Philosophiae Doctor - PhD / In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode. / South Africa

Les interventions chirurgicales avec prothèses pour défauts de soutènement ont déjà nécessité l'implantation de plus d'un million de prothèses dans le monde. L'indication des prothèses de soutènement synthétiques non résorbables a permis de diminuer les récidives à court terme mais présente une incidence non négligeable de complications postopératoires. Le taux de réinterventions reste encore trop élevé. Cette thèse a pour objectif d'apporter de nouvelles propriétés à ces prothèses de polypropylène, pour à la fois améliorer leur résistance à l'infection et permettre leur visualisation en IRM clinique. Des treillis libérant des antibiotiques de façon contrôlée sont développés par enduction de polymère dégradable et biocompatible contenant des antibiotiques. Cette enduction présente une activité antibactérienne in vivo significative. Une autre enduction de polymères dégradables ou non dégradables, par une technique de pulvérisation par aérographie, permet une visualisation en IRM des treillis in vitro et après implantation. La stabilité du polymère greffé avec l'agent de contraste autorise une visualisation des treillis pendant au moins douze mois. / Surgical procedures with synthetic meshes have yet allowed more than one million operations. Non absorbable synthetic mesh used has permitted to decrease clinical recurrence at short term, but post operative complications still exist. Re operation rate is still too high. This study aims to develop new properties for those polypropylene meshes, such as infection resistance and MRI visualization. Meshes with controlled release of antibiotics were obtained after polymer coating and showed a significant in vivo antibacterial effect. Another mesh coating, with an aerograph procedure, has allowed MRI mesh visualization. To visualize by MRI, meshes after implantation, two new MRI visible polymer (degradable and non degradable) were coated onto meshes using an airbrush system. This coating allows the visualization of meshes in vitro and in vivo with experimental and clinical MR equipments. The stability of the MRI visible polymers permits to in vitro to visualize meshes during at least one year.

Among non-viral vectors, cationic polymers, such as poly(propylene imine) (PPI), play a prominent role in nucleic acid delivery. However, limitations of polycationic polymer-based DNA delivery systems are (i) insufficient target specificity, (ii) unsatisfactory transgene expression, and (iii) undesired transfer of therapeutic DNA into non-target cells. We developed single-chain antibody fragment (scFv)-directed hybrid polyplexes for targeted gene therapy of prostate stem cell antigen (PSCA)-positive tumors. Besides mono-biotinylated PSCA-specific single-chain antibodies (scFv(AM1-P-BAP)) conjugated to neutravidin, the hybrid polyplexes comprise -cyclodextrinmodified PPI as well as biotin/maltose-modified PPI as carriers for minicircle DNAs encoding for Sleeping Beauty transposase and a transposon encoding the gene of interest. The PSCA-specific hybrid polyplexes efficiently delivered a GFP gene in PSCA-positive tumor cells, whereas control hybrid polyplexes showed low gene transfer efficiency. In an experimental gene therapy approach, targeted transposition of a codon-optimized p53 into p53-deficient HCT116p53 /PSCA cells demonstrated decreased clonogenic survival when compared to mock controls. Noteworthily, p53 transposition in PTEN-deficient H4PSCA glioma cells caused nearly complete loss of clonogenic survival. These results demonstrate the feasibility of combining tumor-targeting hybrid polyplexes and Sleeping Beauty gene transposition, which, due to the modular design, can be extended to other target genes and tumor entities.

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No description available.

Well-defined heterobifunctional homopolyethers and amphiphilic block copolyethers containing a variety of functionalities were designed, synthesized, and characterized via GPC and 1H NMR. These have included controlled molecular weight cholesterol-PEO-OH, mono- and trivinylsilyl-PEO-OH, monovinylsilyl-PEO-PPO-OH, monovinylsilyl-PEO-PPO-PEO-OH, maleimide-PEO-OH, stearyl alcohol-PEO-OH, propargyl alcohol-PEO-OH, trivinylsilyl-PPO-OH, trivinylsilyl-PPO-PEO-OH, and benzyl alcohol-initiated poly(allyl glycidyl ether)-OH. The focus of polymers utilized in this study involved the mono- and trivinylsilyl polyethers. The vinylsilyl endgroups on these materials were functionalized with various bifunctional thiols through free radical addition of SH groups across the vinylsilyl double bonds. The resultant end-functional polyethers were adsorbed onto magnetite nanoparticles and the stabilities of the polymer-magnetite complexes were compared as a function of the type of anchoring moiety and the number of anchoring moieties per chain. Anchoring chemistries investigated in this work included carboxylates, alkylammonium ions, and zwitterionic phosphonates. The anchor group-magnetite bond stability was investigated in water and phosphate buffered saline (PBS). Through these studies, the zwitterionic phosphonate group was shown to be a better anchoring group for magnetite than either carboxylate or ammonium ions. Tri-zwitterionic phosphonate anchor groups provided stability of the complexes in PBS for a broad range of polymer loadings. Thus, investigations into the stability of polyether-magnetite complexes in PBS focused on hydrophilic zwitterionic phosphonate-PEO-OH and amphiphilic zwitterionic phosphonate-PPO-b-PEO-OH oligomer coatings on the surface of magnetite. Superparamagnetic magnetite nanoparticles are of interest as potential contrast-enhancement agents for MRI imaging. Thus, transverse NMR relaxivities of these complexes were studied as a function of chemical composition and nanostructure size and compared to commercial contrast agents. The amphiphilic polyether-magnetite nanoparticles were shown to be stable in both aqueous media as well as physiological media and have much higher transverse relaxation values, r2, than those of commercial contrast agents and other materials in the literature. / Ph. D.

