Dissertations / Theses on the topic 'Polyp growth'
To see the other types of publications on this topic, follow the link: Polyp growth.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Polyp growth.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Stevenson, Christopher Eric, and Chris Stevenson@aihw gov au. "A microsimulation study of the benefits and costs of screening for colorectal cancer." The Australian National University. National Centre for Epidemiology and Population Health, 2001. http://thesis.anu.edu.au./public/adt-ANU20040611.162207.
Full textAbstract:
This thesis examines the benefits and costs of screening for colorectal cancer in the context of an organised population screening programme. It uses microsimulation modelling to derive an optimally cost-effective screening protocol for various combinations of the available screening tests. ¶
First a mathematical model for the natural history of colorectal cancer is derived, based on analyses of Australian population and hospital-based cancer registries combined with data from published studies. Then a model for population based screening is derived based mainly on data from published screening studies, including the four major published randomised controlled trials of faecal occult blood test (FOBT) screening. These two models are used to simulate the application of a screening programme to the Australian population. The simulations are applied to a period of 40 years following 1990 (the studys base year), with both costs and benefits discounted back to the base year at an annual rate of 3%.¶
The models are applied to simulating a population screening programme based on FOBT with a colonoscopy follow up of positive tests. This simulation suggests that the optimal application of such a programme would be to offer annual screening to people aged 50 to 84 years. Such a programme would lead to a cumulative fall in years of life lost to colorectal cancer (YLL) of 28.5% at a cost per year of life saved (YLS) of $8,987. These costs and benefits are consistent with those arising from other currently funded health interventions. They are also consistent with the cost per YLS which Australian governments appear willing to pay for health interventions when justified on the basis of cost-effectiveness. The fall in colorectal cancer deaths from this screening programme should be first detectable by a national monitoring system after around three years of screening. However the full benefits from screening would not be realised before around 30 years of screening.¶
These simulations are based on the standard guaiac FOBT, but the results suggest that significant cost-effective gains could be made by using the newer immunochemical FOBT. Further cost-effect gains could be made by offering sigmoidoscopy every five years in addition to annual FOBT.¶
The models are then applied to simulating population screening programmes using colonoscopy and sigmoidoscopy as primary screening tools. Offering colonoscopy every ten years to all people aged from 45 to 85 leads to an overall fall in cumulative YLL of 37.6%, at a cost of $15,585 per YLS. Offering sigmoidoscopy every three years to all people aged 40 to 85 leads to an overall fall in cumulative YLL of 29.1%, at a cost of $4,862 per YLS. Both of these cost and benefit results are also consistent with the cost per YLS which Australian governments appear willing to pay. The fall in deaths with colonoscopy screening would also be detectable after three years of screening but the fall with sigmoidoscopy screening would not be detectable until after six years of screening. Sigmoidoscopy would need around 35 years of screening to reach its potential gains while colonoscopy screening would not reach its full potential during the 40 year screening period.¶
Finally the models are applied to targeting people at higher risk of cancer. The results show that offering colonoscopy every five years to people at higher risk because of a family history of colorectal cancer is a cost-effective addition to the annual FOBT screening programme.¶
An earlier version of chapter two of this thesis has been published as
Stevenson CE 1995. Statistical models for cancer screening. Statistical Methods in Medical Research; 4: 1923.¶
An expanded version of chapter two, along with parts of chapter one, has been published as
Stevenson CE 1998. Models of screening. In: Encyclopedia of Biostatistics. Armitage P, Colton T, eds. John Wiley and Sons Ltd, pp 39994022.
2
Bernard, Alexandre. "Polylactide Growth on Various Oxides: Towards New Materials." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275480586.
Full text
3
Marinetti, Loris. "The effect of poly(lactide)-poly(carbonate) based block copolymers on the morphology and crystallization of double crystalline poly(lactide)/poly(ε-caprolactone) blends." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11965/.
Full textAbstract:
Block copolymers of poly(lactide) and poly(carbonate) were synthetized in three different compositions and characterized by 1H-NMR and ATR analyses. The compatibilization effect of this copolymers on 80/20 (w/w%) PLA/PCL blend was evaluated. SEM micrographs show that all the blends exhibit the typical sea-island morphology characteristic of immiscible blends with PCL finely dispersed in droplets on a PLA matrix. Upon the addiction of the copolymers a reduction on PCL droplets size is observable. At the same time, a Tg depression of the PLA phase is detected when the copolymers are added in the blend. These results indicate that these copolymers are effective as compatibilizers. The copolymer that acts as the best compatibilizer is the one characterized by the same amount of PLA and PC as repeating units. As result, in the blend containing this copolymer PLA phase exhibits the highest spherulitic growth rate. An analyses on PLA phase crystallization behaviour from the glassy state within the blends was evaluated by DSC experiments. Isothermal cold crystallization of the PLA phase is enhanced up an order of magnitude upon the blending with PCL. Annealing experiments demonstrated that the crystallization of the PCL phase induces the formation of active nuclei in PLA when cooled above cooled below Tg. When the crystallization rate of PCL is retarded, a reduction on PLA nucleation is observed.
4
Kappenberger, Rhea. "Das System LaFeAsO in Poly- und Einkristallen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-235308.
Full textAbstract:
In dieser Arbeit wurde die Ausgangsverbindung der eisenbasierten Supraleiter, LaFeAsO, durch die Synthese und Charakterisierung von poly- und einkristallinen Proben untersucht. Supraleitung kann in den eisenbasierten Supraleitern durch Elektronen- oder Lochdotierung hervorgerufen werden. Die Substitution von Eisen durch Mangan, formal eine Lochdotierung, hat hingegen einen destruktiven Effekt auf die Supraleitung. Dieser ist bei optimal fluordotiertem LaFeAs(O,F) um Größenordnungen stärker ausgeprägt als bei Nd- oder Sm-FeAs(O,F). Indem Lanthan partiell durch das kleinere Yttrium substituiert wurde, konnte gezeigt werden, dass diese unterschiedlich starke Mangantoleranz durch die Unterschiede im Seltenerdmetall-Ionenradius bedingt ist. Weiterhin finden sich Anzeichen, dass die Unterdrückung der Supraleitung durch Mangan mit Elektronenlokalisierung korreliert ist.
Das Fehlen von großen dreidimensionalen Einkristallen der SEFeAsO-Verbindungsklasse stellt ein großes Hindernis in der Erforschung der elektronischen Eigenschaften der eisenbasierten Supraleiter dar. Im Rahmen dieser Arbeit konnte gezeigt werden, dass das Verfahren der Festkörper-Einkristallzüchtung ein geeignetes Mittel darstellt, um große, facettierte SEFeAsO-Einkristalle mit ausgeprägtem Wachstum in c-Richtung zu erhalten.
Mit diesem neu entwickelten Einkristallzüchtungsverfahren konnte ein aktualisiertes Phasendiagramm von La(Fe,Co)AsO erstellt werden. Die Substitution von Eisen durch Cobalt entspricht einer Elektronendotierung und führt zu Supraleitung mit einer maximalen Sprungtemperatur von 12 K. Die Ausgangsverbindung LaFeAsO zeigt bei etwa 156 K einen strukturellen Phasenübergang von einer tetragonalen zu einer orthorhombischen Struktur, weiterhin tritt unterhalb von etwa 138 K eine Spindichtewelle auf. In Einklang mit dem bekannten Phasendiagramm werden mit Cobaltdotierung die beiden Übergänge unterdrückt, mit höheren Cobaltkonzentrationen kommt es zu Supraleitung.
Anders als beim bekannten Phasendiagramm kann eine deutliche Aufspaltung zwischen magnetischem und strukturellen Übergang bei kleinen Cobaltkonzentrationen beobachtet werden. Außerdem findet sich eine Region der Koexistenz zwischen Supraleitung und Spindichtewelle. Bisher konnte ein solcher Zustand im SE(Fe,Co)AsO-System nicht beobachtet werden.
5
Rincón-Rosenbaum, Charlene. "Development of poly(3-octylthiophene) thin films for regulating osteoblast growth." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26493.
Full textAbstract:
The overall objective of this work was to assess the suitability of poly(3-octylthiophene) (P3OT) to sustain MC3T3-E1 osteoblast attachment and growth. The central hypothesis was that specific P3OT film properties (i.e., thickness, film preparation conditions, and level of doping) are able to regulate osteoblast functions (i.e., attachment and proliferation). Discrete and combinatorial techniques were utilized to prepare and characterize thin films of P3OT, a semiconductor in its undoped state, and to study its interaction with MC3T3-E1 osteoblasts.
In this work we demonstrate that P3OT is a suitable surface to sustain MC3T3-E1 attachment and proliferation with no observed cytotoxicity. We show that P3OT has an effect on MC3T3-E1 attachment and proliferation as area, circularity, and proliferation ratio are significantly different for P3OT compared to control surfaces. We also demonstrate that P3OT doping and film preparation conditions have an effect on osteoblast attachment and proliferation but that thickness over a low and high range does not affect osteoblast functions.
This work is significant because it contributes to the growing area of conducting polymers in biomedical applications and establishes P3OT as a potential cell substrate that sustains MC3T3-E1 attachment and promotes high levels of cell proliferation.
6
Rincón-Rosenbaum, Charlene. "Development of poly(3-octylthiophene) thin films for regulating osteoblast growth." Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26493.
Full textAbstract:
Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: J. Carson Meredith; Committee Member: Hang Lu; Committee Member: Joseph Schork; Committee Member: William Koros; Committee Member: Yadong Wang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
7
Hrabálková, Lenka. "The importance of poly(A)-binding protein 4 (PABP4) in healthy pregnancy." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/22923.
Full textAbstract:
Healthy pregnancy requires a tightly regulated materno-fetal dialogue for processes such as embryo implantation, endometrial decidualisation (in the mouse), placentation and maternal adaptation to occur. Disruption of placental development as well as maternal adaptation can lead to fetal intrauterine growth restriction (IUGR) which increases the risk of late miscarriage/stillbirth (e.g. 53% of preterm stillbirth and 26% of term stillbirth are found to be IUGR). Furthermore, IUGR is a risk factor for neurodevelopmental conditions in childhood and for a spectrum of related adult health disorders such as cardiovascular disease and type II diabetes, often termed metabolic syndrome. Despite these pregnancy disorders being common (e.g. 1 in 200 pregnancies results in stillbirth in the UK) the molecular lesion(s) underlying their pathophysiology are poorly understood and in particular those with placental and/or maternal aetiologies most frequently remain unexplained. Here we investigate the hypothesis that poly(A)-binding protein 4 (PABP4) is required for healthy pregnancy in mice. PABP4 is an RNA-binding protein and a member of the PABP family which are central regulators of mRNA translation and stability. Using all four permutations of wild-type and knock-out crosses, we find that maternal PABP4-deficiency results in a reduced litter size and IUGR. The number of implantations at e8.5 were not reduced in Pabp4-/- females, implying that the reduced litter size was not a consequence of decreased ovulation, fertilisation or implantation frequency. Further longitudinal analysis (at e13.5, e15.5 and e18.5) reveals that fetal death primarily occurred between e18.5 and birth, suggesting these mice may provide a unique opportunity to inform on the maternal causes of stillbirth. The onset of IUGR, which was found to be symmetrical in nature, was established by e15.5 preceding the majority of fetal death. During pregnancy, a materno-fetal dialogue directs and responds to changes in gene expression to give rise to the placenta and adapt the maternal physiology. Defects in these processes may result in reduced growth and/or fetal death and were examined in Pabp4-/- mice to shed light on the mechanistic basis of these related phenotypes. Fetal to placental (F:P) weight ratio, whose changes can be indicative of placental insufficiency or placental adaptation in an attempt to aid fetal growth, was found to be increased in Pabp4-/- dams at e15.5 and e18.5 due to the presence of IUGR fetuses with placentas of normal weight. Consistent with this observation, placental volume was unchanged at e18.5. Total placental weight and volume alone fails to discriminate potential differences in the individual placental zones which include the labyrinth zone, where materno-fetal gas and nutrient exchange occur; the junctional zone, which has endocrine functions including those that promote maternal adaptation; and the decidua basalis, derived from the maternal endometrium and is the site of trophoblast invasion and maternal vascular remodelling in early pregnancy. Therefore, volumetric analysis of these zones and the maternal blood spaces, which transcend the decidua basalis and junctional zone, was undertaken. This showed no change in the maternal blood spaces or the labyrinth, the latter being the zone whose size is most frequently altered in IUGR. Critically however, the size of the maternally-derived decidua basalis was increased with a concurrent decrease in the size of the junctional zone. These morphological changes may play a causative role either through directly affecting placental function and/or by the reduced junctional zone failing to promote appropriate maternal adaptation. Alternatively, they may reflect compensatory adaptations to a primary defect elsewhere in the mother. Complementing these morphological studies, functional studies were undertaken: remodelling of maternal vasculature and the resistance index of vessels delivering blood to the fetus were assessed; as was delivery of nutrients to the fetus (measured by fetal glucose); and systemic maternal adaptations (maternal hormonal profile, circulating glucose levels and organ weights). Uterine, umbilical and decidual spiral arteries were examined, but displayed no apparent differences suggestive of normal blood supply to the fetus. However fetal blood glucose was reduced suggesting a reduced delivery of nutrients important for fetal growth. This was not due to lower circulating maternal blood glucose levels, and mRNA levels of the placental glucose transporters Glut-1 and Glut-3 were not reduced but upregulated, suggestive of an attempt to compensate for reduced fetal glucose. Furthermore, upregulation of at least one system A amino acid transporter mRNA, Snat-2, was observed. The maternal physiological state of PABP4-deficient dams showed deviations in some organ weights (e.g. spleen weight is reduced at e13.5 and e15.5) and the levels of some circulating hormones (e.g. estradiol is deceased whereas progesterone is increased at e18.5). However, future work will be required to determine which, if any, of these changes are primary defects rather than downstream consequences and to identify which mis-regulated mRNAs/pathways within in the materno-fetal dialogue underlie the phenotype. Taken together, my results suggest that the regulation of mRNA translation/stability by PABP4 is critical to achieving the correct pattern of gene expression within the materno-fetal dialogue to enable appropriate placentation and maternal adaptation. Furthermore, my results suggest that Pabp4-/- mice provide a unique opportunity to further understand the maternal causes of a spectrum of related pregnancy complications including IUGR, late miscarriage and stillbirth.
8
Li, Bingbing. "Phase Behavior of Poly(Caprolactone) Based Polymer Blends As Langmuir Films at the Air/Water Interface." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/26210.
