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Matériaux polymères à mémoire de forme et autoréparables contrôlés par la lumière via un effet photothermiqueZhang, Hongji January 2014 (has links)
Au cours des dernières décennies, le concept de « matériaux intelligents » a suscité un intérêt en croissance rapide en raison de l'apparition de plusieurs nouveaux types de matériaux polymères qui sont capables d'accomplir une fonction désirée en réponse à un stimulus spécifique de façon prédéterminée et contrôlée. Deux exemples représentatifs sont les polymères à mémoire de forme (SMPs) et les polymères autoréparables or réparables par un stimulus (SHPs). Ils sont sujets de cette thèse. D'une part, les SMPs sont des matériaux qui ont la capacité de mémoriser une forme spécifique. Après avoir été déformés et fixés à une forme temporaire, ils peuvent récupérer la forme originale et permanente sous l'effet d'un signal stimulant comme la chaleur, la lumière ou un champ électrique. Bénéficiant de la mise en œuvre relativement facile, les SMPs sont une alternative intéressante aux alliages à mémoire de forme bien établis; et ils ont trouvé un large éventail d'applications potentielles allant des implants pour la chirurgie non-invasive aux actionneurs sensibles aux environnements. D'autre part, les SHPs sont des matériaux qui sont capables de réparer des dommages mécaniques (fissures ou fractures) par eux-mêmes ou avec l'aide d’un stimulus externe. Leur développement a un grand intérêt pour améliorer la sécurité, prolonger la durée de vie et réduire le coût de l'entretien des matériaux. Sauf quelques matériaux souples (certains gels et élastomères) qui sont guérissables de façon vraiment autonome, la plupart des SHPs nécessitent l'intervention d'un stimulus comme c’est le cas pour les SMPs. L'objectif principal de cette thèse est de développer de nouveaux SMPs et SHPs contrôlables par un rayonnement lumineux. La stratégie que nous avons utilisée est basée sur l'ajout d'une petite quantité de nanoparticules d'or (AuNPs ) ou de nanotiges d'or (AuNRs) dans un SMP ou SHP pour absorber la lumière visible ou proche infrarouge. L’idée est d’utiliser la chaleur dégagée par les nanoparticules lors de l’absorption de la lumière due à la résonance plasmonique de surface (SPR) pour contrôler les transitions de phase dans les polymères et, par conséquent, de dicter leurs processus de mémoire de forme ou de guérison. Bien qu’un effet photothermique est à l'origine de ces processus, tous les avantages de l'utilisation de la lumière comme stimulus sont conservés, tels que l'activation à distance et le contrôle spatiotemporel. Plusieurs travaux de recherche ont été réalisés au cours de cette thèse, dont les résultats, nous l'espérons, peuvent constituer une contribution de base faisant l'utilisation d’AuNPs et AuNRs une technologie de plate-forme pour le développement des SMPs et SHPs contrôlables par la lumière.
En ce qui concerne les SMPs, nous avons d’abord préparé un nouveau matériau nanocomposite AuNP-polymère à base d’oligo(ε-caprolactone) ramifié et réticulé. En faisant usage de chauffage localisé induit par la lumière, nous avons prouvé que la lumière visible peut être utilisée pour activer un processus de récupération de forme de manière sélective spatialement, et pour réaliser plusieurs formes intermédiaires sur-demande. En outre, nous avons constaté qu'en ajustant l'intensité de la lumière laser ou la quantité d’AuNPs, l'élévation locale de la température dans le matériau peut être importante et atteindre une amplitude prédéterminée sans influence défavorable sur ses environs. Cette caractéristique intéressante permet d'utiliser le même SMP pour des applications couvrant un large domaine de températures environnantes. De plus, dans cette étude, nous avons démontré comment l'énergie libérée dans un processus de récupération de forme contrôlé par la lumière peut être utilisée pour accomplir un travail mécanique.
