A capsule-based self-healing cementitious material, capable of autonomically repairing its own cracks, can extend the service life of concrete structures and decrease the costs associate with repair and maintenance actions. However, the size, shell thickness, shell material and mechanical properties of the capsules still need to be optimised to ensure self-healing performance. Thus, the objective of this research was to explore the controlled microfluidic encapsulation to investigate the production of microcapsules for physically triggered self-healing in cementitious materials. A flow-focusing microfluidic device was used to produce double emulsions to be selectively photopolymerised to generate a core-shell structure. Subsequently, the physical triggering was assessed by embedding the produced microcapsules in cement paste, fracturing it and observing the cracked surface in the SEM. The results showed the production of microcapsules with 80-140 μm of diameter with excellent control over size and shell thickness. Using water-in-oil-in-water (w/o/w) double emulsion, microcapsules were synthesised containing water, colloidal silica solution and sodium silicate solution as core material. In addition, an oil-in-oil-in-water (o/o/w) double emulsion was used to encapsulate mineral oil and emulsified healing agents. The formation of the core-shell structure with aqueous and organic cores was characterised using optical microscopy and SEM. It was demonstrated that the water is not retained inside of the capsule, resulting in the formation of dimples and buckled capsules, particularly for shells thickness ~7 μm. On the other hand, TGA confirmed the retention of mineral oil for shells thickness of ~2 μm and the encapsulation efficiency was demonstrated to be 66%. When the capsules were added to the cement paste, four key factors were observed to prevent physical triggering: (i) thick shells, (ii) buckling of thinner shells due to the loss of water core, (iii) mechanical properties and (iv) poor interfacial bonding. As a result, a mechanical characterisation of the shell material was performed, indicating brittle fracture at room temperature, reduced Young’s modulus when compared with cementitious matrix and stress at rupture of 15-36 MPa. In addition, an innovative methodology was proposed to functionalise the surface of the microcapsules with hydrophilic groups in order to increase the interfacial bonding between the cement paste and the microcapsules. Thus, microcapsules with low tensile strength, low shell thickness, organic core and good interfacial bonding were successfully synthesised and demonstrated to rupture upon crack formation. These results experimentally demonstrate the importance of reduced shell thickness, core retention and interfacial bonding as valuable guides during the design of microcapsules for physically triggered self-healing in cementitious materials.

No description available.

Colloidal Microcapsules (MCs), i.e. capsules stabilized by nano-/microparticle shells are highly modular inherently multi-scale constructs with applications in many areas of material and biological sciences e.g. drug delivery, encapsulation and microreactors. These MCs are fabricated by stabilizing emulsions via self-assembly of colloidal micro/nanoparticles at liquid-liquid interface. In these systems, colloidal particles serve as modular building blocks, allowing incorporation of the particle properties into the functional capabilities of the MCs. As an example, nanoparticles (NPs) can serve as appropriate antennae to induce response by external triggers (e.g. magnetic fields or laser) for controlled release of encapsulated materials. Additionally, the dynamic nature of the colloidal assembly at liquid-liquid interfaces result defects free organized nanostructures with unique electronic, magnetic and optical properties which can be tuned by their dimension and cooperative interactions. The physical properties of colloidal microcapsules such as permeability, mechanical strength, and biocompatibility can be precisely controlled through the proper choice of colloids and preparation conditions for their This thesis illustrates the fabrication of stable and robust MCs through via chemical crosslinking of the surface engineered NPs at oil-water interface. The chemical crosslinking assists NPs to form a stable 2-D network structure at the emulsion interface, imparting robustness to the emulsions. In brief, we developed the strategies for altering the nature of chemical interaction between NPs at the emulsion interface and investigated their role during the self-assembly process. Recently, we have fabricated stable colloidal microcapsule (MCs) using covalent, dative as well as non-covalent interactions and demonstrated their potential applications including encapsulation, size selective release, functional devices and biocatalysts.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Hemophilia A is an X-linked recessive bleeding disorder caused by the deficiency of coagulation factor VIII [1]. Current treatment for hemophilia A consists of prophylactic or on demand replacement therapy of either plasma-derived or recombinant FVIII concentrates [2]. Albeit effective, there are several limitations associated with factor concentrates, including high cost that limits its availability for close to 80% of hemophilia patients in developing countries [3-5]. An alternative treatment would thus be desirable. Gene therapy for hemophilia has seen many successes in animal models and represents a more cost-effective alternative to the current treatment modalities [6]. In the current work, I present a gene therapy system for hemophilia that uses mouse fetal myoblasts engineered to secrete FVIII, enclosed in immuno-protective alginate-poly-L-lysine-alginate (APA) microcapsules, as a sustained source of FVIII. In this study, a thorough examination of the encapsulated myoblasts using a novel flow cytometry assay was performed. This method yielded an accurate and precise method for encapsulated cell viability calculation, and also allowed for analysis of several other parameters such as health (cell morphology), cell size and distribution. Flow cytometry was also used to monitor the time-course proliferation profile of encapsulated myoblasts secreting cFVIII, using the division tracking dye CFSE. We found that encapsulated cells display a decreased proliferation rate as well as lower viability than non-encapsulated cells. Implantation of encapsulated G8 myoblasts secreting cFVIII into hemophilia A mice resulted in maximum plasma levels of protein on day 1 ( ~18% of normal canine FVIII levels). Delivery of cFVIII in hemophilic mice also offered protection against blood loss after the mice were subjected to injury (as measured by hematocrit levels); indicating that biologically functional cFVIII continued for at least 7 days post-capsule implantation. Low levels of FVIII antigen returned on day 28 after a transient disappearance on day 14. However, the presence of antigen must be reconciled with appearance of anti-cFVIII antibodies that were detected in the plasma of treated mice at the end of five weeks. The neutralizing nature of these antibodies still needs to be characterized by Bethesda assay Overall, our study demonstrates the feasibility of delivering therapeutic levels of FVIII using encapsulated G8 fetal myoblasts. The presence of functional FVIII protein on day 7, suggests that this treatment was not met by transcriptional repression in vivo, thereby overcoming one of the major obstacles faced by using the transformed C2C12 cell line secreting hFVIII [7] If such levels of FVIII were achieved in humans, it would be sufficient to convert a severe hemophiliac into a mild phenotype. Thus, this gene therapy strategy may be a suitable therapeutic alternative for hemophilia patients. Further work ought to focus on the long-term persistence of FVIII in hemophilia A mice, and also determining the protection following trauma over time to determine if the FVIII remains functional. Other cell lines should be explored for higher expression, reduced immunogenicity and improved viability Still, there is a need to develop human cells expressing high levels of biologically active hFVIII with similar properties to the fetal cells described in this study [8, 9] / Thesis / Master of Applied Science (MASc)