Full textAbstract:
Poly (caprolactone) (PCL) has been widely studied as a model system for investigating polymer crystallization. In this thesis, PCL crystallization along with other phase transitions in PCL-based polymer blends are studied as Langmuir films at the air/water (A/W) interface.
In order to understand the phase behavior of PCL-based blends, surface pressure induced crystallization of PCL in single-component Langmuir monolayers was first studied by Brewster angle microscopy (BAM). PCL crystals observed during film compression exhibit butterfly-shapes. During expansion of the crystallized film, polymer chains detach from the crystals and diffuse back into the monolayer as the crystals â meltâ . Electron diffraction on Langmuir-Schaefer films suggests that the lamellar crystals are oriented with the chain axes perpendicular to the substrate surface, while atomic force microscopy (AFM) reveals a crystal thickness of ~ 7.6 nm. In addition, the competition between lower segmental mobility and a greater degree of undercooling with increasing molar mass produces a maximum average growth rate at intermediate molar mass.
PCL was blended with poly(t-butyl acrylate) (PtBA) to study the influence of PtBA on the morphologies of PCL crystals grown in monolayers. For PCL-rich blends, BAM studies reveal dendritic morphologies of PCL crystals. The thicknesses of the PCL dendrites are ~ 7-8 nm. BAM studies during isobaric area relaxation experiments at different surface pressure reveal morphological transitions from highly branched dendrites, to six-arm dendrites, four-arm dendrites, seaweedlike crystals, and distorted rectangular crystals. In contrast, PCL crystallization is suppressed in PtBA-rich blend films.
For immiscible blends of PCL and polystyrene (PS) with intermediate molar masses as Langmuir films, the surface concentration of PCL is the only factor influencing surface pressure below the collapse transition. For PS-rich blends, both BAM and AFM studies reveal that PS nanoparticle aggregates formed at very low surface pressure form networks during film compression. For PCL-rich blends, small PS aggregates serve as heterogeneous nucleation centers for the growth of PCL crystals. During film expansion, BAM images show a gradual change in the surface morphology from highly continuous networklike structures (PS-rich blends) to broken ringlike structures (intermediate composition) to small discontinuous aggregates (PCL-rich blends).Ph. D.
9
Merrett, Kim. "Interactions of corneal cells with transforming growth factor-beta modified poly(dimethyl siloxane) surfaces." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6410.
Full textAbstract:
Although the growth of native corneal epithelial cells over the anterior surface of an artificial corneal implant is desired, the growth of these cells on the interface located between the implant and the stromal layer of the host eye tissue (i.e. epithelial cell downgrowth) poses a significant problem to be overcome in developing a suitable implant. In this study the growth factor surface modification of a polymer substrate was examined as a means of inhibiting the proliferation of corneal epithelial cells while promoting corneal stromal cell growth. Two separate studies were conducted in which transforming growth factor-beta1 (TGF-beta1) and transforming growth factor-beta2 (TGF-beta2) respectively, were immobilized via a bifunctional poly (ethylene glycol) (PEG) spacer, MW 3400, to poly(dimethyl siloxane) surfaces (PDMS) that had been aminated by the plasma polymerization of allylamine. The modified surfaces were chemically and biologically characterized. The effect of the surface modification with TGF-beta1 and TGF-beta2 respectively, on interactions with corneal epithelial and corneal stromal cells was examined using in vitro cell culture. (Abstract shortened by UMI.)
10
Kennedy, Mary A. "Crystallization and melting behavior studies of un-nucleated and silica-nucleated isotactic polystyrene and isotactic poly(propylene oxide)." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75765.
Full textAbstract:
The effect of silica on the crystallization and melting behavior of a highly isotactic, well characterized isotactic polystyrene (i-PS) have been investigated. The origins of the various endotherms obtained upon heating have been defined by partial scanning experiments and by a study of the effect of heating rate using differential scanning calorimetry (DSC). The presence of 1 part silica in 100 parts polymer (1 pph) decreases the maximum degree of crystallinity considerably but has a minimal effect on the rate of crystallization. Analysis by the Avrami method shows that the silica does not affect the overall rate of crystallization significantly. The decrease in the crystallinity indicates that silica affects the level of secondary crystallization, thus the crystal perfection.The surface morphologies and growth rates of i-PS spherulites, as studied by photomicroscopy, were not affected by 1 pph of silica. The experimental data were fitted to a modified form of the Hoffman-Lauritzen equation.
The effect of silica on spherulite growth rates and surface morphologies of isotactic poly(propylene oxide) (i-PPO) have also been investigated by optical microscopy. Two distinct i-PPO samples of different molecular weights were used, each of which was highly isotactic. The addition of silica has a pronounced effect on the morphology of the spherulites, producing dendritic type morphology. Upon step-crystallization, the spherulites exhibited mixed morphologies, i.e., fibrillar and ringed. Silica depresses the spherulite growth rates throughout the entire temperature range. The effects were more profound as the quantity of filler increased. The growth rate-temperature behavior was analysed in terms of the classical Hoffman-Lauritzen equation and a modified version to take into account the polymer-filler interaction.
11
Kayunkid, Navaphun. "Epitaxy of regioregular poly(3-hexylthiophene) : from structure determination to the growth of highly oriented Shish-Kebab fibers." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE045.
Full textAbstract:
Le poly(3-hexylthiophène) régiorégulier (rr-P3HT) est l’un des matériaux phare pour les applications en électronique plastique. Afin d’améliorer les performances des dispositifs, il est important de comprendre et de contrôler la structure et la morphologie de la couche active. Des films minces de rr-P3HT cristallins et orientés peuvent être obtenus par epitaxie directionnelle par cristallisation (DEC) de 1,3,5-trichlorobenzène (TCB). Dans ce travail de thèse, nous présentons les avantages de la méthode DEC pour (i) déterminer la structure cristalline du rr-P3HT et pour (ii) étudier les fibres « shish-kebab », une morphologie alternative du rr-P3HT. La première partie de ce manuscrit consiste en l’analyse structurale par diffraction électronique de la forme I du P3HT obtenue dans les films epitaxiés. Afin d’affiner le modèle structural, nous avons fait varier la conformation des chaînes latérales. Dans un deuxième temps, nous avons appliqué ce même protocole afin de résoudre la structure du second polymorphe du P3HT (forme II) grâce à l’obtention de monocristaux parself-seeding. La deuxième partie du manuscrit est consacrée à l’élaboration de fibres orientées dites en « shish-kebab » par épitaxie dans un mélange TCB/Pyridine. La cinétique de croissance ainsi que l’orientation des chaînes de P3HT sont étudiés afin d’optimiser la méthode de préparation des fibres. L’effet de la masse moléculaire sur leur formation a également été évalué. Finalement les propriétés de transport de charges au sein de ces fibres ont été étudiées grâce à l’élaboration de transistors à effet de champRegioregular poly(3-hexylthiophene) (rr-P3HT) is one of the promising materials for plastic electronic applications. Understanding as well as controlling the structure and morphology of the active layer is essential to improve the device efficiency. Highly crystalline and highly oriented rr-P3HT thin films can be obtained via directional epitaxial crystallization (DEC) in 1,3,5-trichlorobenzene (TCB). In this dissertation, we present the benefits of DEC method to (i) determine the crystal structure of rr-P3HT and (ii) to study shish-kebab fibers, an alternative morphology of rr-P3HT. The first part of this dissertation is related to the structural analysis of rr-P3HT form-I by using electron diffraction analysis on the epitaxied film. Furthermore, the modification of side chain conformation is used to improve the structural model. Finally, the determination protocol is also applied to resolve the preliminary crystal structure of rr-P3HT form II prepared by self-seeding method. The second part of thisdissertation is related to highly oriented shish-kebab fibers of rr-P3HT prepared by epitaxial crystallization in a mixture of TCB and pyridine. The investigations of growth kinetics and orientation of P3HT chains in the fiber are performed in order to determine the optimization of preparation conditions and growth mechanism of the fibers. In addition, the effect of molecular weight on the formation of the fibers is investigated. Finally, the charge transport properties of the fibers are measured by using the field effect transistor configuration
12
Thomas, Matthew James. "In Vitro Growth of Osteoblasts on Poly Lactic-co-Glycolic Acid Scaffolds Created Via Gas Foaming." DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1944.
Full textAbstract:
This study analyzed the feasibility of using gas foaming to create Poly Lactic-co-Glycolic Acid (PLGA) scaffolds for use as a substrate in bone tissue engineering and set out to determine whether the presence of osteoblasts on these scaffolds enhanced their material stiffness. The process of bone formation involves osteoblasts depositing extracellular matrix and calcifying this matrix with calcium phosphate crystals (Hasegawa et al., 2017) and pits between 30-40μm in diameter on tissue engineering scaffold surfaces have been shown to best promote osteogenic activity in the presence of bone-forming cells (Halai et al., 2014).The scaffolds were determined to contain pits within this 30-40μm range and the ability of osteoblasts to lay down and calcify extracellular matrix on gas foamed PLGA scaffolds was confirmed by the image analysis of inverted optical microscope images of Alizarin Red S-stained scaffold cryosectionsThe presence of osteogenic activity combined with the desired scaffold porosity led us to conclude that gas foaming PLGA scaffolds are a feasible method of scaffold fabrication for bone tissue engineering and allowed us to optimize the gas foaming apparatus as an instrument to be used in further bone tissue engineering experiments at California Polytechnic State University, San Luis Obispo.However, this study failed to determine whether the presence of osteoblasts improved the material stiffness of the PLGA scaffolds due to a lack of statistical significance in compression testing results.
13
Sutherland, Ashley B. "Fabrication of Responsive Polymer Brushes for Patterned Cell Growth and Detachment." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1376981495.
Full text
14
Tiwari, Ashutosh, Yashpal Sharma, Shinya Hattori, Dohiko Terada, Ashok K. Sharma, Anthony P. F. Turner, and Hisatoshi Kobayashi. "Influence of poly(N-isopropylacrylamide)-CNT-polyaniline three-dimensional electrospun microfabric scaffolds on cell growth and viability." Linköpings universitet, Biosensorer och bioelektronik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-85583.
Full textAbstract:
This study investigates the effect on: 1) the bulk surface; and 2) the three-dimensional non-woven microfabric scaffolds of poly(N-isopropylacylamide)-CNT-polyaniline on growth and viability of mice fibroblast cells L929. The poly(N-isopropylacylamide)-CNT-polyaniline was prepared using coupling chemistry and electrospinning was then used for the fabrication of responsive, nonwoven microfabric scaffolds. The electrospun microfabrics were assembled in regular three-dimensional scaffolds with OD: 400-500 mm; L: 6-20 cm. Mice fibroblast cells L929 were seeded on the both poly(N-isopropylacylamide)-CNT-polyaniline bulk surface as well as non-woven microfabric scaffolds. Excellent cell proliferation and viability was observed on poly(N-isopropylacylamide)-CNT-polyaniline non-woven microfabric matrices in compare to poly(N-isopropylacylamide)-CNT-polyaniline bulk and commercially available Matrigel™ even with a range of cell lines up to 168 h. Temperature dependent cells detachment behaviour was observed on the poly(N-isopropylacylamide)-CNT-polyaniline scaffolds by varying incubation at below lower critical solution temperature (LCST) of poly(N-isopropylacylamide). The results suggest that poly(N-isopropylacylamide)-CNT-polyaniline non-woven microfabrics could be used as a smart matrices for applications in tissue engineering.European Commission FP7 (PIIF-GA-2009-254955), JSPS, JST-CREST and MEXT
15
Leonard, A. J. "Studies of the use of highly hydrated poly-(methacrylate) hydrogels as substrates for cell adhesion and growth." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359473.
Full text
16
Uysal, Ahmet Kerim. "Effects of an Early Life Immune Challenge on Body Growth, Personality, Mating Behaviors, and Brain Development of Zebra Finches (Taeniopygia guttata)." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6969.
Full textAbstract:
The developmental stress hypothesis predicts that an aversive condition, such as decreased food intake, predation, and social isolation, in the early developmental stage could have long term effects on behaviors and brain development of an animal. In nature, bird nestlings are susceptible to various factors, such as malnutrition, infections, and parasites. Effects of early life stress on adulthood have been extensively studied with some stressors including malnutrition. However, immune challenges as an early life stressor and their long-term programming effects on adult behaviors are yet to be studied in detail. The goal of the current study was to investigate changes in growth rate, personality, mate selection behaviors and brain development in zebra finch nestlings after injection with a viral infection mimicking agent, Polyinosinic: polycytidylic acid (Poly I:C). By using Poly I:C, it was possible to isolate long-term effects to the immune response of the bird. After Poly I:C injection on post-hatch day (PD) 14, morphological measures were conducted to detect changes in body growth rate. When birds became sexually mature (> ~PD 200), behaviors of birds were observed in different conditions to detect changes associated with the personality traits of animals. In mate choice trials, both attractiveness of males and mate selection behaviors of males and females were investigated. Finally, the development and neuronal activity of specific brain nuclei involved in courtship (i.e., HVC and RA) and social/sexual behaviors (nucleus taeniae of the amygdala, TnA) were investigated. The results showed that nestlings’ growth rate was not affected. However, Poly I:C injection had some effects on certain, but not all, personality traits observed in the study. Such effects were found only in female zebra finches, suggesting that there was a limited sex-specific influence of an early life immune challenge on personalities of adults. The results also showed that Control females tended to choose untreated males over Poly I:C injected males in mate choice trials. Finally, Poly I:C injection negatively affected the overall development of targeted brain nuclei. In addition, neuronal activity in TnA was higher in Poly I:C injected birds. Results of the present study suggest that one time injection with Poly I:C early in the life causes long term effects on adulthood. These findings are further discussed regarding their relevance to the developmental stress hypothesis.
17
Kleissler, Charles Richard. "Comparison of poly(vinyl alcohol) backbone-grafted ethers and chain-growth crown ether polymers in selective cation adsorption." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/10115.
Full text
18
Hordy, Nathan. "Direct growth of carbon nanotubes from stainless steel grids and plasma functionalization for poly(vinyl alcohol) composite production." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104672.