Sur la base du projet précédent, nous avons ensuite fait la première démonstration que la polarisation de la lumière peut également être utilisée pour contrôler l'effet de mémoire de forme ainsi que le processus de récupération de forme. À cette fin, nous avons conçu et préparé un SMP anisotrope contenant des AuNRs orientés par étirage de films de poly(alcool de vinyle) (PVA). L'idée est que la quantité de chaleur dégagée par les nanotiges d’or lors de l'exposition à la lumière proche infrarouge, est déterminée par l’absorption de photons qui, pour un matériau anisotrope, est dépendante de la polarisation de la lumière incidente. Nous avons montré qu’en effet, changeant la direction de polarisation du laser incident par rapport à la direction d'étirage du film tout en conservant toutes les autres conditions inchangées, permet de contrôler le degré d'élévation de température dans le matériau, ce qui détermine le processus de récupération de forme. En découvrant ce nouveau moyen de control, cette étude a élargi la boîte à outils pour les SMPs contrôlables par voie optique.
Sur le côté SHPs, notre motivation d’exploiter l'approche photothermique est d'aborder la question difficile de la guérison de matériaux mécaniquement forts et dues. En général, une force mécanique élevée (ou une grande dureté) d'un matériau entrave sa capacité d’auto-guérison ou guérison induite par des stimuli en raison du manque de mobilité de chaînes du polymère, sachant que cette mobilité est cruciale pour la diffusion du polymère dans une région fracturée conduisant à la cicatrisation. Nous avons proposé la stratégie consistant à utiliser l'effet photothermique pour provoquer la transition de phase « fusion – cristallisation » pour la réparation. Dans une première étude, par le chargement d'une très petite quantité d’AuNPs dans deux polymères cristallins, le poly(oxyde d' éthylène ) (PEO, T[indice inférieur m~]63 °C) et le polyéthylène de basse densité (LDPE , T[indice inférieur m~]103 °C), nous avons réussi une guérison optique très rapide et efficace, fusionnant deux morceaux de polymère en contact en un seul avec des propriétés mécaniques bien récupérées. Nous avons confirmé le mécanisme de guérison basé sur la fusion des chaînes cristallisées lors de l’exposition à la lumière, suivie de la cristallisation lors du refroidissement après l'extinction du laser. Cette cristallisation des chaines ayant diffusé à travers les surfaces de coupe a pour effet de les fusionner pour la guérison. En plus de l'activation à distance et la capacité de cicatrisation rapide, nous avons aussi démontré le control spatial de la guérison optique car elle a lieu uniquement dans les régions fracturées exposées au laser.
Après avoir appris comment utiliser l'effet photothermique découlant de la SPR d’AuNPs pour réaliser le control des processus de mémoire de forme et de guérison dans des polymères séparés, nous avons continué notre effort pour développer des matériaux qui possèdent les deux fonctions de mémoire de forme et de guérison commandées par la lumière. La réalisation d’un tel matériau est aussi une tâche difficile en raison de l'incompatibilité structurelle entre les SMPs et SHPs, puisque la structure de réseau réticulé nécessaire pour le mémoire de forme réduit généralement la mobilité de chaînes requise pour la guérison. Grâce aux connaissances générées par nos recherches, nous avons proposé un design de matériau consistant à réticuler chimiquement un polymère cristallin (PEO) chargé d’une petite quantité d’AuNPs. Notre étude a montré que ce matériau polymère acquise l’effet de mémoire de forme contrôlable par la lumière et la guérison optique rapide dus au même effet de chauffage localisé induit par un laser. En effet, l'effet photothermique peut activer le processus de récupération de la forme du matériau en élevant sa température au-dessus de la T[indice inférieur m] de la phase cristalline et, dans le même temps, permet la cicatrisation de fissures par l'intermédiaire de fusion des chaînes cristallisées sous exposition au laser et la cristallisation ultérieure lors du refroidissement après l’éteinte du laser. De plus, nous avons démontré que ces deux fonctions peuvent être exécutées de manière séquentielle sur le même matériau, sans interférence entre elles. La mise en œuvre simultanée des deux fonctions distinctes dans un seul matériau peut élargir les applications possibles de SMPs et SHPs.
