Cell encapsulation aims to treat a variety of hormone- and enzyme-deficiency disorders by immobilizing therapeutic cells within a semi-permeable protective membrane. The membrane allows for in-diffusion of oxygen and nutrients and out-diffusion of waste and therapeutic proteins while simultaneously providing protection from immune cells and antibodies. Many cell therapies aim to provide long-term treatment for diseases, and designing materials that can match the longevity is critical. Synthetic polymers offer an attractive route to long-term encapsulation due to their tunable degradability and the ease of incorporating reactive moieties for covalent crosslinking. The primary goal of the work presented in this thesis was the development of non-degradable covalently crosslinked hydrogels formed by mutually reactive polymers for use as cell immobilizing platforms. Due to research showing that polycations incite immune responses in vivo this project aimed to avoid the use of polycations entirely. The covalent crosslinking occurs in the presence of cells, making it essential to select reactions that do not require toxic catalysts or form offensive by-products. Diels-Alder and thiol-ene Michael Addition click reactions were chosen due to their proven cytocompatibility and modular nature. In chapters 2 and 3, poly(methyl vinyl ether-alt-maleic anhydride) (PMMAn) was functionalized with furfurylamine (FFA) and N-2-(aminoethyl)maleimide (MAL) to form PMM-FFA and PMM-MAL, Diels-Alder reactive furan- and maleimide-bearing pendant polymers. Aqueous solutions of the polymers form bulk gels at higher concentrations (>5% w/v) and the chemical and physical properties of the gels were investigated and found to be highly tunable, with promise for use in controlled drug delivery applications. Alginate-templated matrix beads were also prepared at significantly lower polymer loading percentages (0.5 – 1.5% w/v each) and at physiological pH, and properties such as swellability and permeability were explored. This work demonstrates the first use of Diels-Alder crosslinking to reinforce alginate beads, and the matrix beads were found to have good initial cell viability post-encapsulation with 3T3 cells. In chapter 4, PMMAn was functionalized with cysteamine vinyl sulfone (CVS) to form PMM-CVS, a vinyl sulfone-bearing pendant polymer, and aqueous solutions were mixed with equimolar PEG-dithiol to form bulk hydrogels at concentrations between 2.5 and 7.5% w/v PMM-CVS. Thiol-ene crosslinking allowed for much more rapid gelation compared to the Diels-Alder system. Physical and chemical properties of the gels were explored, and excellent cytocompatibility of the crosslinking reaction was demonstrated. The ability to rapidly post-functionalize the gels in a step-wise fashion offers a versatile route to post-modification with various molecules. In chapter 5, PMMAn was functionalized with 2-pyridylthio cysteamine (SPy) to form PMM-SPy, a protected thiol. Alginate-templated matrix beads containing PMM-CVS and PMM-SPy were treated with TCEP to deprotect the thiol, allowing covalent crosslinking to occur in a controlled manner. Physical and chemical properties of the beads were explored in detail and the system was found to be highly tunable. / Thesis / Doctor of Philosophy (PhD) / Cell encapsulation aims to treat various hormone- and enzyme-deficiency disorders such as diabetes mellitus by encapsulating cells within a protective membrane that permits the in-diffusion of oxygen and nutrients and the outward diffusion of waste and therapeutic proteins, such as insulin. The membrane must also protect the encapsulated cells from the immune system. The primary goal of this project was to design polymeric materials for use in cell encapsulation. A series of mutually reactive polymers were developed, and the resulting polymeric hydrogels were characterized for suitability in biomedical applications by exploring properties such as swelling, stiffness, porosity and cytocompatibility. The materials were found to have tunable physical properties, and good cytocompatibility, showing promise for future use in cell encapsulation.

