Hydrogels are three-dimension networks of water-soluble polymer chains and have attracted interest in biomedical engineering, targeted drug delivery, tissue engineering, and regenerative medicine due to their ability to retain water coupled with their highly tunable physicochemical and biological properties. In the specific context of wound care, hydrogels can both maintain high wound hydration as well as absorb and manage wound exudate, both of which are major challenges in wound care. Hydrogel wound dressings can simultaneously deliver medication directly to the wound to suppress or treat infections, including antibiotic-resistant strains such as Methicillin-resistant S. aureus (MRSA). This thesis develops two wound care products that can address challenges in the selection and delivery of drugs to treat antibiotic-resistant strain infections: (1) in situ-gelling poly(oligoethylene glycol methacrylate) (POEGMA) hydrogel wound dressings containing self-assembled nanoparticles encapsulated with fusidic acid; and (2) an in situ calcium-crosslinked alginate scaffold produced using pressurized gas expanded liquids (PGX) technology impregnated with fusidic acid or tigecycline using supercritical adsorptive precipitation (sc-AP). The POEGMA hydrogel wound dressings helped supress MRSA infection and prevent systemic infection during the course of treatment, facilitating a 1-2 fold decrease in bacterial load in the wound bed. The sc-AP technology was shown to be compatible with loading clinically-relevant doses of both antimicrobial compounds, while the resulting wound dressings were effective in treating MRSA wound infections. In case of tigecycline loaded alginate scaffolds, the infection was completely cleared. In tissue engineering applications, injectable macroporous hydrogels are particularly limited by two factors: (1) their need for invasive administration, typically implantation; and (2) their generally weak mechanics. In the first case, reports of injectable hydrogels often involve toxic compounds or by-products that result in loss of cell viability. This thesis addresses this challenge by design and development of a POEGMA-based macroporous hydrogel scaffold based on a novel, non-cytotoxic pore forming emulsion based on perfluorocarbons. Use of the pore-forming emulsion significantly improved cell viability in vitro 14 days after injection and was well tolerated in vivo with minimal to no inflammatory response. In the second case, an interpenetrating “hard-soft” nanofibrous hydrogel network was fabricated by co-electrospinning POEGMA with poly(caprolactone) (PCL). The PCL phase significantly enhanced the mechanical properties of the electrospun POEGMA hydrogel scaffold making handling and manipulating the scaffolds possible, while the presence of the POEGMA phase significantly improved the biological properties of PCL scaffolds in terms of supporting significantly enhanced cell proliferation and delayed bacterial adhesion. Collectively, the advances made in this work address key challenges in the application of hydrogels in tissue engineering and wound care, with future potential to be applied to solve practical clinical challenges. / Dissertation / Doctor of Philosophy (PhD) / Hydrogels have been studied in various applications like targeted drug delivery, tissue engineering, regenerative medicine, and medical devices due to their tunable nature and their capacity to retain water. In many of these applications the pore size and porosity are the key to the performance of a hydrogel in a given application. In particular, the rate at which nutrients or wastes can move through a hydrogel, the stiffness of a hydrogel, and the interactions of a hydrogel with cells are all strongly dependent on the porosity of a hydrogel. Therefore, many techniques have been developed to produce hydrogels with well-defined pore sizes, in particular “macroporous” hydrogels that have larger pores at or above the size of a cell. However, the typical techniques used to make such hydrogels often require additives or manufacturing steps that make them challenging to implement in different applications. This thesis addresses challenges in the fabrication of controllable porosity of hydrogels for applications in wound care (including the treatment of antibiotic-resistant infected wounds) and regenerative medicine, in the latter case enabling minimally invasive injection of a macroporous hydrogel as well as enhancing its mechanics to better mimic native tissues. Each of these solutions aims to bring effective novel treatments to patients, offering alternative therapies for existing challenges in healthcare.

