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1
Kosto, Kimberly Bryan 1977. "Hindered transport in composite hydrogels." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28358.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2004.Includes bibliographical references (leaves 143-152).
The ultimate goal of this research was to develop a greater understanding of the structural components needed to describe transport within the glomerular basement membrane (GBM). Specifically, dimensionless diffusive and convective hindrance factors were investigated by measuring macromolecular permeability through synthetic, two-fiber, agarose-dextran hydrogels at very small or very high Pe, respectively. By comparing diffusion and convection in the synthetic hydrogel with corresponding measurements in isolated rat GBM, further insight regarding the structure responsible for transport through the GBM was gained. In order to compare diffusive hindrances in the synthetic gels with those in isolated GBM, partitioning in agarose-dextran hydrogels was also examined. Additionally, hindered transport theories were tested. In studying diffusion, partitioning, and convection, macromolecules with Stokes-Einstein radii (r) ranging from 2.7 to 5.9 nm were used. Gels with agarose volume fractions of 0.040 and 0.080 were studied with dextran volume fractions (assuming dextran acts as a fiber) ranging from 0 to 0.0076 and 0 to 0.011, respectively. For the diffusion studies, two globular proteins (ovalbumin and bovine serum albumin) and three narrow fractions of Ficoll, a spherical polysaccharide, were used. For the partitioning and convection studies, four narrow fractions of Ficoll were used. Diffusivities of fluorescein-labeled macromolecules were measured in dilute aqueous solution (D[infinity]), agarose gels (D[alpha]), and agarose-dextran composite gels (D) using fluorescence recovery after photobleaching.
(cont.) For both agarose concentrations, the Darcy permeability (K) decreased by an order of magnitude as the dextran concentration in the gel was increased from zero to its maximum value. For a given gel composition, the relative diffusivity (D/D[infinity]) decreased as r increased, a hallmark of hindered diffusion. For a given test molecule, D/D[infinity] was lowest in the most concentrated gels, as expected. As the dextran concentration was increased to its maximum value, 2-3 fold decreases in relative diffusivity resulted for both agarose gel concentrations. The reductions in macromolecular diffusivities caused by incorporating various amounts of dextran into agarose gels could be predicted fairly accurately from the measured decreases in K, using an effective medium model. This suggests that one might be able to predict diffusivity variations in complex, multicomponent hydrogels (e.g. those in body tissue) in the same manner, provided that values of K can be obtained. Equilibrium partition coefficients ([Phi],the concentration in the gel divided by that in free solution) of fluorescein-labeled Ficolls in pure agarose and agarose-dextran composite gels were measured as a function of gel composition and Ficoll size. As expected, [Phi] generally decreased as the Ficoll size increased (for a given gel composition) or as the amount of dextran incorporated into the gel increased (for a given agarose concentration and Ficoll size). The decrease in [Phi] that accompanied dextran addition was predicted well by an excluded volume theory in which agarose and dextran were both treated as rigid, straight, randomly positioned and oriented fibers ...
by Kimberly Bryan Kosto.
Ph.D.
2
Perez, Edward Peña. "Bilayer composite hydrogels for corneal prostheses." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11786.
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Yang, Xianpeng. "Strong Cellulose Nanofiber Composite Hydrogels via Interface Tailoring." Kyoto University, 2020. http://hdl.handle.net/2433/253333.
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Binti, Adrus Nadia [Verfasser], Mathias [Akademischer Betreuer] Ulbricht, and Christian [Akademischer Betreuer] Mayer. "Stimuli-Responsive Hydrogels and Hydrogel Pore-Filled Composite Membranes / Nadia Adrus. Gutachter: Christian Mayer. Betreuer: Mathias Ulbricht." Duisburg, 2012. http://d-nb.info/1021899720/34.
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Li, Chao. "Synthesis and evaluation of porous composite hydrogels for tissue engineering applications." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/1388.
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The purpose of this dissertation was to synthesize and evaluate porous poly(2- hydroxyethyl methacrylate) (PHEMA) and PHEMA composite hydrogels containing various concentrations of titanium dioxide (TiO2) nanoparticles, silicon dioxide (SiO2) nanoparticles, and multi-walled carbon nanotubes (CNTs) for tissue engineering applications. Eighteen PHEMA nanocomposite hydrogels and five control PHEMA hydrogels were prepared in varying concentrations of water (60-90 wt.%) via a free radical polymerization process. Four of these hydrogels were modified further with an OVICOLL®CLEAR collagen, a mixture of type I and type III collagen, for the improvement of cell activities.Gravimetric analysis and X-ray diffraction analysis, as well as scanning electron microscopy (SEM), were used to examine the presence of the nanoadditives contained in the hydrogel polymers. The presence of collagen also was confirmed using a Fourier transform infrared spectroscope, an ultraviolet-visible spectrophotometer and an SEM.All hydrogels appeared opaque and exhibited various porous structures, which then were studied using a SEM. The porous structures were found to be dependent largely on the HEMA:water concentrations in the polymerisation mixtures. There was no significant difference in the porous structure for PHEMA and PHEMA composite hydrogels containing additives. The results from the polymer volume fraction study also indicated the porous structures of the resultant hydrogels.The tensile properties of the hydrogels were examined using a SINTECH200/M material testing workstation. The viscoelastic properties of the hydrogels were investigated using a HAAKE MARS III Modular Advanced Rheometer System. The mechanical properties of the hydrogels, apparently, were affected by the presence of the porous structures. In general, higher tensile and elastic moduli were seen for hydrogels with less porous structures. In contrast, lower tensile and elastic moduli were seen for more porously structured hydrogels. The addition of TiO2 particulates did not show significant influence on tensile and elastic moduli. However, the addition of CNTs increased the viscoelastic moduli of PHEMA hydrogels, which can be attributed to their fibre characteristics. The hydrogels produced in this study have shown a great range of linear viscoelasticity and a quick recovery characteristic, dependent on the macroporous structures and the presence of the TiO2 nanoadditives.The delivery of a model molecule, methylene blue and three biomolecules, including prednisolone 21-hemisuccinate sodium salt, caffeine, and bovine serum albumin were carried out under static and dynamic conditions. Rheological stimulations were used for the dynamic conditions. The delivery of both single and dual molecules was investigated. It was found that increasing the frequency and the shear strain of the stimulations accelerated the relative biomolecule release under dynamic conditions. However, in comparison to the static conditions, the relative delivery of the biomolecules was slowed by the application of rheological stimulations, due to the reabsorption of the biomolecule into the hydrogel matrix under the dynamic conditions. The release profiles of the biomolecules were affected by the concentrations of the biomolecules and their molecular weights, as well as the porous structures of the hydrogels. When dual biomolecules were utilised in the system, the delivery profile of each of the biomolecules was the same as the single biomolecule delivery profile. The relative release also was dependent on the porous structures and the molecular weights.The biomineralisation of the hydrogels was evaluated with a calcification study. The infiltration of the calcium phosphate was found to be more vigorous in a more porously structured hydrogel, and it was significantly enhanced after TiO2 nanoparticles were incorporated. An assay indicated that PHEMA and its nanocomposite hydrogels were tolerated well by the NIH 3T3 fibroblast cells. However, the cell growth on both PHEMA and PHEMA composite hydrogels was relatively slow. The presence of collagen significantly increased numbers of viable cells on modified hydrogels in comparison to that seen on hydrogels containing no collagen molecules. This was true for two other types of cell, including green fluorescent protein-transfected 253 human melanoma cells and human mesenchymal stem cells.In summary, porous PHEMA composite hydrogels make an excellent family of scaffolding materials for soft tissue regeneration. Their porous structures and mechanical properties can be tailor-made, simply by adjusting the chemical composition in the formulae to meet the requirements of specific applications. The bioactivities of the hydrogels also can be improved by tethering natural molecules without altering the porous structure or the mechanical properties. Biomolecules can be preloaded into the hydrogel matrices by a simple diffusion process at room temperature due to the presence of large pores. The preloaded concentrations and the subsequent delivery of these biomolecules can easily be adjusted by changing the concentrations of the stock solutions. This is highly desirable for an ideal tissue scaffold, which not only can provide interconnected pores and dictated mechanical properties, but also is capable of delivering essential signalling biomolecues for the tissue regeneration process. Therefore, these preliminary investigations of PHEMA and PHEMA composite hydrogels have demonstrated their great potential for tissue engineering applications.
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Way, Amanda E. "Stimuli-Responsive Nanofiber Composite Materials: From Functionalized Cellulose Nanocrystals to Guanosine Hydrogels." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1390388160.
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Barnes, Devon. "In vitro bioengineering applications of melt electrowritten and hydrogel composite scaffolds." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/212352/1/Devon_Barnes_Thesis.pdf.
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Two-dimensional cell cultures provide an inaccurate representation of how cells develop and are affected by disease and injury. Scaffold-based tissue engineering techniques that combine novel biomaterials and printing methods could assist in the design of more physiologically relevant, three-dimensional experimental tissue models. This thesis investigated the application of carbohydrate glass as a sacrificial material toward producing perfusable hydrogel devices using melt electrowriting, the development and optimisation of a three-dimensional bioengineered bone marrow microenvironment, and a literature review of the approaches toward the development, imaging and analysis of resulting three-dimensional models.
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Barros, Manuel João Salazar Guedes de. "Fabrication of hydrogel-bioactive glass composite scaffolds for bone tissue engineering." Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/17461.
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Mestrado em Materiais e Dispositivos BiomédicosBone is an extremely important connective tissue in the human body, as it provides support and protection of internal organs, being also metabolically relevant as the main mineral reservoir and assuring haematopoiesis through the bone marrow. Due to the current ageing of the population, an increase in bone tissue related diseases is noticeable. Thus, more efficient therapies for treating bone diseases is crucial. Tissue Engineering appears as a promising technology for treating several of those problems, such as bone loss and joint problems. In the present work, composite biomaterials composed of a polymeric hydrogel matrix reinforced with bioactive glass particles were prepared. Individually, these materials have a high water content, which enhances their diffusive transport properties, and display osteogenic properties, respectively. The selected polymer was RGD functionalized pectin, due to its interesting properties, such as biocompatibility, cell-adhesive characteristics and adequacy for cell entrapment, and the bioactive glass selected was a novel alkali-free formulation of 70% diopside and 30% tricalcium phosphate (Di-70), composed of SiO2, CaO, MgO and P2O5. Several different composite formulations were tested, in which pectin concentration, bioactive glass content and glass particle size were varied. The biocomposite’s viscoelastic properties were assessed, as well as their biological behaviour through cytotoxicity assays, and osteogenic character by incubating mesenchymal stem cell (MSC)-laden composites into both basal and osteogenic media for up to 21 days. The results obtained demonstrated that a composite biomaterial with tuneable mechanical properties was successfully prepared, with in situ crosslinking ability within therapeutically relevant timeframes, and not requiring additional crosslinking strategies besides its own composition. Furthermore, its intrinsic osteogenic properties due to the glass composition provided the adequate conditions for promoting the differentiation of MSCs without osteogenic stimulation. The combined properties achieved indicate that the biocomposites prepared are suitable candidate cellularized biomaterials for bone tissue engineering applications.
