Poly ethylene glycol (PEG) based microgels were synthesized and investigated. The PEG microgel has the same phase transition as the traditional poly N-isopropylacrylamide (PNIPAM). As a good substitute of PNIPAM, PEG microgel exhibits many advantages: it is easier to control the lower critical solution temperature (LCST) of the microgel by changing the component of copolymers; it has a more solid spherical core-shell structure to have a double thermo sensitivity; it is straightforward to add other sensitivities such as pH, magnetic field or organic functional groups; it readily forms a photonic crystal structure exhibiting Bragg diffraction; and, most importantly, the PEG microgel is biocompatible with human body and has been approved by FDA while PNIPAM has not. PEG microgels with core-shell structure are synthesized with a two-step free radical polymerization and characterized with DLS, SLS and UV–Vis. The dynamic mechanics of melting and recrystallizing of the PEG core-shell microgel are presented and discussed. Photonic crystals of PEG microgels were synthesized and characterized. The crystal can be isolated in a thin film or a bulk column. The phase transition of PEG microgel was simulated with the mean field theory. The enthalpy and entropy of phase transition can be estimated from the best fit to theoretical calculation with experimental data.

This thesis presents a study of pH-responsive doubly crosslinked microgels (DX MGs) and associated investigations to enhance their performance. The potential application of this material is soft tissue engineering, so the research concerns mechanical properties, other properties like swelling, microporous and conductivity are also discussed. The MG particles are based on poly(EA/MAA/x), where EA is the ethyl acrylate, MAA is the methacrylate acid and x represents the crosslinker. The particles were subsequently functionalised using glycidyl methacrylate (GMA) to introduce vinyl groups in the MG particles. The formation of DX MGs includes a pH triggered swelling of MG particles in the dispersion to form a physical gel and a heat-triggered free-radical reaction to form a covalent hydrogel. The starting point of this study was using graphene oxide (GO) nanosheets to prepare DX MGs composites with a high modulus. We mixed low concentrations of GO with MG particles and formed DX MG/GO gels. Both shear and compressive modulus linearly increased with the concentration of GO, but the ductility of gels was slightly reduced. The moduli for the DX MG/GO gels was increased by a factor of 5 - 6 when only 1.0 wt.% of GO was included. The next study used muti-wall carbon nanotubes (CNTs) which are widely used to prepare electrical conductive composites. A big challenge for applying CNTs is that they easily form large aggregates in water, which was solved by the space-filling and volume excluded properties of MG particles. The ductility of the composite DX gels increased with CNT concentration, as did the modulus. The conductivity of gels significantly increased with the concentration of CNT and they had a very low percolation threshold. The cytotoxic study for the composite gels showed that they were not toxic, so they may be suitable for soft tissue engineering. The effect of crosslinking monomers in MG preparation was studied in the last part of the research. Three types of poly(EA/MAA/x) MGs were studied and compared. The x value was 1 mol. % of divinylbenzene (DVB); 1,4-butanediol diacrylate (BDDA) or a 1:1 mixture of both DVB and BDDA. The MGs containing DVB demonstrated higher swelling and more ductile properties and could withstand ~76% of compressive deformation. Moreover, the effects of intra-MG crosslinking of the MGs on the swelling behaviour and the mechanical properties were investigated.

Research into the synthesis of sequential, poly(n-butyl acrylate), PnBA/polystyrene, PS, IPN microgel (μ-gel) dispersions in organic media was performed. Poly(styreneco- divinylbenzene), PSIDVB (0, 1, 5 & 10 weight % DVB), particles were synthesised by emulsion copolymerisation and these microgels were characterised by dynamic mechanical thermal analysis (DMT A), gel permeation chromatography and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy.