Three-dimensional macroporous structures (‘opals’ and ‘inverse opals’) can be produced by colloidal crystal templating, one of the most intensively studied areas in materials science today. There are several potential advantages of lithium-ion battery electrodes based on inverse opal structures. High electrode surface, easier electrolyte access to the bulk of electrode and reduced lithium diffusion lengths allow higher discharge rates. Highly open structures provide for better mechanical stability to volume swings during cycling. Silicon is one of the most promising anode materials for lithium-ion batteries. Its theoretical capacity exceeds capacities of all other materials besides metallic lithium. Silicon is abundant, cheap, and its use would allow for incorporation of microbattery production into the semiconductor manufacturing. Performance of silicon is restricted mainly by large volume changes during cycling. The objective of this work was to investigate how the inverse opal structures influence the performance of silicon electrodes. Several types of silicon-based inverse opal films were synthesised, and their electrochemical performance was studied. Amorphous silicon inverse opals were fabricated via chemical vapour deposition and characterised by various techniques. Galvanostatic cycling of these materials confirmed the feasibility of the approach taken, since the electrodes demonstrated high capacities and decent capacity retentions. The rate performance of amorphous silicon inverse opals was unsatisfactory due to low conductivity of silicon. The conductivity of silicon inverse opals was improved by crystallisation. Nanocrystalline silicon inverse opals demonstrated much better rate capabilities, but the capacities faded to zero after several cycles. Silicon-carbon composite inverse opal materials were synthesised by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals in an attempt to further increase conductivity and achieve mechanical stabilisation of the structures. The amount of carbon deposited proved to be insufficient to stabilise the structures, and silicon-carbon composites demonstrated unsatisfactory electrochemical behaviour. Carbon inverse opals were coated with amorphous silicon producing another type of macroporous composites. These electrodes demonstrated significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increased the material conductivity, but also resulted in lower silicon pulverisation during cycling.

Study of Ordered Macroporous Polymer Films by Templating Breath Figures Lulu Song 193 pages Directed by Dr. Mohan Srinivasarao Macroporous films with highly ordered pore patterns have many potential applications. Some examples include microstructured electrode surfaces, photonic band gap materials and filters for cell sorting and bio-interfaces. In this dissertation we discuss a moist-casting method to prepare hexagonally-ordered macroporous films with pore sizes in the range of sub-micron to several microns, where condensed water droplets (breath figures) work as templates. Compared with other templating methods, this one is fast and simple. Well-ordered porous films can be obtained in tens of seconds and the pore size can be easily tailored and dynamically controlled by adjusting the casting conditions. More importantly, there is no need to remove the templates; water droplets just evaporate when the casting processes are finished. This study was carried out with the intention of characterizing the structures, understanding film-formation processes and exploring special properties and possible applications. For the structural characterization, film morphology was studied in detail by normal optical microscopy and laser scanning confocal microscopy (LSCM). Several interesting features have been revealed. Meanwhile, the degree of the order of the porous structures were characterized both in real space via Voronoi diagram and bond-orientational correlation function, and in reciprocal space via Fraunhofer diffraction pattern. To further understand the mechanism, the evaporation of the polymer solutions during the film formation was studied by monitoring their mass over time. Besides, the evolution of breath figures formed on the evaporating polymer solutions was in-situ recorded via a high-speed camera coupled to an optical microscope. Combined with the information on the film structures obtained via LSCM, explanations for some detailed features have been attempted. Wetting property of these films was studied in some detail. The films exhibited lotus effect, mimicking natural non-wetting surfaces. To improve the solvent stability and mechanical properties of the macroporous films for possible applications, crosslinking of the polymer matrix was tried by heating. Crosslinked structures with hexagonal arrays of cone-like air holes were obtained, which might find use as micron-sized beakers for small-quantity analysis.