Yes / The possibility of separating the topographical and chemical information in a polymer nano-composite using low-voltage SEM imaging is demonstrated, when images are acquired with a Concentric Backscattered (CBS) detector. This separation of chemical and topographical information is based on the different angular distribution of electron scattering which were calculated using a Monte Carlo simulation. The simulation based on angular restricted detection was applied to a semi-branched PNIPAM/PEGDA interpenetration network for which a linear relationship of topography SEM contrast and feature height data was observed. / EPSRC

Polysaccharide-decorated complexation hydrogels were investigated for use as oral insulin delivery systems. Several different polysaccharide modifications of poly(methacrylic acid-grafted-ethylene glycol) hydrogels were developed using dextran and pullulan. Polymerizable groups were added to the polysaccharides, dextran and pullulan, by methacrylation. These macromers were then copolymerized with methacrylic and poly(ethylene glycol) to form P(MAA-g-EG-co-Dextran) and P(MAA-g-EG-co-Pullulan) gels using a UV-initiated free radical polymerization. The synthesis of these materials was confirmed using Fourier transform-infrared spectroscopy. The pH-responsive swelling of these systems was investigated using dynamic and equilibrium swelling measurements. Swelling of polysaccharide-modified hydrogels occurred with increasing pH. In acidic conditions, these materials were in a collapsed state while in neutral conditions these materials were swollen. The ability to load insulin into these hydrogels using was demonstrated with loading efficiencies as high as 88% were observed for P(MAA-g-EG-co-Dextran 6000) hydrogel microparticles. Almost zero release of insulin occurred in acidic conditions while an increase in pH was shown to trigger release. The use of dextran and pullulan-modified complexation hydrogels for oral delivery applications was investigated using in vitro cellular viability assays and mucoadhesion experiments. These systems were shown to cause little cytotoxicity to an intestinal epithelium Caco-2 cell model over a range of concentrations as high as 1 mg/ml. The adherence of polysaccharide-modified hydrogels to reconstitituted mucin gels was quantified with the P(MAA-g-EG-co-Dextran 6000) performing the best. Further evaluation of polysaccharide-modified complexation hydrogels for oral insulin delivery was evaluated through in vitro insulin drug transport studies using a mucus-producing Caco-2/HT29-MTX co-culture model. The results showed that the P(MAA-g-EG-co-Dextran 6000) allowed transport of insulin across the cell monolayers and did not adversely affect the integrity of the epithelial monolayer. / text

The pursuit of optimizing soft contact lens performance has been extensive, given that approximately over 140 million contact lens wearers globally seek the convenience and visual acuity they offer. However, a persistent challenge is the prevalence of ocular dryness and discomfort experienced by almost half of these wearers, particularly towards the end of the day. The occurrence of these symptoms is primarily attributed to diminished compatibility between the contact lens and the ocular surface leading to contact lens discontinuation. A promising method to improve overall contact lens properties is to incorporate novel monomers with unique functionalities during the initial manufacturing stage. Monomers bearing ionic functional groups have been extensively explored to improve bulk and surface properties of biomaterials. The incorporation of cationic and zwitterionic monomers in the fabrication of hydrogel materials has shown to have anti-fouling and anti-bacterial properties and improved surface wetting. In this work, a series of novel materials using cationic and zwitterionic monomers were prepared and their impact on bulk and surface properties of contact lens materials were assessed. Furthermore, the impact of a novel hydrophilic silicone-based monomer bearing zwitterionic phosphocholine was investigated for water-based extraction, physiochemical and structural stability in candidate contact lens materials. In Chapter 2, a library of eleven positively charged (cationic) and electrically neutral with both positive and negative charges (zwitterionic) functional methacrylate ester monomers was produced through the reaction of 2-(dimethylamino) ethyl methacrylate (DMAEMA) with different alkyl halides. The Menshutkin reaction was carried out with a