Full textAbstract:
Over the past 20 years carbon nanotubes (CNTs) have received a great deal of attention in the scientific community due to their extraordinary properties. Although much work has been done to increase the quality of CNT while lowing the cost of production, their high cost is still a major obstacle in preventing their use in everyday life. This issue is especially significant in composite research where a high volume of CNTs is needed. This work presents a simple, inexpensive and scalable method to grow CNTs directly from stainless steel (SS) mesh, without any pretreatment or the use of external catalyst. In addition, the growth substrate is shown to be recyclable for multiple uses. The effect of carbon input on the density, morphology and removal of CNTs was examined. It was found that increased carbon input leads to the growth of larger diameter multi-walled CNTs with stronger adhesion to the surface. The study on the growth of CNTs was done in parallel with a study on the use of CNTs as filler material in poly vinyl alcohol (PVA) composites. However, due to their high surface energies, CNTs often agglomerate together when introduced into polymers and solvents. Surface functionalization of the CNTs via a C2H6/O2 capacitively-coupled RF plasma discharge was used to overcome the issue of agglomeration. The aqueous nanofluids that were created by removal of the CNTs from the substrate through ultrasonication were found to remain stable after boiling and after extended periods of time (> 6 months). The PVA/CNT composites produced were homogenous with good dispersion of the CNTs. Thermally, the composites exhibited a small increase in glass transition and melting point temperatures, as well as a retardation in the degradation of the polymer. Mechanically, the 0.3 wt.% Functionalized-CNT composite showed 28% and 41% increases in tensile strength and modulus, respectively, over the neat polymer.Au cours des vingt dernières années, les nanotubes de carbone (NTCs) ont reçu énormément d'attention au sein de la communauté scientifique en raison de leurs propriétés extraordinaires. Bien que beaucoup de travaux ont été réalisés afin d'améliorer la qualité des NTCs tout en essayant de diminuer leur coût de production, ce coût demeure un obstacle majeur quant à leur utilisation dans la vie quotidienne. Ce problème est particulièrement important dans le contexte des matériaux nanocomposites à base de polymère où des volumes importants de NTCs sont nécessaires. Ce projet de maîtrise avait pour objectif le développement d'une méthode de synthèse simple, peu coûteuse et pouvant facilement être mise à l'échelle. Dans ce contexte, nous avons eu recours à la croissance directe de NTCs sur de l'acier inoxydable, sans utiliser de prétraitement ou catalyseur externe. Nous avons démontré que le substrat de croissance est recyclable pour des usages multiples. Nous avons étudiés l'effet de l'apport de carbone lors de la croissance sur la densité et la morphologie des NTCs, ainsi que sur l'adhésion des tubes à l'acier inoxydable. Nous avons constaté que l'augmentation de l'apport en carbone mène à l'augmentation de nombre de parois de NTCs et à une plus forte adhésion à la surface. L'étude portant sur la croissance des nanotubes de carbone a été effectuée en parallèle avec une étude sur l'utilisation des NTCs comme matériau de remplissage dans les composites à base de polyalcool vinylique (PVA). Il est bien connu qu'en raison de leur énergie de surface élevée, les NTCs ont tendance à s'agglomérer lorsqu'ils sont introduits dans les polymères et les solvants. La fonctionnalisation de surface des NTCs dans une décharge électroluminescente entretenue par couplage capacitif radio fréquentiel (RF) dans un mélange de gaz Ar/C2H6/O2 a été utilisée pour surmonter les problèmes d'agglomération. Cette fonctionnalisation introduit des liens covalents à la surface des NTCs avec des groupes polaires. Des nanofluides NTC/eau distillé créés à partir des NTC fonctionnalisés demeurent stables sur de longues périodes de temps (> 6 mois) et ce, même après chauffage jusqu'au point d'ébullition. Les composites PVA/NTC produits sont homogènes et montrent une bonne dispersion des NTCs. Du point de vue thermique, les composites montrent une légère augmentation de la température de transition vitreuse ainsi que du point de fusion, ainsi qu'un retard dans la dégradation du polymère. Du point de vue mécanique, les composites formés avec une très faible charge massique (0,3 % en masse) montrent des hausses de 28% et 41% dans leur résistance à la traction et module de Young par rapport au polymère pur.
19
Rosenthal, Martin. "Curvy polymer crystals : Why crystalline lamellae twist during growth." Thesis, Mulhouse, 2010. http://www.theses.fr/2010MULH3264/document.
Full textAbstract:
Pour comprendre l'origine de la torsion lamellaire dans le poly(triméthylène téréphtalate), PTT, une étude a été entrepris sur la structure des sphérolites à bandes de PTT en utilisant la micro-diffraction des rayons-X sur une source synchrotrone. Nous avons démontré que les pics de diffraction de la maille triclinique de PTT révèlent une variation périodique de l'intensité en fonction de la distance jusqu'au centre sphérolitique lorsque nous effectuons un balayage avec un micro-faisceau de rayons X. Cela indique que la torsion lamellaire est strictement uniforme et régulière. Celte derrière observation est plus compatible avec le modèle expliquant la torsion comme résultat de contraintes surfaciques que des dislocations-vis géantes. En outre, les données expérimentales montrent que les polymères achiraux ne sont pas indifférents par rapport à l'inversion de la chiralité lamellaire, et que le changement de la chiralité est nécessairement accompagné d'un changement de signe du vecteur de croissance. En plus, nous avons observé que l'inclinaison globale de la chaîne (c'est à dire, l'inclinaison du paramètre c de la maille dans le plan perpendiculaire à la direction de la croissance rapide) n'affecte pas la vitesse et le sens de la torsion. Cela remet en question la seconde hypothèse du modèle de Keith et Padden. Par contre, l'inclinaison des segments de la chaine à l'interface du cristal lamellaire peut être identifiée comme le facteur clé déterminant les contraintes superficielles qui provoquent la torsion lamellaire. Avec la variation de l'épaisseur du cristal la chiralité lamellaire change, ce qui dû au changement de l'angle des segments polymères à l'interfaceTo address the origin of the lamellar twisting in polytrimethylene terephthalate (PTT) an in-depth micro-focus X-ray scattering study was correlated to the data derived using conventional polarized optical microscopy to study the banded spherulite texture for PTT. It is shown that the diffraction peaks of the triclinic lattice of PTT show a periodical pattern as a function of the distance from the spherulite center when scanned with the micro focus X-ray beam. This indicates that the lamellar twist has a strictly uniform and regular nature. The latter observation is more compatible with the model explaining the twist as a result of unbalanced surface stresses than the giant screw dislocations. Moreover, the data shows that achiral polymers are in fact not indifferent to the inversion of the lamellar handedness, and that a change in handedness is necessarily accompanied by a change in the sign of the growth vector. At the same time, we show that the overall chain tilt (i.e., the inclination of the c-parameter of the unit cell in the plane perpendicular to the fast growth direction) does not affect the rate and sense of twisting. This calls into question the second premise of the KP-mod el. Instead, the local inclination of the terminal segment of the crystalline stem protruding the lamellar surface can be identified as the origin of the surface stresses and forcing the lamellar ribbon to twist. With the variation of the crystal thickness as a function of crystallization temperature the angle and direction of this segment is changed, resulting in a change of the lamellar ribbon chirality
20
Luo, Yuanyuan. "Synthesis and Characterization of Poly(Propylene Fumarate) Oligomers via a Chain-Growth Mechanism for Continuous Digital Light Processing (CDLP)." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1427910816.
Full text
21
Goncalves, Rodrigues Juan Jose. "Studies on Biofilm Growth, Attachment and Biokinetic Performance in Biofilters Packed with Macroporous Media." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1195181457.
Full text
22
Failla, Simone. "Crystallization and morphology of the PLLA phase within random poly (L-lactide-ran-ɛ-caprolactone)." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7638/.
Full textAbstract:
This work has mainly focused on the poly (L-lactide) (PLLA) which is a material for multiple applications with performances comparable to those of petrochemical polymers (PP, PS, PET, etc. ...), readily recyclable and also compostable. However, PLLA has certain shortcomings that limit its applications. It is a brittle, hard polymer with a very low elongation at break, hydrophobic, exhibits low crystallization kinetics and takes a long time to degrade. The properties of PLLA may be modified by copolymerization (random, block, and graft) of L-lactide monomers with other co-monomers. In this thesis it has been studied the crystallization and morphology of random copolymers poly (L-lactide-ran-ε-caprolactone) with different compositions of the two monomers since the physical, mechanical, optical and chemical properties of a material depend on this behavior. Thermal analyses were performed by differential scanning calorimetry (DSC) and thermogravimetry (TGA) to observe behaviors due to the different compositions of the copolymers. The crystallization kinetics and morphology of poly (L-lactide-ran-ε-caprolactone) was investigated by polarized light optical microscopy (PLOM) and differential scanning calorimetry (DSC). Their thermal behavior was observed with crystallization from melt. It was observed that with increasing amounts of PCL in the copolymer, there is a decrease of the thermal degradation. Studies on the crystallization kinetics have shown that small quantities of PCL in the copolymer increase the overall crystallization kinetics and the crystal growth rate which decreases with higher quantities of PCL.
23
Sampson, Kaylie C. "Analysis of Cell Growth Capabilities of MC3T3-E1 on Poly)Lactic-Co-Glycolide) /Nanohydroxyaptite Composite Scaffolds Compared to Cellceramtm Scaffolds." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1596703552446322.
Full text
24
Greco, Carey Anne. "Growth and Biofilm Formation by Staphylococcus Epidermidis and Other Relevant Contaminant Bacteria During Storage of Platelet Concentrates." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20253.
Full textAbstract:
Coagulase negative staphylococci (CoNS) are the most prevalent bacterial contaminants of platelet concentrates (PCs), and have been implicated in severe and fatal transfusion reactions. Of this group, Staphylococcus epidermidis is most frequently identified. The preliminary objective of this thesis was to confirm that S. epidermidis could form biofilms under platelet storage conditions. This was achieved using a modified crystal violet staining assay to detect plastic-adherent bacterial cells and examination of attachment processes by scanning electron microscopy. A collection of CoNS isolated from PCs obtained from reportedly healthy donors was then assessed for biofilm-forming potential at the genetic and phenotypic level. Despite the presumable commensal origin of these isolates, a high proportion of S. epidermidis strains displayed a biofilm positive phenotype.
The threat of S. epidermidis biofilm formation during platelet storage identified herein signifies that any alterations made to platelet storage protocols should be evaluated with consideration of this risk. The advent of platelet additive solutions (PASs) as an alternative to plasma for PC storage provides a relevant example, since little is known about the effect of PAS on contaminant bacteria, and vice versa. Growth and biofilm formation by S. epidermidis and the Gram-negative bacterium Serratia liquefaciens were measured in PAS- or plasma-PCs over 5 days, simulating standard platelet storage conditions, after initial inoculation with low, clinically relevant bacterial concentrations. Assays for platelet quality were performed simultaneously. Only S. liquefaciens exhibited a slower doubling time in plasma-PCs than in PAS-PCs. Biofilm formation by both species was reduced during storage in PAS-PCs, increasing bacteria availability for detection. Although S. liquefaciens adversely affected platelet quality in both media, S. epidermidis contamination did not. Ultimately, culture-based detection remains the earliest indicator of bacterial presence in PAS-PCs.
Lastly, since formation of platelet-bacteria aggregates is largely based on receptor-ligand interactions, it was postulated that biofilm formation by contaminant bacteria could be abrogated by receptor shielding. Methoxypoly(ethylene glycol) was applied to covalently modify the platelet surface using a process termed ‘PEGylation’. It is herein demonstrated that PEGylation of PCs inoculated with S. epidermidis results in significantly reduced bacterial binding and biofilm formation during platelet storage.
25
June, Stephen Matthew. "Step-Growth Polymerization Towards the Design of Polymers: Assembly and Disassembly of Macromolecules." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/37619.
Full textAbstract:
Step-growth polymerization provided an effective method for the preparation of several high performance polymers. Step-growth polymerization was used for syntheses of poly(siloxane imides), polyesters, poly(triazole esters), poly(triazole ether esters), and epoxy networks. Each of these polymeric systems exhibited novel structures, and either photoreactive capabilities, or high performance properties.
There is an increasing trend towards the development of photoactive adhesives. In particular these polymers are often used in flip bonding, lithography, stimuli responsive polymers, drug delivery, and reversible adhesives. The ability to tailor polymer properties carefully with exposure to light allows for very unique stimuli responsive properties for many applications. This dissertation primarily investigates photoreactive polymers for reversible adhesion for use in the fabrication of microelectronic devices. In particular cyclobutane diimide functionality within polyimides and poly(siloxane imides) and o-nitro benzyl ester functionality within polyesters acted effectively as chromophores to this end.
Thermal solution imidization allowed for the effective synthesis of polyimides and poly(siloxane imides). 1,2,3,4-Cyclobutane tetracarboxylic dianhydride acted as the chromophore within the polymer backbone. The polyimides obtained exhibited dispersibility only in dipolar, aprotic, high boiling solvents such as DMAc or NMP. The obtained poly(siloxane imides) demonstrated enhanced dispersibility in lower boiling organic solvents such as THF and CHCl3. Dynamic mechanical analysis and tensile testing effectively measure the mechanical properties of the photoactive poly(siloxane imides) and confirmed elastomeric properties. Atomic force microscopy confirmed microphase separation of the photoactive poly(siloxane imides). 1H NMR spectroscopy confirmed formation of maleimide peaks upon exposure to narrow band UV light with a wavelength of 254 nm. This suggested photo-cleavage of the cyclobutane diimide units within the polymer backbone.
Melt transesterification offered a facile method for the synthesis of o-nitro benzyl ester-containing polyesters. 1H NMR spectroscopy confirmed the structures of the photoactive polyesters and size exclusion chromatography confirmed reasonable molecular weights and polydispersities of the obtained samples. 1H NMR spectroscopy also demonstrated a decrease in the integration of the resonance corresponding to the o-nitro benzyl ester functionality relative to the photo-stable m-nitro benzyl ester functionality upon exposure to high-intensity UV light, suggesting photo-degradation of the adhesive. ASTM wedge testing verified a decrease in fracture energy of the adhesive upon UV exposure, comparable to the decrease in fracture energy of a commercial hot-melt adhesive upon an increase in temperature.
Click chemistry was used to synthesize polyesters and segmented block copolyesters. Triazole-containing homopolyesters exhibited a marked increase (~40 °C) in Tg, relative to structurally analogous classical polyesters synthesized in the melt. However, the triazole-containing homopolyesters exhibited insignificant dispersibility in many organic solvents and melt-pressed films exhibited poor flexibility. Incorporation of azide-functionalized poly(propylene glycol) difunctional oligomers in the synthesis of triazole-containing polyesters resulted in segmented block copolyesters which exhibited enhanced dispersibility and film robustness relative to the triazole-containing homopolyesters. The segmented triazole-containing polyesters all demonstrated a soft segment Tg near -62 °C, indicating microphase separation. Dynamic mechanical analysis confirmed the presence of a rubbery plateau, with increasing plateau moduli as a function of hard segment content, as well as increasing flow temperatures as a function of hard segment content. Tensile testing revealed increasing tensile strength as a function of hard segment, approaching 10 MPa for the 50 wt % HS sample. Atomic force microscopy confirmed the presence of microphase separated domains, as well as semicrystalline domains. These results indicated the effectiveness of click chemistry towards the synthesis of polyesters and segmented block copolyesters.