Three-dimensional macroporous structures (‘opals’ and ‘inverse opals’) can be produced by colloidal crystal templating, one of the most intensively studied areas in materials science today. There are several potential advantages of lithium-ion battery electrodes based on inverse opal structures. High electrode surface, easier electrolyte access to the bulk of electrode and reduced lithium diffusion lengths allow higher discharge rates. Highly open structures provide for better mechanical stability to volume swings during cycling. Silicon is one of the most promising anode materials for lithium-ion batteries. Its theoretical capacity exceeds capacities of all other materials besides metallic lithium. Silicon is abundant, cheap, and its use would allow for incorporation of microbattery production into the semiconductor manufacturing. Performance of silicon is restricted mainly by large volume changes during cycling. The objective of this work was to investigate how the inverse opal structures influence the performance of silicon electrodes. Several types of silicon-based inverse opal films were synthesised, and their electrochemical performance was studied. Amorphous silicon inverse opals were fabricated via chemical vapour deposition and characterised by various techniques. Galvanostatic cycling of these materials confirmed the feasibility of the approach taken, since the electrodes demonstrated high capacities and decent capacity retentions. The rate performance of amorphous silicon inverse opals was unsatisfactory due to low conductivity of silicon. The conductivity of silicon inverse opals was improved by crystallisation. Nanocrystalline silicon inverse opals demonstrated much better rate capabilities, but the capacities faded to zero after several cycles. Silicon-carbon composite inverse opal materials were synthesised by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals in an attempt to further increase conductivity and achieve mechanical stabilisation of the structures. The amount of carbon deposited proved to be insufficient to stabilise the structures, and silicon-carbon composites demonstrated unsatisfactory electrochemical behaviour. Carbon inverse opals were coated with amorphous silicon producing another type of macroporous composites. These electrodes demonstrated significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increased the material conductivity, but also resulted in lower silicon pulverisation during cycling.

La technologie supercondensateur a fait l'objet d'un grand intérêt ces dernières années. Cependant, tandis qu'une grande attention a été donnée aux électrodes, aux électrolytes et aux électrolytes de polymère gélifiée, peu d'études ont été centrées sur l'amélioration des séparateurs macroporeux. Dans le cadre du projet SEPBATT/DURAMAT, les séparateurs macroporeux à base de poly(fluorure de vinylidène) (PVdF) ont été préparés par inversion de phase, pour les supercondensateurs. Nos membranes présentent également une bonne stabilité thermique, en revanche leurs propriétés mécaniques sont significativement plus faibles que celles des membranes commerciales. De plus le séparateur PVdF de porosité 80% rempli par l'électrolyte à base d'AN atteint, à 25°C, 18mS/cm, tandis que dans les mêmes conditions mais avec le séparateur commercial en cellulose, la conductivité n'atteint que 10 mS/cm. Ce travail a été complété par l'étude de techniques de renforcement (addition de composites, réticulation par l'irradiation) appliquées aux membranes précédemment préparées, pour augmenter leur tenue mécanique. Ces membranes ont montré un renforcement des propriétés mécaniques sans nuire aux propriétés de conduction ionique (15 mS/cm). / Abstract In recent years a strong interest has been devoted to supercapacitor technology. However, while great attention has been paid to electrodes, electrolytes and gel polymer electrolytes, only few reports have been dedicated to macroporous separators. Hereby, in the frame of project SEPBATT/DURAMAT, macroporous poly(vinylidene fluoride) (PVdF) based separators were prepared by phase inversion technique for applications of supercapacitors. Their mechanical properties are relatively lower than those of commercial membranes nevertheless such membranes exhibit good thermal stability. Whereas commercial cellulose based separators filled with tetraethyl ammonium tetrafluoroborate + CH3CN electrolyte show 10 mS/cm (at 25°C), our PVdF macroporous separators exhibit significantly higher conductivity (18 mS/cm) under the same conditions. This study was completed with application of reinforcement techniques (addition of composites, crosslinking by irradiation) on to previously prepared membranes in order to increase their mechanical strength. Reinforced membranes showed good high mechanical strength whereas the ionic conductivity is almost maintained (15mS/cm).

No description available.