high level of success, resulting in moderate to high yields of the desired monomers. The monomers were purified and characterized using analytical techniques, including 1H-NMR (proton nuclear magnetic resonance), 13C-NMR (carbon-13 nuclear magnetic resonance), LCMS (liquid chromatography-mass spectrometry), and XRD (X-ray diffraction). Six monomers were chosen based on controlled end group hydrophilicity and chain length to investigate the relationship between chemical structure and overall performance in hydrogel and silicone hydrogel systems. In Chapters 3 and 4, model hydrogel and silicone hydrogel systems via UV free-radical polymerization at increasing input concentrations (10 and 20 wt%) were manufactured using the monomers and HEMA (hydrogel) or HEMA + SIGMA (silicone hydrogel). The novel materials demonstrated an increase in bulk equilibrium water content, reduced contact angle and nonspecific lysozyme and albumin adsorption, while maintaining optical transparency at higher than 90%. In vitro studies demonstrated the ionically charged hydrogel materials did not show any toxicity to human corneal epithelial cells. In Chapter 5, a super hydrophilic silicone-based SIGMAPC monomer was synthesized using the siloxane functional monomer (SIGMA) as the main building block. The introduction of the novel hydrophilic SIGMAPC monomer led to significant improvements in the silicone materials. The hydrogels showed increased water content and reduced water contact angles, indicating their superior hydrophilicity. Moreover, the rate of dehydration was decreased, and the nonspecific deposition of lysozyme and albumin was minimized. Importantly, the optical transparency of the hydrogel silicone remained above 90%. Based on these findings, it can be concluded that the siloxane-based monomer bearing a zwitterionic phosphocholine has great potential for applications in contact lenses, given its desirable properties and biocompatibility. Furthermore, in Chapter 6, 31P-NMR and weight extraction analysis showed model contact lens materials made with SIGMAPC were effectively extracted in aqueous media at elevated temperature. Candidate materials showed good dimensional and optical stability pre- and post-thermal sterilization and over 6-month storage period. / Thesis / Doctor of Philosophy (PhD)

No description available.

Polymer gels have been studied extensively due to their ability to simulate biological tissues and to swell or collapse reversibly in response to external stimuli. This work presents a variety of studies using poly-N-isopropylacrylamide (PNIPA) hydrogels. The projects have been carried out both in the lab of Dr. Zhibing Hu and in collaboration with others outside of UNT: (1) an analysis of the swelling kinetics of microgel spherical shells prepared using a novel design of microfluidic devices; (2) a comparison of the drug-release rates between nanoparticle structures having either core or core-with-shell (core-shell) designs; (3) an investigation into the thermodynamics of swelling for microgels of exceedingly small size.

Magnetic particles offer attractive features, so its development in a wide range of disciplines, including medical applications, has been very fruitful. As a result of the special physical properties of magnetic nanoparticles, many potential applications are made available in biomedicine. The most important feature of these particles is its magnetic forces, and it has been utilized in applications such as magnetic separation, drug delivery, hyperthermia and magnetic resonance imaging contrast agent. The important properties of magnetic particles for biomedical applications are nontoxicity, biocompatiblilty, injectability, and high-level accumulation in the target tissue or organ to two most important property among those mentioned above are nontoxicity and biocompatiblilty for available clinical trials. Some researchers have used polymers or polysaccharides coating on these surface of the magnetic material to improve the material's nontoxicity and biocompatiblilty. Common materials are dextran, polyethylene glycol, polyvinyl alcohol, starch and chitin and so on. We embedd Fe3O4 magnetic nanoparticles into agar hydrogels in the experiment, then made into powder by drying and grinding, using XRD, FTIR, TEM, SQUID, TGA and zeta potential identification of material properties. We examined its toxicity and the possibility for large scale production. This method can make use of simple and inexpensive way to mass-produce synthetic these biocompatible magnetic materials.