Hydrogels have been widely explored for cell therapy applications due to their favourable biochemical and mechanical properties. However, the dimensions of bulk hydrogels limit the diffusion of nutrients to cells and cell products to the surrounding environment, negatively affecting cell viability and the therapeutic potential of the encapsulated cells. In addition, invasive procedures are often required for the administration of bulk hydrogels into patients that pose a practical barrier to cell therapy. To address these issues, micrometer sized hydrogels (microgels) have been designed with controlled shapes, sizes, and structures to enable sufficient biomolecule diffusion and injectable administration. In this thesis, in situ gelling poly(oligoethylene glycol methacrylate) (POEGMA) and zwitterionic microgels are fabricated based on delayed dynamic hydrazone crosslinking between cell friendly functionalized polymers without the need for any additional crosslinking agents. Two microgel fabrication strategies were explored: (1) droplet-based microfluidics and (2) droplet extrusion printing. In the first case, microgels with controlled degrees of porosity were fabricated via the incorporation of a non-toxic evaporable porogen into a microfluidic device. Porous microgels had significantly improved diffusion of small molecules compared to nonporous microgels, and cells encapsulated in the porous microgels showed significantly increased viability over 10 days. In the second case, droplet extrusion printing was employed to print a bioink on a hydrophobic surface, resulting in the fabrication of disk-shaped microgels with a height below the maximum pathlength of oxygen and nutrient diffusion. Cells encapsulated in the microgels maintained high viability, with the microgels also supporting effective cell proliferation over 10 days. Overall, the work presented in this thesis poses solutions to challenges around nutrient/cell product diffusion and the invasive procedures typically associated with hydrogel-based cell therapy, providing potentially new translatable therapeutic options for disease treatment. / Thesis / Master of Applied Science (MASc) / Cell therapy is used to improve or replace the function of damaged cells or tissues that currently exist in the body by delivering healthy cells and the therapeutic products they naturally produce to the site of interest. Delivering these cells to the body has many challenges, including attacks from the immune system and substantial cell death caused by mechanical forces applied upon injection. To overcome these problems, the cells can be loaded into hydrogel-based microparticles (microgels), highly hydrated polymer networks that can protect the encapsulated cells from the immune system and mechanical forces while providing an environment that can support cell viability and growth. This thesis is focused on designing microgels with suitable dimensions and structures that allow for nutrients to flow from the environment to the cells and wastes/cell products from the cells to the environment while also supporting long-term cell viability, allowing the therapeutic molecules the cells produce to potentially treat diseases.

Le but de cette thèse est de faire évoluer les connaissances et la compréhension des systèmes lubrifiants en milieux aqueux, synthétiques comme biologiques. Pour cela, nous élaborons des systèmes de monocouches auto-assemblées de microgels thermosensibles de pNIPAM cationiques afin d’en étudier les propriétés mécaniques et nanotribologiques. Nous mettons au point plusieurs synthèses de microgels afin d’étudier l’effet de l’élasticité sur le comportement tribologique. Nous regardons également l’effet de la nature du greffage des microgels en sur-face, en élaborant une méthode de couplage chimique novatrice, pour comparer les propriétés de monocouches physi- et chimisorbées. Nous étudions les propriétés mécaniques en mi-lieux aqueux des couches des différents microgels en fonction de la température, de la nature du greffage et du sel en présence, à l’aide d’une Microbalance à Cristal de Quartz avec mesure de Dissipation (QCM-D). Le coeur de notre étude est réalisé à l’aide d’un Appareil de Forces de Surface (SFA) modifié pour permettre des mesures tribologiques, dont les résultats seront traités en deux parties. La première consiste à caractériser les forces normales de surface lors-que l’on comprime deux surfaces décorées de microgels. La seconde est constituée de l’ana-lyse de ces surfaces sous compression et cisaillement. Nous explorons les propriétés lubrifiantes du système et observons l’apparition une force de normale dépendant de la vitesse de cisaillement, et dont nous cherchons l’origine. Nous avons ainsi découvert un mécanisme propre au substrat souple, décoré de particules discrètes avec un contact répulsif sans friction à longue portée. / The aim of this project is to advance the knowledge and understanding of lubricating systems, whether synthetic or biological, in aqueous media. For this purpose, we develop self-assem-bled monolayer 2D-arrays of cationic pNIPAM thermosensitive microgels in order to study their mechanical and nanotribological properties. We establish several synthetic routes to modulate the microgel rigidity and study its effect on the tribological behaviour. We also look at the effect of the grafting nature of microgels on the substrate, by developing an innovative chemical coupling method, to compare the properties of physisorbed and chemisorbed mon-olayers. We probe the mechanical properties of the microgel layers in aqueous environment while varying the temperature, the nature of the grafting and the salts added to the system, primarily by using a Quartz Crystal Microbalance with Dissipation monitoring (QCM-D). The core of our study is performed using a modified Surface Forces Apparatus (SFA) which allows for tribological measurements, the results of which will be treated in two parts. First, we char-acterise the normal surface forces when compressing two surfaces decorated with the micro-gel layers. Second, we study the behaviour of these surfaces under compression and shear. We explore their lubricant properties and observe the appearance of a shear-induced velocity-dependent lift force, whose origin we seek to determine. We thus discovered a mechanism specific to a compliant substrate, decorated with discrete particles presenting a repulsive con-tact without friction at long range.

