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Proper functioning of instruments requires precise calibration and routine quality assurance. In a clinical setting, this is achieved through the use of phantoms, which mimic the physical characteristics of tissues. Polyvinyl alcohol (PVA), a non-toxic, water-soluble polymer is well-suited for use as clinical phantom material. Through successive freezing and thawing, solutions of PVA in water can be solidified into rigid cryogels (PVA-C). The number of freeze-thaw cycles affects the properties of the material, including its optical characteristics. A double integrating sphere system was used in conjunction with the Inverse Adding Doubling (IAD) algorithm to characterize the optical properties of thin slab samples. The setup was evaluated using liquid phantoms. Liquid emulsion and food colouring were used to impart scattering and absorbing properties in the range characteristic of human tissue. Measured values of normalized reflectances and transmittances were entered into IAD, and a set of optical properties (μ′s,μa,g) retrieved. The reduced scattering coefficient was found to increase linearly with increasing lipid concentration, while a consistent overestimation of the absorption coefficient was observed. Measurements of PVA cryogels revealed a linear increase in the reduced scattering coefficient with an increasing number of freeze-thaw cycles up to five cycles. Scattering was also observed to increase with concentration up to PVA concentrations of 15%, and to spontaneously increase during the lifetime of the slab samples. These findings suggest it is possible to tune the optical scattering of PVA-C via different purely physical mechanisms. / Thesis / Master of Science (MSc)

Made available in DSpace on 2014-06-11T19:22:55Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-06-28Bitstream added on 2014-06-13T18:49:57Z : No. of bitstreams: 1 semenzim_vl_me_sjrp_parcial.pdf: 77605 bytes, checksum: f58727b3dd34087fa9d922f29bac067e (MD5) Bitstreams deleted on 2014-11-14T12:16:55Z: semenzim_vl_me_sjrp_parcial.pdf,Bitstream added on 2014-11-14T12:17:43Z : No. of bitstreams: 1 000696944.pdf: 398566 bytes, checksum: 3105a99c9e8591292c70a0dc96958d0a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Partículas poliméricas com tamanho e morfologia controlados e propriedades físico-químicas adequadas são amplamente utilizadas em várias aplicações biomédicas, especialmente em embolização, uma técnica cirúrgica minimamente invasiva utilizada em tratamentos de diversas doenças vasculares e quimioembolização, que associa a embolização e a quimioterapia. Ela é realizada com uso de materiais denominados agentes embólicos, sendo as partículas de poli(vinil álcool) (PVA) amplamente utilizadas por apresentarem um alto grau de desempenho. As partículas de PVA estão disponíveis no mercado nas morfologias esféricas e floculares, sendo as esféricas as que apresentam menores riscos para o procedimento. Dessa forma, o presente trabalho teve como objetivo sintetizar e caracterizar microesferas de PVA para serem utilizadas em embolização e quimioembolização. Juntamente com a equipe de pesquisadores da empresa Braile Biomédica, a intenção é desenvolver um produto que ainda não é fabricado pela indústria nacional para ser comercializado a menores custos. Materiais e Métodos: As microesferas de poli(vinil álcool) (PVA) foram sintetizadas pelo método de polimerização em suspensão, seguida de hidrólise alcalina (ou saponificação). Na etapa de saponificação, diferentes concentrações de NaOH foram utilizadas. As amostras sintetizadas foram caracterizadas por Microescopia Eletrônica de Varredura (MEV), Difração de Raios-X (DRX), Calorimetria Diferencial de Varredura (DSC), Ressonância Magnética Nuclear de 13 C - cross polarization / magic angle spinning ( 13 C RMN CP/MAS) e Potencial Zeta (ζ). Resultados: A análise de MEV indicou que foram obtidas partículas esféricas. Os dados complementares de DRX, DSC e 13 C RMN CP/MAS indicam que à medida que se aumenta a concentração... / Polymeric particles with size and morphology controlled and appropriate physicochemical properties are widely used in several biomedical applications, especially in embolization, a minimally invasive procedure routinely used in treatments of some vascular diseases, and chemoembolization, which combines embolization and chemotherapy. It is