Par la suite, nous avons appliqué la stratégie établie avec des polymères cristallins aux hydrogels polymères. Il est connu depuis longtemps qu’il est très difficile d’obtenir des hydrogels mécaniquement robustes pouvant être réparés par effets de stimuli. Nous avons conçu et préparé un hydrogel hybride en chargeant une petite quantité d’AuNPs dans un hydrogel formé par copolymérisation du N, N-diméthylacrylamide (DMA), de l'acrylate de stéaryle (SA) et du N, N'- méthylène bisacrylamide (MBA). La force mécanique de cet hydrogel est donnée par une réticulation chimique qui coexiste avec une réticulation physique due aux chaînes latérales d’alkyles hydrophobes cristallisées. Encore une fois, par le contrôle de la transition de phase de « fusion-cristallisation » des chaînes SA à l'aide d'un laser, l'hydrogel hybride montre à la fois la fonction de mémoire de forme contrôlé par la lumière et la fonction de guérison optique efficace. Une grande contrainte à la rupture supérieure à 2 MPa a été obtenue pour un hydrogel coupé en deux et puis réparé par la lumièr.
La dernière, mais non la moindre, contribution portée par l’étude dans cette thèse est une découverte que nous avons faite sur les SHPs. Nous avons observé que l’hydrogel de PVA physiquement réticulé, étant préparé par la méthode de congélation/décongélation, peut s’auto-guérir à la température ambiante sans l’utilisation d’un stimulus ou d'un agent de guérison. Cette découverte est importante étant donné que cet hydrogel est biocompatible et un matériau largement utilisé pour des applications. Notre étude a montré que la clé pour obtenir une guérison autonome efficace de l'hydrogel de PVA ayant une force mécanique relativement élevée est d'avoir une quantité suffisante de groupements hydroxyle libres sur les chaînes de PVA pour ponts-hydrogène et une bonne mobilité de chaîne assurant la diffusion du polymère à travers les surfaces de coupe.
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Children's responses to culturally relevant oracy practicesWaldron, Sarah Winona 05 September 2014 (has links)
The purpose of this qualitative action research was to explore how early primary children respond to the implementation of culturally relevant oracy practices in an inclusive classroom. This study, which took place over five months in an inner city school in Western Canada, focused on children’s oracy skills following four events facilitated by an Aboriginal Elder. Data consisted of an oral assessment, transcriptions of the four events, artefacts created by the students, photographs, and the teacher’s research journal. Data analysis consisted of a comparative assessment of the student’s oral language skills and a content and discourse analysis of the transcriptions. Data analysis revealed that children respond favourably to culturally responsive oracy practices, that they are able to meet the B.C. Ministry of Education prescribed learning outcomes, and such practices adhere to the Aboriginal Enhancement Agreement (2005). / Graduate / 0727 / 0524 / winona.waldron@shaw.ca
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Synthesis of Stimuli-responsive Hydrogels from GlycerolSalehpour, Somaieh 18 January 2012 (has links)
Due to an increased environmental awareness and thus, concerns over the use of fossil-based monomer for polymer production, there is an ongoing effort to find alternatives to non-renewable traditional monomers. This has ushered in the rapid growth in the development of bio-based materials such as green monomers and biodegradable polymers from vegetable and animal resources. Glycerol, as a renewable bio-based monomer, is an interesting candidate for sustainable polymer production. Glycerol is a renewable material that is a by-product of the transesterification of vegetable oils to biodiesel. Utilization of the excess glycerol derived from the growing biodiesel industry is important to oleochemical industries. The main objective of this thesis was to produce high molecular weight polyglycerol from glycerol and synthesize stimuli-responsive polyglycerol hydrogels. The work began with an investigation of the step-growth polymerization of glycerol to relatively high molecular weight polyglycerol using several catalysts. The catalytic reaction mechanisms were compared and the polymer products were fully analyzed. High molecular weight partially branched polyglycerol with multimodal molecular weight distributions was obtained. The polymerization of glycerol proceeded fastest with sulphuric acid as catalyst as indicated by the highest observed conversion of monomer along with the highest molecular weights. Theoretical models were used to predict the gel point and to calculate monomer functionality. High molecular weight polyglycerol was used to synthesize novel stimuli-responsive hydrogels. Real-time monitoring of step-growth polymerization of glycerol was investigated using in-line and off-line Attenuated Total Reflectance/Fourier Transform infrared (ATR-FTIR) technique.