A range of microgels with two different functionalities were synthesized, and their utility in novel bioapplications was examined. Cationic microgels with varying properties were developed by tuning synthesis conditions. Their size and primary amine content was analyzed, and one microgel system was selected as a model construct. Its primary amine groups were conjugated to two dyes with properties favorable for utilization as contrast agents in photoacoustic imaging. The concentration of contrast agent in single particles was determined. The implications of a high local dye concentration in the generation of high intensity photoacoustic signals, are discussed. The second bioapplication involved the targeted delivery of fibrinolytics to fibrin clots, in order to bring about dissolution of abnormal thrombi. For this purpose, core/shell microgels with carboxylic acid groups in their shells were synthesized in three size ranges. Following this, their dimension based differential localization in and around porous fibrin clots was examined. Fibrin-specific peptides were then conjugated onto the shells of these particles and the conjugates were shown to demonstrate strong interactions with the fibrin clots. The microgels conjugated to the peptide with the highest binding affinity to fibrin, were observed to bring about disruption of fibrin clots, merely through interference in the dynamic interactions among clot fibers, due to the equilibrium nature of the fibrin polymer. The implications of these novel results and future studies required to facilitate a better understanding of the phenomena involved, are discussed.

Significant quantities of hydrocarbon are bypassed during conventional waterfloods. This is the direct result of fluid channeling through high permeability zones within the reservoir. Conformance control offers a mean of increasing vertical and areal sweep efficiency, thus decreasing the amount of hydrocarbon bypassed. This, in turn, results in increased hydrocarbon production, decreased water cut, and field life extension. This thesis focuses on the use of polymer microgels as a relatively novel conformance control agent. Polymer-microgel-enhanced waterflooding tackles fluid channeling by “plugging” high permeability channels, or thief zones, and diverting trailing flooding fluid to adjacent poorly swept areas of the reservoir. The first major objective of this thesis was to provide an extensive literature survey on polymer microgel technology, which can serve as the go-to reference on this topic. Colloidal Dispersion Gels (CDGs), Preformed Particle Gels (PPGs), temperature-sensitive polymer microgels (Bright Water), and pH-sensitive polymer microgels are all discussed in detail, and an attempt is made to highlight the potential mechanisms by which they plug thief zones and improve oil recovery. This thesis then outlines the results of simulating numerous polymer microgel floods, ranging from experimental cases to field cases. Specifically, Colloidal Dispersion Gels (CDGs) were chosen for the simulations undergone. All simulations were run using UTGEL, a newly developed in-house simulator designed exclusively for the simulation of polymer, gel, and microgel floods. The simulations performed provide insight on the polymer microgel flooding process, and also served as a means of validating UTGEL’s polymer microgel (CDG) models. The development of the UTGEL simulator was important as it enables the optimization of polymer microgel floods for maximized hydrocarbon recovery efficiency. The results of a simulation study, using a synthetic field case, are also outlined. This sensitivity study provides additional insight on optimal operational conditions for polymer microgel technology. More specifically, this study aimed to investigate the effectiveness of microgel flooding treatments in layered reservoirs of varying permeability contrasts, vertical-to-horizontal permeability ratios, and under a variety of different injection concentrations. / text