O osso é um tecido conjuntivo de extrema importância no organismo humano, tendo funções como suporte ou proteção de órgãos internos, sendo também metabolicamente relevante como o principal reservatório de minerais e assegurando a hematopoiese com a medula óssea. Dado o envelhecimento da população, tem-se verificado um aumento da incidência de doenças degenerativas deste tecido, sendo assim essencial aplicar terapias altamente eficientes para o tratamento dessas patologias. A Engenharia de Tecidos surge como uma tecnologia promissora no tratamento destes problemas, como a perda de massa óssea e problemas nas articulações. Neste trabalho, foram produzidos biomateriais compósitos, baseados numa matriz polimérica sob a forma de hidrogel reforçada com partículas de vidro bioativo. Individualmente, estes materiais apresentam um elevado teor em água favorável ao transporte de nutrientes, e propriedades osteogénicas, respetivamente. O polímero selecionado foi a pectina funcionalizada com RGD, dadas as suas propriedades interessantes como a biocompatibilidade, capacidade de promover a adesão celular e adequabilidade para o encapsulamento de células, e o vidro bioativo apresenta uma composição de 70% de diópsido e 30% de fosfato tricálcico (Di-70) isento de alcalinos e sendo composto por SiO2, CaO, MgO e P2O5. Diferentes formulações de hidrogéis compósitos foram testadas, em que se variou a concentração de polímero, a concentração de biovidro e o seu tamanho de partícula. Analisaram-se as propriedades viscoelásticas dos biocompósitos, bem como o seu comportamento biológico, com ensaios de citotoxicidade, e ainda as propriedades osteogénicas do material, pela incubação de hidrogéis contendo células estaminais mesenquimais (MSCs) em meio basal e osteogénico durante 21 dias. Os resultados deste trabalho indicam que foi possível preparar um biomaterial compósito de propriedades mecânicas ajustáveis, com capacidade de reticular in situ em tempos clinicamente desejáveis sem necessitar agentes reticulantes externos. Para além disso, as propriedades osteogénicas intrínsecas do biovidro forneceram as condições adequadas para a promoção da diferenciação de MSCs sem estimulação osteogénica adicional. As propriedades combinadas alcançadas indicam que os biocompósitos preparados têm potencial para ser aplicados em engenharia de tecido ósseo.
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Tay, Pei Kun Richie. "Synthesis of composite hydrogels incorporating D,L-cyclic peptide nanotubes as a platform for materials engineering." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78244.
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Thesis (S.M.)--Harvard-MIT Program in Health Sciences and Technology, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 27-30).
Composite hydrogels find increasing use as biomaterials because the addition of a filler often improves on the material properties of the original matrix, or provides new optical, magnetic, conductive or bioactive functionalities not inherent to the hydrogel. In this work we synthesized nanocomposite gelatin methacrylate (GelMA) hydrogels that incorporate D,L-cyclic peptide nanotubes. These nanotubes are biocompatible, stiff and their physical and chemical properties can be tailored simply by changing the amino acid sequence of the peptide. We show that the nanotubes successfully integrated into the hydrogel matrix and provided some mechanical reinforcement, without affecting hydrogel porosity or hydration characteristics. We will be using this composite system as a platform for engineering hydrogels with unique physical and biological properties to the hydrogel, for application as biological scaffolds.
by Pei Kun Richie Tay.
S.M.
10
Ehrenhofer, Adrian, and Thomas Wallmersperger. "Active hydrogel composite membranes for the analysis of cell size distributions." SPIE, 2019. https://tud.qucosa.de/id/qucosa%3A74237.
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Active membranes with switchable pores that are based on hydrogels can be used to measure the cell size distribution in blood samples. The system investigated in the present research is based on a polyethylene terephthalate (PET) membrane that is surface polymerized with poly (N-isopropyl acrylamide) (PNiPAAm) to form active pores of arbitrary geometry. The PET membrane provides the functionality of a backbone for mechanical rigidity, while the soft PNiPAAm hydrogel forms the active pores. Modeling and simulation of the active hydrogel behavior proved to adequately predict the opening and closing of the pores under application of an activating stimulus, e.g. temperature. The applied model is called Temperature-Expansion-Model and uses the analogy of thermal expansion to model the volume swelling of hydrogels. The Normalized Extended Temperature-Expansion-Model can englobe arbitrary hydrogels and large geometric displacements. Studies of pore opening - performed by using commercial finite element tools - show good agreement of the experimentally measured shape change of active pores. Based on these studies, the particulate fluid flow through the switchable pores is analyzed. Through application of a membrane process, i.e. a given variation of applied pressure and switching stimulus for the hydrogel, the size profile of the blocking particles can be measured directly using the flux difference under constant pressure. This allows the measurement of the cell size distribution in blood samples, e.g. to detect circulating tumor cells or anomalies in the distribution that hint to anemia.
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Wang, Chunhua, C. Mu, and W. Lin. "A Novel Microspheres Composite Hydrogels Cross-linked by Methacrylated Gelatin Nanoparticles - 45: Enhanced Mechanical Property and Biocompatibility." Verein für Gerberei-Chemie und -Technik e. V, 2019. https://slub.qucosa.de/id/qucosa%3A34268.
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Content: Nowadays, protein-based nanoparticle as a biodegradable, biocompatible product attracts considerable interest for new uses in specialized technical areas. Gelatin is a denatured, biodegradable,
and nonimmunogenic protein obtained by controlled hydrolysis of the triple-helix structure of collagen into single-strain molecules. As an amphiphilic biopolymer, gelatin can easily assemble into different kinds of aggregates under the defined pH and temperature and the resulting gelatin nanoparticles have been developed to be applied in the food industry and biomedical fields. Herein we report a novel
macromolecular microsphere composites (MMC) hydrogels with the use of prepared methacrylated gelatin nanoparticles (MA-GNP) as the cross-linker. MA-GNP have the ability of chemical crosslinking by the
polymerization of C=C bonds, such that the composite hydrogels can be formed by radical polymerization of acrylamide (AAm) on the surface of MA-GNP. The smooth spherical particles with an average size of
~100 nm have been synthesized through a modified two-step desolvation method as proved by atomic force microscopy (AFM). The results of nuclear magnetic resonance and dynamic light scattering further
confirm the presence of reactive groups (C=C bonds) in the particles and its narrow sizes distribution. The resulting composite hydrogels (MA-GNP/PAAm) are porous materials with tunable pore sizes and exhibit enhanced compressive resistance and elasticity as well. Increasing appropriately the dosage of MA-GNP reduces the equilibrium swelling ratio and improves thermal stability of the gels. Moreover, all the hydrogels exhibit prolonged blood-clotting time, nonhemolytic nature and strong suitability for cell proliferation, indicating the improved antithrombogenicity and excellent cyto-compatibility. It suggests
that the novel MA-GNP/PAAm hydrogels have potential application as tissue engineer scaffold materials, and the MA-GNP can be a promising macromolecular microsphere cross-linker for application in biomedical materials. The present work not only exploits new strategies to fabricate MMC hydrogels but also advance the potential application of biodegradable gelatin-based nanoparticles in biomedical fields.
Take-Away:
1. A well-dispersed methacrylated gelatin nanoparticle (MA-GNP) with an average size of ~100 nm is presented by a modified two-step desolvation method.
2. MA-GNP is readily introduced into the polyacrylamide (PAAm) system as a cross-linker to prepare macromolecular microsphere composites (MMC) hydrogels via a free radical polymerization reaction.
3. MA-GNP is an effective cross-linker, improving both the compressive resistance and elasticity of MMC hydrogels as well as the biocompatibility.
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Jordan, Alex Michael. "FIBER-COMPOSITE IN SITU FABRICATION: MULTILAYER COEXTRUSION AS AN ENABLING TECHNOLOGY." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1467832877.
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Ehrenhofer, Adrian, Manfred Hahn, Martin Hofmann, and Thomas Wallmersperger. "Mechanical behavior and pore integration density optimization of switchable hydrogel composite membranes." Sage, 2019. https://tud.qucosa.de/id/qucosa%3A74211.
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Switchable hydrogel-layered composite membranes can be used for the analysis of particle size distributions. This functionality is provided by pores with controllable diameter. In order to obtain a device that can be used to measure the cell size distribution in native biological samples, lots of switchable pores are required. In the current work, we model and simulate the mechanical behavior of active composite membranes with switchable pores. This is done in order to find the maximum number of pores that can be integrated into a membrane without cross-influencing effects on the actuation of the pores. Therefore, we investigate (1) the interaction of active pores inside the multifunctional composite and (2) the membrane bending under microfluidic pressure load. We show that through miniaturization, sufficient pores can be added to a permeation control membrane for processing native blood samples. The envisioned device allows a parallelized measurement of cell sizes in a simple lab-on-a-chip setup.
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Frayssinet, Antoine. "Hydrogels composites collagène/acide hyaluronique cellularisés et biomimétiques pour la régénération du Nucleus Pulposus." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS312.
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50 % des douleurs dorsales chroniques sont associées à une dégénérescence du disque intervertébral (IVD). Nous avons émis l'hypothèse qu'un hydrogel biomimétique favoriserait la régénération du Nucleus Pulposus, la partie centrale de l’IVD, en fournissant des signaux physiques adéquats à des cellules souches mésenchymateuses (MSC) pour se différencier en nucléopulpocytes. Avec des teneurs différentes en acide hyaluronique fonctionnalisé (HA-Tyr), des hydrogels composites Collagène/HA-Tyr ont été synthétisés et caractérisés par microscopies électroniques à balayage et à transmission, rhéologie, DSC, par test de dégradation enzymatique in vitro accélérée et par tests de capacité à absorber l’eau. Des MSC ont ensuite été incorporées dans les composites Col/HA-Tyr, puis cultivées pendant 28 jours. La viabilité cellulaire a été évaluée, et leur différenciation en nucléopulpocytes analysée par PCR quantitative et par immunohistochimie indirecte. La présence de plusieurs marqueurs de différenciation des nucléopulpocytes, tels que le Collagène de type II, l'Agrécane et le KRT 18 a été suivie. Le processus de fabrication a permis la génération d'hydrogels hautement hydratés (> 90%), mécaniquement biomimétiques, résistants à la dégradation enzymatique et dans lesquels la fibrillogenèse du collagène a été préservée. En absence de facteur de différenciation, l’élasticité et la structure des hydrogels composites Col/HA-Tyr semble suffire pour induire la différenciation des MSC incorporées en nucléopulpocytes. Développée suivant une approche biomimétique, cette plateforme d'hydrogels composites Col/HA-Tyr parait donc prometteuse pour la régénération du disque intervertébralHalf of chronic back pain is associated with intervertebral disc (IVD) degeneration. We hypothesized that a biomimetic hydrogel would promote the regeneration of the Nucleus Pulposus, the central part of IVD. Hydrogels will provide cues to incorporated mesenchymal stem cells (MSC) to in situ differentiate into nucleopulpocytes. With different contents of functionalized hyaluronan (HA-Tyr), Collagen/HA-Tyr hydrogels were produced and characterized using scanning and transmission electron microscopy, rheology, DSC, accelerated in vitro enzymatic degradation and tested for their ability to absorb water. MSC were then incorporated within Col/HA-Tyr composites and cultured over 28 days. Cell viability was assessed and cell differentiation was analysed by quantitative PCR and indirect immunohistochemistry. The presence of several nucleopulpocytes differentiation markers, such as type II Collagen, Aggrecan and KRT 18 was monitored. The manufacturing process allowed the generation of highly hydrated hydrogels (> 90%), mechanically biomimetic, resistant against enzymatic degradation, in which collagen fibrillogenesis was preserved. Without any differentiation factor, both elasticity and structure of the Col/HA-Tyr composite hydrogels seems to be sufficient to induce the differentiation of the incorporated MSCs into nucleopulpocytes. In addition, the presence of collagen was necessary for an adequate cell adhesion. Developed according to a biomimetic approach, this platform of Col-HA-Tyr hydrogels appears promising for the intervertebral disc repair
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Walker, Ezekiel Lee. "Electromagnetically Modulated Sonic Structures." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc799496/.