As one of the few 3D microfabrication techniques available to researchers, multiphoton lithography (MPL) has generated considerable interest in the scientific community. By allowing researchers to localize photochemistry to a femtoliter volume, MPL has permitted the fabrication of intricate, 3D microstructures from a range of materials, including protein hydrogels. MPL can be used to fabricate functional hydrogels on the scale of 100 μm, with features on the order of 1 μm. This dissertation examines existing MPL techniques to discover ways in which current processes can be modified to produce hydrogel products that are more useful for biomedical applications like tissue engineering. A new material is introduced that enables the fabrication of fully unconstrained hydrogel microstructures. In this context, A structure can be classified as “unconstrained” when it is free to translate and rotate without hindrance in three dimensions, and is not attached to the substrate or any other structure. New processes are demonstrated that permit the fabrication of larger MPL hydrogels without sacrificing feature resolution. This allows the fabrication of millimeter-scale, high aspect ratio structures with features smaller than 10 μm. Methods are described for tuning and measuring the mechanical properties of MPL-fabricated hydrogels, and ways of tuning the functional properties of the hydrogels are also examined. / text

Abstract: Stimuli-responsive polymers and their assemblies, such as micelles, block copolymer (BCP) vesicles and hydrogels, can be dissociated or become relatively permeable upon excitation with a stimulus. This stimuli-responsive feature has made them very attractive carriers or vectors in drug delivery applications, since it is possible to realize controllable release of payloads from these systems by using, for example, light as a trigger enabling remote activation, and spatial and temporal control of the release. The research work presented in this thesis consists of two parts. The first part is focused on the design, synthesis and study of several novel photoresponsive polymers forming micelles, vesicles and hydrogels, as well as their exploitation for potential drug delivery applications. The second part concerns a study of the use of a different stimulus, namely, dissolved carbon dioxide (CO2). A general approach of using dissolved gases to manipulate the structural and morphological transition of BCP vesicles is described. The core of this thesis is five publications resulting from different projects that constitute the research work accomplished in our studies. In the first project, we developed a new strategy to prepare photo-dissociable BCP vesicles. By synthesizing a novel photoresponsive BCP with spiropyran and controlling the preparation conditions, a kinetically stable BCP vesicle was obtained at high pH (pH=8) due to the glassy membrane. Upon UV irradiation, fast BCP vesicle dissociation was achieved through a cascade of events triggered by the photoinduced isomerization from neutral spiropyran to charged merocyanine in the membrane. In second project, we demonstrated a novel strategy to tune the permeability of BCP vesicle membrane by taking advantage of the photoinduced liquid crystal (LC) order-disorder transition occurring inside the membrane. To this end, we designed and synthesized two series of amphiphilic BCPs of which the hydrophobic block is a side-chain liquid crystalline polymer bearing a small amount of azobenzene groups. Both BCPs could form giant BCP vesicles in aqueous solutions, facilitating their direct observation by optical microscopy. From polarized optical measurement, it was found that a photoinduced LC order—disorder transition could occur inside the vesicle membrane in aqueous solutions. This photoinduced transition has a softening effect on the membrane similar to that caused by good organic solvents. By using a fluorescent probe, we found that this photoinduced softening effect could increase the membrane permeability to proton diffusion. In the third project, we demonstrated a possibly universal solution to solve the problem of requiring UV or visible light excitation to trigger the response of many photosensitive materials developed for biomedical applications. The strategy consists in disrupting photoresponsive BCP micelles by using near-infrared (NIR) light excitation of upconverting nanoparticles (UCNPs). By encapsulating UCNPs