performed using materials called embolic agents, being poly(vinyl alcohol) (PVA) particles often used because its high performance. These particles are commercially available in spherical and flocculate morphologies, however spherical particles present lower risks than flocculates ones during the procedure. Thus, this study proposes to develop and improve spherical PVA particles to be used in embolization and chemoembolization. The development are being conducted by the researchers group from Braile Biomédica, the goal is to develop a product that is not yet produced in the national industry, commercializing it at lower costs. Materials and Methods: PVA microspheres were synthesized by suspension polymerization method, followed by alkali hydrolysis (or saponification). In the saponification step, different concentrations of NaOH were used. The samples synthesized were characterized by Scanning Electronic Microscopy (SEM), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), 13 C Nuclear Magnetic Resonance - cross polarization / magic angle spinning ( 13 C CP/MAS NMR) and Zeta Potential (ζ). Results: SEM analysis indicated that spherical particles were obtained. The complementary data of XRD, DSC and 13 C CP/MAS NMR indicate that the use of high NaOH concentrations (in the saponification process) determines reordering in the lateral chains of the polymer, which causes an increase of material’s crystallinity. Zeta Potential (ζ) data of the samples indicated that, in an... (Complete abstract click electronic access below)

Orientador: Hermes Adolfo de Aquino / Banca: Newton Luiz Dias Filho / Banca: Aldo Eloizo Job / Resumo: Neste trabalho foram obtidos e caracterizados filmes de polivinil álcool (PVAl) puro e híbrido polivinil álcool/sulfeto de cádmio (PVAl/CdS). A síntese foi realizada usando o método "hidrotérmico in situ". O híbrido é composto pela matriz orgânica o PVAl e a outra fase inorgânica é o CdS. As amostras foram obtidas na forma de filmes pelo método "casting" a partir de soluções de PVAl/CdS sintetizadas, as quais possuem concentrações de (0.05 %); (0.1 %); (0.2 %); (0.4 %) e (0.7 %) em peso de CdS. A morfologia e as propriedades ópticas, térmicas e elétricas do filme de PVAl e do híbrido PVAl/CdS foram caracterizadas pelas técnicas de Difração de Raios -X (DRX), Espectroscopia na Região do Ultravioleta-visível (UV-vis), Calorimetria Diferencial Exploratória (DSC) e Espectroscopia de Impedância. A análise de DRX utilizando o software composto por um banco de dados de cristalografia indicou a formação de nanopartículas de CdS que possuem estrutura hexagonal. Através de cálculos usando a equação de Scherrer obteve-se o tamanho das nanopartículas que variaram entre (70 e 113 nm). As medidas de UV-vis também confirmaram que as partículas possuem diferentes tamanhos. A presença das nanopartículas é indicada por um pequeno deslocamento da banda de absorção característica do material em determinado comprimento como o CdS "bulk" (490 nanômetro (nm)). O deslocamento desta banda, característica para comprimento de onda menor (de 490 para 485 nm) indica que os tamanhos das partículas são suficientemente pequenos para produzir o chamado efeito quântico. A análise térmica de DSC indicou o comportamento térmico e a influência das partículas CdS sobre os tipos de transformações básicas do polímero como a temperatura de transição vítrea (Tg), temperatura de fusão (Tm), temperatura... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work were obtained and characterized films of pure polyvinyl alcohol (PVAl) and hybrid PVAl/CdS. The synthesis was performed using the "hydrothermal in situ" method. The hybrid is composed by one organic part, called matrix polyvinyl alcohol (PVAl) and an inorganic phase, cadmium sulfide (CdS). The samples were obtained as films by the "casting" method from PVAl/CdS solutions with (0.05 %); (0.1 %); (0.2 %); (0.4 %) and (0.7 %) concentration of CdS. The morphology, optical properties, thermal properties and electrical properties of pure PVAl film and hybrid PVAl/CdS were characterized by techniques such as X-ray diffraction (XRD) spectroscopy in the ultraviolet-visible (UV-vis), Differential Scanning Calorimetry (DSC) and impedance spectroscopy. The analysis of XRD using programs with crystallography data stored shows the formation of CdS nanoparticles which have hexagonal structure. Through calculation using