The composition and stability of polymer-magnetite complexes is essential for their use as a treatment for retinal detachment, for drug targeting and delivery, and for use as a MRI contrast agent. This work outlines a general methodology to design well-defined, stable polymer-magnetite complexes. Colloidal modeling was developed and validated to describe polymer brush extension from the magnetite core. This allowed for the observation of deviations from expected behavior as well as the precise control of polymer-particle complex size. Application of the modified Derjaguin-Verwey-Landau-Overbeek (DLVO) theory allowed the determination of the polymer loading and molecular weight necessary to sterically stabilize primary magnetite particles. Anchoring of polyethers to the magnetite nanoparticle surface was examined using three different types of anchor groups: carboxylic acid, ammonium, and zwitterionic phosphonate. As assessed by dynamic light scattering (DLS), the zwitterionic phosphonate group provided far more robust anchoring than either the carboxylic acid or ammonium anchor groups, which was attributed to an extremely strong interaction between the phosphonate anchor and the magnetite surface. Coverage of the magnetite surface by the anchor group was found to be a critical design variable for the stability of the zwitterionic phosphonate groups, and the use of a tri-zwitterionic phosphonate anchor provided stability in phosphate buffered saline (PBS) for a large range of polymer loadings. Incorporation of an amphiphlic poly(propylene oxide)-b-poly(ethyelene oxide) (PPO-b-PEO) diblock copolymer attached to the magnetite surface was examined through colloidal modeling and DLS. The relaxivity of the complexes was related to aggregation behavior observed through DLS. This indicated the presence of a hydrophobic interaction between the PPO layers of neighboring complexes. When this interaction was large enough, the complexes exhibited an increased relaxivity and cellular uptake. Thus, we have developed a methodology that allows for design of polymer-magnetite complexes with controlled sizes (within 8% of predicted values). Application of this methodology incorporated with modified DLVO theory aids in the design of colloidally stable complexes with minimum polymer loading. Finally, determination of an anchor group stable in the presence of phosphate salts at all magnetite loadings allows for the design of materials with minimum polymer loadings in biological systems. / Ph. D.

The goal of this work is to examine the applicability of the Lauritzen-Hoflinan (LH) surface nucleation theory to the crystallization kinetics of poly(ε-caprolactone), PCL. This theory has successfully predicted a number of experimental observations such as the temperature dependence of spherulitic growth rates and the inverse relation between undercooling and the lamellar thickness. Claims have appeared in the literature that analysis of growth rate data using the LH theory does not yield physically meaningful parameters. This work will show that the lateral and fold interfacial free energy parameters, σ and σₑ, found by analysis with the LH theory are related to the chemical structure of the polymer chain in the case of PCL. The fold interfacial free energy is related to the chain stiffness, and a recent proposal relates σ to the characteristic ratio, C_∞. This work will examine the validity of the proposed relationship for the case of PCL. The effect of polymer chain architecture on the crystallization behavior was also investigated. The crystallization behavior of poly(ε-caprolactone) was compared and contrasted to that of a triblock copolymer containing (ε-caprolactone) blocks. / Ph. D.

