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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Estudo de fibroína dopada com terras raras para potenciais aplicações fotônicas / Study of rare earth doped fibroin for potential photonic applications

Pugina, Roberta Silva 01 February 2018 (has links)
A fibroína da seda (SF) é uma proteína estrutural encontrada nos casulos do Bombyx mori e que possui propriedades potencialmente aplicáveis em fotônica. Esta matriz biocompatível é um substrato interessante para diferentes íons ou moléculas; além disso, o seu índice de refração variável permite que fótons sejam guiados neste material, possibilitando seu uso como guias de ondas biocompatíveis e reabsorvíveis, que pode ser utilizado para fornecer energia ótica para diversas aplicações, por exemplo, terapia ou imagem dentro de tecidos vivos. A sua boa adequação em sistemas ópticos deve-se principalmente a propriedades como: ser mecanicamente robusta, apresentar superfícies muito lisas, altamente transparentes (> 95%) em toda a região visível do espectro e ser modelável. Além disto, há uma característica adicional: a viabilidade de funcionalização bioquímica, o que pode conferir uma maior versatilidade a estes dispositivos. Já os íons terras raras (TR) possuem um papel amplamente conhecido no ramo da fotônica; porém, não há nenhum estudo envolvendo a produção de luz em SF dopada com íons TR, e a combinação das propriedades mecânicas e óticas desta matriz com a multifuncionalidade destes íons pode ser uma forma de se produzir dispositivos fotônicos novos e distintos. Desta forma, o presente trabalho teve como objetivo estudar a estrutura da matriz de SF na presença de diferentes íons TR (Eu3+ e Tb3+), bem como a interação existente entre os aminoácidos que constitui a matriz e estes íons. Os resultados apresentados nesta dissertação mostraram as interações TR-SF e suportam os mecanismos de transferência de energia para excitação de diferentes íons TR nesta matriz, sendo importante para futuras aplicações em fotônica / Silk fibroin (SF) is a structural protein found in Bombyx mori cocoons and has properties that are potentially applicable in photonics. This biocompatible matrix is an interesting substrate for different ions or molecules. Furthermore, its variable refractive index allows for photons to be guided in this material enabling their use as biocompatible and resorbable waveguides, which can be used to provide optical energy for various applications, e. g., therapy or imaging into living tissue. Its suitability in optical systems is mainly due to its properties such as: being mechanically robust, presenting very smooth surfaces, highly transparent (> 95%) throughout the visible region of the spectrum and being moldable. In addition, there is an extra feature: the possibility of biochemical functionalization, which may confer greater versatility to these devices. On the other hand, rare earth ions (RE) play a widely known role in the field of photonics. However, there is no studies involving the production of light in doped SF with RE ions and the combination of the mechanical and optical properties of this matrix with the multifunctionality of these ions can be a way to produce new photonic devices. Thus, the aim of the present work was to study the SF matrix structure in the presence of different RE ions (Eu3+ and Tb3+) as well as the interaction between the amino acids from the matrix and these RE ions. The results presented in this manuscript have characterized the RE-SF interactions and supported the mechanisms of energy transfer for excitation of different RE ions in this matrix being important for future applications in photonics
82

Preparo e avaliação comparativa das propriedades físico-químicas de hidrogéis de fibroína de seda com conteúdo variado de sericina obtidos a partir dos cloretos de cálcio e lítio em sistemas distintos de solventes / Preparation and comparative evaluation of the physical-chemical properties of silk fibroin hydrogels with varied sericin content obtained from calcium salts and lithium in various solvent systems