into micelles of a photoresponsive BCP containing o-nitrobenzyl groups, UV photons emitted from UCNPs upon 980 nm NIR light excitation using a continuous-wave diode laser can be absorbed by o-nitrobenzyl groups in the micelle core, activating their photocleavage reaction and resulting in micelle dissociation and release of co-loaded hydrophobic compounds. The idea of using UCNPs as a nanoscale UV or visible light source upon NIR light excitation to activate photoreactions in photosensitive materials is of great significance. The strategy is general and can be applied to many photosensitive polymeric materials whose potential for biomedical applications is limited due to the wavelength issue. In the fourth project, we further investigated the generality of using UCNPs to circumvent the wavelength problem of most photoresponsive polymer systems. We extended the application of the approach to photoresponsive hydrogels. UCNPs were loaded into a hydrogel whose gel-sol transition requires UV light-induced breaking of the network structure. Upon 980 nm laser irradiation, the gel-sol transition was achieved by UV light emitted from UCNPs. This feature allowed us to realize NIR light-triggered release of large, inactive biomacromolecules (protein and enzyme) entrapped in the hydrogel into aqueous solution "on demand", where their bioactivity is recovered. The last project dealt with the use of CO2 as a smart trigger to switch a specific property or function of stimuli-responsive polymers. We put forward a general way to prepare CO2-responsive BCP vesicles by using the commercially available poly(N,N',-diethylaminoethyl methacrylate) (PDEAEMA) as the hydrophobic block forming the vesicle membrane. We showed that vesicles can either be completely dissociated (with uncrosslinked PDEAEMA) or undergo reversible volume expansion up to 2100% (with slightly crosslinked PDEAEMA) upon introduction of the gas into the solution. The drastic changes induced by dissolved CO2 are unprecedented. This study is a new demonstration of designing easily accessible CO2-responsive polymers and opens perspectives for valorizing CO2 in polymer and material sciences.//Résumé: Les polymères répondant aux stimuli et leurs assemblages sous forme de micelles, de vésicules ou d'hydrogels, peuvent être dissociés ou devenir relativement perméables des suites de l'application d'une excitation. Cette fonctionnalité stimuli-réponse les rend très attrayants en tant que transporteurs ou comme vecteurs pour le relargage ciblé de médicaments. Elle permet de réaliser la libération contrôlée des charges utiles de ces systèmes en utilisant, par exemple, la lumière comme un déclencheur permettant l'activation à distance, et le contrôle temporel de la libération. Les travaux présentés dans cette thèse sont regroupés en deux parties. La première décrit la conception, la synthèse et l'étude de nouveaux polymères photosensibles formant des micelles, des vésicules et des hydrogels, ainsi que leur exploitation pour largage de molécules modélisant des agents thérapeutiques (i.e., médicaments). La seconde partie porte sur une étude de l'utilisation d'un stimulus différent, à savoir le dioxyde de carbone (CO2 ). Une approche générale basée sur l'utilisation de gaz afin de manipuler la transition structurale et morphologique des vésicules est décrite. Le noyau de cette thèse est constitué de cinq publications issues de différents projets qui sont représentatifs des travaux de recherche accomplis dans ces études de doctorat. Dans le premier projet, nous avons développé une nouvelle stratégie pour préparer des vésicules photo-dégradables. La synthèse d'un nouveau copolymère photosensible comprenant des unités spiropyranes et le contrôle des conditions de préparation a permis la préparation de vésicules cinétiquement stables à un pH élevé (pH = 8 ) en raison du caractère vitreux de la membrane. Lors d'irradiations UV, une dissociation rapide des vésicules a été accomplie grâce à une cascade d'événements déclenchés par l'isomérisation photo-induite de la spiropyrane (neutre) en mérocyanine (chargée) au sein de leur membrane. Dans le second projet, nous avons démontré une nouvelle stratégie pour moduler la perméabilité de la membrane des vésicules en exploitant une transition liquide-cristalline photo-induite afin d'accroître le désordre au sein de la membrane. À cet effet, nous avons conclu et synthétisé deux séries de copolymères à blocs