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Study and Implementation of Patient Data Collection and Presentation for an eHealth ApplicationSong, Qunying, Xu, Jingjing January 2013 (has links)
This degree project is a part of information and communication technology supported self-care system for the diabetes, mainly in diabetes data collection and visualization. The report is organized in four main sections: investigation and internet search, literature review, application design and implementation, system test and evaluation. Existed applications and research studies has been compared and, a responsive web application is developed aiming at providing relevant functionalities and services regarding diabetes self-management.
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Bio-Inspired Supramolecular Hydrogels Comprising Multi-Component and/or Out-of-Equilibrium Systems / 多成分・非平衡なバイオインスパイアード超分子ヒドロゲルNakamura, Keisuke 23 March 2022 (has links)
京都大学 / 新制・課程博士 / 博士(工学) / 甲第23924号 / 工博第5011号 / 新制||工||1782(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 浜地 格, 教授 古川 修平, 教授 杉安 和憲 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
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Desenvolvimento de filmes nanoestruturados Layer-by-Layer com foco em sistemas de materiais sensíveis a estímulos. /Campos, Paula Pereira January 2018 (has links)
Orientador: Marystela Ferreira / Resumo: Neste trabalho foram desenvolvidos diferentes tipos de filmes Layer-by-Layer (LbL) sensíveis a variação de pH, temperatura, exposição a luz e presença de carboidratos, com o objetivo de criar sistemas com resposta a estímulos que podem ser aplicados na área médica e ambiental para a entrega modificada de fármacos e pesticidas. O trabalho foi dividido em três partes, sendo o primeiro focado na liberação da emodina. Foram fabricados filmes com a emodina imobilizada diretamente e outra em que o fármaco foi encapsulado nos lipossomos formados por dipalmitoil fosfatidil glicerol (DPPG) e palmitoil fosfatidil glicerol (POPG) e então intercalado com polieletrólitos. Ambos os filmes foram expostos a condições fisiológicas e liberaram a emodina por um período prolongado em função da mudança de pH e temperatura. A segunda parte do trabalho é focado na construção de filmes com um polímero baseado em espiropirano (poli(SP-R)), um composto que quando recebe luz UV é convertido para a forma aniônica merocianina (poli(MC-R)) mudando sua cor e carga superficial. O filme foi composto pelo policátion poli(alilamina hidroclorada) (PAH) formando o (PAH/poli(SP-R))n que se desprendeu do substrato pelo processo disassembly após longo tempo de exposição à luz branca. Na terceita parte do trabalho foram desenvolvidos filmes com o polímero baseado em ácido fenil borônico (PBA), que tem a capacidade de se ligar covalentemente à açucares. Foram fabricados intercalado com PVS resultando no filme (PEI/PV... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work, we developed some types of Layer-by-Layer (LbL) films sensible to pH and temperature changes, light exposition and carbohydrates solutions, with the aim of to create stimuli responsive system that can be applied to medical and environmental area to drug and pesticide modulated delivery. The work was divided in three parts, the first one is based on delivery emodin. One film was fabricated with emodin immobilized directly and other the drug was encapsulated on liposomes formed by dipalmitoyl phosphatidyl glycerol (DPPG) e palmitoyl phosphatidyl glycerol (POPG) and the carrier was intercalated with polyelectrolytes. Both systems were exposed to physiologic conditions and released the emodin for prolonged time in function of pH and temperature changes. On second part of this work it was focused on construction of film with spyropiran (SP) based polymer (poli(SP-R)). The UV irradiation over (poli(SP-R)) causes the conversion to anionic and purple merocyanine molecule (poli(MC-R)) changing the color and surface charge. The film were composed by poly(allylamine hydrochloride) (PAH) and poly(SP-R) forming the (PAH/poli(SP-R))n LbL film which disassemble after long time exposed to white light. On third part of work, films were developed with phenyl borônico acid (PBA) based polymer that has the capacity to bind covalently on sugars. The films were intercalated with PVS creating the coating (PEI/PVS)2(PBAp/PVS)n. It were prepared also a film with the pyranine (PYR), the ... (Complete abstract click electronic access below) / Doutor