the Scherrer equation, the sizes of the nanoparticles were obtained in a gap between (70 and 113 nm). The measurements of UV-vis also showed that the particles have different sizes and that the CdS particles have dimensions in nanometric scale. The presence of nanoparticles is indicated by a small shift of the absorption band of the material characteristic as in the CdS bulk, (490 nm). When such characteristic band shift occurs to shorten wavelength from (490 to 485 nm), it indicates that the particle size decreased due to quantum effects. It is confirmed by the XRD technique. The thermal analysis of DSC studied the thermal behavior and the influence of CdS particles on the types of transformations as the basic polymer glass transition temperature (Tg), melting temperature (Tm), crystallization temperature (Tc). The external factor that most affect the T m and Tg is the presence of plasticizers. It could be noted when intentionally added the CdS... (Complete abstract click electronic access below) / Mestre

Wheat gluten, wheat gliadin, and corn zein agricultural proteins were evaluated as multifunctional additives that: (1) provided reinforcement, (2) improved thermal stability, and (3) lowered the cost of polymer composites. Wheat proteins were utilized in two polymer matrices: poly(vinyl alcohol) (PVA) and synthetic cis-1,4-polyisoprene rubber (IR). The proteins were hydrolyzed and dispersed in the polymer matrix, where they cooperatively self-assembled into nanostructures called amyloids. Amyloids have the potential for high rigidity and stability due to high β-sheet content. In Chapter II, trypsin hydrolyzed wheat gluten (THWG) proteins were incubated in aqueous PVA solutions, then the composite solutions were air dried and compression molded into films. Anisotropic protein aggregates formed through a typical mechanism of β-sheet self-assembly, where a greater molding time and pressure and/or a lower PVA molecular weight allowed for more protein aggregation. The larger protein structures provided less reinforcement. In Chapters III and IV, THWG and trypsin hydrolyzed gliadin (THGd), a component protein in wheat gluten, were compounded in synthetic polyisoprene rubber to form nanocomposites. The reinforcement correlated to the protein β-sheet content and varied with protein concentration, protein batch preparation, processing temperature, and compounding time. The isotropic β-sheet containing structures were very thermally stable, even under harsh rubber compounding conditions. By optimizing the processing parameters uniform protein dispersion and optimal IR reinforcement were achieved, although the protein and IR phases had poor compatibility. In Chapter V, the THGd-IR composites were cured using a typical cure package and molding process. Protein aggregation into nanostructured β-sheets was observed during the curing process. Rubber reinforcement increased as a function of protein concentration and curing time. In Chapter VI, a hydrophobic protein (zein) was substituted for the hydrophilic protein (gliadin) used previously to improve protein-IR compatibility. The zein protein was better at reinforcing IR, while gliadin improved mechanical stability. Both zein and gliadin improved the thermal stability of IR. The results from Chapters II-VI showed an interesting concept: in situ filler formation in polymer matrices where the choice of protein, polymer, and processing conditions influenced the final morphology and composite properties. / Doctor of Philosophy / We use plastics every day for a wide range of applications, from food packaging to automobile tires. Many of these plastics are composite materials, called “polymer composites,” meaning they are made of two or more chemically distinct materials where one material is a polymer. For reference, a polymer is a long chain molecule made of many (“poly-”) units (“- mer”). Polymer composites often contain additives which modify the properties of the polymer. For example, many soft polymers, such as tire rubber, need to be made stiffer and so a “reinforcing additive” is used to improve the stiffness of the rubber. Many composite materials are made stiffer so less material can be used. This process is called “lightweighting.” The automotive industry and food packaging industry use this process to reduce weight and fuel costs. In this research, plant proteins are tested as reinforcing additives