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Phononic crystals are structures composed of periodically arranged scatterers in a background medium that affect the transmission of elastic waves. They have garnered much interest in recent years for their macro-scale properties that can be modulated by the micro-scale components. The elastic properties of the composite materials, the contrast in the elastic properties of the composite materials, and the material arrangement all directly affect how an elastic wave will behave as it propagates through the sonic structure. The behavior of an elastic wave in a periodic structure is revealed in its transmission bandstructure, and modification of any the elastic parameters will result in tuning of the band structure. In this dissertation, a phononic crystal with properties that can be modulated using electromagnetic radiation, and more specifically, radio-frequency (RF) light will be presented.
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Lehmann, Swen [Verfasser], Walter [Akademischer Betreuer] Richtering, and Alexander [Akademischer Betreuer] Böker. "Smart crowding in poly-Acrylamide/Poly(N-isopropylacrylamide) composite hydrogels, studied by two-focus fluorescence correlation spectroscopy / Swen Lehmann ; Walter Richtering, Alexander Böker." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1156630037/34.
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Desprez, Valérie. "Caractérisations, applications et modélisation d'électrodes modifiées par des hydrogels : laponite-oligosilsesquioxanes(-enzyme)." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10108.
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Ce memoire est consacre a la caracterisation, aux applications et a la modelisation cinetique d'electrodes modifiees par des hydrogels de laponite expansee par des oligosilsesquioxanes et fonctionnalisee par des especes electrocatalytiques (microparticules de metaux nobles, mediateurs redox, enzymes). Les etudes physico-chimiques et electrochimiques de ce nouveau materiau hybride d'electrode ont mis en evidence l'intercalation des oligosilsesquioxanes et l'existence d'une micro-porosite induite susceptible d'etre conservee en milieu organique. La stabilite des films obtenus ainsi que leur propriete d'echange d'ions offrent de larges potentialites d'application qui ont ete demontrees par plusieurs exemples en electrocatalyse (hydrogenation electrocatalytique) et en electroanalyse (biocapteurs amperometriques). En particulier, l'immobilisation de la polyphenol oxydase (ppox) permet l'elaboration d'un capteur sensible aux composes phenoliques aussi bien en milieux aqueux qu'en milieu organique. Les performances analytiques de ce capteur, tant en sensibilite, temps de reponse qu'en seuil de detection, comptent parmi les meilleures jusqu'ici decrites pour de tels systemes. Enfin, la modelisation cinetique du systeme electroenzymatique catechol/ppox qui met en jeu dans son fonctionnement une regeneration electrochimique du substrat de l'enzyme, a permis de rationaliser le processus d'amplification electroenzymatique responsable des limites de detection extremement basses de ce type de capteur. L'ensemble de ces etudes nous a ainsi permis de proposer une structure mesoporeuse de l'hydrogel enzyme-laponite expansee et de quantifier les modes de transport et d'amplification electroenzymatique.
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Kola-Mustapha, Adeola Tawakalitu. "Novel biomimetic polymeric nanoconjugates as drug delivery carriers for poorly soluble drugs." Thesis, De Montfort University, 2013. http://hdl.handle.net/2086/10243.
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Active Pharmaceutical Ingredients with poor solubility have presented significant difficulties in drug product design and development including slow and ineffective absorption leading to inadequate and variable bioavailability. Therefore it has become increasingly desirable to overcome the low aqueous solubility of drug candidates and develop more novel and innovative formulation approaches to increase the dissolution rate of the poorly soluble drugs. This work focuses on the formulation of novel amorphous ibuprofen-polymer nanoconjugates based on the polymer-drug complexation in order to improve its physical and dissolution characteristics without the use of toxic organic solvents. Plain and ibuprofen-loaded binary and ternary nanoconjugates were prepared using four modified co-precipitation techniques including melt solubilization; alkaline solubilization; surfactant solubilization and hydrotropic complexation techniques. A remarkably high loading capacity was achieved ranging from 89.05 to 99.49% across the four techniques and polymer-polymer ratio of 50:50 was found to be most efficient. All the four techniques reduced the size of ibuprofen (2.87 μm) significantly in the presence of 2.0 x10-3 mM of Diethylaminoethyl Dextran (DEAE-Dextran) in the order melt solubilization (203.25 nm) > alkaline solubilization (185.68 nm) > surfactant (Tween 80) solubilization (122.17 nm) > hydrotropic complexation (77.92 nm). 5.0 x 10-4 mM of chitosan also reduced the size of ibuprofen from 2872.12 to 10.70 nm (268-fold reduction). The FTIR spectroscopic analysis revealed electrostatic, hydrophobic and hydrogen bonding interaction between solubilized ibuprofen and the cationic polymers (DEAE-Dextran and chitosan) to form a new product (an amide). Polymer-polymer complexation also occurred between DEAE-Dextran and gellan as well as chitosan and gellan to a different extent depending on the mixing ratios. 1H and 13C NMR analysis confirmed the conjugation between ibuprofen and each of the cationic polymers as well as the formation of a new amide product. DSC thermal analysis showed that the nanoconjugates exhibited new broad and diffuse peaks confirming that they did exist in amorphous state as multiple complexes. The TGA thermograms of the binary nanoconjugates exhibited one step degradation profile compared with the physical mixture which exhibited two steps. However the ternary nanoconjugates exhibited two steps degradation profile confirming the formation of multiple complexes. Marked enhancement of drug release was achieved by the four techniques compared with the ibuprofen control. All the DG (DEAE-Dextran - Gellan) complexes exhibited a higher release profile than ibuprofen control. Fickian and non-Fickian anomalous mechanisms were deduced for the drug release of ibuprofen from the binary conjugates. The ternary nanoconjugates exhibited non-Fickian (anomalous) diffusion, Fickian diffusion and Super Case II transport release mechanisms. The ternary nanoconjugate hydrogels exhibited complete release (100%) within 48 h. The lowest concentration of DEAE-Dextran, Gellan - Ibuprofen - DEAE-Dextran (GIbDD) 2:0.125, increased the release of ibuprofen by 13.4% however higher concentrations of DEAE-Dextran decreased the release profile steadily. It was concluded that DEAE-Dextran has potentials in the formulation of modified (extended) release of ibuprofen. The most prominent mechanism of release of ibuprofen from the nanoconjugate hydrogel was Super Case II transport. SEM and AFM micrographs of the drug loaded composite pharmaceutical films exhibited concentric spheres with two and three layers for the binary and ternary films respectively. This supports the evidence of internalization of ibuprofen by the polyelectrolyte complex. The FTIR and DSC results confirmed electrostatic and hydrophobic interactions between ibuprofen and DEAE-Dextran as well as between gellan and DEAE-Dextran. Thermal analysis revealed that plain bilayer films were thermally more stable than composite films. The addition of ibuprofen significantly increased (p < 0.05, n = 4) the swelling ratio of the films compared with films without the drug. The drug loaded bilayer films exhibited Fickian diffusion mechanism while the dominating mechanism for composite films was anomalous (Non-Fickian) transport. From the foregoing, it was evident that ibuprofen-polymer nanoconjugate present a novel tool for the delivery of ibuprofen with potential application for transdermal delivery.
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Roux, Rémi. "Élaboration d'assemblages colloïdaux à partir de nanoparticules de poly(acide lactique) et de chitosane." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10088/document.
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Les assemblages colloïdaux représentent une nouvelle piste très prometteuse dans le domaine de l'ingénierie tissulaire. Idéalement, ce type d'assemblage permet l'obtention de matériaux injectables et gélifiants sur le site lésionnel, favorisant par la suite le développement de néo-tissus viables. Ce travail porte sur la formation de tels assemblages à base de chitosane et de poly(acide lactique) (PLA). Deux types d'assemblages ont été conçus et étudiés dans ce travail. Dans une première approche, le mélange de particules anioniques de poly (acide lactique) (PLA) avec du chitosane en solution faiblement acide conduit à la formation de « gels composites », résultant des interactions colloïde-polymère. Des analyses rhéologiques et de diffusion des rayons X aux petits angles ont permit de mettre en évidence le mode de formation et l'influence de plusieurs paramètres sur les propriétés finales de ces gels. Notamment, ils présentent des propriétés rhéofluidifiantes et un caractère réversible, c'est-à-dire que le gel peut se reformer après déstructuration mécanique. Le second type d'assemblage résulte du mélange de particules anioniques de PLA et de nanogels cationiques de chitosane, conduisant à la formation de « gels colloïdaux », par interactions colloïde-colloïde. L'influence de plusieurs facteurs sur la formation et les propriétés de ces gels a également été étudiée par mesures rhéologiques. Notre étude s'est notamment orientée sur la caractérisation et la stabilité des hydrogels physiques de chitosane sous forme colloïdale, ainsi que sur l'optimisation de leur cohésionColloidal assemblies may be a promising pathway to obtain injectable scaffolds favoring the development of neo-tissue in regenerative medicine. This work investigates the formation of such assemblies composed of chitosan, soluble or in suspension (nano-hydrogel), and poly(lactic acid) (PLA) nanoparticles. Two types of assemblies are studied. As a first approach, mixing negatively charged PLA particles and chitosan solution leads to the formation of “composite gels”, based on colloidpolymer interactions. Rheological and Small Angle X-Ray Scattering measurements highlighted the formation process and the influence of various parameters on final properties of these gels, which features shear-thinning and reversibility behavior, that is, the capacity to gel again after yielding. PLA nanoparticles could also be mixed with cationic chitosan nanoparticles, which are crosslinker free nano-hydrogels, leading to the formation of “colloidal gels”, based on colloid-colloid interactions. Influence of various parameters on gel synthesis and properties are investigated through rheological measurements. The study also focuses on the characterization and control of the morphological and cohesion properties of chitosan nanogel
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Kianbakhsh, Pejman. "Recycling polymer composite hydrogen pressure vessels." Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546472.
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By 2002 the world market for polymer composites was 7.2 Million Tons. The automotive and industrial vehicle industry consumes 25% of the world's composite material output. Composite materials benefit the automotive industry in multiple ways. Regulatory pressure that encourages recyclablity and reduction of energy consumption pushes automotive manufacturers to consider new technologies to meet these environmental standards. The work being undertaken in this research is part of an ED integrated Project under the "Sixth Framework of Research and Development Funding". The project title is "Hydrogen Storage Systems for Automotive Application (StorHy)". Within this project, the Recycling Work Package (WP5) aims to develop recycling techniques for glass and carbon fibre reinforced polymer composite pressure vessels that were proposed for hydrogen storage. This thesis describes the development of a SIze reduction technique for the carbon/epoxy and glass/PP pressure vessels with respect to the particle size and investigates ways of preparing the granulated fractions for subsequent processing. An image analysis technique was successfully developed for the characterisation of the reground material from the carbon/epoxy pressure vessel. The same image analysis technique could not be used to analyse the reground material produced from the thermoplastic vessel. Alternatively, the reground material from the thermoplastic vessel were characterised through a sieve analysis technique. The reground material from the thermoset vessel produced in this work could be processed in a fluidized bed rig which is mentioned in a number of publications. In this work, the reground material from the thermoplastic vessel was successfully processed using an injection moulding machine, with mechanical properties as good as comparable to commercial composites. In this study micro mechanical models available in the short fibre composite literature such as Halpin-Tsai and the rule of mixtures were used to predict the stiffness of the injection moulded composites. The trend observed for the Halpin-Tsai model appeared not to be in a good agreement with the experimental data but the rule of mixtures model was found to predict the experimental data more accurately.