Bexiga, Natália Marchesan 25 June 2014 (has links)
A fibroína de seda é uma proteína sintetizada pela espécie Bombyx mori, popularmente conhecida como bicho-da-seda. O casulo de Bombyx mori é composto por fibras de fibroína e pela sericina, responsável por unir os fios de fibroína. A fibroína é um polímero natural bastante versátil e pode ser processada de maneira a formar materiais como filmes, microesferas e hidrogéis. Os hidrogéis são redes tridimensionais formadas por macromoléculas e capazes de absorver grande quantidade de água sem perder sua integridade estrutural. Devido à características como biocompatibilidade, elevado teor de água e boas propriedades de difusão de oxigênio e nutrientes, os hidrogéis são amplamente utilizados em pesquisa biomédica. A fibroína é biodegradável, termicamente estável, altamente cristalina, flexível, resistente à tração, além de insolúvel em água e na maioria dos solventes orgânicos. A fibroína derivada das sedas Frison Extra e Meada 21 Denier foi separada da sericina pelo processo de degomagem, onde as fibras de seda foram imersas em soluções alcalinas e submetidas à aquecimento com posterior remoção de sericina. Os fios de fibroína foram dispersos nas soluções de CaCl2:H2O, LiCl:H2O e LiCl:EtOH:H2O. Diferenças nos tempos de dispersão para amostras distintas degomadas ou não foram observadas, bem como para cada um dos sistemas salino/solvente empregados. Após o processo de dispersão da fibroína as dispersões obtidas foram caracterizadas quanto à textura e reologia. As amostras não degomadas apresentaram maior firmeza e aumento do módulo elástico G\'. Algumas amostras contendo sericina ou etanol apresentaram comportamento newtoniano. Em uma segunda etapa, as amostras foram dialisadas para a produção do hidrogel e em seguida liofilizadas. Não houveram diferenças entre os tempos de gelificação para amostras distintas. Finalmente objetivou-se a caracterização dos hidrogéis obtidos por meio de ensaios termogravimétricos, difratométricos, espectrofotométricos e microscópicos. Todos os hidrogéis de fibroína de seda apresentaram alta resistência térmica, com presença predominante da conformação em folha-β da fibroína. Morfologicamente, os hidrogéis obtidos a partir de dispersões em LiCl:EtOH:H2O e CaCl2:EtOH:H2O apresentaram aspecto de rede enovelada, enquanto que os hidrogéis oriundos de dispersões em LiCl:H2O apresentaram estrutura lamelar. / The silk fibroin is a protein synthesized by Bombyx mori species, popularly known as silkworm silk. The Bombyx mori cocoon is composed of fibroin fibers and the sericin protein, which is responsible for joining the fibroin yarns. The fibroin is a quite versatile natural polymer and can be processed to form materials such as films, microspheres and hydrogels. Hydrogels are three-dimensional networks formed by macromolecules and capable of absorbing large quantities of water without losing their structural integrity. Due to biocompatibility, ability to mimic biological tissues, high water content and good diffusion properties of oxygen and nutrients, hydrogels are widely used in biomedical research. The fibroin is biodegradable, thermally stable, highly crystalline, flexible and tensile resistant. Besides, it is insoluble in water and in most organic solvents. The fibroin from Frison Extra and Meada 21 Denier silks was separated from the sericin by the degumming process, whereby the silk fibers were immersed in alkaline solutions and subjected to heating with subsequent dissolution and removal of sericin. Fibroin yarns were dispersed in various solutions: CaCl2:H2O; LiCl:H2O; and LiCl:EtOH:H2O. It was observed that according to the fibroin type and solvent solution used the time to achieve dispersion varied. Texture and rheology were determined for every sample after dispersion. All non-degummed samples had shown increased firmness and elastic module G\'. It was observed that the samples presented a wide behavior range, some that contained sericin or ethanol presented Newtonian behavior. Subsequently the samples were dialyzed to obtain the hydrogels and lyophilized. All samples (with exception of two) have formed hydrogels in a 24 hours period. The lyophilized hydrogels were analyzed by thermogravimetry, diffractometry, spectrophotometry and microscopy. All silk fibroin hydrogels presented high thermic resistance with β-sheet predominance. Morphologically, all hydrogels obtained from LiCl:EtOH:H2O and CaCl2:EtOH:H2O solutions had shown entangled aspect wile hydrogels from LiCl:H2O solutions had shown lamellar structures.
83

Propriedades ópticas de membranas à base de polímeros naturais e nanopartículas de carbono / Optical properties of membranes based on natural polymers and carbon nanoparticles