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DEVELOPMENT OF NOVEL MULTI-RESPONSIVE MATERIALS CHARACTERIZED BY POTENTIAL CONTROLLED RELEASE PROPERTIESChikh Alard, Ibaa 05 December 2018 (has links) (PDF)
With the emergence of novel and more effective drug therapies, increased importance is being placed upon the methods by which these drugs are being delivered to the body. In conventional drug delivery systems, there is very little control over the release of drug. The effective concentration at the target site can be achieved by intermittent administration of grossly excessive doses, which, often results in constantly, unpredictable variations in plasma concentrations, with the risk of reaching levels below or above the therapeutic range leading to marked side effects. A plethora of formulation strategies mainly based on polymeric/lipid nanoparticles, are described in literature. Even though these systems are therapeutically advantageous in comparison to conventional systems, they remain insensitive to the changing metabolic states of the body although the symptoms of most metabolic diseases follow a rhythmic pattern.A more appropriate and effective approach of managing some of these conditions lies in the chronotherapy. This approach allows for pulsed or self-regulated drug delivery which is adjusted to the staging of biological rhythms, since the onset of certain diseases exhibits strong circadian temporal dependence. In order to reach the objective of mimicking the biophysical and biochemical processes of pathological states, many innovations in material design for drug delivery systems (DDS) that are able to release the therapeutic payload-on-demand were done to release the therapeutic agent only when it is required, according to the physiological need. The development of multidisciplinary research teams has brought huge advantages in the design, fabrication and utilization of such smart systems, especially in the pharmaceutical field. Interestingly, numerous smart polymeric materials exhibit a response to a specific stimulus. A step further, the elaboration of purpose-built monomers can give rise to compounds with tunable sensitivities or multi-stimuli responsiveness. These smart polymers demonstrate an active responsiveness to environmental (or external) signals and change their physicochemical properties as designed (e.g. conformation, solubility, shape, charge or size). As far as the stimuli are concerned, they consist of physical (e.g. temperature, ultrasound, light, electricity, magnetic or mechanical stress), chemical (e.g. pH, ionic strength) and biological signals (e.g. enzymes, biomolecules). Due to the intrapersonal variabilities which may make internal stimuli hazardous, externally controlled systems rely on externally applied stimuli that are produced by stimuli-generating devices, which results in pulsed drug delivery. This type of delivery may be rapid and allows a transient release of a determined amount of drug within a short period of time immediately after a pre-determined off-release period. A novel strategy for the formation of multi-stimuli responsive materials endowed with pH, magnetic and light sensitivity was achieved. The approach relied on the incorporation of magnetic tetrahalogenoferrate(III) anions along a polymeric backbone based on poly(2-(N,N-dimethylamino) ethyl meth-acrylate) (PDMAEMA). Starting from the same PDMAEMA, quaternized pending amine groups with various halide derivatives gave rise to magnetic materials after anion metathesis. Measuring the magnetic susceptibility of these materials exhibited that the magnetic susceptibility increased as the substituted group size decreased (become smaller) which was apparently related to the steric hindrance around the ionic pendants. Additionally, a good correlation between the magnetic susceptibility and ferric content was found. Additional experimental and theoretical Raman analyses allowed the