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Shi, Guoqiang. "Preparation and properties of polymeric bacteriostatic composite hydrogel." Магістерська робота, Kyiv National University of Technology and Design, 2021. https://er.knutd.edu.ua/handle/123456789/19545.
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The master's thesis is devoted to developing and preparing a composite hydrogel material that can meet the long-term antibacterial properties through a simple physical cross-linking method. The specific research content is as follows: Using PVA and PHMG as raw materials, without introducing initiator and cross-linking agent, through the freezing-thawing method, an antibacterial hydrogel material was prepared. By controlling the PHMG content, freezing time, the number of freeze-thaw cycles and other conditions, the performance of the hydrogel can be adjusted. The best formulation of the hydrogel is found through characterization methods such as light transmittance, swelling rate, dissolution rate, mechanical properties, biocompatibility, and in vitro antibacterial. Prove that the hydrogel has excellent performance-especially long-term antibacterial ability and safety.Магістерська робота присвячена розробці та виготовленню композитного гідрогелевого матеріалу, який може мати довготривалі антибактеріальні властивості за допомогою простого фізичного методу поперечного зшивання. Зміст дослідження полягає в наступному. Використовуючи в якості сировини ПВА та ПГМГ, без введення ініціатора та зшиваючого агента методом заморожування-розморожування було виготовлено антибактеріальний гідрогелевий матеріал. Контролюючи вміст ПГМГ, час заморожування, кількість циклів заморожування-відтавання та інші умови, можна регулювати рівень характеристик гідрогелю. Найкращий склад гідрогелю знайдено шляхом дослідження таких характеристик, як світлопропускання, швидкість набухання, швидкість розчинення, механічні властивості, біосумісність та антибактеріальний ефект in vitro. Доведено, що гідрогель має чудові характеристики, особливо довгострокові антибактеріальні властивості та безпечність у застосуванні.
Магистерская работа посвящена разработке и изготовлению композитного гидрогелевого материала, который может обладать длительными антибактериальными свойствами с помощью простого физического метода поперечной сшивки. Содержание исследования состоит в следующем. Используя в качестве сырья ПВА и ПГМГ, без введения инициатора и сшивающего агента методом замораживания-размораживания был изготовлен антибактериальный гидрогелевый материал. Контролируя содержание ПГМГ, время замораживания, количество циклов замораживания-оттаивания и другие условия можно регулировать уровень характеристик гидрогеля. Лучший состав гидрогеля найден путем исследования таких характеристик, как светопропускание, скорость набухания, скорость растворения, механические свойства, биосовместимость и антибактериальный эффект in vitro. Доказано, что гидрогель обладает отличными характеристиками, особенно долгосрочными антибактериальными свойствами и безопасностью в применении.
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Mottet, Léopold. "Hydrogel composite conducteur pour l'encapsulation de bactéries électroactives." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066583/document.
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Ce travail de thèse est principalement axé sur la création d'un nouveau réacteur biocompatible permettant l'encapsulation et l'étude de bactéries électroactives. Ce compartiment de taille millimétrique, réalisé par coextrusion, est une capsule à coeur liquide possédant une membrane d'hydrogel conducteur. La synthèse de ce bioréacteur a nécessité la formulation d'un hydrogel composite alginate/nanotubes de carbone en deux étapes. Une première étape rapide crée la matrice d'hydrogel par diffusion d'ions divalents dans un mélange Alginate/nanotubes de carbone. Une seconde étape, plus lente, permet la dialyse du tensioactif stabilisant les nanotubes et la création d'un réseau conducteur au sein de l'hydrogel pour des pourcentages massiques de charges supérieurs à 0,5 %. Ce matériau composite présente alors une conductivité macroscopique d'environ 0,1 S/m. Une étude du matériau par voie électrochimique permet entre autres de suivre cinétiquement la connexion des nanotubes de carbone. Des bactéries peuvent adhérer à la surface de cet hydrogel composite. Nous démontrons qu'il est alors possible de mesurer l'électroactivité d'un biofilm bactérien développé sur la paroi interne d'une capsule conductrice. Ce nouveau compartiment biocompatible ouvre la voie vers le développement d'un outil de criblage pour la sélection de bactéries électroactives mais offre également des perspectives innovantes pour la fabrication de piles bactériennesThis work focuses on the creation of a new biocompatible reactor allowing the encapsulaion and the study of electroactive bacteria. Made by co-extrusion, this millimeter bioreactor is a liquid core capsule with a conducting hydrogel membrane. To create such an object, we formulate a composite hydrogel of alginate/carbon nanotubes in two steps. The first step is rapid and creates the hydrogel matrix by diffusion of divalent ions inside the alginate/carbon nanotubes mix. The second step is slower and permits the dialysis of the surfactant used to stabilize the nanotubes. During this last step, the carbone nanotube network percolates, creating a conducting network in the hydrogel for sufficient nanotube contents (above 0.5 %). This composite material has a macroscopic conductivity around 0.1 S/m. An electrochemical study of this material allows to follow the nanotube connection inside the hydrogel. Bacteria can adhere on this composite hydrogel. Then, we demonstrate that the electroactivity of a biofilm developped on the inner side of the conductive capsule shell can be measured. This new biocompatible and electron-conducting compartment opens the way towards the development of a screening tool for the selection of electroactive bacteria but also brings innovative perspectives in the field of microbial fuel cells fabrication
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Haji, Aminoddin, Komeil Nasouri, Ahmad Mousavi Shoushtari, and Ali Kaflou. "Reversible Hydrogen Storage in Electrospun Composite Nanofibers." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35201.
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Composite nanofibers containing single-walled carbon nanotubes (SWNT) were prepared by using elec-trospinning technique and hydrogen adsorption/desorption isotherms were carried out by a Sieverts appa-ratus at room temperature. The SEM analysis of the nanofibers revealed that the deformation of the nano-fiber increases with increasing SWNT concentration. The diameter of neat nanofibers was below 200 nm and had smooth surface. The surface of the composite nanofibers was rough even by adding low quantity of SWNT. The hydrogen storage results showed an improvement in the adsorption capacity with increasing the SWNT content in composite nanofibers. These nanofibers were evacuated again to remove the ad-sorbed hydrogen at room temperature. Moreover, even though specific surface area and total pore volume were important factors for increasing the capacity of hydrogen adsorption. Finally, maximum adsorption capacity was 0.29 wt % in case of nanofibers with 10 wt % SWNT under 30 bar at 298 K.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35201
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Ehrenhofer, Adrian, and Thomas Wallmersperger. "Adjustable fluid and particle permeation through hydrogel composite membranes." Sage, 2017. https://tud.qucosa.de/id/qucosa%3A74231.
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Membranes act as smart structures in respect to their permeation abilities. Control of particle and fluid permeation through a synthetic membrane can be achieved by using different effects like size-exclusion or electromagnetic interactions that occur between the particles and membrane pores. The simulation of controlled permeability provides an insight into the smart behavior of membranes for chemical signal processing, sensing interfaces or lab-on-a-chip devices. In the current work, we model the underlying physical processes on a microfluidic level using the engineer’s approach of laminar flow through pipes. Different pore geometries inside a composite membrane system consisting of a polyethylene terephthalate support membrane and a poly(N-isopropylacrylamide) hydrogel-layer are investigated. Simulations for different states of thermally induced pore opening are performed for free and blocked states. From the results we derive paradigms for the design of a membrane system for microfluidic cell-size profiling considering stimulus-range, pore shape and measurement setup.
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Samchenko, Yu M., S. O. Kryklia, T. P. Poltoratska, Леонід Федорович Суходуб, Леонид Федорович Суходуб, Leonid Fedorovych Sukhodub, Yu O. Isheikina, V. I. Makarenko, and V. V. Konovalova. "Hybrid Hydrogel Materials with Incorporated Nanoparticles." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35464.
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Synthesis and physico-chemical studies of new promising hybrid hydrogels based on polyvinyl alcohol (PVA) acetales and copolymer hydrogels based on vynil monomers have been studied. Acrylamide and Acrylnitrile were used as some of components that carry various fillers . Sponge acetales of polyvinyl alco-hol were used as enforcing net. The synthesized composites demonstrated high strength as compared to standard hydrogels- Yung-module varied in the range of 80 to 300 kPa depending on the extent of PVA ac-etale matrix filling with hydrogel component. The materials showed high sorbability to water and water solutions. Study of swelling kinetics as compared to solvents of various nature (water, ethanol, sunflower oil ) was carried out.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35464
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Roellinger, Bettina. "De nouveaux hydrogels composites pour la production et le stockage énergétique." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLET053.
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Les hydrogels sont des matériaux poreux visco-élastiques formés d'un réseau tridimensionnel généralement de polymères capables d'absorber une grande quantité d'eau. Du fait de leurs propriétés, on les utilise principalement dans l'industrie pharmaceutique, agroalimentaire et dans le domaine des biotechnologies. Au cours de cette thèse, nous proposons d’ouvrir une voie encore peu exploitée qui est l’intégration des hydrogels pour le stockage et la production d’énergie. Dans un premier temps, les étapes qui ont conduit à la formulation ainsi qu’à la caractérisation physico-chimique d’une électrode poreuse à base d’alginate, un polyélectrolyte naturel,et de nanotubes de carbone sont décrites. Une première application consiste à encapsuler des bactéries électro-actives dans la matrice composite de carbone pour la production d’énergie. Le métabolisme particulier de la bactérie anaérobie Geobacter sulfurreducens permet des transferts d’électrons avec le milieu extérieur grâce à des réactions d’oxydo-réduction. Le suivi du courant dans le temps permet ainsi de montrer la prolifération et la viabilité des bactéries dans l’hydrogel jusqu’à déplétion du milieu en nutriments. Une seconde application est l’incorporation de particules d’intercalation du lithium dans cet hydrogel hybride, un matériau potentiellement utilisé dans des batteries en écoulement aqueuse. La caractérisation électro-chimique des couples redox MnO2/LiMn2O4 et FePO4/LiFePO4 au sein de l'hydrogel, montrera qu’il est possible de développer une batterie ion-lithium aqueuse d’une tension nominale de 0.65 V. Ce travail aura donc permis de mettre en avant l'intérêt et les perspectives de cet hydrogel conducteur pour le domaine énergétiqueHydrogels are highly water-absorbent three dimensional viscoelastic networks, mainly based on polymers used in numerous fields such as biotechnology, food and pharmaceutical industry. However, the potential use of these materials in the energy domain has not yet been fully investigated. To bring new insights and perspectives, we have developed during this PhD thesis a spherical macroporous electrode made of a conductive hydrogel. It is composed of sodium alginate, a polyelectrolyte that can form a biocompatible hydrogel when mixed with water in presence of divalent cations. The addition of carbon nanotubes in the solution before gelation leads to the formation of an electronically conductive network. The formulation and the physicochemical characterization are first discussed. Then two direct applications will be detailed. The first one consists in encapsulating electroactive bacteria inside the composite hydrogel. The peculiar metabolism of Geobacter sulfurreducens allows electron transfer with the external medium through oxydo-reduction reactions. Current monitoring allows us to show proliferation and viability of the cells until depletion of nutrients in the medium. The second one is the incorporation of intercalation lithium particles in the same matrix for semi-solid redox flow battery domain. Characterization of the redox couple MnO2/LiMn2O4 and FePO4/LiFePO4 inside the hydrogel, will enable us to develop a Li-ion battery with a 0.65 V nominal tension
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Holdforth, Rachel Katherine. "Conductive carbon nanotube-hydrogel composites for nerve repair." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609184.
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Lizardo, Daniel (Daniel H. ). "Architectural scale biomimetic composites based on chitosan and alginate hydrogels." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98654.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, June 2015.Cataloged from PDF version of thesis. "May 2015."
