268140989690.

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博士
國立中興大學
生物醫學研究所
105
Recently, autophagy has emerged as a major cell response to metabolic stress, drug toxicity, environmental pollutants and lipogenetic disturbance. Most of effort has focused on the proteins and protein interaction in autophagosome formation. However, the role of lipids has not been investigated. In this study, we examined the role of autophagy in the initiation of lipid increases in renal epithelial HK2 cells. We found that trivalent chromium [Cr (III)] induced autophagy by activating sphingomyelin phosphodiesterase 2 (SMPD2). SMPD2 increases levels of ceramide and other lipids. Our recent studies found that signals of ceramide overlapped with LC3 demonstrated by confocal immunofluorescence microscopy study, suggesting that ceramide might play an important role in the formation of autophagosome. In conclusion, our data indicate that Cr (III) induces autophagy via structural aberration of organelle membrane, in particular by the increase of lipid compositions in addition to autophagy-associated proteins.

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49

Saha, Bhaskar Prasad. « Processing Of Zirconia Based Honeycombs And Evaluation Of Thermo Mechanical Properties ». Thesis, 2008. https://etd.iisc.ac.in/handle/2005/818.

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Résumé :

Ceramic cellular solids, mainly honeycombs and foams, are a novel class of composite materials where one phase is an interconnected network of solid struts or plates and the other one an empty phase or possibly a fluid. Honeycombs are an array of two dimensional prismatic cells whereas in foams the arrangements of cells are three dimensional polyhedral cells. Unlike solids, the properties of honeycombs are based on three major variables i.e. a) relative density (p* /p s where p* is the density of the cellular material and ps that of the solid of which it is made) b) cell wall material and c) geometry of the cells. Because of the flexibility in tailoring these variables, cellular solids can be engineered to exhibit a unique combination of mechanical and thermal properties for diversified thermostructural applications. Ceramic based honeycombs fabricated out of cordierite (2MgO.2Al2O35SiO2), mullite (3Al2O32SiO2), cordierite: mullite (2MgO.2Al2O35SiO2) with specific configurations are the leading candidates for many of the applications such as substrates for catalytic converters, molten metal filters, air heaters and heat exchangers etc. Zirconia by the virtue of its high fracture toughness and low thermal conductivity and high refractoriness is an interesting ceramic material and explored for versatile applications. However, no significant efforts have been reported to produce zirconia/alumina and their composite based honeycomb structures and also they have not been explored for their thermo-mechanical and energy absorption based applications. In the present study, looking at the possible potential applications of the honeycombs of Zirconia/alumina and their composites such as solid oxide fuel cells, high temperature filters, blast protection tiles etc., attempts are made to fabricate honeycomb structures. Chapter 1 of the thesis describes the detailed literature survey that has been carried out using advanced search packages regarding the evolution of ceramic honeycomb structures and their properties followed by the advantages of zirconia/alumina and their composites as candidate materials for targeted applications. Literature survey also covers the various processing techniques, characterization procedures with special emphasis on the thermo-mechanical properties. Chapter II describes attempts on developing an optimum scheme of processing of zirconia honeycomb which includes selection of precursor oxides, mixing of formulations, dough making based on viscosity measurements, shaping by extrusion, microwave drying, debinding and sintering to obtain the defect free monolithic structures keeping in view of the scale up possibilities. The chapter also describes a specially developed die fabrication process with innovative machining procedures. (Patent no. 198045). Sintered honeycombs were also characterized for their critical physiochemical properties. In chapter III mechanical characterization of honeycomb samples is reported after subjecting them to compression testing with varying cell channel orientation, compositions and configurations. It is observed that all honeycombs, irrespective of the composition and configuration exhibited anisotropic behavior. In addition, the anisotropy increases with the rib thickness and decreases with increase in the unit cell length. Thermal conductivity measurement studies of the honeycombs are reported in chapter IV. Two types of measurement techniques viz. laser diffraction and monotonic heating technique have confirmed the reduction of thermal conductivity of the honeycomb samples as compared to their solid counterpart. It is observed that the finer channel honeycombs offer low thermal conductivity as compared to the coarser channel when tested across the channel direction. For equivalent relative density, the thermal conductivity value for triangular channel is found to be more as compared to the square channel. Also, the thermal conductivity values were found less when measured across the channel as compared to the values when measured along the channels. The thermal conductivity value for fine channel zirconia-alumina composite honeycombs was found much less than the thermal conductivity of the alumina matrix. Chapter V summarises the implications of the study, conclusions and the target applications.