Click chemistry was also used for the synthesis of photoactive polyesters and segmented block polyesters. The preparation of 2-nitro-p-xylylene glycol bispropiolate allowed for the synthesis of triazole-containing polyesters, which exhibited poor dispersibility and flexibility of melt-pressed films. The synthesis of segmented photoactive polyesters afforded photoactive polyesters with improved dispersibility and film robustness. 1H NMR spectroscopy confirmed the photodegradation of the o-nitro benzyl functional groups within the triazole-containing polyesters, which indicated the potential utility of these polyesters for reversible adhesion.
Synthesis of the glycidyl ether of 2,2,4,4-tetramethyl-1,3-cyclobutane diol (CBDOGE) allowed for the subsequent preparation of epoxy networks which did not contain bisphenol-A or bisphenol-A derivatives. Preparation of analogous epoxy networks from the glycidyl ether of bisphenol-A (BPA-GE) provided a method for control experiments. Tensile testing demonstrated that, dependent on network Tg, the epoxy networks prepared from CBDOGE exhibited similar Youngâ s moduli and tensile strain at break as epoxy networks prepared from BPAGE. Dynamic mechanical analysis demonstrated similar glassy moduli for the epoxy networks, regardless of the glycidyl ether utilized. Tg and rubbery plateau moduli varied as a function of diamine molecular weight. Melt rheology demonstrated a gel time of 150 minutes for the preparation of epoxy networks from CBDO-GE and 78 minutes for the preparation of epoxy networks from BPA-GE, with the difference attributed to increased sterics surrounding CBDO-GE. These results indicated the suitability of CBDO-GE as a replacement for BPA-GE in many applications.Ph. D.
26
Xie, Qiongdan. "Nanoscale Confinement Effects on Poly(ε-Caprolactone) Crystallization at the Air/Water Interface & Surfactant Interactions with Phospholipid Bilayers." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/37477.
Full textAbstract:
Two-dimensional (2D) nanoscale confinement effects on poly(ε-caprolactone) (PCL) crystallization were probed through crystallization studies of PCL-b-poly(tert-butyl acrylate) (PCL-b-PtBA) copolymers, PCL with bulky tri-tert-butyl ester endgroups (PCL triesters), PCL with triacid end groups (PCL triacids), and magnetic nanoparticles stabilized by PCL triacid (PCL MNPs) at the air/water (A/W) interface. Thermodynamic analyses of surface pressure-area per monomer (Π−A)) isotherms for the Langmuir films at the A/W interface showed that PCL-b-PtBA copolymers, PCL triheads and PCL MNPs all formed homogenous monolayers below the dynamic collapse pressure of PCL, ΠC ~11 mN•m⁻¹. For compression past the collapse point, the PCL monolayers underwent a phase transition to three-dimensional (3D) crystals and the nanoscale confinements impacted the PCL crystalline morphologies. Studies of PCL-b-PtBA copolymers revealed that the morphologies of the LB-films became smaller and transitioned to dendrites with defects, stripes and finally nano-scale cylindrical features as the block length of PtBA increased.
For the case of PCL triester, irregularly shaped crystals formed at the A/W interface and this was attributed to the accumulation of bulky tert-butyl ester groups around the crystal growth fronts. In contrast, regular, nearly round-shaped lamellar crystals were obtained for PCL triacids. These morphological differences between PCL triacids and PCL triesters were molar mass dependent and attributed to differences in dipole density and the submersion of carboxylic acid groups in the subphase. Nonetheless, enhanced uniformity for PCL triacid crystals was not retained once the polymers were tethered to the spherical surface of a PCL MNP. Instead, the PCL MNPs exhibited small irregularly shaped crystals. This nano-scale confinement effect on the surface morphology at the A/W interface was also molar mass dependent. For the small molar mass PCL MNPs, two layers of collapsed nanoparticles were observed.
In a later chapter, studies of polyethylene glycol (PEG) surfactant adsorption onto phospholipid bilayers through quartz crystal microbalance with dissipation monitoring (QCM-D) measurements revealed a strong dependence of the adsorption and desorption kinetics on hydrophobic tail group structure. PEG surfactants with a single linear alkyl tail inserted and saturated the bilayer surface quickly and the surfactants had relatively fast desorption rates. In contrast, PEG lipids, including dioleoyl PEG lipids and cholesterol PEGs, demonstrated slower adsorption and desorption kinetics. The interactions of Pluronics and Nonoxynol surfactants with phospholipid bilayers were also studied. Pluronics showed no apparent affinity for the phospholipid bilayer, while the Nonoxynol surfactants damaged the lipid bilayers as PEG chain length decreased.
âPh. D.
27
Bernard, Alexandre. "Green Polymers: Part 1: Polylactide Growth on Various Oxides: Towards New Materials Part 2: Poly(epoxides-co-anhydrides) from porphyrin catalysts." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343059362.
Full text
28
St-Jean, Guylaine. "Physical properties of polymers : I. Gelation of poly-4-methylpentene-1. II. Growth rate of isotactic polypropylene spherulites in immiscible blends." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74574.
Full textAbstract:
The first part of this research concerns gelation in reversible gels. On the basis of calorimetric, viscometric, and spectroscopic results, a novel mechanism of gelation is described. It is proposed that the formation of the gel network leads to an increase in entropy which is sufficient to overcome the unfavorable gelation enthalpy. Gelation is, therefore, said to be entropy driven. The role of the solvent in the gelation process is also discussed.The second part of the research is a study of spherulitic growth rate in blends of isotactic polypropylene (iPP) and a compatibilizer. Using time-lapse photomicroscopy it was found that addition of small amount of compatibilizer can enhance the growth rate of iPP. Similar results were obtained with chemically modified compatibilizers. The enhancement is explained in terms of partial miscibility between iPP and compatibilizers. A mathematical model of the kinetics of spherulitic growth rate in partially miscible blends is described.
29
Nam, Sunghyun. "Dynamics of Cyclic and Linear Poly(oxyethylene) and Threading Conformation in Their Blends." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14135.
Full textAbstract:
Chemically identical but topologically different cyclic and linear polymers not only result in marked differences in dynamics, but also lead to unique transport properties of their blends, where cyclic polymers have chances to be threaded onto the linear polymers. This dissertation addresses the effect of ring architecture on dynamics using different time/length scale techniques: self-diffusion coefficients, NMR spin-spin relaxation time (T2) and bulk viscosity.
In deuterated water, synthesized cyclic poly(oxyethylene) (CPOE) (400-1500 g/mol) diffused faster than corresponding linear POE (LPOE) and linear POE dimethyl ether (LPOEDE). However, the self-diffusion coefficients in melts were arranged in the following manner: LPOEDE > CPOE > LPOE, in excellent agreement with T2 and viscosity data, showing topological and chain end effects. Compared to LPOEDE, both CPOE and LPOE had higher activation energies for viscosity with less dependence on the molecular weight.
In the blends of CPOE and LPOE for 900 and 1500 g/mol, the diffusion coefficient and viscosity in melts were higher and lower than the values predicted by a binary mixing rule, respectively. These deviations were attributed to the threading conformation, and the weight fraction of the threaded chains for 1500 g/mol was estimated by a three-term mixing rule. This threading conformation also appeared to influence such important bulk properties as the glass transition and spherulitic growth rate of the blends.
30
Cartwright, Luke. "The potential of poly (ADP-ribose) polymerase (PARP) inhibitors to improve plant growth and yield : novel crop protection agents under stressed conditions." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19289/.
Full textAbstract:
Chemical inhibition of the activity of poly (ADP-ribose) polymerases (PARPs) is associated with enhanced stress tolerance and growth in response to a broad range of abiotic plant stressors. This led to the suggestion that PARP inhibitors might have application in future crop protection strategies. However, the vast majority of studies to date have involved short-term, in vitro assays which are not representative of the conditions crop plants experience in the field. This work aimed to quantify the impact of chemical PARP inhibitor application on photosynthesis, growth and yield in planta, under well-watered and droughted conditions. In Chapter 2, a protocol for the quantification of the impact of drought stress on photosynthesis was developed, mainly using chlorophyll fluorescence imaging. In Chapter 3, the impacts of PARP inhibitors on photosynthesis, growth and survival in response to drought were measured. PARP inhibitors enhanced survival to severe stress but there was a cost associated with application under well-watered and moderate drought conditions. Chlorophyll fluorescence and growth measurements indicated that PARP inhibitors also had a damaging effect. Results from Chapter 4 suggested that PARP and PSII inhibitors had broadly negative impacts on yield. There was a strong relationship between growth (maximum plant object sum area) and yield under stress, which enabled the effects that compounds had on yield to be predicted approximately 40 days earlier than measuring at harvest. By fitting a model to the growth data it was possible to predict the impacts even earlier still. In Chapter 5, application of a PARP inhibitor reduced stomatal conductance but did not alter opening/closing kinetics, indicating the compound had an anti-transpirant effect. The enhanced stress tolerance of PARP-deficient plants likely protected against severe drought. However, a trade-off arises because of the costs associated with application under more moderate conditions. If PARP inhibitors are to be used in agriculture the cost/benefit balance will have to be carefully considered.
31
Van-Straaten, Manon. "Dépôt de films minces de poly(méthacrylates) par iCVD : des mécanismes de croissance à la Polymérisation Radicalaire Contrôlée." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1154.
Full textAbstract:
Les récentes avancées dans les micros et nanotechnologies ont nécessité le développement de nouvelles techniques de synthèse de films minces de nouveaux matériaux. Parmi eux, les polymères possèdent des propriétés intéressantes, notamment pour des domaines comme la microélectronique ou le biomédical. Pour pallier ce besoin, les techniques de dépôt de vapeur chimique (Chemical Vapor Deposition, CVD) se sont multipliées. Ces travaux portent sur la synthèse de couches minces de poly(méthacrylates) par un une nouvelle méthode de dépôt chimique en phase vapeur par une polymérisation amorcée in-situ ou initiated Chemical Vapor Deposition (iCVD). Cette technique possède de nombreux avantages parmi lesquels se trouvent ses conditions opératoires douces (absence de solvant, emploi de faibles températures), sa versatilité et sa conformité. Afin de mieux comprendre le procédé de synthèse des films minces de polymères par iCVD, une partie de ces travaux de thèse concerne l’étude de la cinétique de croissance des poly(méthacrylates). Une cinétique en deux régimes a été identifiée pour les deux polymères. Les analyses microscopiques et macroscopiques de couches minces issues des deux régimes ont permis la proposition d’un modèle de croissance. Le premier régime, au début de la croissance, est caractérisé par une faible vitesse de dépôt et des polymères de faibles masses molaires. Lorsque le second régime est atteint, la vitesse de dépôt est plus importante et devient constante. Les chaînes synthétisées possèdent des masses molaires plus élevées. Ce changement a pu être expliqué en mettant en avant la capacité du film en formation à se gorger de monomères, ce qui augmente la concentration locale de monomères. La cinétique de croissance des poly(méthacrylates) a aussi été étudiée sur des sous-couches de polymères et d’organosiliciés poreux. L’iCVD s’est révélée être une méthode capable de remplir de manière quasiment instantanée les pores nanométriques d’une couche mince. De plus, pour obtenir un meilleur contrôle des polymères synthétisés par iCVD au niveau de leur architecture macromoléculaire ou de leur masse molaire, la mise en place d’une technique de polymérisation radicalaire contrôlée est discutée. La dernière parte de cette thèse concerne l’application du procédé de polymérisation RAFT (polymérisation radicalaire par transfert de chaînes réversible par addition/fragmentation) en iCVD à l’aide de coupons de silicium fonctionnalisés au préalable avec des agents RAFTRecent progress in micro and nanotechnologies require the development of new synthesis process for various material thin films. Polymers, thanks to their properties, are very interesting for fields like microelectronic or biomedical. To respond to this need, many Chemical Vapor Deposition (CVD) technologies are studied. This work focuses on a new method called initied Chemical Vapor Deposition (iCVD). This deposition method gives many advantages as its soft operational conditions (solvent free, low temperature), versatility and conformity. In order to improve the understanding of synthesis mechanism in iCVD, the first part of this work is about the poly(methacrylates) thin films growth kinetic. The study reveals two-regime growth kinetics. A model for the growth mechanism based on the microscopic and macroscopic analysis of thin layers from the two regimes is proposed. The first regime, at the early stage of the growth, is characterized by a slow deposition rate and polymers with low molecular mass. When the second regime appears, the deposition rate is higher and constant and polymers have higher molecular mass. These evolutions could to be explain by the growth film ability to stock monomers and thus increase the local monomer concentration. Poly(methacryaltes) growth kinetics are also investigated on polymeric and porous organosilicate layers. It appears than iCVD is a deposition method that can fill nanometrics pores with polymer really quickly. Moreover, to have a better control on polymer synthesized by iCVD (molecular weight, macromolecular architecture), the possibility to used a Reversible-Deactivation Radical Polymerization (RDRP) method with iCVD process is discussed. The last part of this work concerns the use of Reversible Addition Fragmentation chain Transfer (RAFT) polymerization with the iCVD process thanks to silicon samples pre-functionalized with RAFT agent
32
Burney, Kareem S. "Evalulation [sic] of sustained release of antisense oligonucleotide from Poly DL (Lactide-Co-Glycolide) microspheres targeting fibrotic growth factors CTGF and TGF-Beta1." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0001194.
Full text
33
Huang, Zhenyu. "Crystallization and Melting Behavior of Linear Polyethylene and Ethylene/Styrene Copolymers and Chain Length Dependence of Spherulitic Growth Rate for Poly(Ethylene Oxide) Fractions." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29211.