Includes bibliographical references (pages 44-46).
Developmental research and characterization was conducted on novel biomaterials for a larger project of product and architectural scale digital fabrication using natural bioplastics and hierarchical computational design carried out by the Mediated Matter team, led by Laia Mogas-Soldevila and Jorge Duro-Royo. Chitosan and alginate (among other natural polymers) are processed from shellfish waste and algae, respectively, and highly viscous solutions are extruded as a layer-by-layer printing material which dries into a solid, single material product with spatially variable functionality. Additional solid materials are added including cellulose microfibers and kaolinite platelets as volumetric aggregates, strengthening or stiffening aggregates, and as modes for directional properties. All materials used for aggregates, like that of the hydrogel matrices, were naturally sourced and recyclable. These composite materials were analyzed through microscopy and mechanical testing to begin to determine their agency in the aforementioned purposes. The most promising materials were selected and then discussed at length in an attempt to understand the factors behind ease of production, scalability, and potential for optimization, and as the research continues, they will be tested in the digital fabrication platform at the installation scale.
by Daniel Lizardo.
S.B.
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Kurban, Z. "Electrospun nanostructured composite fibres for hydrogen storage applications." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1333231/.
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The urgent realisation of the low carbon economy requires the development of cheap, safe and lightweight hydrogen storage, both for commercialisation of hydrogen fuel cell vehicles, and for the use of hydrogen as a reservoir of energy from intermittent renewable energy sources. The primary motivation of this PhD project was to investigate (co)electrospinning, a cheap and scalable fibre production technique, for nanostructuring potential solid state hydrogen storage materials. Solid state storage of hydrogen is being extensively investigated worldwide. However, many of the candidate materials are still not able to meet the practical requirements for mobile applications. The principal drawbacks are that these materials either have low capacity for hydrogen storage (physisorption systems), even at cryogenic temperatures, or high release temperatures with slow release rates (chemisorption systems). Because kinetic and thermodynamic properties can be improved by nanoscale processing, nanoengineering of selected materials has emerged as one of the most effective ways of overcoming their associated performance barriers. In this thesis I present two successful approaches to nanostructuring using electrospinning: firstly, by encapsulating chemical hydrides in polymeric nanofibres, as demonstrated by the development of co-axial ammonia borane-encapsulated polystyrene (AB-PS) fibres, and secondly, by post-processing of single-phase electrospun PAN fibres, resulting in the synthesis of potassium-intercalated graphitic nanofibres (K-GNFs). The results show that the micro and nano-structure imparted through electrospinning, can have the effect of reducing dehydrogenation temperatures in AB-PS fibres (from 110 to ~85 °C) and improving the (de)hydrogenation rates by an order of magnitude in both composite fibres (from ~50 to <5 mins in K-GNFs and from ~150 minutes to as low as 15 minutes in AB-PS fibres). The details of co-axial electrospinning as a novel approach to nanoengineering chemical hydrogen storage materials and as a way of possibly overcoming issues regarding reversibility, stability and clean hydrogen release from many of these materials is discussed. The solution selection method I have developed for use in the synthesis of co-axial composite fibres can be applied as an efficient solution selection formula for multi-phase electrospinning in general.
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Mistry, P. "Development of a core-shell composite hydrogel for 3D bioprinting." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/50395/.
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Recently, 3D printing has become popular in the field of tissue engineering, where materials and biology are combined with the aim of producing functional tissues for regenerative medicine therapies and for in vitro disease and toxicology models. However, current 3D printing techniques are not able to produce functional tissue-engineered constructs that are physiologically-relevant in the long-term. Challenges arise when combining desired mechanical properties with biological properties in a single construct. Often, cell-supportive materials lack mechanical stability and mechanically-robust materials are unable to support cell growth and function. In addition, many native tissues and organs are heterogeneous, with graded properties. The recapitulation of these factors will help to produce more physiologically-relevant tissue replacements and in vitro models with better predictability. This thesis seeks to combine biological and mechanical properties in a single core–shell strand: a mechanically-robust shell hydrogel encapsulating biologically active cell-laden core. This body of work has been split into three sections, the assessment of a hybrid material for use in the shell, the production of 3D printed constructs with core–shell strands, and the incorporation of gradients into these printed constructs. First, the mechanical properties of a poly(ethylene glycol) diacrylate (PEGDA)/alginate hybrid hydrogel was assessed using tensile testing. The hybrid hydrogels demonstrated synergy in their mechanical properties in a composition-dependent manner. In the second part of this thesis, a coaxial printing method was developed by combining a coaxial needle with a commercial extrusion-based 3D printer. Extruded strands displayed distinct core and shell regions and were able to support cell viability and function for up to 6 weeks. In the final part of this thesis, gradients were incorporated into the shell of core–shell strands. Both soluble factors gradients and stiffness gradients were characterised, and their longevity within these printed constructs was studied. In summary, core–shell strands have been shown to be a viable method to combine optimal mechanical and biological properties in a single construct. The core–shell technique could be made more complex with the addition of gradients, bringing printed constructs closer to their in vivo counterparts. With further research, this technique will help to create more physiologically-relevant tissue engineered constructs, which can drive research a step closer towards better disease models and future therapies.
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Wright, Lee David. "Tissue Engineering Cartilage with a Composite Electrospun and Hydrogel Scaffold." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/37553.
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Osteoarthritis is the most prevalent musculoskeletal disease in humans, severely reducing the standard of living of millions of people. Osteoarthritis is characterized by degeneration and loss of articular cartilage which leads to pain, and loss of joint motility and function. Individuals suffering from severe osteoarthritis are commonly treated with full knee replacements. The procedure does eliminate the problem of degrading cartilage tissue; however, it does not fully restore function and its lifetime can be limited. To overcome the disadvantages of current treatments, tissue engineering has become a focus of research to regenerate cartilage. Tissue engineering attempts to repair or replace damaged tissue with cells, biomaterials, and/or molecular signals. Biodegradable scaffolds serve as a temporary replacement for the tissue until it has regenerated. Two types of scaffolds that have been used in tissue engineering are electrospun scaffolds and hydrogels. We have proposed and fabricated a scaffold for cartilage tissue engineering that incorporates an electrospun cylinder and a thermosetting hydrogel in order to provide improved properties compared to either individual material.
Electrospun cylinders were created by sintering electrospun mats that include salt pores. The addition of salt pores decreased the mechanical properties of the electrospun materials while also improving the capability of cells to infiltrate into the scaffold. The sintering process involved the connecting of one electrospun mat to an adjacent one. Specifically, poly(d,l-lactide) was capable of sintering to an adjacent electrospun mat when exposed to either heat (near the glass transition temperature) or tetrahydrofuran vapor. The sintering process did not deteriorate the structure or function of the electrospun material. Sintering allowed the creation of unique structures of electrospun material that previously could not be produced.
A thermosetting hydrogel was added to the scaffold to replicate the function of proteoglycans present in articular cartilage. A composite scaffold of electrospun polymer and hydrogel showed improved mechanical properties and better integration of the scaffold in vivo compared to an electrospun scaffold with no hydrogel. In conclusion, the composite electrospun and hydrogel scaffold could become an excellent tissue engineering scaffold to treat patients suffering from osteoarthritis.Ph. D.
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Han, Ning. "Hydrogel-Electrospun Fiber Mat Composite Materials for the Neuroprosthetic Interface." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1292881087.
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Yata, Tomoya. "Development of efficient amplification method of DNA hydrogel and composite-type DNA hydrogel for photothermal immunotherapy." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215494.
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Annamalai, Perushini. "Electrospinning of porous composite materials for hydrogen storage application." University of the Western Cape, 2016. http://hdl.handle.net/11394/5654.
Full textAbstract:
>Magister Scientiae - MScDue to the rapid depletion of fossil fuel reserves and the production of environmentally harmful by-products such as carbon dioxide, there is an urgent need for alternate sustainable clean energy. One of the leading candidates in this endeavour is hydrogen, which can be used as an energy carrier since it has a high energy density, zero emissions and is produced from non-depletable resources such as water. The major challenge hindering a hydrogen economy is the lack of safe and effective storage technologies for mobile applications. A prospective solution to this problem lies in the use of porous powdered materials, which adsorb the hydrogen gas. However, the integration of these powdered materials into a storage tank system, results in the pipelines being contaminated during filling cycles. This necessitates the shaping of the porous powdered materials. Among the many shaping techniques available, the electrospinning technique has been proposed as a promising technology since it is a versatile process that is easily scaled-up making it attractive for the applications of the study. Furthermore, the electrospinning process enables the synthesis of nano-sized fibres with attractive hydrogen sorption characteristics. In this regard, the current study employs the electrospinning technique to synthesise electrospun composite fibres for mobile hydrogen storage applications. After electrospinning three polymers, polyacrylonitrile (PAN) was selected as the most suitable polymer because it yielded bead-free electrospun fibres. However, the diameter of the PAN fibres was large/thick which prompted further optimisation of the electrospinning parameters. The optimised electrospinning conditions that yield unbeaded fibres within the desired diameter range (of 300-500 nm) were a PAN concentration of 10 wt%, a flow rate of 0.4 mL/h, a distance of 10 cm between the needle tip and collector plate, and an applied voltage of 8 kV. The study then progressed to the synthesis and characterisation of the pristine porous powdered materials which adsorb hydrogen gas. The porous powdered materials investigated were commercial zeolite 13X, its synthesised templated carbon derivative (ZTC) and Zr (UiO-66) and Cr (MIL-101) based metal-organic frameworks (MOFs). ZTC was synthesised via liquid impregnation coupled with chemical vapour deposition (CVD), and the MOFs were synthesised by the modulated solvothermal method. Analysis of the ZTCs morphology and phase crystallinity show that the carbon templated process using zeolites was successful, however, ZTC was amorphous compared to crystalline zeolite template. The BET surface area was assessed with the aid of nitrogen sorption isotherms for both zeolite 13X and ZTC, and values of 730 and 2717 m²/g, respectively were obtained. The hydrogen adsorption capacity for zeolite 13X was 1.6 wt% and increased to 2.4 wt% in the ZTC material at 77 K and 1 bar. The successful synthesis of well defined, crystalline MOFs was evident from X-ray diffraction and morphological analysis. The BET surface area and hydrogen adsorption for Zr MOF were 1186 m²/g and 1.5 wt%, respectively at 77 K and 1 bar. Cr MOF had a BET surface area of 2618 m²/g and hydrogen adsorption capacity of 1.9 wt% at 77 K and 1 bar. The main focus of the study was to synthesise electrospun composite fibres that can adsorb hydrogen gas and thus provide significant insight in this field of research. As such it examined composite fibres that incorporates porous powdered materials such as zeolite 13X, ZTCs, UiO-66 (Zr) MOF and MIL-101 (Cr) MOF and investigated their ability to adsorb hydrogen gas, which have not been reported previously. The synthesis of composite fibres was achieved by incorporating the porous powdered materials into the PAN resulting in a polymeric blend that was then electrospun. Morphological analysis illustrated that the porous powdered materials were successfully supported by or incorporated within the PAN fibres, forming composite fibres. The BET surface area of the 40 wt% zeolite-PAN and 12.5 wt% ZTC-PAN composite fibres were 440 and 1787 m²/g respectively. Zr MOF and Cr MOF composite fibres had a BET surface area of 815 and 1134 m²/g, respectively. The BET surface area had reduced by 40, 34, 31 and 57% for zeolite 13X, ZTC, Zr MOF and Cr MOF, respectively after these porous powdered materials were incorporated into PAN. The hydrogen adoption capacity for 40 wt% zeolite-PAN, 12.5 wt% ZTC-PAN, 20 wt% Zr MOFPAN and 20 wt% Cr MOF-PAN composite fibres was 0.8, 1.8, 0.9 and 1.1 wt%, respectively. This decrease was attributed to the limited amount of porous powdered materials that could be incorporated into the fibres since only 40 wt% of zeolite 13X, 12.5 wt% of ZTC and 20 wt% of the MOFs were loaded into their respective composite fibres. This was due to the fact that incorporation of greater amounts of porous powdered materials resulted in a viscous polymeric blend that was unable to be electrospun. It is evident from the study that electrospinning is a versatile process that is able to produce composite fibres with promising properties that can potentially advance the research in this field thus providing a practical solution to the problem of integrating loose powdered materials into an on-board hydrogen storage system.