determination of the nature of the magnetic species constituting the materials. This strategy further offers the opportunity to tailor the magnetic response through partial ammonium salt formation. In order to merge the magnetic properties of ferric-based materials with another stimuli-responsive functionality, random copolymers containing DMAEMA (D) with diazobenzene (A) unit were prepared. So, three copolymers PDA were synthesized (with targeted D/A ratios 4/6 (PDA4), 6/4 (PDA6) and 8/2 (PDA8)). Meanwhile, different degrees of amine quaternization (10, 50 and 100 %) were applied, which led to the following polymeric salts PDAX/Y where X = 4, 6, 8 (referring to the percentage of the DMAEMA unit) and Y = 10, 50 and 100 (referring to the percentage of quaternized amine groups). Finally, the aforementioned materials were converted into magnetic polymers by anion exchange. As a result, magnetic responses correlated well with amount of iron oxide in these compounds and the amount of ionic pending groups along the backbone. Moreover, the remaining tertiary amines conferred pH sensitivity to the polymers whereas the diazobenzene units ensured light responsiveness through the well-established trans-to-cis isomerization.In order to functionalize these materials in the pharmaceutical field, an intelligent delivery system was prepared. Firstly, an attempt to formulate riboflavin-5’-phosphate sodium (RPS) loaded on PDA8 microspheres was made using double emulsion evaporation method. Meanwhile, prednisolone (PRD) microspheres were prepared using s/o/w emulsion technique. Subsequently, coating systems of cochineal red tablets were developed. These tablets were coated with polymer solution (using each of three types of copolymers: PDA8, PDA6, and PDA4) until the desired percentage of the coating was achieved (10, 15, and 20 % w/w). The cumulative release profiles of cochineal red tablets coated with PDA8, PDA6, and PDA4 showed a pH-sensitive release behavior. The release in the neutral media (pH ≈ 7.0) was very slow (less than 3 % after one hour). Then, after changing the pH to 1.2, an increase in the release of cochineal was observed. Furthermore, the cumulative release of cochineal red was at the highest value for the PDA8 and the lowest for PDA4 depending on the percentage of PDMAEMA moieties. Moreover, by increasing the percentage of the coating from (10, 15 to 20 % w/w), the cumulative release of cochineal decreased. Therefore, the copolymer PDAX can be used for controlling the release of drug by changing the pH value.Finally, the cochineal tablets coated with PDA6 (10 %) showed features of light sensitivity. The release of cochineal red from coated tablets was only due to the switching in the conformational trans/cis isomerization of azobenzene moieties upon irradiation, which was confirmed by comparing the release of coated tablets with uncoated tablets upon irradiation. / Doctorat en Sciences biomédicales et pharmaceutiques (Pharmacie) / info:eu-repo/semantics/nonPublished
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RESPONSIVE IMAGES : Comparing techniques for implementing responsive images to websitesBjörnsson, Jafet Bjarkar January 2014 (has links)
This thesis explores responsive images for websites, i.e., content images that respond to users display size, pixel density and bandwidth. We look into responsive web design and how it is related to responsive images. Different responsive image techniques are discussed and various use cases for responsive images are explored along with technologies that are needed to implement responsive images. A testing website is built and responsive image techniques are applied one by one, tested and compared and its effect on the websites load time is measured. The process of implementing the techniques is described with code examples and images. The results indicate that responsive images can certainly have positive effect on loading time of a website. Weather or not responsive images should be implemented depends on how much image data the website has and how fast the Internet connection is. Websites with more images can certainly profit from using responsive image techniques, especially if only slower bandwidths are available.