Full textAbstract:
The crystallization and melting behavior of linear polyethylene and of a series of random ethylene/styrene copolymers was investigated using a combination of classical and temperature modulated differential scanning calorimetry. In the case of linear polyethylene and low styrene content copolymers, the temporal evolutions of the melting temperature, degree of crystallinity, and excess heat capacity were studied during crystallization. The following correlations were established: 1) the evolution of the melting temperature with time parallels that of the degree of crystallinity, 2) the excess heat capacity increases linearly with the degree of crystallinity during primary crystallization, reaches a maximum during the mixed stage and decays during secondary crystallization, 3) the rates of shift of the melting temperature and decay of the excess heat capacity lead to apparent activation energies that are very similar to these reported for the crystal ac relaxation by other techniques. Strong correlations in the time domain between the secondary crystallization and the evolution of the excess heat capacity suggest that the reversible crystallization/melting phenomenon is associated with molecular events in the melt-crystal fold interfacial region.
In the case of higher styrene content copolymers, the multiple melting behavior at high temperature is investigated through studies of the overall crystallization kinetics, heating rate effects and partial melting. Low melting crystals can be classified into two categories according to their melting behavior, superheating and reorganization characteristics. Low styrene content copolymers still exhibit some chain folded lamellar structure. The shift of the low melting temperature with time in this case is tentatively explained in terms of reorganization effects. Decreasing the crystallization temperature or increasing the styrene content leads to low melting crystals more akin to fringed-micelles. These crystals exhibit a lower tendency to reorganize during heating. The shift of their melting temperature with time is attributed to a decrease in the conformational entropy of the amorphous fraction as a result of constraints imposed by primary and secondary crystals.
To further understand the mechanism of formation of low melting crystals, quasi-isothermal crystallization experiments were carried out using temperature modulation. The evolution of the excess heat capacity was correlated with that of the melting behavior. On the basis of these results, it is speculated that the generation of excess heat capacity at high temperature results from reversible segmental exchange on the fold surface. On the other hand, the temporal evolution of the excess heat capacity at low temperature for high styrene content copolymers is attributed to the reversible segment attachment and detachment on the lateral surface of primary crystals. The existence of different mechanisms for the generation of excess heat capacity in different temperature ranges is consistent with the observation of two temperature regimes for the degree of reversibility inferred from quasi-isothermal melting experiments.
In a second project, the chain length and temperature dependences of spherulitic growth rates were studied for a series of narrow fractions of poly(ethylene oxide) with molecular weight ranging from 11 to 917 kg/mol. The crystal growth rate data spanning crystallization temperatures in regimes I and II was analyzed using the formalism of the Lauritzen-Hoffman (LH) theory. Our results are found to be in conflict with predictions from LH theory. The Kg ratio increases with molecular weight instead of remaining constant. The chain length dependence of the exponential prefactor, G0, does not follow the power law predicted by Hoffman and Miller (HM). On this basis, the simple reptation argument proposed in the HM treatment and the nucleation regime concept advanced by the LH model are questioned. We proposed that the observed I/II regime transition in growth rate data may be related to a transition in the friction coefficient, as postulated by the Brochard-de Gennnes slippage model. This mechanism is also consistent with recent calculations published by Toda in which both the rates of surface nucleation and substrate completion processes exhibit a strong temperature dependence.Ph. D.
34
Mohammadi, Hadi. "On the Melting and Crystallization of Linear Polyethylene, Poly(ethylene oxide) and Metallocene Linear Low-Density Polyethylene." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/84921.
Full textAbstract:
The crystallization and melting behaviors of an ethylene/1-hexene copolymer and series of narrow molecular weight linear polyethylene and poly(ethylene oxide) fractions were studied using a combination of ultra-fast and conventional differential scanning calorimetry, optical microscopy, small angle X-ray scattering, and wide angle X-ray diffraction.
In the case of linear polyethylene and poly(ethylene oxide), the zero-entropy production melting temperatures of initial lamellae of isothermally crystallized fractions were analyzed in the context of the non-linear Hoffman-Weeks method. Using the Huggins equation, limiting equilibrium melting temperatures of 141.4 ± 0.8oC and 81.4 ± 1.0oC were estimated for linear polyethylene and poly(ethylene oxide), respectively. The former and the latter are about 4oC lower and 12.5oC higher than these predicted by Flory/Vrij and Buckley/Kovacs, respectively. Accuracy of the non-linear Hoffman-Weeks method was also examined using initial lamellar thickness literature data for a linear polyethylene fraction at different crystallization temperatures. The equilibrium melting temperature obtained by the Gibbs-Thomson approach and the C2 value extracted from the initial lamellar thickness vs. reciprocal of undercooling plot were similar within the limits of experimental error to those obtained here through the non-linear Hoffman-Weeks method.
In the next step, the Lauritzen-Hoffman (LH) secondary nucleation theory was modified to account for the effect of stem length fluctuations, tilt angle of the crystallized stems, and temperature dependence of the lateral surface free energy. Analysis of spherulite growth rate and wide angle X-ray diffraction data for 26 linear polyethylene and 5 poly(ethylene oxide) fractions revealed that the undercooling at the regime I/II transition, the equilibrium fold surface free energy, the strength of the stem length fluctuations and the substrate length at the regime I/II transition are independent of chain length. The value of the equilibrium fold surface free energy derived from crystal growth rate data using the modified Lauritzen-Hoffman theory matches that calculated from lamellar thickness and melting data through the Gibbs-Thomson equation for both linear polyethylene and poly(ethylene oxide). Larger spherulitic growth rates for linear polyethylene than for poly(ethylene oxide) at low undercooling is explained by the higher secondary nucleation constant of poly(ethylene oxide). While the apparent friction coefficient of a crystallizing linear polyethylene chain is 2 to 8 times higher than that of a chain undergoing reptation in the melt state, the apparent friction coefficient of a crystallizing poly(ethylene oxide) chain is about two orders of magnitude lower. This observation suggests that segmental mobility on the crystal phase plays a significant role in the crystal growth process.
In case of the statistical ethylene/1-hexene copolymer, the fold surface free energies of the copolymer lamellae at the time of crystallization and melting increase with increasing undercooling, approaching the same magnitude at high undercooling. As a result of this temperature dependence, the experimental melting vs. crystallization temperature plot is parallel to the Tm = Tc line and the corresponding Gibbs-Thomson plot is non-linear. This behavior is attributed to the fact that longer ethylene sequences form a chain-folded structure with lower concentration of branch points on the lamellar surface at lower undercooling, while shorter ethylene sequences form lamellar structures at higher undercooling exhibiting a higher concentration of branch points on the lamellar surface. Branch points limit the ability of lamellar structures to relax their kinetic stem-length fluctuations during heating prior to melting.Ph. D.
35
Khanduyeva, Natalya. "Conjugated Polymer Brushes (Poly(3-hexylthiophene) brushes): new electro- and photo-active molecular architectures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1232556562686-70575.
Full textAbstract:
The aim of the present work was to screen the main methods for the synthesis of conjugated polymers for their suitability in the preparation of conductive polymer brushes. The main focus was put on the grafting of intrinsically soluble substituted regioregular polyalkylthiophenes because of their excellent optoelectronic properties. The resulting polymer films were characterized and their optoelectrical properties studied. For the first time, a synthesis of conductive polymer brushes on solid substrates using “grafting-from” method was performed. The most important, from my opinion, finding of this work is that regioregular head-to-tail poly-3-alkylthiophenes – benchmark materials for organic electronics - can be now selectively grafted from appropriately-terminated surfaces to produce polymer brushes of otherwise soluble polymers - the architecture earlier accessible only in the case of non-conductive polymers. In particular, we developed a new method to grow P3ATs via Kumada Catalyst Transfer Polymerization (KCTP) of 2-bromo-5-chloromagnesio-3-alkylthiophene. Exposure of the initiator layers to monomer solutions leads to selective chain-growth polycondensation of the monomers from the surface, resulting into P3AT brushes in a very economical way. The grafting process was investigated in detail and the structure of the resulting composite films was elucidated using several methods. The obtained data suggests that the grafting process occurs not only at the poly(4-bromstyrene) (PS-Br)/polymerization solution interface, but also deeply inside the swollen PS-Br films, penetrable for the catalyst and for the monomer The grafting process was investigated in detail and the structure of the resulting composite film was elucidated using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and Conductive atomic force microscopy (C-AFM). The obtained data suggests that the grafting process occurs not only at the poly(4-bromostyrene), PS-Br/polymerization solution interface, but also deeply inside the swollen PS-Br film, which is penetrable for the catalyst and the monomer. The process results in an interpenetrated PS-Br/P3HT network, in which relatively short poly(3-hexylthiophene), P3HT grafts emanate from long, cross-linked PS-Br chains. A further method investigated during our work was to covalently graft regioirregular P3HT to substrates modified by macromolecular anchors using oxidative polymerization of 3HT with FeCl3. P3HT layers with variable thicknesses from 30 nm up to 200 nm were produced using two steps of polymerization reaction. The P3HT obtained by oxidative polymerization had always an irregular structure, which was a result of the starting monomer being asymmetric, which is undesired for electronic applications. The third method for the production of conductive polymer brushes was to graft regioregular poly(3,3''-dioctyl-[2,2';5',2'']terthiophene) (PDOTT) by electrochemical oxidative polycondensation of symmetrically substituted 3,3''-dioctyl-[2,2';5',2'']terthiophene (DOTT). A modification of the supporting ITO electrode by the self-assembled monolayers (SAMs) of compounds having polymerizable head-groups with properly adjusted oxidative potentials was found to be essential to achieve a covalent attachment of PDOTT chains. The polymer films produced show solvatochromism and electrochromism, as well as the previous two methods. After polymerization, the next step towards building organic electronic devices is applying the methods obtained in nano- and microscale production. Block copolymers constitute an attractive option for such surface-engineering, due to their ability to form a variety of nanoscale ordered phase-separated structures. However, block copolymers containing conjugated blocks are less abundant compared to their non-conjugated counterparts. Additionally, their phase behaviour at surfaces is not always predictable. We demonstrated in this work, how surface structures of non-conductive block copolymers, such as P4VP-b-PS-I, can be converted into (semi)conductive P4VP-b-PS-graft-P3HT chains via a surface-initiated polymerization of P3HT (Kumada Catalyst Transfer Polymerization (KCTP) from reactive surface-grafted block copolymers. This proves that our method is applicable to develop structured brushes of conductive polymers. We believe that it can be further exploited for novel, stimuli-responsive materials, for the construction of sensors, or for building various opto-electronic devices. The methods developed here can in principle be adapted for the preparation of any conductive block copolymers and conductive polymers, including other interesting architectures of conductive polymers, such as block copolymers, cylindrical brushes, star-like polymers, etc. To this end, one needs to synthesize properly-designed and multi-functional Ni-initiators before performing the polycondensation.
36
Khanduyeva, Natalya. "Conjugated Polymer Brushes (Poly(3-hexylthiophene) brushes): new electro- and photo-active molecular architectures." Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23635.
Full textAbstract:
The aim of the present work was to screen the main methods for the synthesis of conjugated polymers for their suitability in the preparation of conductive polymer brushes. The main focus was put on the grafting of intrinsically soluble substituted regioregular polyalkylthiophenes because of their excellent optoelectronic properties. The resulting polymer films were characterized and their optoelectrical properties studied. For the first time, a synthesis of conductive polymer brushes on solid substrates using “grafting-from” method was performed. The most important, from my opinion, finding of this work is that regioregular head-to-tail poly-3-alkylthiophenes – benchmark materials for organic electronics - can be now selectively grafted from appropriately-terminated surfaces to produce polymer brushes of otherwise soluble polymers - the architecture earlier accessible only in the case of non-conductive polymers. In particular, we developed a new method to grow P3ATs via Kumada Catalyst Transfer Polymerization (KCTP) of 2-bromo-5-chloromagnesio-3-alkylthiophene. Exposure of the initiator layers to monomer solutions leads to selective chain-growth polycondensation of the monomers from the surface, resulting into P3AT brushes in a very economical way. The grafting process was investigated in detail and the structure of the resulting composite films was elucidated using several methods. The obtained data suggests that the grafting process occurs not only at the poly(4-bromstyrene) (PS-Br)/polymerization solution interface, but also deeply inside the swollen PS-Br films, penetrable for the catalyst and for the monomer The grafting process was investigated in detail and the structure of the resulting composite film was elucidated using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and Conductive atomic force microscopy (C-AFM). The obtained data suggests that the grafting process occurs not only at the poly(4-bromostyrene), PS-Br/polymerization solution interface, but also deeply inside the swollen PS-Br film, which is penetrable for the catalyst and the monomer. The process results in an interpenetrated PS-Br/P3HT network, in which relatively short poly(3-hexylthiophene), P3HT grafts emanate from long, cross-linked PS-Br chains. A further method investigated during our work was to covalently graft regioirregular P3HT to substrates modified by macromolecular anchors using oxidative polymerization of 3HT with FeCl3. P3HT layers with variable thicknesses from 30 nm up to 200 nm were produced using two steps of polymerization reaction. The P3HT obtained by oxidative polymerization had always an irregular structure, which was a result of the starting monomer being asymmetric, which is undesired for electronic applications. The third method for the production of conductive polymer brushes was to graft regioregular poly(3,3''-dioctyl-[2,2';5',2'']terthiophene) (PDOTT) by electrochemical oxidative polycondensation of symmetrically substituted 3,3''-dioctyl-[2,2';5',2'']terthiophene (DOTT). A modification of the supporting ITO electrode by the self-assembled monolayers (SAMs) of compounds having polymerizable head-groups with properly adjusted oxidative potentials was found to be essential to achieve a covalent attachment of PDOTT chains. The polymer films produced show solvatochromism and electrochromism, as well as the previous two methods. After polymerization, the next step towards building organic electronic devices is applying the methods obtained in nano- and microscale production. Block copolymers constitute an attractive option for such surface-engineering, due to their ability to form a variety of nanoscale ordered phase-separated structures. However, block copolymers containing conjugated blocks are less abundant compared to their non-conjugated counterparts. Additionally, their phase behaviour at surfaces is not always predictable. We demonstrated in this work, how surface structures of non-conductive block copolymers, such as P4VP-b-PS-I, can be converted into (semi)conductive P4VP-b-PS-graft-P3HT chains via a surface-initiated polymerization of P3HT (Kumada Catalyst Transfer Polymerization (KCTP) from reactive surface-grafted block copolymers. This proves that our method is applicable to develop structured brushes of conductive polymers. We believe that it can be further exploited for novel, stimuli-responsive materials, for the construction of sensors, or for building various opto-electronic devices. The methods developed here can in principle be adapted for the preparation of any conductive block copolymers and conductive polymers, including other interesting architectures of conductive polymers, such as block copolymers, cylindrical brushes, star-like polymers, etc. To this end, one needs to synthesize properly-designed and multi-functional Ni-initiators before performing the polycondensation.