CSIR Young Researchers Establishment Fund (YREF)
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El-Zarouk, Khaled Mohamed. "Composite inorganic membranes for hydrogen reaction, separation and purification." Thesis, Robert Gordon University, 2007. http://hdl.handle.net/10059/1249.
Full textAbstract:
Silica-alumina composite membranes for hydrogen separation and high temperature chemical reactions were prepared using both conventional and modified dip-coating techniques. These were deposited on commercially available a.-alumina macroporous support of 10 millimetre (mm) outer diameter, 7 mm inner diameter and average pore size of 6000 nanometre (nm) wash coated with Titania. The reactants of the coating technique were silicone elastomer and isopentane promoted by a catalyst. The catalyst (silicone curing agent) was added as a templating agent to control the eventual adhesion and densification of the elastomer sol. In particular, the microporous membranes were prepared by creating suction in the bore side of the membrane and involved continuous stirring of the coating mixture during the process, and their pore characteristics were analysed. Then, the effects of thermal treatment on the gas transport and micro pore structure of the resulting membranes were investigated. The pore size of the silica membrane prepared by conventional technique was in the range of approximately 8 to 11 nm while that prepared by modified dip-coating was in the range of about 3 to 4 nm. In addition, the membranes were segmented into five categories; silica membrane for hydrogen reaction, silica membrane for separation, silica membrane for purification, palladium (Pd)-impregnated membrane and silica on gamma -alumina (y-alumina). The hydrogen permeation of the silica membrane prepared for hydrogen reaction was of the order of 10-7 mol/m2.s.pa, while the nitrogen permeance was of the order of 10- mollm2.s.pa. at pressure differential of 0.5-2.0 bar and temperature range of 323-473 Kelvin (K). The maximum hydrogen I nitrogen (H2 I N2) selectivity, determined from single-component permeances to H2 and N2 was approximately 3.58. These permeances were decreased for the silica membrane prepared for hydrogen separation when the dip coating, drying and calcination was applied 7 times instead of 3 times as in the case of the hydrogen reaction membrane. The silica membrane for H2 separation provides permeances of about 5.8 x 10-9 mole.meter-2.second-l.pascarl (mol!m2.s.pa) for H2 and 9.4 x 10-10 mol/m2.s.pa for N2, with higher H21N2 selectivity of about 8. Higher mixed gas separation factors of H2:N2 > 400 and H2 permeance of 4.1 x 10-9 ol!m2.s.pa were achieved with silica membrane for H2 purification prepared with the modified dip-coating using suction technique with silicone elastomer as precursor. This technique was especially effective in plugging the macroporous support which possessed a wide pore size distribution. The membrane permeated gases except propane (C3Hg) by the activated diffusion mechanism at permeation temperature range of 298 -573 K, and the activation energies are in the order of 10.6 - 13 kilojoules I mole (kJ/mol) and 26.1-28.7 kJ/mol for H2 and N2 respectively. The tests have demonstrated that this composite membrane has the capability to separate hydrogen from gas mixtures with almost complete H2 selectivity and to produce high purity H2 (up to 99.0 %) from a 50 I 50 % H21N2 mixture stream. A theoretical model for a propane dehydrogenation reaction scheme in tubular and annular membrane reactors is developed. This model is applied to three different membranes namely: a silica-alumina membrane, a silica-y-alumina membrane and a Pd impregnated membrane. Results indicate that the Pd impregnated membrane provided very high theoretical conversions (82 % at 600°C) compared with the other two composite membranes.
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GUPTA, PREETI. "HYDROGEL BASED WOUND DRESSING MATERIAL." Thesis, DELHI TECHNOLOGICAL UNIVERSITY, 2021. http://dspace.dtu.ac.in:8080/jspui/handle/repository/18806.
Full textAbstract:
Weak mechanical strength of hydrogels in wet condition limits their use for load
bearing applications. Their mechanical strength can be raised by grafting them over
some support or by converting them into nanofibrous form. Present thesis is focused on
the preparation of poly (acrylamide-co-acrylic acid) hydrogel grafted over cotton fabric
using two different cross-linkers i.e. PEG and MBAAm for making medicated dressing
and nanofibers of hydrogel of poly (acrylamide-co-acrylic acid). FTIR was used to
confirm the insertion of cross-links into the polymer chains. Grafting of uniform
hydrogel layer on cotton surface and formation of hydrogel nanofibers were confirmed
by using SEM. The average fibre diameter was found to be 275±94.5 nm.
Swelling of composite prepared using PEG followed first-order kinetic model
at acidic and neutral pH whereas second-order kinetic model at pH 8.5 while that
prepared using MBAAm followed second-order kinetic equation at all the pHs studied.
The kinetics of swelling was also governed by Peppas model at all pHs. Release of drug
from both the composites was studied in phosphate buffers having pH 5.5,7 and 8.5 at
37±0.1°C and observed that it was fastest in phosphate buffer having pH 7. On fitting
drug release data into different models, it was observed that drug release was diffusion
controlled and followed Fickian diffusion mechanism in case of composite prepared by
using PEG as cross-linker whereas it was controlled by diffusion as well as chain
relaxation in case of composite prepared by using MBAAm. Mechanical testing using
Universal Testing Machine supported a higher mechanical strength of the hydrogel
composite as compared to its film. Swelling behaviour of Nanofibrous mats was found to be highest at neutral pH and it followed second order kinetics at all pHs. The drug release kinetics was further
evaluated and found that it took place by Fickian diffusion (n < 0.5) and followed
second order release kinetics. Antimicrobial tests were performed to show the
effectiveness of drug loaded within the hydrogel samples.
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Nwakwuo, Christopher Chinedu. "Reactive hydride composites for efficient hydrogen energy storage." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:8a3e1081-8655-41db-b1c0-8986658371a1.
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Solid state chemical storage of hydrogen in metals offers promising advantages over compressed hydrogen gas and condensed liquid hydrogen, especially for mobile applications with respect to safety and energy efficiency. However, no single metal hydride simultaneously satisfies the essential performance criteria for onboard hydrogen storage namely, high gravimetric and/or volumetric energy density, fast kinetics and favorable thermodynamics. Recently, a breakthrough achievement was made by the development of reactive hydride composites in which two metal hydride systems (e.g. NaBH4 and MgH2) are mixed together resulting in better sorption properties than the individual pure systems. In this approach, the formation of MgB2 by exothermic reaction destabilizes the composite and consequently reduces the overall enthalpy and sorption temperature of the endothermic desorption reaction. In this work the thermodynamic and kinetic properties of reactions in 2NaH + MgB2 + 4H2 ↔ 2NaBH4 + MgH2 and 3NaH + MgB2 + 4H2 ↔ 2NaBH4 + NaMgH3 were established using multiple experimental techniques like volumetric measurements, ex-situ and in-situ X-ray diffraction, calorimetry, and especially electron microscopy. Under the applied experimental conditions of 50 bar hydrogen and 400 °C during the hydrogenation of 2NaH + MgB2 and 0.1 bar hydrogen and 450 °C during the dehydrogenation of 2NaBH4 + MgH2, both reactions were kinetically limited and proceeded in multisteps. The absorption reaction was partial, being restricted by the unexpected formation of NaMgH3 which limits the formation of NaBH4 while the desorption reaction was complete and limited by the growth of MgB2 through some intermediate complexes at the Mg/NaBH4 interface where the intermediate phase forms a barrier to diffusion. Conversely, in the 3NaH + MgB2 system, absorption in 100 bar hydrogen and 300 °C was complete but slow, while in the 2NaBH4 + NaMgH3 system, complete desorption was achieved in multisteps under 0.1 bar hydrogen and 450 °C. The formation of intermediate and stable complexes during these reactions poses a significant restraint to hydrogen sorption reactions. However, lower onset sorption temperatures have been established in these systems than in the pure compounds due to their simultaneous destabilization in the composite state. This study have demonstrated the complexity of desorption and absorption mechanisms in these composite systems and the difficulty of obtaining such reactions at low temperatures required for mobile applications. This understanding of the rate limiting reaction steps in reactive hydride composites provides the basis for further optimization of these materials for efficient hydrogen storage applications.
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Calvert, Nick. "Composite Hydrogel Scaffolds with Eggshell Particles as a Novel Bone Regeneration Material." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39481.
Full textAbstract:
The development of bone regeneration materials to support new bone formation is an active field of research. This report describes the development and characterization of a novel composite scaffold made of a chitosan-alginate co-polymer hydrogel matrix and eggshell (ES) particles. Scaffolds with ES particles or with nanotextured ES (NTES) particles following treatment with phosphoric acid were compared to scaffolds without particles. The scaffolds with particles exhibited a higher porosity and a larger median pore size. Their mechanical strength remained low, but both scaffold types were more resistant to deformation following compression than the scaffolds without particles. The osteogenic potential of the scaffolds was then evaluated with human bone-marrow derived mesenchymal stem cells (MSCs) from four different donors. Results showed that the inclusion of ES or NTES particles significantly increased MSC adherence and viability, as well as alkaline phosphatase activity in the scaffolds. A change of cell morphology and a small, although not statistically significant, increase of osteogenic protein expression (RUNX2 and osteopontin) were also observed at later time points (days 14 and 21). Overall, this research highlights the potential of ES for bone regeneration applications, opening the door for a high-value repurposing of a current industrial waste product.
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Al-Hajjaj, A. A. "A nanostructured composite material for hydrogen storage : design & analysis." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/348877/.
Full textAbstract:
Hydrogen has long been considered an ideal energy carrier for a sustainable energy economy, for both direct combustion and as a fuel for polymer-electrolyte fuel cells. One of the main challenges associated with the use of hydrogen is to find efficient methods of storage. Any method must be safe, reversible, cost-effective and practical. In this thesis, a general introduction to hydrogen energy and the hydrogen economy is provided, together with descriptions of incumbent and emerging storage methods. A mathematical framework for simulating sorption isotherms in microporous materials is developed. This framework provides explicit expressions for the excess, condensed, compressed and absolute hydrogen masses. Furthermore, key parameters such as the surface area and adsorption volume can be estimated (for the first time) using a single-step nonlinear regression analysis, with the use of any isotherm model. Values are derived for three classes of porous materials, showing consistency with experimental data. A novel composite consisting of titanate nanotubes decorated with nanostructured metal cyanide frameworks, e.g., cadmium ferricyanide (Cd3[Fe(CN)6]2), are synthesised. The equilibrium and kinetic hydrogen sorption properties of the titanate-nanotube/Cd3[Fe(CN)6]2 composite are studied at low, intermediate and high pressure (up to 150 bar), revealing uptake values of ca. 14 weight %, which compare favourably with known materials for hydrogen storage. The role of mass transport in the sorption process is investigated, including the effects of boundary-layer diffusion and intraparticle diffusion. The results suggest that the composite possesses good hydrogen mass transfer characteristics. The effects of the reaction environment during synthesis are explored and the samples are thoroughly characterised. Significant differences in the loading of Cd3[Fe(CN)6]2 on the titanate nanotubes are seen. Hydrogen and nitrogen sorption analyses reveal the role of the pore size distribution on the effective surface area for adsorption and, therefore, the hydrogen uptake.