Caetano, Laís Galvão [UNESP] 21 December 2016 (has links)
Submitted by LAÍS GALVÃO CAETANO null (laisgalvao@iq.unesp.br) on 2017-02-06T13:41:04Z No. of bitstreams: 1 Dissertação Mestrado Laís Galvão Caetano.pdf: 2178003 bytes, checksum: 2239574ffc48afbca6a43b06084d326b (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-02-09T17:06:10Z (GMT) No. of bitstreams: 1 caetano_lg_me_arafo.pdf: 2178003 bytes, checksum: 2239574ffc48afbca6a43b06084d326b (MD5) / Made available in DSpace on 2017-02-09T17:06:10Z (GMT). No. of bitstreams: 1 caetano_lg_me_arafo.pdf: 2178003 bytes, checksum: 2239574ffc48afbca6a43b06084d326b (MD5) Previous issue date: 2016-12-21 / A fibroína da seda extraída dos casulos do bicho-da-sêda é um co-polímero particularmente atraente para aplicações em dispositivos fotônicos e opticoeletrônicos devido a sua transparência óptica, biocompatibilidade e propriedades mecânicas. Esta tese apresenta a obtenção de suspensões e filmes iridescentes-luminescentes de fibroína contendo nanopartículas luminescentes de carbono (“carbon dots”) obtidos a partir de carvão vegetal. As nanopartículas luminescentes de carbono apresentam biocompatibilidade, baixa toxicidade, propriedades de fotoluminescência interessantes e possibilidade de modificação da superfície. Redes de difração foram produzidas nestes filmes utilizando como molde um DVD comercial. Os materiais obtidos foram caracterizados por um conjunto de técnicas de análise: Microscopia de Força Atômica (AFM), Microscopia Eletrônica de Varredura (MEV), Microscopia Eletrônica de Transmissão (MET), Espectroscopia de absorção na região do UVVis, Espectrofotometria de absorção molecular na região do infravermelho com transformada de Fourier (FTIR) e Luminescência. Medidas de luminescência mostram que os carbon dots emitem múltiplas cores entre toda a região do visível. Planos cristalinos foram observados nas imagens de MET das nanopartículas, no qual foram asssociadas a estrutura do grafite. Pela análise de UV-Vis dos carbon dots observou-se que a absorção óptica decai gradualmente à medida em que ocorre deslocamento para o vermelho e para os filmes de fibroína observou-se um ombro referente a transição eletrônica da tirosina (aminoácido de sua composição). A partir dos espectros de FTIR observou-se que não houve mudança na estrutura da fibroína após a adição dos carbon dots. As imagens de AFM e MEV comprovam a presença dos micropadrões periódicos na superfície dos filmes. Os resultados mostraram que os filmes de fibroína contendo carbono dots tem um grande potencial para a biomedicina, principalmente devido os seus parâmetros de luminescência se extenderem em toda a região do visível e por apresentar uma matriz sustentável, com excelentes propriedades ópticas e mecânicas. / Silk fibroin extracted from silkworm cocoons is a particularly attractive copolymer for applications in photonics and optoelectronics devices due its optical transparency, biocompatibility and high mechanical strength. This thesis presents the preparation of suspensions and iridescent-luminescent films of silk fibroin containing luminescent carbon nanoparticles (carbon dots) obtained from vegetal coal. Luminescent carbon nanoparticles present high biocompatibility, low toxicity, interesting photoluminescence properties and possibility of surface modification. Diffraction gratings were produced in these films using a commercial DVD as a template. The materials obtained were characterized by a set of analysis techniques: Atomic-Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), UV-Visible Spectroscopy, Fourier transform infrared spectroscopy (FTIR), and Luminescence. Luminescence measurements show that carbon dots emit light at the entire visible region. Crystalline planes were observed in the TEM images of the nanoparticles, where upon the graphite structure was associated. By analyzing the UV-Vis spectra of the carbon dots it was observed that the optical absorption gradually decreases as the red shift occurs. In the UV-Vis spectra of the silk fibroin films it was observed a shoulder referring to the electronic transition of the tyrosine (amino acid of its composition). From the FTIR spectra it was observed that there was no change in the silk fibroin structure after addition of the carbon dots. The AFM and SEM images confirm the presence of the periodic micro-patterns on the surface of the films. The results showed that the silk fibroin films containing carbon dots have a great potential for biomedicine, mainly due to its luminescence parameters extending throughout the visible region and due to a sustainable platform with excellent optical and mechanical properties.
84

Expression Systems for Synthetic Spider Silk Protein Production

Hugie, Michaela R. 01 December 2019 (has links)
Spider silk is a biodegradable and biocompatible natural material that is stronger than steel and more elastic than nylon. These properties make spider silk a desirable material for many commercial products, ranging from textiles to biomedical materials. Due to spiders’ cannibalistic and territorial nature it is impossible to farm them to produce spider silk at a high enough yield to meet product demands. Therefore, a bioengineered synthetic process is necessary to produce spider silk. Synthetic spider silk has been produced in bacteria, goats, yeast, plants, mammalian cells and silkworms, but none of these processes provided a commercially viable yield or were able to express recombinant spider silk proteins (rSSps) that can mechanically imitate the natural spider silks. The overall goal of this research was to increase the yield and mechanical characteristics, e.g. strength and elasticity, to create a commercially viable spider silk. Three different hosts were used: E. coli, alfalfa and an insect cell line. Each host addresses issues with synthetic protein production in both the short-term and long-term scheme. Through this research yields were increased, while the mechanical properties of the synthetic silks were improved and groundwork for future research into the improvement of synthetic spider silk production were identified.
85