37
Schmidmaier, Gerhard. "Einfluss der lokalen Applikation von Wachstumsfaktoren aus einer biodegradierbaren Poly(D,L-Laktid)-Beschichtung von Biomaterialien auf die Frakturheilung." Doctoral thesis, Humboldt-Universität zu Berlin, Medizinische Fakultät - Universitätsklinikum Charité, 2004. http://dx.doi.org/10.18452/13910.
Full textAbstract:
Wachstumsfaktoren sind wichtige Steuerelemente des Knochenzellmetabolismus. Im Verlauf der Frakturheilung kommt es zur Ausschüttung von zahlreichen Wachstumsfaktoren, Zytokinen und Botenstoffen im und um den Bereich des Frakturspalts, die systemisch oder lokal, endokrin, parakrin oder autokrin wirksam werden können. Für verschiedene Wachstumsfaktoren konnten in zahlreichen Studien osteoinduktive und die Frakturheilung positiv beeinflussende Wirkungen nachgewiesen werden. In vitro und in vivo Studien belegen, dass einige dieser Faktoren wie Insulin-like growth factor-I (IGF-I), Transforming growth factor-beta1 (TGF-beta1) und Bone morphogenetic protein-2 (BMP-2) einen stimulierenden Effekt auf osteo- und chondrogene Zellen aufweisen und somit die Knochenheilung stimulieren. Der genaue Wirkmechanismus dieses positiven Effektes der Wachstumsfaktoren und ihre Interaktion im Verlauf der Frakturheilung ist nicht bekannt. Die lokale Applikation der Faktoren für einen therapeutischen Einsatz bei der Frakturheilung stellte bisher jedoch ein Problem dar. Mit der entwickelten biodegradierbaren Poly(D,L-Laktid)-Beschichtung von Implantaten können eingearbeitete Wachstumsfaktoren kontrolliert und lokal direkt an der Fraktur freigesetzt werden. Das beschichtete Implantat dient dabei der Stabilisation der Fraktur und gleichzeitig als Wirkstoffträger. Die Beschichtung weist eine hohe mechanische Stabilität auf. Die eingearbeiteten Wachstumsfaktoren behalten ihre biologische Aktivität in der Beschichtung und werden kontrolliert lokal freigesetzt. Um den Effekt lokal applizierter Wachstumsfaktoren auf die Frakturheilung zu untersuchen, wurde ein standardisiertes geschlossenes Frakturmodell entwickelt, das der klinischen Situation möglichst nahe ist und reproduzierbar durchgeführt werden kann. Untersucht wurde der Effekt der Wachstumsfaktoren IGF-I, TGF-beta1 und BMP-2 und des Trägermaterials PDLLA sowie lokale und systemische unerwünschte Wirkungen. Die Ergebnisse zeigten einen signifikant grösseren stimulierenden Effekt von IGF-I auf die Frakturheilung im Vergleich zur TGF-beta1 Applikation. Die kombinierte Gabe beider Faktoren ergab einen signifikant grösseren Effekt auf die torsionale Stabilität und die Kallusreifung im Vergleich zur Einzelapplikation. Beide Faktoren scheinen einen synergistischen Effekt auf die Frakturheilung zu haben. Die lokale Applikation von BMP-2 beschleunigte ebenso, wie die lokale Freisetzung von IGF-I und TGF-beta1 die Frakturheilung signifikant. Deutliche Unterschiede zwischen IGF-I / TGF-beta1 und BMP-2 konnten nicht festgestellt werden.Allerdings zeigte sich bei der Verwendung von BMP-2 auch ausserhalb der Frakturzone eine grössere Mineralisation der Kortikalis, die bei IGF-I / TGF-beta1 nicht zu beobachten ist. Auch im Grosstiermodell bestätigte sich die Wirksamkeit dieser bioaktiven Oberflächen-beschichtung auf die Osteotomieheilung. Die PDLLA-Beschichtung alleine, ohne eingearbeitete Wachstumsfaktoren, zeigte bereits einen positiven Effekt auf die Frakturheilung. Die Untersuchungen belegen, dass die lokale Freisetzung von Wachstumsfaktoren aus einer biodegradierbaren PDLLA-Beschichtung von Implantaten die Frakturheilung signifikant beschleunigt, wobei keine unerwünschten lokalen oder systemischen Wirkungen beobachtet werden konnten. Bei dem Vergleich lokaler (durch Wachstumsfaktoren) mit systemischer Stimulationsmöglichkeit (durch Wachstumshormon) der Frakturheilung lässt sich zusammenfassend feststellen, dass die kombinierte Anwendung beider Stimulationsmöglichkeiten zu keiner weiteren Steigerung der Heilungsvorgänge führte. Weitere Untersuchungen wurden hinsichtlich der genauen Rolle und Interaktion der Wachstumsfaktoren durchgeführt. Vor allem die Frühphase scheint hierbei eine entscheidende Rolle bei der Frakturheilung einzunehmen. Es zeigte sich hierbei eine deutliche Stimulation der Osteoblastendifferenzierung mit einer Erhöhung der Kollagen-1 Produktion in vitro sowie eine Steigerung der Proliferationsrate und Angiogenese mit einem schnelleren Ablauf der Phasen der Frakturheilung in vivo durch lokal appliziertes IGF-I und TGF-beta1. Weitere Anwendungen der entwickelten Beschichtungstechnologie stellen die lokale Applikation von Wachstumsfaktoren von beschichteten PDLLA-Cages bei der intervertebralen Spondylodese sowie die lokale Applikation von Antibiotika aus einer PDLLA-Beschichtung von Implantaten zur Prophylaxe der Implantat-assoziierten Osteomyelitis dar.Basierend auf diesen Ergebnissen steht der Einsatz PDLLA-Gentamicin beschichteter intramedullärer Tibianägel kurz vor der klinischen Anwendung.Eine Zulassung durch die entsprechenden Behörden ist erfolgt.Die klinische Anwendung Wachstumsfaktoren-beschichteter Implantate ist bereits in der Vorbereitung.Growth factors are important regulators of bone metabolism. During fracture healing many growth factors or cytokines were locally released at the facture site. In several studies, different growth factors demonstrated osteoinductive and fracture stimulating properties. In vitro and in vivo studies showed a stimulating effect of Insulin-like growth factor-I (IGF-I), Transforming growth factor-beta1 (TGF-beta1) and Bone morphogenetic protein-2 (BMP-2) on osteo- and chondrogenetic cells. The exact effectiveness and the interaction of these growth factors during fracture healing is not known so far. Further, the local application of these factors for therapeutically use in fracture treatment is still a problem. The developed biodegradable poly(D,L-lactide)-coating of implants allows the local and controlled release of incorporated growth factors directly at the fracture site. The coated implant serves on the one hand for fracture stabilization and on the other hand as a drug delivery system. The coating has a high mechanical stability. The incorporated growths factors remain biologically active in the coating and were released in a sustained and controlled manner. To investigate the effect of locally released growth factors IGF-I, TGF-beta1 and BMP-2 and the carrier PDLLA on fracture healing, standardised closed fracture models were developed with a close relationship to clinical situation. Further, possible local and systemic side effects were analysed. The results demonstrated a significantly higher stimulating effect of IGF-I on fracture healing compared to TGF-beta1. The combined application of both growth factors showed a synergistic effect on the mechanical stability and callus remodeling compared to single treatment. The local release of BMP-2 also enhanced fracture healing significantly - comparable to combination of IGF-I and TGF-beta1. However, a higher rate of mineralisation was measurable outside the fracture region using BMP-2 in a rat fracture model. Using a large animal model on pigs with a 1 mm osteotomy gap, the effectiveness of locally released growths factors could be confirmed. Further, the PDLLA-coating without any incorporated growth factors demonstrated a significantly effect on healing processes in both models. These investigations showed, that the local release of growth factors from PDLLA coated implants significantly stimulate fracture healing without any local or systemic side effects. Comparing systemic with local stimulation techniques, we found an improvement of fracture healing by systemic administration of growth hormone and local application of IGF-I and TGF-beta1. However, the combined use of both simulation techniques did not lead to a further increase of healing processes. Investigations on the effectiveness and the interaction of growth factors during fracture healing demonstrated an dramatic effect in the early phases of healing processes. The growth factors stimulate the differentiation of osteoblasts with a higher production of collagen I in vitro and increase osteogenesis and vascularisation of the fracture callus in vivo. Further applications of the coating technology are the use of PDLLA and growth factor coated cages for the stimulation of intervertebral fusion and the use of PDLLA and Gentamicin coated implants in order to prevent implant associated infections. The clinical use of antibiotic and growth factor coated implants are in preparation.
38
Slavíčková, Radka. "Optimalizace produkce vybraných enzymů pomocí Bacillus subtilis." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2012. http://www.nusl.cz/ntk/nusl-216884.
Full textAbstract:
In this thesis, optimization of production of lipolytic enzymes by submerzed cultivation of Bacillus subtilis (BS) was studied. Production of lipolytic enzymes was tested in three nutrient media, which differed mainly in main sources of carbon, respectively of nitrogen. The first medium contained mainly extract from calf brain and beef heart (BHIB), the second medium contained peptone and yeast extract (NB) and the third one contained peptone and yeast extract with the addition of 2% (w/v) glucose (NBG). The highest lipolytic activity (0.0784 Uml-1) was measured in NBG medium. Maximum of lipolytic activity was observed before the end of the exponential phase of BS growth in all the media. Temperature optimum in NBG medium was determined from 30 to 50 °C, pH optimum in the range of 5 to 11 and subsequently the temperature stability of lipolytic enzymes produced by the BS was estimated. The activity value was determined spectrometrically using p-nitrophenyllaurate as a substrate. Produced lipolytic enzymes showed maximum activity at 37 °C in the alkaline pH of 8.0. Measurement of temperature stability showed that lipolytic enzymes are relatively thermostable enzymes retaining 100 % of the activity even after 1 hour of cultivation at 30 - 50 °C. The presence of 1% (w/v) olive oil in medium NBG caused a decrease in lipolytic activity by 65 % as well as in pH from 6.5 to 5.4 after 14 days of cultivation. After substitution of glucose by fructose in medium NBG, lipolytic activity showed comparable values during the first week of cultivation. On the other hand, the decrease of lipolytic activity by 29 % in the medium with fructose was observed after 14 days of cultivation. A procedure for the identification of lipolytic enzymes of BS by peptide massfingerprinting was developed to understand the potential of synthetic polyester - poly(e-caprolactone) as a lipase inductor. Degradation study of commercial polyester poly(e-caprolactone) was carried out by submerged cultivation of Bacillus subtilis in NBG medium at initial pH 7.0 and 30 °C for 14 days. PCL (Mn = 10,000, Mw = 14 000) was studied in the form of films (1.0 x 1.0 cm), which were prepared by melt-pressing, rapid cooling of the melt to 4 °C and evaporation of the solvent from 2 % dichlormethane solution. The evaluation of the films shown occurrence of weight loss (7.8 - 17.0 wt.%) together with the formation of numerous holes and cracks in the sample surface in relation to the method of the films preparation. Lipolytic activity values increased by 9 - 17 % in the degradation media compared to control samples. Densitometric monitoring showed also higher increase in cell mass in the degradation medium compared with control samples. Based on the results obtained, the degradation process induced by BS could be suggested.
39
Baddour, Joelle. "An Approach to Lens Regeneration in Mice Following Lentectomy and the Implantation of a Biodegradable Hydrogel Encapsulating Iris Pigmented Tissue in Combination with Basic Fibroblast Growth Factor." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1335916825.
Full text
40
Sheth, Swapnil Suhas. "Self-Consistency of the Lauritzen-Hoffman and Strobl Models of Polymer Crystallization Evaluated for Poly(ε-caprolactone) Fractions and Effect of Composition on the Phenomenon of Concurrent Crystallization in Polyethylene Blends." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23904.
Full textAbstract:
Narrow molecular weight fractions of Poly(ε-caprolactone) were successfully obtained using the successive precipitation fractionation technique with toluene/n-heptane as a solvent/nonsolvent pair. Calorimetric studies of the melting behavior of fractions that were crystallized either isothermally or under constant cooling rate conditions suggested that the isothermal crystallization of the samples should be used for a proper evaluation of the molecular weight dependence of the observed melting temperature and degree of crystallinity in PCL. The molecular weight and temperature dependence of the spherulitic growth rate of fractions was studied in the context of the Lauritzen-Hoffman two-phase model and the Strobl three-phase model of polymer crystallization. The zero-growth rate temperatures, determined from spherulitic growth rates using four different methods, are consistent with each other and increase with chain length. The concomitant increase in the apparent secondary nucleation constant was attributed to two factors. First, for longer chains there is an increase in the probability that crystalline stems belong to loose chain-folds, hence, an increase in fold surface free energy. It is speculated that the increase in loose folding and resulting decrease in crystallinity with increasing chain length are associated with the ester group registration requirement in PCL crystals. The second contribution to the apparent nucleation constant arises
from chain friction associated with segmental transport across the melt/crystal interface. These factors were responsible for the much stronger chain length dependence of spherulitic growth rates at fixed undercooling observed here with PCL than previously reported for PE and PEO. In the case of PCL, the scaling exponent associated with the chain length dependence of spherulitic growth rates exceeds the upper theoretical bound of 2 predicted from the Brochard-DeGennes chain pullout model. Observation that zero-growth and equilibrium melting temperature values are identical with each other within the uncertainty of their determinations casts serious doubt on the validity of Strobl three-phase model.
A novel method is proposed to determine the Porod constant necessary to extrapolate the small angle X-ray scattering intensity data to large scattering vectors. The one-dimensional correlation function determined using this Porod constant yielded the values of lamellar crystal thickness, which were similar to these estimated using the Hosemann-Bagchi Paracrystalline Lattice model. The temperature dependence of the lamellar crystal thickness was consistent with both LH and the Strobl model of polymer crystallization. However, in contrast to the predictions of Strobl’s model, the value of the mesomorph-to-crystal equilibrium transition temperature was very close to the zero-growth temperature. Moreover, the lateral block sizes (obtained using wide angle X-ray diffraction) and the lamellar thicknesses were not found to be controlled by the mesomorph-to-crystal equilibrium transition temperature. Hence, we concluded that the crystallization of PCL is not mediated by a mesophase.