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Akis, B. Ceylan. "Preparation of Pd-Ag/PSS composite membranes for hydrogen separation." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-113019.
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Thèvenot, Caroline. "Synthèses, caractérisations et propriétés électrostimulables d'hydrogels composites polyacrylamide-nanoparticules de polystyrène/polyaniline." Pau, 2006. http://www.theses.fr/2006PAUU3028.
Full textAbstract:
De nouveaux matériaux adaptatifs, des hydrogels composites (HC) électrostimulables ont été élaborés. Ils sont composés d'un réseau de poly(acrylamide) réticulé par du N-N'méthylènebisacrylamide (BisAM) emprisonnant deux types de nanoparticules : (i) de polystyrène (PS) réticulé, (ii) cœur-écorce (CS) constituées d'un cœur de PS et d'une couronne de polymère intrinsèquement conducteur (polyaniline). Ces nanoparticules ont été synthétisées par polymérisation radicalaire en dispersion puis caractérisées. Elles sont de composition et de taille bien définies (400 à 450 nm). La synthèse des HC a été optimisée pour s'affranchir des incompatibilités chimiques entre réseau et nanoparticules. La dispersion de celles-ci dans le réseau a été étudiée par microscopie électronique. Un suivi cinétique en RMN a permis de conclure à la formation d'inhomogénéités du réseau dues à la différence de réactivité entre les monomères (rAM = 0,52, rBISAM = 5,2) et à une conversion quasi-totale. Les HC élaborés ont été caractérisés par rhéologie : ils ont montré une augmentation très importante du G' en fonction de la quantité de nanoparticules incorporées. Par ailleurs, une instrumentation simple, originale, basée sur la reconnaissance de forme a été développée pour permettre le suivi cinétique du gonflement des HC. L'étude menée a démontré que les nanoparticules se comportent en spectatrices sans modifier le processus de gonflement. Deux applications des HC ont été démontrées : les propriétés électrostimulables des HC à base de CS à travers le relargage d'espèces ioniques quand un champ électrique est appliqué (1V) ainsi qu'un effet mécano-électrique pour les HC à base de PSNew électroactives materials, “composite hydrogels” (HC) have been developed. They are composed of a poly(acrylamide) network crosslinked by N-N'methylenebisacrylamide (BisAM) and may contain two kinds of nanoparticles : (i) of crosslinked polystyrene (PS) or (ii) “core-shell” (CS) made of a core of PS with a conducting polymer shell (polyaniline). These aforementioned nanoparticles were synthesized by water dispersion and well characterized. The chemical compositions as well as particle sizes were controlled. The synthesis of HC was optimized by taking into account of the network and the nanoparticles chemical and experimental condition requirements. The particles dispersion into the hydrogel network was also characterized with electronic microscopy. A kinetic study done by NMR showed the formation of inhomogeneities in the network structure due to the values of the reactivity ratios of the monomers (rAM=0,52, rBISAM=5,2) and a quasi-total conversion. The HC were characterized by rheology: it showed a significant increase of G' with the nanoparticles content. Otherwise, a new simple and original system based on pattern recognition was developed to monitor the swelling kinetics of the HC. Swelling equilibrium and diffusion phenomena showed that nanoparticles are not involved in the process of swelling. Two applications were developed: the electroactives properties of HC containing CS particles i. E. Release of ionic species when an electric field is applied (1V) and a mechano-electric effect for the HC containing PS latexes
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Abkhalimov, E. V., R. D. Solovov, and B. G. Ershov. "Composite Ag-Pt Nanoparticles in Aqueous Solution." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35033.
Full textAbstract:
It is shown that the saturation of an aqueous solution containing K2PtCl4 with hydrogen in the presence of 6.3 nm silver nanoparticles leads to the reduction of platinum on the silver surface and the formation of Ag/Pt core-shell nanoparticles. The Ag:Pt molar ratio is varied from 9:1 to 1:9 for synthesizing Pt
shell layer of different thickness. An apparent shift of Ag surface plasmon band from 405 nm to 230 nm
and broadening of one with decrease of Ag:Pt ratio was observed. The TEM images and SAED pattern of
Pt@Ag nanoparticles has been obtained. The UV-Vis and TEM data confirms a formation of Ag/Pt coreshell nanoparticles.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35033
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Marcasuzaa, Pierre. "Composites conducteurs à base de PANI : vers une architecture contrôlée de 2D à 3D." Pau, 2009. http://www.theses.fr/2009PAUU3047.
Full textAbstract:
Les polymères intrinsèquement conducteurs (PIC) sont une catégorie de matériaux qui connaissent actuellement un important essor. Cependant, leur principal inconvénient est leur insolubilité dans les solvants usuels. C’est pour cela que de nombreuses études les associent avec des matrices polymère pour former des composites. Lors de cette étude, nous avons synthétisé des copolymères à blocs conducteurs dont la structure chimique est contrôlée. Ces copolymères sont composés d’un bloc "matrice" et d’un second bloc conducteur. La première partie, polystyrène ou polyacrylate, est synthétisée par polymérisation radicalaire contrôlée (ATRP) afin de maîtriser les masses molaires (entre 5 000 et 15 000 g/mol) et la polymolécularité (Ip). La partie conductrice est un oligomère d’aniline. Puis, les deux blocs sont couplés pour former un copolymère dibloc. Cette synthèse est réalisée par voie conventionnelle (chauffage bain d’huile) et sous irradiation micro-onde. Une autre architecture de copolymère est réalisée, il s’agit du greffage de polyaniline sur un polymère naturel, le chitosane. En effet, celui-ci apporte des propriétés filmogène, mais également la possibilité de réaliser des hydrogels par réticulation du copolymère greffé. Ainsi un réseau dans lequel la PANI est répartie de façon homogène est obtenuIntrinsically conducting polymers (ICPs) are a recent category of materials which currently make strong great strides. However, their main inconvenience is their insolubility in the usual solvents. That’s why lots of studies associate them with polymer matrices to make composites. During this study, conductive blocks copolymers with controlled architecture were obtained. These copolymers consist of a "matrix" block and a second conductive block. The first part, polystyrene or polyacrylate, is synthesized by controlled radical polymerization (ATRP) to control the molecular weight (between 5 000 and 15 000 g / mol) and the polydispersity (Ip). The conductive part is an oligomer of aniline. Then, both blocks are coupled to obtain a diblock copolymer. This synthesis is realized by conventional heating (bath of oil) and under microwave irradiation. Other architecture of copolymer is realized, it consists on the graft of polyaniline onto a natural polymer, the chitosane which brings coating properties, and the possibility of realizing hydrogels by crosslinking of grafting copolymer. So a network in which the PANI is distributed in a homogeneously is obtained
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Montoya, Anthony Tristan. "Synthesis of carbon nitrides and composite photocatalyst materials." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6479.
Full textAbstract:
This thesis describes the synthesis, characterization and photocatalytic applications of carbon nitride (C3N4) and titanium dioxide (TiO2) materials. C3N4 was prepared from the thermal decomposition of a trichloromelamine (TCM) precursor. Several different reactor designs and decomposition temperatures were used to produce chemically and thermally stable orange powders. These methods included a low temperature glass Schlenk reactor, a high mass scale stainless steel reactor, and decomposition at higher temperatures by the immersion of a Schlenk tube into a furnace. These products share many of the same structural and chemical properties when produced by these different methods compared to products from more common alternate precursors in the literature, determined by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and elemental analysis. C3N4 is capable of utilizing light for photocatalysis due to its moderate band gap (Eg), measured to be between 2.2 and 2.5 eV. This enables C3N4 to be used in the photocatalytic degradation of organic dyes and the production of hydrogen via the water-splitting reaction. C3N4 degraded methylene blue dye to less than 10% of its initial concentration in less than an hour of UV light illumination and 60% under filtered visible light in 150 minutes. It also degraded methyl orange dye to below 20% in 70 minutes under UV light and below 60% in 150 minutes under visible light. Using precious metal co-catalysts (Pt, Pd, and Ag) photo-reduced onto the surface of C3N4, hydrogen was produced from a 10% aqueous solution of triethanolamine at rates as high as 260 μmol h-1 g-1.
C3N4 was also modified by mixing the precursor with different salts (NaCl, KBr, KI, KSCN, and NH4SCN) as hard templates. Many of these salts reacted with TCM by exchanging the anion with the chlorine in TCM. The products were mostly prepared using the high temperature Schlenk tube reactor, and resulted in yellow, orange, or tan-brown products with Eg values between 2.2 and 2.7 eV. Each of these products had subtle differences in the IR spectra and elemental composition. The morphology of these C3N4 products appeared to be more porous than unmodified C3N4, and the surface area for some increased by a factor of 4. These products demonstrated increased activity for photocatalytic hydrogen evolution, with the product from TCM-KI reaching a peak rate as high as 1,300 µmol h-1 g-1. C3N4 was coated onto metal oxide supports (SiO2, Al2O3, TiO2, and WO3) with the goal of utilizing enhanced surface area of the support or synergy between two different semiconductors. These products typically required higher temperature synthesis conditions in order to fully form. The compositions of the SiO2 and Al2O3 products were richer in nitrogen and hydrogen compared to unmodified C3N4. The higher temperature reactions with C3N4 and WO3 resulted in the formation of the HxWO3 phase, and an alternate approach of coating WO3 on C3N4 was used. The degradation of methyl orange showed a significant increase in adsorption of dye for the composites with SiO2 and Al2O3, which was not seen with any of the individual components. The composite between C3N4 and TiO2 showed improved activity for hydrogen evolution compared to unmodified C3N4.
The surface of TiO2 was modified by the reductive photodeposition of several first row transition metals (Mn, Fe, Co, Ni, and Cu). This process resulted in the slight color change of the white powder to shades of light yellow, blue or grey. Bulk elemental analysis showed that these products contained between 0.04-0.6 at% of the added metal, which was lower than the targeted deposit amount. The Cu modified TiO2 had the largest enhancement of photocatalytic hydrogen evolution activity with a rate of 8,500 µmol h-1 g-1, a factor of 17 higher than unmodified TiO2.
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Guillaud, Nicolas. "Tolérance aux dommages générés par impact de structures composites épaisses. Application aux réservoirs composites hyperbares." Thesis, Paris, ENSAM, 2015. http://www.theses.fr/2015ENAM0040/document.