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pH-responsive, redox-sensitive hollow particles for the repair of load-bearing soft tissueBird, Robert January 2012 (has links)
This thesis presents an investigation of pH-responsive, redox-sensitive poly(MMA-co- MAA) and poly(EA-co-MAA) hollow particles for the repair of load-bearing soft tissues, such as articular cartilage and the intervertebral disc. Hollow particles continue to attract major interest due to their numerous potential applications. The new method for hollow particle preparation presented in this thesis does not require the use of a colloidal template and is well suited for scaling up. Hollow particles were formed using linear poly(MMA-co-MAA) and poly(EA-co-MAA) aliphatic copolymers synthesised using free-radical chain copolymerisation performed in solution. These copolymers were dissolved in dichloromethane using methanol as a cosolvent and emulsified in water. Diffusion of the methanol into the aqueous phase prompts precipitation of the copolymer at the droplet/water interface. The more hydrophobic copolymers containing less MAA showed improved morphology compared to copolymers containing more MAA. Also, poly(EA-co-MAA) hollow particles had a more spherical morphology than poly(MMA-co-MAA) hollow particles with equivalent MAA contents. This was attributed to the lower Tg of the EA structural monomer, which resulted in more flexible particle shells. Unusually, during potentiometric titration of uncrosslinked hollow particles, the pH of the system decreased with increasing neutralisation. This behaviour is thought to be due to the unfolding of copolymer chains, exposing shielded carboxyl groups. The random structure of the copolymers is believed to be necessary for this behaviour. Crosslinked particles became swollen when the pH was increased using buffers. Concentrated dispersions formed self supporting gels, due to steric confinement, at 5 wt.%. The crosslinking process was performed by functionalising with cystamine using carbodiimide chemistry. This introduced disulphide crosslinks; which could be cleaved under reducing conditions at high pH, dissolving the gels. This ability to reduce the hollow particle shells to their constituent linear copolymer chains gives potential for natural removal from the body via extraction by the renal system. pH-triggered loading and release of a hydrophilic dye using crosslinked hollow particles was demonstrated. The similarity of the particle formation process to traditional solvent evaporation also allowed the loading of a hydrophobic dye. However, these particles were not crosslinked so release following swelling could not be investigated. Cystamine-crosslinked systems suffered from degradation due to thiol-disulphide exchange at high pH (~ pH 8). Crosslinking of one system was performed using 2-amino ethyl methacrylate (AEM). This introduced covalent, vinyl intra-shell crosslinking; which did not break down at high pH. Additional AEM was also used to allow inter-particle UVcrosslinking to form doubly crosslinked (DX) hollow-particle hydrogels. These gels did not re-disperse in buffer. To our knowledge, this is the first example of a covalent hydrogel formed from pH-responsive hollow particles. The DX gels offer improved mechanical properties compared to the singly crosslinked, physical gels. Freeze-dried samples of all of the gels produced during this study showed highly porous structures when observed using SEM. The rapid diffusion of FITC-dextran through a sample of DX gel indicates that these pores were interconnected. This is beneficial as it encourages tissue ingrowth, in addition to allowing the rapid diffusion of nutrients, oxygen and cell waste in vivo.
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Synthesis of Stimuli-responsive Hydrogels from GlycerolSalehpour, Somaieh January 2012 (has links)
Due to an increased environmental awareness and thus, concerns over the use of fossil-based monomer for polymer production, there is an ongoing effort to find alternatives to non-renewable traditional monomers. This has ushered in the rapid growth in the development of bio-based materials such as green monomers and biodegradable polymers from vegetable and animal resources. Glycerol, as a renewable bio-based monomer, is an interesting candidate for sustainable polymer production. Glycerol is a renewable material that is a by-product of the transesterification of vegetable oils to biodiesel. Utilization of the excess glycerol derived from the growing biodiesel industry is important to oleochemical industries. The main objective of this thesis was to produce high molecular weight polyglycerol from glycerol and synthesize stimuli-responsive polyglycerol hydrogels. The work began with an investigation of the step-growth polymerization of glycerol to relatively high molecular weight polyglycerol using several catalysts. The catalytic reaction mechanisms were compared and the polymer products were fully analyzed. High molecular weight partially branched polyglycerol with multimodal molecular weight distributions was obtained. The polymerization of glycerol proceeded fastest with sulphuric acid as catalyst as indicated by the highest observed conversion of monomer along with the highest molecular weights. Theoretical models were used to predict the gel point and to calculate monomer functionality. High molecular weight polyglycerol was used to synthesize novel stimuli-responsive hydrogels. Real-time monitoring of step-growth polymerization of glycerol was investigated using in-line and off-line Attenuated Total Reflectance/Fourier Transform infrared (ATR-FTIR) technique.
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