Metallocene-catalyzed linear low-density (m-LLDPE with 3.4 mol% 1-octene) and conventional low-density (LDPE) polyethylene blends of different compositions were investigated for their melt-state miscibility and concurrent crystallization tendency. Differential scanning calorimetric studies and morphological studies using atomic force microscopy confirm that these blends are miscible in the melt-state for all compositions. LDPE chains are found to crystallize concurrently with m-LLDPE chains during cooling in the m-LLDPE crystallization temperature range. While the extent of concurrent crystallization was found to be optimal in blends with highest m-LLDPE content studied, strong evidence was uncovered for the existence of a saturation effect in the concurrent crystallization behavior. This observation leads us to suggest that co-crystallization, rather than mere concurrent crystallization, of LDPE with m-LLDPE can indeed take place. Matching of the respective sequence length distributions in LDPE and m-LLDPE is suggested to control the extent of co-crystallization.Ph. D.
41
Gacal, Bahadır [Verfasser], and Volker [Akademischer Betreuer] Abetz. "The Effect of Polymer Modification on Gas Transport Properties and The Synthesis of Poly(ethylene glycol) (PEG) Containing Polymers via Step-Growth Click Coupling Reaction for CO2 Separation / Bahadır Gacal. Betreuer: Volker Abetz." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2015. http://d-nb.info/1070624926/34.
Full text
42
Berthet, Morgane. "Nanoparticules biodégradables et multifonctionnelles pour la régénération tissulaire de plaies cutanées profondes." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1213.
Full textAbstract:
L'objectif de cette thèse était de mettre en oeuvre le développement d'une thérapie des plaies cutanées profondes basée sur l'utilisation de nanoparticules (NP) biodégradables de poly(acide lactique) (NP-PLA) vectrices de médiateurs de la cicatrisation. Le but était d'accélérer la cicatrisation cutanée et de favoriser la reconstruction d'un derme fonctionnel. La méthode a été de (i) réduire la réaction inflammatoire pour en contenir les effets délétères et (ii) stimuler la réépithélialisation pour accélérer la cicatrisation et réduire le risque infectieux. Les moyens ont été l'utilisation d'un antioxydant, la vitamine E (VE) et d'un facteur de croissance des fibroblastes (le FGF2) vectorisés par des nanoparticules biocompatibles et biodégradables de poly(acide lactique) (PLA). Nos NP-PLA contiennent l'antioxydant (VE) dans leur coeur hydrophobe, et portent le facteur de croissance fibroblastique (FGF2) à leur surface. Ces formulations ont été (i) caractérisées par des méthodes physico-chimiques et (ii) testées par des méthodes in vitro pour évaluer leurs effets potentiels, en tant que système de délivrance de VE et de FGF2, sur la cicatrisation des plaies. Des modèles expérimentaux in vivo ont été développés et caractérisés pour mettre en évidence l'efficacité des NP-PLA fonctionnalisées pour la cicatrisation cutanée et la reconstruction dermique fonctionnelle. Nos résultats montrent que l'activité antioxydante de la VE n'est pas perturbée par l'encapsulation dans des NP-PLA et qu'elle est légèrement supérieure à celle de la VE libre dans un système in vitro. De même, l'activité biologique du FGF2 sur la prolifération et la migration des fibroblastes dans un système in vitro n'est pas altérée par son adsorption sur des NP-PLA. Aucune de ces deux NP-PLA fonctionnalisées n'a de cytotoxicité avérée in vitro. Deux modèles expérimentaux de plaies cutanées profondes ont été développés sur souris sans poils SKH1 saines : (i) Un modèle robuste de brûlure cutanée thermique de 3ème degré qui se caractérise par une inflammation massive de la plaie et par un stade de granulation tardif après 16 jours de cicatrisation. (ii) Un modèle de plaie d'excision cutanée a également été utilisé. Un modèle de cicatrisation retardée a été obtenu par induction chimique d'un diabète de type I stable avant réalisation des plaies d'excision ou de brûlure. Ces modèles de plaies cutanées ont été caractérisés tout au long du processus de cicatrisation par des études (i) macroscopiques de cinétique de fermeture des plaies, (ii) histologiques d'inflammation, de nécrose et de réépithélialisation, (iii) physiologiques de perfusion sanguine cutanée. L'expression de 84 gènes impliqués dans le processus de cicatrisation a été étudiée sur le tissu cicatriciel 14 jours après formation de la plaie. Pour conclure, nos résultats mettent en évidence le potentiel de vectorisation de molécules thérapeutiques des NP de PLA pour le développement de futures stratégies de délivrance ciblée de VE et de FGF2 dans les plaies cutanées profondes. Les modèles expérimentaux in vivo développés et caractérisés, ouvrent la voie aux études précliniques d'efficacité des NP-PLA fonctionnalisées dans le processus de cicatrisation des plaies profondesThe objective of this thesis was to develop a therapy of cutaneous deep wounds based on biodegradable poly (lactic-acid) nanoparticles (PLA-NP) releasing wound healing mediators. The goal was to accelerate wound healing and to promote the reconstruction of a functional dermis. Our method was (i) to reduce the inflammatory reaction in the aim of limiting its deleterious effects, (ii) to stimulate reepithelialization to accelerate wound healing and to reduce the risk of infections. The implementation of means was based on the use of an antioxidant (vitamin E, VE) and a fibroblast growth factor (FGF2) carried by biocompatible and biodegradable poly(lactic-acid) based nanoparticles. Our PLA-NP contained the antioxidant (VE), in their hydrophobic core and carried the fibroblastic growth factor (FGF2) on their surface. These formulations were (i) characterized by physico-chemical methods and (ii) tested by in vitro methods to evaluate their effects as a delivery system of VE and FGF2 on wound healing. Experimental in vivo models have been developed and characterized in the aim of studying the potential beneficial effect of functionalized PLA-NP on wound healing and functional reconstruction of dermis. Our results show that the antioxidant activity of VE was not inhibited by encapsulation into PLA-NP and was lightly increased compared with free VE in an in vitro system. The biological activity of FGF2 on proliferation and migration of fibroblasts in an in vitro system was not altered by adsorption onto PLA-NP as well. No cytotoxicity of these functionalized PLA-NP was detected in vitro. Two experimental models of deep cutaneous wounds were developed on the healthy SKH1 hairless mouse: (i) A robust third degree thermal burn model that was characterized by massive inflammation of the wound and a late granulation stage after 16 days of healing. (ii) A model of excisional skin wound was also used. A model of delayed wound healing was established by chemical induction of stable type I diabetes prior to excision and burn injuries. The healing process of these models of cutaneous wounds was characterized by (i) macroscopic studies of wound closure, (ii) histological studies of inflammation, necrosis and reepithelialization, and (iii) by physiological studies of cutaneous blood perfusion. A study of the expression of 84 genes involved in the healing process was carried out on the scar tissue 14 days post-wound. In conclusion, our results highlight the potential efficacy of PLA-NP as a vector of therapeutic molecules for the development of future strategies for targeted delivery of VE and FGF2 in deep skin wounds. The developed and characterized in vivo experimental models open the way to preclinical studies of efficacy of functionalized PLA-NP on the healing process of deep wounds
43
Suckow, Marcus. "Konzepte zur ionischen Modifizierung von Brombutylkautschuk mit polyionischen Flüssigkeiten zur Herstellung von selbstheilenden Materialien." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-217174.
Full textAbstract:
Elastomere werden während ihrer Lebensdauer meist mechanisch und thermisch besonders stark beansprucht. Dadurch sind sie einem hohen Verschleiß und einer Abnutzung ausgesetzt, die zum Versagen des Materials führen. Dabei können schwerwiegende Folgen für Maschine und Mensch entstehen. Eine elegante Möglichkeit diesen Erscheinungen entgegenzuwirken bietet die Entwicklung von selbstheilenden Materialien. Durch reversible Vernetzungen können Mikro- und Makrorisse verschlossen und die Lebensdauer von elastomeren Werkstoffen erheblich gesteigert werden. Eine mögliche reversible Vernetzung ist die Bildung ionischer Cluster. Die in den letzten Jahren mehr und mehr in den Fokus gerückten polyionischen Flüssigkeiten (PIF) bieten, aufgrund ihres hohen Anteils an ionischen Gruppen (meist in jeder Wiederholeinheit), eine gute Voraussetzung für eine ionische Modifizierung von Elastomeren.
Ziel dieser Arbeit war es in kommerziell erhältlichem Brombutylkautschuk (BIIR) durch Modifizierung mit polyionischen Flüssigkeiten (PIF) selbstheilende Eigenschaften hervorzurufen. Dabei sollte die Reversibilität der ionischen Clusterbildung ausgenutzt werden. Aufgrund des zu erwartenden großen Einflusses der Beweglichkeit der ionischen Komponente wurden drei unterschiedliche Konzepte verfolgt, bei denen die Mobilität der PIF-Phase durch Reaktionen mit der BIIR-Matrix im unterschiedlichen Maße eingeschränkt wurde. Zum einen wurde der BIIR reaktiv mit PIF geblendet, sodass sowohl kovalente als auch nichtkovalente Vernetzungen erfolgten (Konzept 1). Nach diesem Konzept ist die Mobilität der ionischen Gruppen stark begrenzt. In einem weiteren Konzept erfolgte eine einseitige Pfropfung von PIF an den BIIR (Konzept 2). Dadurch wurde eine kovalente Vernetzung vermieden und die Beweglichkeit der PIF nur leicht eingeschränkt. Weiterhin erfolgte nach Konzept 3 ein nichtreaktives Blenden mit PIF, wodurch die freie Beweglichkeit der PIF-Phase gewährleistet war. Dafür war vorgesehen den BIIR zunächst mit niedermolekularen Alkylimidazolen ionisch zu modifiziert. Dadurch sollten alle reaktiven Stellen im BIIR blockiert und die Kompatibilität mit der PIF erhöht werden.
Als Blendkomonenten wurden drei unterschiedliche PIF synthetisiert. Neue PIF (A Serie) konnten über polymeranaloge Umsetzungen von Poly(butadien-co-maleinsäureanhydrid) hergestellt werden. Hierzu wurden zunächst die Anhydridgruppen des Polymers mit 1,(3 Aminopropyl)imidazol und dann in einem zweiten Schritt mit Alkylbromid umgesetzt. In einer weiteren Serie (B-Serie) wurde Polyvinylimidazol mit Alkylbromid umgesetzt. Beide Synthesemethoden haben den Vorteil, dass durch variable Umsetzung mit verschiedenen Alkylbromiden bzw. durch Co-Umsetzung mit Alkylamiden (A-Serie) sowie durch Ionenaustausch das Eigenschaftsniveau in weitem Maße variiert und dem entsprechenden Anwendungsfall angepasst werden kann. Insbesondere konnten durch Teilumsetzung Proben erhalten werden, welche reaktive Gruppen besitzen, die für die kovalente Bindung mit BIIR geeignet waren.
Bei einer weiteren Serie (C-Serie) erfolgte die Synthese über eine Stufenwachstumsreaktion eines AB Monomers. Hierbei stand im Mittelpunkt inwieweit ein gerichteter Kettenaufbau erfolgt. Das war insofern wichtig, da diese Monomere für die einseitige Pfropfung mit BIIR vorgesehen waren, bei der eine kovalente Vernetzung vermieden wird. Durch MALDI-TOF-Untersuchungen konnte dieser gerichtete Kettenaufbau nachgewiesen werden.
Die mechanischen Eigenschaften der nach den drei Konzepten hergestellten Blends wurden mit DMA-Untersuchungen und Zug-Dehnungsexperimenten ermittelt. Vergleichend wurde ein konventionell mit Schwefel vernetzter BIIR herangezogen. Besonders gute mechanische Eigenschaften wurden mit den Blends nach Konzept 2 und 3 erreicht, welche vergleichbar und teils deutlich besser waren als der schwefelvernetzte BIIR. Nach diesen beiden Konzepten erfolgte die Vernetzung ausschließlich über die Bildung ionischer Cluster. Diese reversiblen Bindungen sorgen für eine starke Vernetzung des BIIR die vergleichbar bzw. stärker ist als die kovalenten Bindungen mit Schwefel. Eher schlechte mechanische Eigenschaften konnten für die Blends nach Konzept 1 beobachtet werden. Die kovalenten Verknüpfungen über die PIF sorgen für eine relativ lose und weitmaschige Vernetzung des BIIR. Die ermittelten Vernetzungsdichten sind deutlich niedriger im Vergleich zum schwefelvernetzten BIIR. Die zusätzlichen reversiblen Vernetzungspunkte durch die ionische Clusterbildung wirken sich aufgrund der eingeschränkten Mobilität schwächer aus als in den anderen Konzepten.
Neben den hergestellten Blends wurden auch die ionisch modifizierten BIIR-Proben separat untersucht. Diese zeigten besonders bei der Verwendung von kurzkettigen Alkylimidazolen herausragende mechanische Eigenschaften. Die Ursache dafür liegt vermutlich in der Bildung von stärkeren und kompakteren ionischen Clustern.
Für die Testung der Selbstheilungseigenschaften wurden an zerschnittenen und geheilten Probekörper Zugversuche durchgeführt und mit den Werten der unbehandelten Probekörper verglichen. Um eine reproduzierbare Probenvorbereitung zu gewährleisten, wurde im Rahmen dieser Arbeit eine Schneidevorrichtung entwickelt, in der die Heilungsversuche unter gleichen Bedingungen durchgeführt werden konnten.
Gute Selbstheilungseigenschaften konnten für die Blends nach Konzept 3 beobachtet werden. Die vorherige Modifizierung des BIIR mit längeren Alkylimidazolen wirkte sich dabei besonders vorteilhaft auf die Heilung der Proben aus. Ebenfalls sehr gute Heilungsraten konnten für die Blends nach Konzept 1 ermittelt werden. Jedoch zeigt diese Art der Modifizierung aufgrund der geringen mechanischen Stabilität das geringste Potential für mögliche industrielle Anwendungen. Für die Blends nach Konzept 2 wurden eher schlechte Heilungsraten ermittelt. Die ausschließlich ionisch modifizierten Proben zeigten die mit Abstand beste Selbstheilung, wobei die Verwendung von langkettigen Alkylimidazolen für die Heilung vorteilhaft ist. Im Vergleich mit aus der Literatur bekannten elastomeren Materialien konnten deutlich bessere Bruchspannungen für geheilte und unbehandelte Probekörper erreicht werden.