Microbial electrosynthesis (MES) is an emerging biotechnology platform for the conversion of CO2 feedstocks into value-added chemical commodities. In MES, microbial catalysts use the cathode (electrons/ H2) as a sole source of energy for the reduction of CO2. Integrating MES technology with renewable energy sources, such as solar power, to convert CO2 to storable chemicals is an example of a perfect circular economy and a sustainable climate change mitigation strategy. However, many knowledge gaps need to be addressed to scale-up MES as an economically viable chemical production process. Therefore, different in-depth approaches were tested in this dissertation by optimizing the cathode architecture and exploring the saline application to enhance MES performance. A balance between various bio-physicochemical phenomena at the MES cathode, i.e., the three-phase interface between CO2 gas, cathodic-biofilm, and electrolyte, is desirable for efficient microbial electrochemical CO2 capture and utilization. To address this problem, this thesis investigated alternatives to the benchmark carbonbased plane cathode by applying a dual-functioning (cathode as well as a CO2 gas-transfer membrane) electrode architecture on MES performance. High Faradaic efficiencies for CO2 reduction were achieved with this novel cathode architecture. This hollow-fiber electrode architecture was also applied to MES operation in saline conditions (i.e., Saline-MES). Because seawater potentially acts as an endless source of saline electrolyte, and its high electrical conductivity useful to minimize the concentration overpotential losses occurs in MES. However, exploring robust halophilic microbial catalysts with high selectivity towards CO2 reduction to the desired end product(s) is necessary to develop the saline-MES process. Therefore, this thesis investigated natural saline habitats with hyper (Red sea brine pool) and moderate salinity (mangrove and salt marsh sediment) as a source of inoculum. Emphasis was placed on improving new knowledge in the direction of halophilic CO2 reducing communities enrichment using cathode selective pressure in the saline-MES. The fundamental insights demonstrated in this dissertation are useful for further development of MES technology, to bring MES one step closer to full-scale applications, for overcoming the bottlenecks associated with reactor scaling-up related to cathode architecture, strategies for the enrichment of halophilic CO2 reducing microbial communities, and saline-MES process optimization.

The development of structured macroporous hydrogels are of great interest in many industries due to their high permeabilities, large surface areas and large pore volumes. In drug delivery and wound healing applications, these macropores may theoretically be utilized as large drug reservoirs to deliver anti-inflammatory drugs to a wound site, while simultaneously absorbing exudate and maintaining a hydrated environment in which the wound may heal. However, current methods of generating macroporous structured hydrogels are low-throughput, expensive, and require the use of organic solvents, salts, and other additives that are difficult to remove from the crosslinked hydrogel scaffold. In contrast, the Pressurized Gas eXpanded liquid (PGX) processing technology, patented by the University of Alberta and licensed for all industrial applications by Ceapro Inc., has been shown to generate purified and exfoliated biopolymer scaffolds in a less expensive and more efficient way. Herein, the tunability of the PGX processing method was investigated in depth, varying solvent/anti-solvent ratios, nozzle mixing volume, polymer molecular weight, and polymer concentration to examine the resulting effects on produced polymer morphologies. PGX-processed chitosan and alginate scaffolds were stabilized as bulk hydrogels through post-processing crosslinking methods using anti-solvents, solid-state chemistries, and/or rapid gelation kinetics. The mechanical strength, swelling/degradation kinetics, affinity for protein uptake, and cytotoxicity of these stabilized scaffolds were subsequently examined and compared to hydrogels produced without the use of PGX processing. Furthermore, in situ crosslinking methods were explored, in which alginate and poly(oligoethylene glycol methacrylate) polymers were shown to form stable aerogels during the standard PGX processing method. Finally, the PGX apparatus was reconfigured to enable the impregnation of a model hydrophobic drug into pre-processed polymer scaffolds via circulation of supercritical CO2. The total loading was calculated and the release kinetics from loaded-scaffolds examined. In conclusion, this work outlines a novel method of creating structured macroporous hydrogels from PGX processed biopolymers with the potential to provide improved drug loadings and sustained release profiles. It is expected that this work will provide a basis for a great deal of research into the further stabilization of scaffolds for use in other applications, the investigation of a larger range of bioactive molecules for impregnation and release, and the exploration of PGX hydrogel scaffolds for in vivo wound healing. / Thesis / Master of Applied Science (MASc)