We investigated the depletion interactions of colloids and hindrance behavior of hard and soft colloidal particles near neighboring walls. We first used numerical modeling to compute depletion interaction strengths for simple geometries which eventually guided our experiments to make interactions highly selective. The model helped us in identifying the important parameters to finetune these interactions and shed light on geometric design rules to optimize desirable shape-selective interactions on a variety of complex geometries. We further reported experimental studies that highlight the differences in the dynamics of hard and soft colloids under confinement using video microscopy and particle tracking. It was found that both soft sphere systems that we investigated (swollen polymer particles, core/shell microgels) behave differently from hard sphere systems under all degrees of confinement that were measured. Our findings suggest that soft sphere systems have lesser hindrance compared to hard sphere counterparts and the hindrance varies as a function of softness. In order to understand the soft sphere confinement dynamics more clearly, implications for future research are discussed.

No description available.

Microgels, colloidal networks of crosslinked water-soluble polymers with dimensions < 1 μm, have been demonstrated to be useful materials in a wide range of biomedical and environmental applications. In particular, temperature-responsive microgels based on poly(N- isopropylacrylamide) (PNIPAM) have attracted significant research interest in drug delivery applications. However, conventional precipitation-based PNIPAM microgels are functionally non-degradable, problematic for biomedical applications. To resolve this issue, a thermally- driven self-assembly approach based on hydrazide and aldehyde functionalized PNIPAM oligomers to form an acid-labile hydrazone bond was developed in the Hoare Lab to produce thermoresponsive, colloidally stable, monodisperse and degradable microgels. In this thesis, the internal structure of these self-assembled microgels was investigated using small and ultra-small angle neutron scattering and surface force experiments. Contrary to expectations based on the assembly technique, all these characterization strategies suggested that self-assembled microgels have a homogeneously cross-linked internal structure. It is anticipated that these well-defined degradable and homogeneous nanoscale gel networks offer opportunities for addressing challenges in drug delivery, biosensing, and optics by exploiting the predictable diffusive and refractive properties of the homogeneous microgel networks. In addition, the co-self-assembly of a moderately hydrophobic anti-inflammatory drug (dexamethasone) during the microgel self-assembly process was demonstrated to enable five-fold higher drug encapsulation (75-80%) relative to the conventional partition/diffusion- based drug loading processes. This result addresses a key challenge in delivering hydrophobic drugs using conventional precipitation-based microgel systems due to the inherent hydrophilicity of the crosslinked network. The potential of the self-assembly approach to fabricate multi-responsive smart microgels was demonstrated by incorporating pH-ionizable functional groups (via the copolymerization of acrylic acid and 2-dimethylaminoethylmethacrylate to introduce anionic and cationic charges respectively) into the hydrazide and aldehyde-functionalized precursor polymers prior to self-assembly. The self-assembled charged microgels showed the same pH- responsive swelling behaviours of conventional microgels, including amphoteric microgels that can be formed at any desired cationic:anionic charge density by simply mixing different ratios of cationic and anionic precursor polymers. Such microgels offer significant potential to improve the performance of microgels in applications demanding dual pH/temperature specific drug delivery. / Thesis / Master of Applied Science (MASc) / Medications can exist in many different forms. From pills to injections, existing drug delivery systems require a high frequency of drug administration and often result in low efficacy of drug once administered to the human body. Polymer-based drug delivery systems have the potential to improve this delivery. In particular, microgels, water-filled crosslinked polymer networks with a size less than one micron, offer promise as a drug delivery vehicle. The size and chemical composition of microgels can be tailored to enable their use in a wide array of drug delivery applications. In addition, microgels can be loaded with a therapeutic agent and transported in the blood stream to deliver drug at a rate and/or location tunable based on the internal structure of the microgel. “Smart” microgels have the particularly attractive ability to change their properties in response to certain environmental stimuli (i.e. temperature or pH). However, current smart microgel systems are non-degradable and would accumulate in the body, causing undesired side-effects. In this thesis, a new self-assembly approach has been used to produce degradable microgels with the potential to switch properties in response to both temperature and pH. Water-insoluble drugs can be encapsulated more efficiently with this method, and the dual-responsive behaviour is expected to improve our capacity to deliver drug at the rate and location desired in the body.