Zusammenfassend lässt sich sagen, dass über die ionische Modifizierung von BIIR nach den drei vorgestellten Konzepten Materialien mit sehr guten mechanischen Eigenschaften und herausragender Selbstheilung hergestellt werden konnten. Es zeigte sich, dass diese Eigenschaften eng mit der Mobilität der für die reversible Vernetzung verantwortlichen ionischen Gruppen verknüpft sind. Der Vergleich mit einem konventionell schwefelvernetzten BIIR zeigte, dass die physikalische Vernetzung über die Bildung von ionischen Clustern (Konzept 2 und 3) vergleichbar bzw. stärker ist. Weiterhin sind diese Materialien rezyklierbar, da bei höheren Temperaturen ein Schmelzen durch Auflösen der ionischen Cluster zu erwarten ist. Diese Verbesserungen gegenüber dem schwefelvernetzten BIIR zeigen deutlich das Potential dieser Materialen für mögliche Anwendungen in der Industrie.
44
Waack, Indra [Verfasser], Herbert de [Akademischer Betreuer] Groot, Peter [Akademischer Betreuer] Horn, and Carsten [Akademischer Betreuer] Schmuck. "Untersuchungen zum Einfluss und zur Bioverträglichkeit von Perfluordekalin-gefüllten Poly(laktid-co-glykolid)-Mikrokapseln in einem Modell der Ratte / Indra Waack. Gutachter: Peter Horn ; Carsten Schmuck. Betreuer: Herbert de Groot." Duisburg, 2014. http://d-nb.info/1047079267/34.
Full text
45
Nakanishi, Marcio. "Polipose nasal: caracterização da infiltração dos eosinófilos, mastócitos, miofibroblastos e células TGF-beta positivas em indivíduos com e sem asma." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/5/5143/tde-09102014-141937/.
Full textAbstract:
Para identificar, quantificar e correlacionar os eosinófilos, mastócitos, miofibroblastos e células TGF-beta positivas nos pólipos nasais de pacientes com e sem asma foi realizado a imunoistoquímica. A quantidade de eosinófilos, miofibroblastos e células TGF-beta positivas esteve aumentada no pólipo nasal de indivíduos asmáticos. O número de mastócitos não mostrou diferença entre os grupos. O miofibroblasto foi o denominador comum na correlação entre eosinófilos, mastócitos, células TGF-beta positivas e presença de asmaIntroduction: Nasal polyposis is a chronic inflammatory disease of the nasal mucosa or paranasal sinuses characterized by the formation of benign polyps. The pathogenesis is not known, although nasal polyps are associated with several systemic diseases, with asthma being the most frequent. The aim of the present study was to identify, quantify, compare and correlate eosinophils, mast cells, myofibroblasts and TGF-ß-positive cells in nasal polyps of patients with and without asthma. Material and Methods: Seventy-eight subjects with nasal polyps undergoing endoscopic sinus surgery were selected. Control specimens were obtained from eight subjects with a normal sinus mucosa. One group consisted of polyps from 56 patients with asthma and the other of polyps from 22 patients without asthma. Immunohistochemistry was performed using monoclonal antibodies against eosinophil cationic protein to stain eosinophils, against tryptase to stain mast cells, against alpha-smooth muscle actin to stain myofibroblasts, and against TGF-ß to stain TGF-ß-positive cells. Results: The number of eosinophils, myofibroblasts and TGF-ß-positive cells was significantly higher in the asthma group than in the nonasthma group, whereas no significant difference in the number of mast cells was observed between the two groups. The number of eosinophils, mast cells, myofibroblasts and TGF-ß-positive cells was significantly higher in nasal polyps than in the control group. Myofibroblasts showed a significant correlation with eosinophils, mast cells, TGF-ß-positive cells, and asthma. Conclusion: Eosinophils, mast cells, myofibroblasts and TGF-ß-positive cells were identified in all nasal polyps, although the number of eosinophils, myofibroblasts and TGF-ß-positive cells was higher in the asthma group. The number of mast cells was similar regardless of the presence or absence of asthma. Myofibroblasts were a common denominator in the correlation between eosinophils, mast cells, TGF-ß-positive cells, and asthma
46
永正, 邵., and Yongzheng Shao. "Study on the effects of matrix properties on the mechanical properties of carbon fiber reinforced plastic composites." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902982/?lang=0, 2015. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902982/?lang=0.
Full textAbstract:
It was found that a significant improvement of mechanical properties of CFRPs can be achieved by the adjustment of the matrix properties such as toughness and CF/matrix adhesion via the chemical modification, as well as the physical modification by a small amount of cheap and environment-friendly nano fibers. Based on investigation of fracture mechanisms at macro/micro scale, the effects of matrix properties and nano fiber on the mechanical properties of CFRP have been discussed. Subsequently, the relationship has been characterized by a numerical model to show how to modulate the parameters of the matrix properties to achieve excellent fatigue properties of CFRP.博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
47
Pugliano, Marion. "Conception et optimisation d'un implant thérapeutique combiné à des organoïdes de cellules souches pour la nanomédecine régénérative ostéoarticulaire." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAJ111.
Full textAbstract:
Notre équipe a mis au point une stratégie innovante d’implants thérapeutiques biphasiques, pour une régénération plus efficace et plus durable du cartilage articulaire, dans le cadre du traitement des lésions ostéochondrales. Ces implants pourraient représenter de meilleures alternatives aux traitements actuellement utilisés en chirurgie orthopédique. Dans un premier temps, nous avons élaboré un modèle d’implant thérapeutique à base de collagène de type II dérivé de méduse, fonctionnalisé par des nanoréservoirs de facteurs de croissance TGF-β3 et équipé de cellules souches mésenchymateuses humaines (hCSMs) dérivées de la moelle osseuse. La biocompatibilité et les propriétés chondrogéniques de cet implant ont été validées par des analyses in vitro, confirmant son potentiel thérapeutique pour la régénération du cartilage articulaire. Dans un second temps, nous nous sommes plus particulièrement concentrés sur la régénération de l’unité ostéochondrale. Il est en effet essentiel de régénérer un os sous-chondral sain, pour permettre une régénération stable du cartilage articulaire en surface. Dans ce but, nous avons développé un implant thérapeutique doté de deux compartiments : (i) un premier compartiment élaboré à partir d’un biomatériau synthétique de poly-ε-caprolactone (PCL), doté de nanoréservoirs de facteur de croissance BMP-7, pour la régénération de l’os sous-chondral : (ii) un second compartiment à base d’un hydrogel d’alginate et d’acide hyaluronique, ensemencé d’organoïdes hybrides de hCSMs et de chondrocytes humains, pour la régénération du cartilage articulaire. L’efficacité de cet implant biphasique a été confirmée in vitro et in vivo chez la souris. Dans un troisième temps, nous avons évalué notre stratégie d’implant thérapeutique biphasique en site intra-articulaire, chez l’animal de grande taille (brebis). Ces travaux ont permis de valider la faisabilité et l’efficacité de notre stratégie, combinant cette fois-ci : (i) un implant collagénique commercial, doté de nanoréservoirs de facteur de croissance BMP-2, pour la régénération de l’os sous-chondral ; (ii) un hydrogel d’alginate et d’acide hyaluronique, incorporant des organoïdes de CSMs de moelle osseuse de brebis, pour la régénération du cartilage articulaire. En conclusion, ces médicaments combinés de thérapie innovante, associant des biomatériaux naturels ou synthétiques (dispositif médical implantable), des molécules thérapeutiques et des cellules souches mésenchymateuses (médicament de thérapie innovante), permettent la régénération de l’unité ostéochondrale dans son ensemble. Cette stratégie novatrice permettra sans nul doute de grandes avancées en nanomédecine régénérative ostéoarticulaire, dans l’optique d’améliorer toujours plus le traitement et le confort des patientsOur team has developed an innovative strategy based on biphasic therapeutic implants allowing a more effective and long-lasting regeneration of articular cartilage in the treatment of osteochondral lesions. These implants may represent better alternatives to the current treatments used in orthopaedic surgery. First, we developed a jellyfish type II collagen therapeutic implant model, functionalized with TGF-β3 growth factor nanoreservoirs, and equipped with human bone marrow-derived mesenchymal stem cells (hMSCs). The biocompatibility and chondrogenic properties of this implant have been validated in vitro, confirming its therapeutic potential for the regeneration of articular cartilage. In a second time, we focused more on the regeneration of the osteochondral unit. Indeed, it is crucial to regenerate a healthy subchondral bone, to allow a stable regeneration of articular cartilage on the surface. To this end, we have developed a therapeutic implant with two compartments : (i) a first compartment based on a synthetic poly-ε-caprolactone (PCL) biomaterial, equipped with BMP-7 growth factor nanoreservoirs, for the regeneration of the subchondral bone ; (ii) a second compartment based on a hydrogel of alginate and hyaluronic acid, seeded with hybrid organoids of hMSCs and human chondrocytes, for the regeneration of the articular cartilage. The effectiveness of this biphasic implant has been confirmed in vitro and in vivo in mice. Thirdly, we evaluated our biphasic therapeutic implant strategy in the large animal (sheep). This work validated the feasibility and effectiveness of our strategy, by combining : (i) a commercial collagen implant with BMP-2 growth factor nanoreservoirs, for the regeneration of the subchondral bone ; (ii) a hydrogel of alginate and hyaluronic acid, incorporating organoids of sheep bone marrow MSCs, for the regeneration of articular cartilage. In conclusion, these combined advanced medicinal products (ATMPs), combining natural or synthetic biomaterials (implantable medical device), therapeutic molecules and mesenchymal stem cells, allow the regeneration of the entire osteochondral unit. This innovative strategy will undoubtedly lead to major advances in osteoarticular regenerative nanomedicine, aiming to improve the treatment and comfort of patients
48
Täuber, Daniela. "Characterization of heterogeneous diffusion in confined soft matter." Doctoral thesis, Universitätsbibliothek Chemnitz, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-77658.
Full textAbstract:
A new method, probability distribution of diffusivities (time scaled square displacements between succeeding video frames), was developed to analyze single molecule tracking (SMT) experiments. This method was then applied to SMT experiments on ultrathin liquid tetrakis(2-ethylhexoxy)silane (TEHOS) films on Si wafer with 100 nm thermally grown oxide, and on thin semectic liquid crystal films. Spatial maps of diffusivities from SMT experiments on 220 nm thick semectic liquid crystal films reveal structure related dynamics. The SMT experiments on ultrathin TEHOS films were complemented by fluorescence correlation spectroscopy (FCS). The observed strongly heterogeneous single molecule dynamics within those films can be explained by a three-layer model consisting of (i) dye molecules adsorbed to the substrate, (ii) slowly diffusing molecules in the laterally heterogeneous near-surface region of 1 - 2 molecular diameters, and (iii) freely diffusing dye molecules in the upper region of the film. FCS and SMT experiments reveal a strong influence of substrate heterogeneity on SM dynamics. Thereby chemisorption to substrate surface silanols plays an important role. Vertical mean first passage times (mfpt) in those films are below 1 µs. This appears as fast component in FCS autocorrelation curves, which further contain a contribution from lateral diffusion and from adsorption events. Therefore, the FCS curves are approximated by a tri-component function, which contains an exponential term related to the mfpt, the correlation function for translational diffusion and a stretched exponential term for the broad distribution of adsorption events. Lateral diffusion coefficients obtained by FCS on 10 nm thick TEHOS films, thereby, are effective diffusion coefficients from dye transients in the focal area. They strongly depend on the substrate heterogeneity. Variation of the frame times for the acquisition of SMT experiments in steps of 20 ms from 20 ms to 200 ms revealed a strong dependence of the corresponding probability distributions of diffusivities on time, in particular in the range between 20 ms and 100 ms. This points to average dwell times of the dye molecules in at least one type of the heterogeneous regions (e.g. on and above silanol clusters) in the range of few tens of milliseconds.
Furthermore, time series of SM spectra from Nile Red in 25 nm thick poly-n-alkyl-methacrylate (PnAMA) films were studied. In analogy to translational diffusion, spectral diffusion (shifts in energetic positions of SM spectra) can be studied by probability distributions of spectral diffusivities, i.e. time scaled square energetic displacements. Simulations were run and analyzed to study contributions from noise and fitting uncertainty to spectral diffusion. Furthermore the effect of spectral jumps during acquisition of a SM spectrum was investigated. Probability distributions of spectral diffusivites of Nile Red probing vitreous PnAMA films reveal a two-level system. In contrast, such probability distributions obtained from Nile Red within a 25 nm thick poly-n-butylmethacrylate film around glass transition and in the melt state, display larger spectral jumps. Moreover, for longer alkyl side chains a solvent shift to higher energies is observed, which supports the idea of nanophase separation within those polymers.
49
Stevenson, Christopher Eric. "A microsimulation study of the benefits and costs of screening for colorectal cancer." Phd thesis, 2001. http://hdl.handle.net/1885/48198.
Full textAbstract:
This thesis examines the benefits and costs of screening for colorectal cancer in the context of an organised population screening programme. It uses microsimulation modelling to derive an optimally cost-effective screening protocol for various combinations of the available screening tests. ¶ First a mathematical model for the natural history of colorectal cancer is derived, based on analyses of Australian population and hospital-based cancer registries combined with data from published studies. Then a model for population based screening is derived based mainly on data from published screening studies, including the four major published randomised controlled trials of faecal occult blood test (FOBT) screening. These two models are used to simulate the application of a screening programme to the Australian population. The simulations are applied to a period of 40 years following 1990 (the study’s base year), with both costs and benefits discounted back to the base year at an annual rate of 3%. ¶ ...
50
Yu, Hongpeng, Kin Leong Pey, Wee Kiong Choi, Eugene A. Fitzgerald, and Dimitri A. Antoniadis. "Poly-Si₁âxGex Film Growth for Ni Germanosilicided Metal Gate." 2004. http://hdl.handle.net/1721.1/7371.
Full textAbstract:
Scaling down of the CMOS technology requires thinner gate dielectric to maintain high performance. However, due to the depletion of poly-Si gate, it is difficult to reduce the gate thickness further especially for sub-65 nm CMOS generation. Fully silicidation metal gate (FUSI) is one of the most promising solutions. Furthermore, FUSI metal gate reduces gate-line sheet resistance, prevents boron penetration to channels, and has good process compatibility with high-k gate dielectric. Poly-SiGe gate technology is another solution because of its enhancement of boron activation and compatibility with the conventional CMOS process. Combination of these two technologies for the formation of fully germanosilicided metal gate makes the approach very attractive. In this paper, the deposition of undoped Poly-Si₁âxGex (0 < x < 30% ) films onto SiO₂ in a low pressure chemical vapor deposition (LPCVD) system is described. Detailed growth conditions and the characterization of the grown films are presented.Singapore-MIT Alliance (SMA)