in polymer composites. Plant proteins, such as wheat gluten, are abundant, non-toxic, sustainable, and can self-assemble into extremely small, stiff structures. For these reasons, plant proteins offer an environmentally friendly alternative to typical reinforcing additives. This dissertation shows that plant proteins can reinforce two polymers with very different properties. The first polymer is poly(vinyl alcohol) (PVA), which is biodegradable, hydrophilic (i.e., “water loving”), and is commonly used in flexible food packaging. The second polymer is synthetic cis-1,4-polyisoprene rubber (IR), which is non-biodegradable, hydrophobic (i.e., “water fearing”), and is commonly used in automotive tires. In Chapters II-V, the wheat gluten protein is hydrolyzed, i.e., chemically “chopped” into short chain peptides, to encourage the self-assembly of the plant protein into small, stiff structures. The self-assembled protein structures survive typical industrial processing techniques, such harsh rubber compounding conditions which involve high heat, pressure, and shear forces (i.e., the material is pushed in opposing directions). In Chapter VI, full corn and wheat proteins are incorporated into IR using standard industrial mixing and curing processes. The corn and wheat proteins reinforce the synthetic rubber and inhibit the degradation of the chemical structure of cured rubber under high heat. At certain protein concentrations, the proteins improve the elasticity and lessen the permanent deformation in the polymer composite. Together, Chapters II-VI show that proteins from diverse plant sources can be used to improve the performance of polymers with dissimilar properties.

Kyoto University (京都大学) / 0048 / 新制・論文博士 / 博士(工学) / 乙第12199号 / 論工博第3988号 / 新制||工||1438(附属図書館) / 26271 / UT51-2008-C969 / (主査)教授 堀井 文敬, 教授 渡辺 宏, 教授 金谷 利治 / 学位規則第4条第2項該当

Ultrasound imaging systems are a safe and affordable imaging modality with the disadvantage of low spatial resolution, especially for assessing smaller vessels. However, with the implementation of super-resolution ultrasound imaging techniques, studies have shown promising results in achieving a resolution below the diffraction limit. Super-resolution ultrasound imaging techniques takes advantage of the point spread function to localize the centroid of the ultrasound contrast agents in an image. By superimposing thousands of these images, a super-resolved image of the localized and tracked contrast agents can be created, which presents an image where vessels down to a few micrometers can be resolved. The purpose of this master’s thesis was to implement super-resolution ultrasound imaging, test different localization methods and analyze them by using different ultrasound contrast agent concentrations. Grayscale ultrasound images were acquired using the Verasonics system for three different microbubble concentrations. The super-resolution ultrasound imaging program was executed on the grayscale images using three different localization methods, Gaussian fit, No-shift and Interpolation based scheme. The microbubbles were localized and tracked over several frames to create a super-resolved image which had the pixel resolution of a 10th of the wavelength. Significant improvements were demonstrated in the super-resolved images compared to the grayscale images. The higher microbubble concentrations resulted in a higher number of localized and tracked microbubbles. While the low concentration exhibited lower values. Comparing the methods, Gaussian fit and No-shift detected higher number of microbubbles than the method Interpolation. Although further analysis is needed, the thesis concluded that using Gaussian fit as a localization method and higher microbubble concentrations, a super-resolved image can be produced even if the program is tested on fewer images. / Ultraljudsavbildning är en säker och billig avbildningsmodalitet med en låg spatial upplösning, framför allt vid avbildning av mindre kärl. Men med implementering av ultraljudsavbildningstekniker med superupplösning har studier visat lovande resultat för att uppnå en upplösning under diffraktionsgränsen. Ultraljudsavbildningstekniker med superupplösning utnyttjar punktspridningsfunktionen för att lokalisera ett ultraljudskontrastmedels centerpunkt i en bild. Genom att överlagra tusentals av dessa bilder skapas en superupplöst bild av det lokaliserade och