La "cryopolymérisation" permet d'obtenir des gels de polymère macroporeux ou "cryogels". Cette méthode a été utilisée pour la synthèse d'hydrogels thermosensibles à base de pNIPA. La température critique TC correspondant à la transition de volume a été déterminée par des mesures de taux de gonflement et par DSC. La macroporosité (distribution de la taille des pores et épaisseur des parois) et son évolution en fonction de T ont été étudiées par la microscopie biphotonique donnant des informations à l'échelle du µm à plusieurs dizaines de µm. La diffusion de rayons X (SAXS et WAXS) a été utilisée pour caractériser la structure multi-échelle (de quelques dixièmes à quelques dizaines de nm) du gel constituant les parois des macropores. Les courbes de diffusion ont été décrites analytiquement. L'évolution des dix paramètres contenus dans l'équation a été étudiée en fonction de T et discutée. Enfin, des expériences utilisant les phonons hyperfréquences générés par la technique des réseaux transitoires avec détection hétérodyne (HD-TG) ont été réalisées. Ces mesures ont permis de déterminer la vitesse de propagation de l'onde ultra-sonore (à 340 MHz), son atténuation, et la constante de diffusion thermique à différentes températures. / "Cryopolymerisation" yields macroporous gels named "cryogels". The method was used to synthesise thermosensitive pNIPA based hydrogels. The critical temperature TC corresponding to the volume phase transition was determined by swelling ratio measurements and DSC. The macroporosity (pore size distribution and wall thickness) and its change with temperature, was investigated by two-photon microscopy yielding information at the micrometer scale (a few tenths to tens of micrometers). X-ray scattering (SAXS and WAXS) was used to characterise the multi-scale structure of the gel forming the pore walls. The scattering curves were described analytically. The variation with temperature of the 10 parameters contained in the equation was investigated and discussed. Finally, heterodyne detected transient grating experiments were performed on a bulk pNIPA gel. These measurements allowed the determination of the speed of the ultrasonic wave (at 340 MHz), its attenuation and the thermal diffusion constant in the gel at different temperatures.

La photo-catalyse est une voie très prisée pour la dépollution de l’eau ou de l’air. Le photo-catalyseur le plus employé est le dioxyde de titane (TiO2) mais l’activité photo-catalytique peut fortement varier d’une poudre à l’autre. De plus, il est très avantageux, voire nécessaire, de le déposer sur un support, pour une manipulation aisée, notamment s’il s’agit d’un monolithe poreux. Le but de cette thèse, menée en collaboration entre le LMCPA et l’IEM, est de produire un photo-catalyseur supporté : une mousse céramique, issue de précurseurs céramiques polymériques (voie PDC), revêtue de TiO2, tout en visant une cristallisation et une intégration du TiO2 dans la mousse, en une seule étape, par voie hydrothermale. Nous avons étudié la synthèse de TiO2 par voie hydrothermale formant ainsi des poudres de diverses natures (anatase, brookite, oxyde hydraté de titane et mélanges de ces phases) ; certaines présentent une activité photo-catalytique supérieure, dans certaines conditions, à celle de la référence commerciale le P25 de Degussa. Cette étude a également permis de produire de la brookite pure à une température relativement basse, bien plus performante que le P25 et l’anatase dans certaines conditions. Parallèlement, divers polymères précéramiques ont été investigués pour la confection de supports macro-poreux via la méthode des charges sacrificielles. Nous avons ainsi réalisé des mousses en céramique amorphe en SiBCN et SiBC, hautement poreuses, ouvertes et robustes. Enfin, les poudres de TiO2 les plus efficaces ont été déposées sur les mousses, par la voie hydrothermale, pour former le photocatalyseur supporté dont l’activité photo-catalytique a été évaluée. / Photocatalysis is a method of choice for water and air depollution. Titanium dioxide (TiO2) is the most used photocatalyst but photocatalytic activity can widely differ from one powder to another. Moreover, it is useful, or even necessary, to immobilize it on a support; in particular, a porous monolithic support for an easier handling. The purpose of this PhD thesis, consisting in a collaboration between the LMCPA and the IEM, is to produce a supported photocatalyst: an amorphous ceramic foam produced from polymeric ceramic precursors (PDC route) coated with TiO2. The objective is also to target a one pot process the crystallization and the incorporation of the photocatalyst, in a single stage, through a hydrothermal treatment. We studied the hydrothermal synthesis of TiO2 powders composed of various crystalline phases (anatase, brookite, titanium oxide hydrate and mixtures of thereof); some of them showed higher photocatalytic activity than the commercial reference, Degussa’s P25. This study also lead to the synthesis of pure brookite, at a relatively low temperature, much more efficient than P25 and anatase under certain conditions. At the same time, various preceramic polymers were studied for the production of macroporous supports through the sacrificial filler technique. We were able to produce highly porous, opened and robust amorphous ceramic foams in the Si-B-C-N and Si-B-C systems. Lastly, the foams were coated with the most efficient TiO2 powders in order to produce supported photocatalysts by the hydrothermal route; their photocatalytic activity was then evaluated.