<p>Crystal structure, morphology and crystallization kinetics of melt-crystallized polypropylene and poly(propylene-stat-ethylene) fractions with 2.7 to 11.0 mol% of ethylene were studied by differential scanning calorimeter, wide- and small-angle X-ray scattering, polarized light microscopy, transmission electron microscopy and infrared spectroscopy. With increasing ethylene content the poly(propylene-stat-ethylene) fractions showed unchanged crystallinity, increased unit cell volume and constant crystal thickness in combination with a shortened helix length. This indicated that a fraction of ethylene defects were incorporated into the crystal structure. During the isothermal crystallization both α- and γ-crystals could be formed. The γ-crystal fraction increased with increasing ethylene content and increasing crystallization temperature. For samples with α- and γ-crystal contents, multimodal melting was observed and a noticeable γ- to α-crystal conversion was observed on slow heating. The spherulitic structure of the copolymers was coarser than that for the homopolymer.</p><p>The crystalline lamellae in copolymers exhibited profound curvature in contrast to the straighter cross-hatched α-crystals typical to the homopolymer. Area dependence of electrical breakdown strength was studied for thin polypropylene homopolymer films. The measurements were performed with an automatic measurement system equipped with a scanning electrode arm. Five different electrodes having areas between 0.045 cm2 and 9.3 cm2 were used and typically 40-80 breakdowns per sample and electrode area were collected. All measurements were performed on dry samples in air at room temperature. The data was analyzed statistically and the Weibull function parameters α and β, the first one related to 63% probability for the sample to break down and the second one to the width of the distribution were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. criteria for the automatic detection of the breakdowns, effect of electrode edge design, partial discharges, DC ramp speed and humidity were critically analyzed. It was concluded that the obtained α-parameter values were stable and repeatable over several years of time. The β-parameter values, however, varied ± 10-30%, more for the large than the small electrodes, and were also sensitive to the changes both in the sample itself and in the measurement conditions.</p><p>Breakdown strengths of over 50 capacitor grade polypropylene films were analyzed. The obtained α-parameter values were between 450 and 850 V/μm, depending on the film grade and electrode area. In addition to the high breakdown strengths, reflected by the obtained α-values, another, sparse distribution consisting of low breakdown strengths was revealed when the amount of measurement points was high enough. This means that more than one Weibull distribution could be needed to describe the breakdown strength behavior of a polypropylene film. Breakdown values showed decreasing area dependence with decreasing electrode area. Breakdown strengths for larger sample areas were predicted from the small area data by area- and Weibull extrapolation. The area extrapolation led to predicted α-values 50% higher than measured at 4 m² whereas the Weibull extrapolation showed an accuracy of ±15 % when predicted and measured values were compared.</p><p>Breakdown strengths were also extrapolated for film areas similar to those in impregnated power capacitors. It turned out that the power capacitors, tested at the factory, performed much better than predicted by the extrapolation. However, a few weak spots with very low breakdown values were also found. For the poly(ethyelene terephtalate) dielectric, which is not swelled by the impregnation liquid, the large area breakdown strength was predictable. This indicates that for polypropylene film processing and impregnation led, in addition to the improved large area breakdown performance, also to sparse weak spots with low breakdown probabilities. Different Weibull distributions were responsible for the breakdown strengths for the processed and impregnated polypropylene than for the dry film samples.</p>

Crystal structure, morphology and crystallization kinetics of melt-crystallized polypropylene and poly(propylene-stat-ethylene) fractions with 2.7 to 11.0 mol% of ethylene were studied by differential scanning calorimeter, wide- and small-angle X-ray scattering, polarized light microscopy, transmission electron microscopy and infrared spectroscopy. With increasing ethylene content the poly(propylene-stat-ethylene) fractions showed unchanged crystallinity, increased unit cell volume and constant crystal thickness in combination with a shortened helix length. This indicated that a fraction of ethylene defects were incorporated into the crystal structure. During the isothermal crystallization both α- and γ-crystals could be formed. The γ-crystal fraction increased with increasing ethylene content and increasing crystallization temperature. For samples with α- and γ-crystal contents, multimodal melting was observed and a noticeable γ- to α-crystal conversion was observed on slow heating. The spherulitic structure of the copolymers was coarser than that for the homopolymer. The crystalline lamellae in copolymers exhibited profound curvature in contrast to the straighter cross-hatched α-crystals typical to the homopolymer. Area dependence of electrical breakdown strength was studied for thin polypropylene homopolymer films. The measurements were performed with an automatic measurement system equipped with a scanning electrode arm. Five different electrodes having areas between 0.045 cm2 and 9.3 cm2 were used and typically 40-80 breakdowns per sample and electrode area were collected. All measurements were performed on dry samples in air at room temperature. The data was analyzed statistically and the Weibull function parameters α and β, the first one related to 63% probability for the sample to break down and the second one to the width of the distribution were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. criteria for the automatic detection of the breakdowns, effect of electrode edge design, partial discharges, DC ramp speed and humidity were critically analyzed. It was concluded that the obtained α-parameter values were stable and repeatable over several years of time. The β-parameter values, however, varied ± 10-30%, more for the large than the small electrodes, and were also sensitive to the changes both in the sample itself and in the measurement conditions. Breakdown strengths of over 50 capacitor grade polypropylene films were analyzed. The obtained α-parameter values were between 450 and 850 V/μm, depending on the film grade and electrode area. In addition to the high breakdown strengths, reflected by the obtained α-values, another, sparse distribution consisting of low breakdown strengths was revealed when the amount of measurement points was high enough. This means that more than one Weibull distribution could be needed to describe the breakdown strength behavior of a polypropylene film. Breakdown values showed decreasing area dependence with decreasing electrode area. Breakdown strengths for larger sample areas were predicted from the small area data by area- and Weibull extrapolation. The area extrapolation led to predicted α-values 50% higher than measured at 4 m2 whereas the Weibull extrapolation showed an accuracy of ±15 % when predicted and measured values were compared. Breakdown strengths were also extrapolated for film areas similar to those in impregnated power capacitors. It turned out that the power capacitors, tested at the factory, performed much better than predicted by the extrapolation. However, a few weak spots with very low breakdown values were also found. For the poly(ethyelene terephtalate) dielectric, which is not swelled by the impregnation liquid, the large area breakdown strength was predictable. This indicates that for polypropylene film processing and impregnation led, in addition to the improved large area breakdown performance, also to sparse weak spots with low breakdown probabilities. Different Weibull distributions were responsible for the breakdown strengths for the processed and impregnated polypropylene than for the dry film samples. / QC 20101027