spårade kontrastmedlet. Med hjälp av superupplösta bilden kan kärl som är några mikrometer urskiljas. Syftet med denna masteruppsats var att implementera ultraljudsavbildning med superupplösning, testa olika lokaliseringsmetoder och analysera de genom att använda olika koncentrationer av mikrobubblor. Gråskale ultraljudsbilder samlades in med hjälp av Verasonics systemet för tre olika koncentrationer av mikrobubblor. Superupplösningsprogrammet var exekverad på gråskalebilderna för tre olika lokaliseringsmetoder, Gaussian fit, No-shift och Interpolation based scheme. Mikrobubblorna lokaliserades och spårades över flera bilder för att skapa en superupplöst bild vilket hade en tiondel av våglängden som pixelupplösning. Resultatet presenterade en märkbar förbättring i de superupplösta bilderna jämfört med gråskalebilderna. De högre koncentrationerna med flera mikrobubblor resulterade i ett högre antal lokaliserade och spårade mikrobubblor, medan den lägre koncentrationen gav färre lokaliserade mikrobubblor. Metoderna Gaussian fit och No-shift detekterade flera mikrobubblor än metoden Interpolation. Slutsatsen visade att användningen av lokaliseingsmetoden Gaussian fit med högre koncentrationer av mikrobubblor ger en superupplöst bild även om programmet exekveras på färre bilder.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In papermaking, fillers and additives are used to enhance paper properties. In this study spherical modified poly(vinyl alcohol) (PVA) particles were prepared for use as fillers. In order to determine the mechanism of adhesion of additives to cellulose (paper) fibres, these particles were modified to have surface functionality, with cationic and anionic surface charges, similar to charged polyelectrolyte additives. Typically, retention aids used to improve the fibre–fibre and fibre–filler bonding are able to conform to the surface of the fibres and fillers. Oppositely charged components show strong affinity for each other, e.g. cationic polyelectrolyte groups adhere to anionic surface charges on the fibres. The spherical PVA particles were prepared by the saponification of spherical poly(vinyl pivalate) (PVPi) precursor particles. These PVPi particles, prepared via suspension polymerisation, were cross-linked with a divinyl ether comonomer. The vinyl pivalate (VPi) suspension polymerisation was successfully carried out and afforded relatively uniformly distributed PVPi particles, with diameters of 0.5–10 mm. The cross-linked PVPi particles were then saponified in tetrahydrofuran (THF) as swelling solvent, to afford PVA with various degrees of saponification (DS). The spherical shape was lost and fibrous material was obtained when uncross-linked PVPi particles were saponified. Cross-linking the spherical PVPi particles (PVA precursor) proved innovative, and essential in maintaining the spherical form during saponification to PVA/PVPi. By varying the saponification time periods, various DS were obtained, as characterised by solid state NMR spectroscopy. Surface modification of the PVA/PVPi particles was carried out with cationic and anionic groups via the Williamson ether synthesis. Ionic modification of these rigid spherical PVA/PVPi particles was carried out in order to study their adherence to cellulose fibres, compared to the adherence of similarly modified starches with cellulose fibres. Fluorescent labelling of the different modified particles was carried out using two complimentary coloured fluorescent markers. Fluorescence imaging and scanning electron microscopy (SEM) enabled the observation of particle– fibre and particle–particle interaction. Results indicated that the negative groups are sparse on the cellulose fibres, and therefore particles with low functionality but which are able change shape and conform and adhere to the surface of the cellulose fibres are required for effective adhesion. These modified spherical PVA/PVPi particles are unique as they mirror the chemistry of functionalised starch and cellulose particles, yet maintain their shape and have a fixed size, measurable by SEM and transmission electron microscopy (TEM). Field-flow fractionation was also used to characterise and measure these relatively large cross-linked and fixed diameter particles. / AFRIKAANSE OPSOMMING: In papierproduksie word vulstowwe en bymiddels gebruik om die eienskappe van papier te verbeter. In hierdie studie is