Novel Methods to Produce Large Recombinant Spider Silk Proteins via Polymerization

Hebert, Nathan L. 01 August 2018 (has links)
Spider silk has long been a subject of scientific research due to its remarkable mechanical properties. Until recently, there has been no way to effectively obtain spider silk except by harvesting it from individual spiders. With advances in technology, the genes that code for the individual spider silk proteins have been isolated and genetically engineered into other hosts to produce recombinant spider silk proteins (rSSp) of varying sizes, Larger rSSp have correspondingly greater mechanical properties in any resulting materials. Using current production methods, larger rSSp cannot be produced in commercially viable quantities while simultaneously being economically viable. The current production methods have shown that small rSSp are easier to produce and purify in genetically engineered systems while maintaining favorable yields. After the small molecular weight rSSp were expressed and purified, they were polymerized to form larger molecular weight rSSp, while having maintained mechanical properties of similarly sized rSSp from other expression systems. To accomplish this polymerization, two systems were designed that can catalyze this reaction: using a Spy System and an intein system. These two systems require no external cofactors or enzymes and occur spontaneously once initiated. The expression and purification of rSSp from both of these systems has been characterized. The Spy System did not produce high enough quantities of rSSp to be economically viable. Whereas the intein system produced yields of 5 g/L, which is higher than previously reported. The rSSp from the intein system have been made into biomaterials, such as films, hydrogels, and aerogels. The mechanical properties of these biomaterials were comparable to biomaterials from other spider silk protein production. Utilizing the intein system, projected cost estimates for the production of rSSp has been lowered from $350 to $40 per kilogram. This decreased cost of rSSp would allow a wider array of commercial applications.
86

Silk Cryogels for Microfluidics

Hinojosa, Christopher David 01 January 2012 (has links)
Silk fibroin from silkworm cocoons is found in numerous applications ranging from textiles to medical implants. Its recent adoption as a biomaterial is due to the material's strength, biocompatibility, self-assembling behavior, programmable degradability, optical clarity, and its ability to be functionalized with antibodies and proteins. In the field of bioengineering it has been utilized as a tissue scaffolding, drug delivery system, biosensor, and implantable electrode. This work suggests a new application for porous silk in a microscale chromatography column. We demonstrate in situ cryotropic polymerization of highly porous structures in microscale geometries by freezing aqueous silk with a solvent. The resulting cryogels are experimentally characterized using flow parameters common in chromatography design; tortuosity, global pressure drop, pore diameter, and porosity. These empirical parameters are put into porous flow models to calculate an order-of-magnitude increase in functional surface area over the blank capillaries and packed-sphere columns used in traditional designs. Additionally, the pressure requirements to produce relevant flow rates in these structures are found not to threaten the integrity of microfluidic seals or connectors.
87

Enhancing Spider-Silk Protein Materials through Continuous Electrospinning and Photo-Initiated Cross-Linking

Gil, Dan 01 August 2018 (has links)
Spider-silk is known as one of the stronger natural materials, unfortunately it is impossible to farm spiders due to their territorial and cannibalistic nature. To address this issue, researchers have studied spider-silk to discover how it is produced in nature. From their results, spider-silk is composed of large sized proteins produced in two different cell types. Using this knowledge, researchers created transgenic organisms capable of producing spider-silk proteins in large quantities. Using these proteins, several groups have created fibers, films, hydrogels, and adhesives with robust and versatile properties. Wet-spinning is a technique commonly used to create fibers from spider-silk proteins. These fibers unfortunately do not compare to the mechanical properties of natural silk. To address this researchers have used a method known as electrospinning to create spider-silk fibers with substantially smaller diameters. In doing so, these electrospun fibers have increased surface area and enhanced mechanical properties. Using this method, our group has modified the electrospinner to be able to produce continuous fine diameter yarns composed of hundreds of nanofibers with mechanical properties surpassing that of natural silk. Fibers aside, spider-silk proteins can be used to create a variety of different biocompatible materials. To further enhance these materials, our group has utilized a technique traditionally used for observation. This technique employs a high intensity light source to initiate cross-links within the proteins. With this method, our spider-silk protein materials have increased their mechanical properties by a factor of seven. These materials can further be modified through post-treatments, resulting in tunable materials with diverse and robust mechanical properties.
88