amphiphiles dont la séquence hydrophobe est un polymère liquide cristallin à chaîne latérale portant une petite quantité de groupes azobenzène. Les deux copolymères furent utilisés pour préparer des vésicules géantes en solutions aqueuses, ce qui a permis leur observation directe par microscopie optique. De plus, une transition ordre-désordre photo-induite a été observée à l'intérieur de la membrane liquide cristalline des vésicules par microscopie à lumière polarisée. Cette transition photo-induite a un effet assouplissant sur la membrane semblable à celle causée par de bons solvants organiques. En utilisant une sonde fluorescente, nous avons observé que cet accroissement de la souplesse de la membrane polymère causait l'augmentation de la perméabilité de la membrane à la diffusion de protons. Dans le troisième projet, nous avons démontré une solution possiblement universelle permettant de résoudre le problème résultant de la nécessité d'utiliser une excitation lumineuse UV ou visible comme stimulus de nombreux matériaux photosensibles développés pour des applications biomédicales. La stratégie consiste à irradier indirectement des micelles de copolymères photosensibles par le biais de la conversion ascendante de la proche infrarouge par des nanoparticules. Les photons UV émis par ces nanoparticules encapsulées à l'intérieur des micelles et irradiées en utilisant une diode laser à onde continue de 980nm sont absorbés par les groupes o-nitrobenzyle dont est constitué le copolymère photosensible, conduisant à l'activation de leur réaction de photo-clivage, à la dissociation des micelles et finalement, à la libération de composés hydrophobes. L'idée d'utiliser la conversion ascendante issue de nanoparticules irradiées dans la proche infrarouge comme source lumineuse nanoscopique dans l'UV ou le visible pour activer des réactions photochimiques dans des matériaux photosensibles est d'une grande importance. La stratégie est générale et peut être appliquée à de nombreux matériaux polymères photosensibles dont le potentiel pour des applications biomédicales est présentement limité en raison de la faible pénétration des rayonnements UV et visible dans les tissus. Dans le quatrième projet, nous avons étudié davantage la généralité de l'utilisation de la conversion ascendante par des nanoparticules afin de contourner le problème de longueur d'onde pour l'activation de la plupart des systèmes polymères photosensibles. Nous avons ainsi étendu l'application de l'approche à des hydrogels photosensibles. Les nanoparticules ont été chargées au sein d'un hydrogel dont la transition gel-sol nécessite de la lumière UV afin d'induire la rupture de la structure du réseau. Sous irradiation à l'aide d'une diode laser à 980 nm, la transition gel-sol a été stimulée par la lumière ultraviolette émise par la conversion ascendante issue des nanoparticules. Cette "fonction" nous a permis de déclencher, par irradiation dans l'infrarouge proche qui pénètre beaucoup plus profondément dans les tissus biologiques, la libération "à la demande" de macromolécules biologiques (protéines et enzymes), inactives lorsque piégées dans l'hydrogel, en solution aqueuse où leur activité est restaurée. Le dernier projet porte sur l'utilisation du CO2 comme un déclencheur intelligent pour activer une propriété ou une fonction spécifique de polymères dont la sensibilité à ce stimulus est programmée au sein de leur structure moléculaire. Nous avons proposé une façon générale pour préparer des vésicules copolymères sensibles au CO2 par l'inclusion d'un bloc hydrophobe de poly (N, N ',-diéthylaminoéthylmethacrylate) (PDEAEMA) disponible commercialement et formant la membrane de la vésicule. On a montré que ces vésicules peuvent être soit complètement dissociées (lorsque le PDEAEMA n'est pas réticulé) ou encore subir une expansion de volume réversible atteignant 2100% (lorsque le PDEAEMA est faiblement réticulé) en réponse à l'introduction de CO2 dissout dans la solution de vésicules. Les changements radicaux induits par la modulation de la concentration du CO2 dissout sont sans précédent. Cette étude est une nouvelle démonstration d'une conception facilement accessible de polymères dont la structure moléculaire est programmée pour répondre à cette modulation dans la concentration du CO2 dissout et ouvre des perspectives de valorisation du CO2 en sciences des matériaux et des polymères. [symboles non conformes]

No description available.