Full textAbstract:
Cette thèse s'est déroulée dans le cadre du projet TOLEDO (Tolérance aux dommages par impact des réservoirs hyperbares) piloté par Air Liquide en partenariat avec le CEA Le Ripault et l'institut PPRIME.L'hydrogène est stocké au sein de réservoirs de type IV à une pression de service de 700 bar.Ces structures composites présentent comme particularités d'être épaisses (> 30 mm), d'avoir une forte courbure et d'être préchargées en pression lors d'un éventuel impact.Notre travail a montré que ces particularités modifient le type, la quantité et la localisation des différents endommagements couramment observés (rupture de fibres, délaminage et fissuration matricielle).Les endommagements ont pu être quantifiés par le biais de méthodes simples et originales.L'influence des particularités sur le comportement à l'impact a pu être déterminée par l'utilisation de deux dispositifs expérimentaux conçus et réalisés au cours de cette thèse.Le premier permet de précontraindre en tension uniaxiale des plaques composites épaisses.Le second permet de précharger en état de membrane un tube composite ce qui a permis de montrer que le cas d'impact le plus critique vis-à-vis des réservoirs est lorsque ces derniers sont vides.Cette étude a permis de mettre en évidence la criticité des ruptures de fibres sur les pertes de performance au sein des réservoirs hyperbares.Un modèle numérique prenant en compte la dispersion des contraintes à rupture et des différents types d'endommagements a été développé.Il permet d'introduire un endommagement initial et a confirmé certains résultats expérimentauxThis thesis took place within the framework of the project TOLEDO (Tolerance in the damage by impact of the hyperbaric reservoirs) managed by Air Liquide in partnership with the CEA Le Ripault and PPRIME institute.The hydrogen is stored within the type IV vessel at a servive pressure of 700 bar.These composite structures present as peculiarities to be thick (> 30 mm), to have a strong curvature and to be precharged in pressure during a possible impact.Our work showed that these peculiarities modify the type, the quantity and the localization of the various usually observed damages (fiber breakage, délamination and matrix cracking).The damages were able to be quantified by means of simple and original methods.The influence of the peculiarities on the behavior in the impact was able to be determined by the use of two experimental devices designed and realized during this thesis.The first one allows to preload a thick composite plates in uniaxial tension thick composite plates.The second allows to preload in state of membrane a composite pipe and allowed to show that the most critical impact towards reservoirs is when they are empty.This study allowed to highlight the criticality of the fiber breakage on the loss of performance within the hyperbaric reservoirs.A digital model taking into account the dispersal of the failure stress and various types of damages was developed.It also allows to introduce an initial damage and confirm some experimental results
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Zou, Yu. "Supported Composite Electrocatalysts for Energy Conversion Applications." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/417198.
Full textAbstract:
Increasing energy demand and environmental awareness have promoted the development of efficient and environment-friendly hydrogen technologies. Water electrolysis (2𝐻2𝑂→2𝐻2+𝑂2) is a promising way to store renewable electricity generated by solar or wind energy into chemical fuel in the form of H2. Water electrolysis is comprised of a hydrogen evolution reaction (HER) on the cathode and an oxygen evolution reaction (OER) on the anode. For both HER and OER, highly catalytic active electrocatalysts are required to lower the overpotentials and to speed up the sluggish kinetics. To date, noble metal catalysts are still the most efficient electrocatalysts for these two reactions, but their high cost and low abundance on Earth limit the scalable application of water electrolysis. Therefore, investigation of alternative catalysts with low cost and high electrocatalytic activity is urgently needed.
This thesis focuses on alkaline electrocatalytic HER, as well as related reactions such as OER, and hydrazine oxidation(HzOR)-assistant HER. In terms of material design, the components are introduced to improve conductivity and mass transfer, as well as boost the intrinsic catalytic activity. Moreover, the mechanism was investigated through exploring the link between structure and performance, as well using density functional theory (DFT) calculations.
The first two experimental chapters employed a two-dimensional (2D) material, MXene, as support. In Chapter 2, ruthenium single atoms were incorporated onto ultrathin Ti3C2Tx MXene nanosheets to unlock its electrocatalytic activity. The RuSA@Ti3C2Tx presented a 1 A cm−2 HER current density with an over potential of 425.7 mV, outperforming the commercial Pt/C benchmark. Operando Raman test under HER potential showed the different protonation level between RuSA@Ti3C2Tx and Ti3C2Tx, suggesting the different hydrogen absorption energy of the oxygen terminal on the Ti3C2Tx basal plane. Finally, the theoretical calculations confirmed that the RuSA not only facilitates water dissociation, but also modulates the hydrogen After increasing the Ru content and conducting electroreduction, RuTi alloy nanoclusters were constructed on the surface of Ti3C2Tx. Surprisingly, the RuTi@Ti3C2Tx showed better performance in HER, and excellent hydrazine oxidation reaction (HzOR) performance. The overpotential to attain a current density of 10 mA cm−2 for HER was only 14 mV, lower than that of the commercial Pt/C. The HzOR catalytic activity also outperformed most reported work. In addition, the overall hydrazine spitting was conducted in an H-type electrolytic cell, demonstrating superior thermodynamic advantage and good stability.
Defect-abundant active carbon (AC-DCD) as support was prepared by the hydrothermal reaction with dicyanamide. Then, the Ru nanoparticles were grown on the surface. Compared to the catalyst with pristine AC as support prepared under same conditions, Ru600@AC-DCD presented a larger electrochemical special area with strain-abundant Ru nanoparticles. Ru600@AC-DCD delivered excellent HER performance in alkaline media, and good catalytic properties in acidic and neutral media.
Finally, another novel metal@carbon composite, Ni nanoparticles encapsulated in graphite carbon layers, was synthesized by directly annealing the Ni-imidazole framework precursors at 350 °C in H2/Ar. By tuning the annealing time under H2/Ar flow, Ni nanoparticles with different crystalline phases were synthesized. These Ni@C samples are di-function electrocatalysts for HER and OER in alkaline condition. The mixed-phase catalyst mix2-Ni@C delivered the highest activity to catalyze HER, while the pure hcp phase catalyst hcp-Ni@C showed best OER activity. This work provided a practical method to prepare low-cost difunctional electrocatalysts for overall water electrolysis.
In summary, the thesis innovatively contributes to the knowledge in material science and water electrolysis in the aspects of: (i) designing novel supported composite electrocatalysts with high catalytic activity for HER, OER, and HzOR; (ii) monitoring the changing of surface terminal by operando Raman spectroscopy to verify the HER mechanism; (iii) development of metal nanostructures, like RuTi alloy, hcp phase Ni and mixed-phase Ni, via facile methods, and investigation of their unique properties; and (iv) application of large current HER and exploration of the kinetics under different potentials.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Hu, Jianbing. "Modeling and simulation of high pressure composite cylinders for hydrogen storage." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Hu_09007dcc805d8846.pdf.
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Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 9, 2009) Includes bibliographical references.
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Mushi, Ngesa Ezekiel. "Chitin nanofibers, networks and composites : Preparation, structure and mechanical properties." Doctoral thesis, KTH, Biokompositer, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155528.
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Chitin is an important reinforcing component in load-bearing structures in many organisms such as insects and crustaceans (i.e. shrimps, lobsters, crabs etc.). It is of increasing interest for use in packaging materials as well as in biomedical applications. Furthermore, biological materials may inspire the development of new man-made material concepts. Chitinmolecules are crystallized in extended chain conformations to form nanoscale fibrils of about 3 nm in diameter. In the present study, novel materialshave been developed based on a new type of chitin nanofibers prepared from the lobster exoskeleton. Improved understanding about effects of chitin from crustaceans and chitin material preparation on structure is provided through Atomic Force Microscopy(AFM) (paper I&II), Scanning Transmission Electron Microscopy(STEM) (paper I&II), X-Ray Diffraction (XRD), Intrinsic Viscosity, solid state 13C Nuclear Magnetic Resonance (NMR) (paper II), Field Emission Scanning Electron Microscopy(FE-SEM) (paper I, II, III, IV & V), Ultraviolet-Visible Spectrophotometryand Dynamic Light Scattering (DLS) (paper III). The presence of protein was confirmed through colorimetric method(paper I & II). An interesting result from the thesis is the new features of chitin nanofiber including small diameter, high molar mass or nanofiber length,and high purity. The structure and composition of the nanofibers confirms this (paper I & II). Furthermore, the structure and properties of the corresponding materials confirm the uniqueness of the present nanofibers: chitin membrane (I & II), polymer matrix composites (III),and hydrogels (paper IV). Improved mechanical properties compared with typical data from the literature were confirmed for chitin nanofiber membranes in paper II, chitin-chitosan polymer matrix composites in paper III, and chitin hydrogel in paper IV. Mechanical tests included dynamic mechanical analysis and uniaxial tensile tests. Mechanical properties of chitin hydrogels were evaluated based onrheological and compression properties (paper IV). The values were the highest reported for this kind of chitin material. Furthermore, the relationships between materials structure and properties were analyzed. For membranes and polymer matrix nanocomposites, the degree of dispersion is an important parameter. For the hydrogels, the preparation procedure is very simple and has interesting practical potential. Chitin-binding characteristics of cuticular proteins areinteresting fornovel bio-inspired material development. In the present work(paper V), chitin nanofibers with newfeaturesincluding high surface area and low protein content were combined with resilin-like protein possessing the chitin-binding characteristics. Hydrated chitin-resilin nanocomposites with similar composition as in rubber-like insect cuticles were prepared. The main objective was to improve understanding on the role of chitin-binding domain on mechanical properties. Resilin is a rubber-like protein present in insects. The exon I (comprising 18 N-terminal elastic repeat units) together with or without the exon II (a typical cuticular chitin-binding domain) from the resilin gene CG15920 found in Drosophila melanogasterwere cloned and the encoded proteins were expressed as soluble products in Escherichia coli.Resilin-like protein with chitin-binding domain (designated as ResChBD) adsorbedin significant amount to chitin nanofiber surface andprotein-bound cuticle-like soft nanocomposites were formed. Although chitin bindingwas taking place only in proteinswith chitin-binding domain, the global mechanical behavior of the hydrated chitin-resilin nanocomposites was not so sensitive to this chitin-resilin interaction. In summary, chitin is an interesting material component with high potential as mechanical reinforcement in a variety of nanomaterials. The present study reports the genesisof novel chitin nanofibers and outlines the basic relationships between structure and properties for materials based on chitin. Future work should be directed towards both bio-inspired studies of the nanocomposite chitin structures in organisms, as well as the industrial applications of chitin waste from the food industry. Chitin nanofibers can strengthen the properties of materials, andprovide optical transparency as well as biological activities such as antimicrobial properties.QC 20141110
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Mukundrao, Khade Shankar. "Development of and characterization of gelatin-poly ethylene glycol composite hydrogels and gelatin-polysaccharide physical hydrogels." Thesis, 2013. http://ethesis.nitrkl.ac.in/4851/1/211BM2010.pdf.
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The present study describes properties of the gelatin/PEG based composite hydrogels and emphasizes on the properties of the gelatin and different polysaccharides based composite physical hydrogels (PHs). The hydrogels were prepared by varying the concentration of gelatin and PEG and PH was prepared by varying the concentration of gelatin and polysaccharides in different ratios. The gels were prepared either with or without glutaraldehyde, a chemical crosslinker. The pH and hemocompatibility properties of the hydrogels were also studied. The in vitro release behavior of metronidazole (MZ, a model drug) was studied. The results suggested that the properties of the hydrogels were dependant on the proportion of the gelatin and PEG & gelatin and different polysaccharides based composite physical hydrogels. The pHs of the hydrogels were in the range of 4.00-6.00 and were hemocompatible in nature. The developed gels may be used as a carrier for controlled drug delivery of bioactive agents.
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Wan, Q., R. A. Plenderleith, M. Dapor, Stephen Rimmer, F. Claeyssens, and C. Rodenburg. "Separating topographical and chemical analysis of nanostructure of polymer composite in low voltage SEM." 2015. http://hdl.handle.net/10454/11367.
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YesThe possibility of separating the topographical and chemical information in a polymer nano-composite using low-voltage SEM imaging is demonstrated, when images are acquired with a Concentric Backscattered (CBS) detector. This separation of chemical and topographical information is based on the different angular distribution of electron scattering which were calculated using a Monte Carlo simulation. The simulation based on angular restricted detection was applied to a semi-branched PNIPAM/PEGDA interpenetration network for which a linear relationship of topography SEM contrast and feature height data was observed.
EPSRC