sferiese poli(vinielalkohol) (PVA) partikels berei vir gebruik as vulstowwe. Om ten einde die meganisme van die bymiddelklewing aan die sellulose vesels (papier) te bepaal, is die oppervlakke van hierdie partikels gewysig met kationiese of anioniese groepe, om 'n oppervlak soortgelyk aan dié van funksionele poliëlektrolietbymiddels te verskaf. Die retensiemiddels wat gebruik word om die vesel–vesel en vesel–vulstof binding te verbeter is tipies in staat om te konformeer aan die oppervlak van die vesels en vulstowwe. Teenoorgesteldgelaaide komponente toon 'n sterk affiniteit vir mekaar, bv. kationiese poliëlektrolietgroepe is vasklewend aan die anioniesgelaaide oppervlakke van die vesel. Die sferiese PVA partikels is berei deur die verseping van sferiese poli(vinielpivalaat) (PVPi) partikels. Hierdie voorloper PVPi partikels, berei deur suspensiepolimerisasie, is gekruisbind met 'n divinieleter ko-monomeer. Die vinielpivalaat (VPi) suspensiepolimerisasie is suksesvol uitgevoer en relatief eenvormig verspreide sferiese PVPi partikels is berei, met deursnitte tussen 0.5–10 mm. Die gekruisbinde PVPi partikels is daarna gesaponifiseer in tetrahidrofuraan (THF) as oplosmiddel, om PVA met verskillende grade van verseping (DS) te berei. Die sferiese vorm raak verlore en veselagtige materiaal is verkry wanneer PVPi partikels met geen kruisbinding verseep is. Kruisbinding van die sferiese PVPi partikels (PVA voorloper) is voordelig en noodsaaklik om die sferiese vorm tydens die verseping tot PVA/PVPi te behou. Deur die tydsduur van verseping te verander, is verskeie grade van verseping verkry en bevestig deur vaste toestand KMR spektroskopie. Oppervlakwysiging van die PVA/PVPi partikels, om kationiese en anioniese groepe aan te heg, is uitgevoer via die Williamson etersintese. Ioniese wysiging van hierdie stram, sferiese PVA/PVPi partikels is uitgevoer om ten einde hul klewing met sellulose vesels te bestudeer en te vergelyk met die klewing van soortgelyk gewysigde stysels. Fluoressensie merking van die verskillende gewysigde partikels is uitgevoer met behulp van twee komplimentêre gekleurde fluoressensie merkers. Fluoressensie beeldvorming en SEM verskaf die waarneming van partikel–vesel en partikel–partikel interaksie. Die resultate dui daarop dat die negatiewe groepe van die sellulose vesels skaars is, en daarom is partikels met ‘n lae funksionaliteit, maar wat in staat is om van vorm te verander, aan te pas en te konformeer aan die oppervlak van die sellulose vesels, nodig vir effektiewe adhesie. Hierdie gewysigde sferiese PVA/PVPi partikels is uniek aangesien hulle die chemie van gewysigde stysel en sellulose partikels naboots, maar steeds hul vorm behou met 'n vaste grootte; meetbaar deur SEM en TEM. Veld-vloei-fraksionering is ook gebruik vir die karakterisering van hierdie relatief groot, stram, gekruisbinde partikels met bepaalde deursneë.

Electrospinning is a method of producing nano structured material from a polymer solution or melt using high strength electric fields. It is a process that has yet to find extensive industrial application yet shows promise if obstacles such as low rate of production overcome perhaps by more complete theoretical modelling. This work examines the effects of adding an ionic salt to a solution of poly(vinyl alcohol) in water. The direct effect was an increase the charge density and electric current. It was found that an increase in charge density decreases the mass deposition rate and forms a thinner initial jet. When the sign of the charge on the polymer solution was changed from positive to negative the charge density increased and the initial jet diameter and mass deposition rate also decreased. It was proposed that a smaller radius of curvature is formed by the Taylor cone at higher charge densities resulting in a smaller “virtual orifice”. The extent of the bending instability was explored and it was found that adding ionic salt results in a decrease in the bending instability resulting in thicker fibres. Changing the sign of the charge on the polymer solution from positive to negative resulted in an increase in the bending instability and resulted in thinner fibres. The charge transfer mechanisms used in different electrospinning models are explored and some assumptions not explicitly stated are discussed. From this discussion a generalized equation describing the charge transport mechanisms is proposed.