Potential Applications of Silk Fibroin as a Biomaterial

Bailey, Kevin 07 June 2013 (has links)
Fibroin is a biopolymer obtained from the cocoons of the Bombyx mori silkworm that offers many unique advantages. In this thesis work, fibroin was processed into a regenerated film and examined for potential biomaterial applications. The adsorption of bovine serum albumin onto the fibroin film was investigated to examine the biocompatibility of the film, and it was found that BSA adsorption capacity increased with an increase in BSA concentration. At 10 mg/mL of BSA, the BSA sorption reached 0.045 mg/cm2. This level of BSA is indicative of good blood compatibility and biocompatibility of the fibroin. The gas permeabilities of oxygen, nitrogen, and carbon dioxide were tested for potential applications in contact lenses and wound dressings. Over a pressure range of 70 – 350 psig, the permeability of oxygen and nitrogen was 5 Barrer, while that of carbon dioxide ranged from 26 to 37 Barrer. The oxygen transmissibility of the fibroin films prepared in this study was on the low end required for use in daily wear contact lenses, but sufficient to aid the healing process for use in wound dressings. The permeability and diffusivity of four model drugs in the fibroin film was investigated for potential applications in controlled drug release. The permeability at higher source concentrations leveled out to 0.8 – 4.3 x 10-7 cm2/s depending on the drug tested. The diffusion coefficient determined from sorption experiments was approximately 1.8 x 10-9 cm2/s, while the diffusion coefficients from desorption experiments were determined to be 0.8 – 2.7 x 10-9 cm2/s. The magnitude of the drug permeability and diffusivity are consistent with many other controlled release materials, and the fibroin film showed good potential for use in controlled release.
89

The Cluster Strategy Improve The Development of Textile Industry-Silk and Filament District

Feng, Yi-Hsin 20 July 2004 (has links)
Since 1990 Porter has advert the conception that cluster could improve the competitive strength of textile industry, it has arouse highly attention of academe, also a lot of developed countries took this appearance of assemblage policy as the development policy for their industries. The textile industry of Taiwan has been developed around 50 years ago, in nearly years, ascribe to the rise of cost, the value of export continually decrease and the increase of abroad competitors, the textile industry has been considered as a declined industry. However, according to the research it¡¦s still one of the most important industry which can create a lot of foreign exchange; on 2001 Council For Economic Planning And Development has planned to build a silk and filament district in Yunlin particular for the textile industry , for assemble the textile industry and push Taiwanese industries into the textile center of Asia-pacific. According to this research we would like to know how the cluster strategy could improve the development of textile industry in Taiwan. Mainly use Location Quotient analysis to know if the textile industry is the most important basal industry in this area, and with all the related documents we could realist the crux element of the development of cluster strategy, then we could have talk with related industries and companies, in this way we may have a complete view of the whole situation in this industry and the project of having this special area. The combination of above descriptions, we could understand this special area of the textile industry and the production environment, find out the lack part and create a millennium for the development of textile industry. The result of this research discovered that according to the analysis of this industry, the textile industry has highly central tendency and it is the main industry of this area; but according to the crux element of the development, it does not have strong enough connection between local companies and it does not have good enough interactive with schools in this area, it may cause the lack of talent people, knowledge and research. In the future, it is going to be a very important issue that we have to consider about, aggrandize the connection between the local companies and the interactive with schools.
90

Vidinė kompozicija / Internal composition

Norkutė, Asta 17 January 2007 (has links)
Holy circle whereat invoke waried in symbol and forms, people superimpose their understanding of life, therein lies phenomenon, secret force. Mandala – wayfaring to centre of a periphery, from emotions and minds topsyturvy to unseen poise, pivot, self. A symbol of mandala – eternal thought, fence in everlasting. Formation, transformation. Conceive symbol, to see him inly sight. They quasi to create the inne link power, the thank to event ones own interior reality. Aburden of my graphic collection ,,Internal composition” l created meditations space. Major only purposeis graphic creation whiteness, sublime.

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