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50

Saha, Bhaskar Prasad. « Processing Of Zirconia Based Honeycombs And Evaluation Of Thermo Mechanical Properties ». Thesis, 2008. http://hdl.handle.net/2005/818.

Texte intégral

Résumé :

Ceramic cellular solids, mainly honeycombs and foams, are a novel class of composite materials where one phase is an interconnected network of solid struts or plates and the other one an empty phase or possibly a fluid. Honeycombs are an array of two dimensional prismatic cells whereas in foams the arrangements of cells are three dimensional polyhedral cells. Unlike solids, the properties of honeycombs are based on three major variables i.e. a) relative density (p* /p s where p* is the density of the cellular material and ps that of the solid of which it is made) b) cell wall material and c) geometry of the cells. Because of the flexibility in tailoring these variables, cellular solids can be engineered to exhibit a unique combination of mechanical and thermal properties for diversified thermostructural applications. Ceramic based honeycombs fabricated out of cordierite (2MgO.2Al2O35SiO2), mullite (3Al2O32SiO2), cordierite: mullite (2MgO.2Al2O35SiO2) with specific configurations are the leading candidates for many of the applications such as substrates for catalytic converters, molten metal filters, air heaters and heat exchangers etc. Zirconia by the virtue of its high fracture toughness and low thermal conductivity and high refractoriness is an interesting ceramic material and explored for versatile applications. However, no significant efforts have been reported to produce zirconia/alumina and their composite based honeycomb structures and also they have not been explored for their thermo-mechanical and energy absorption based applications. In the present study, looking at the possible potential applications of the honeycombs of Zirconia/alumina and their composites such as solid oxide fuel cells, high temperature filters, blast protection tiles etc., attempts are made to fabricate honeycomb structures. Chapter 1 of the thesis describes the detailed literature survey that has been carried out using advanced search packages regarding the evolution of ceramic honeycomb structures and their properties followed by the advantages of zirconia/alumina and their composites as candidate materials for targeted applications. Literature survey also covers the various processing techniques, characterization procedures with special emphasis on the thermo-mechanical properties. Chapter II describes attempts on developing an optimum scheme of processing of zirconia honeycomb which includes selection of precursor oxides, mixing of formulations, dough making based on viscosity measurements, shaping by extrusion, microwave drying, debinding and sintering to obtain the defect free monolithic structures keeping in view of the scale up possibilities. The chapter also describes a specially developed die fabrication process with innovative machining procedures. (Patent no. 198045). Sintered honeycombs were also characterized for their critical physiochemical properties. In chapter III mechanical characterization of honeycomb samples is reported after subjecting them to compression testing with varying cell channel orientation, compositions and configurations. It is observed that all honeycombs, irrespective of the composition and configuration exhibited anisotropic behavior. In addition, the anisotropy increases with the rib thickness and decreases with increase in the unit cell length. Thermal conductivity measurement studies of the honeycombs are reported in chapter IV. Two types of measurement techniques viz. laser diffraction and monotonic heating technique have confirmed the reduction of thermal conductivity of the honeycomb samples as compared to their solid counterpart. It is observed that the finer channel honeycombs offer low thermal conductivity as compared to the coarser channel when tested across the channel direction. For equivalent relative density, the thermal conductivity value for triangular channel is found to be more as compared to the square channel. Also, the thermal conductivity values were found less when measured across the channel as compared to the values when measured along the channels. The thermal conductivity value for fine channel zirconia-alumina composite honeycombs was found much less than the thermal conductivity of the alumina matrix. Chapter V summarises the implications of the study, conclusions and the target applications.

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