A scalable method for the synthesis of polyethylene terephthalamide microcapsules grafted with polyacrylic acid to enable pH responsiveness has been developed. Microcapsules were produced by interfacial polymerisation of an oil-in-water emulsion in a 2 L batch reactor and subsequently circulated through an external loop reactor for UV irradiative surface grafting. Ungrafted microcapsule samples yielded 1.0 - 1.2 g desiccated capsules per experiment. Initial production trials were subject to severe agglomeration, observed during dialysis of the microcapsules with 30 % (v/v) ethanol solution. Lowering of the terephthaloyl dichloride monomer concentration, to 0.2 mol L⁻¹ in the chloroform / cyclohexane (3 : 1) organic solution, alleviated this unwanted agglomeration. Laser diffraction particle size analysis revealed microcapsules were produced with a 51 µm average diameter. A purpose built external loop irradiation reactor was used to facilitate graft polymerisation of acrylic acid on the microcapsules, using 254 nm UV light at 19 mW cm⁻². Characterisation of the external loop flow regime showed a mild deviation from ideal plug flow, with a vessel dispersion number of 0.014 and a Reynolds number of 1310. Confirmation of monomer polymerisation was ascertained by back titration and Fourier transform infrared spectroscopy. No distinction between homopolymer and grafted polyacrylic acid could be made by these characterisation methods. A Taguchi analysis on variables influencing grafting revealed high temperature to contribute most significantly to graft yield, followed by a long irradiation period. The development of a packed column pulse response method for testing pH response showed a high repeatability. However, release profile testing of a microcapsule slurry with an observed graft yield of 1.13 mmol g⁻¹ did not provide a definitive pH-based release of mPEG 5000 or PEGylated TAMRA dye. Determination of acrylic acid polymerisation kinetics following UV irradiation of the microcapsules is required for future optimisation of a functional graft yield.

Particle stabilized emulsions, also known as Pickering emulsions, have been widely used in many industry applications. While the breadth of potential applications for Pickering emulsions keeps growing, our fundamental understanding of Pickering emulsions is still poor. My thesis work addresses both fundamentals and applications of particle stabilized emulsions. In the fundamental part of this thesis work, we investigated the effects of particle charge on particle adsorption and the particle contact angle, and to investigate their ensuing consequences for the stability of Pickering emulsions. We provided the first experimental hint that the widely overlooked image charge repulsion can hinder the adsorption of particle to the oil-water interface and prevent the formation of Pickering emulsions. Consistently with the experimental suggestion, our theoretical model also confirmed that the image charge repulsion has the right order of magnitude, relative to the other forces acting on the particle, to impede particle adsorption and Pickering emulsification. For the conditions in which particle adsorption to the liquid interface does occur, the particle contact angle will play an important role in influencing the stability and type of Pickering emulsions. Our experimental work showed that the equilibrium contact angle of particles at interfaces and the type of emulsions preferentially stabilized by these particles can be strongly affected by the particles' charging state, which we attribute to a free energy contribution from the electric field set up by the charged particle and its asymmetric counterion cloud. A very simplistic calculation considering only the dipole field as the leading contribution and treating the water phase as a perfect conductor, found that the energy stored in the field is indeed strong enough and shows sufficient variation with the particle position to shift the equilibrium position significantly from where it would be based on interfacial tension alone. In a separate, more application oriented part of this thesis work, we have fabricated microcapsules from double Pickering emulsions and demonstrated that the combined use of hard silica particles and pH-responsive dissoluble polymer particles at the emulsion interface imparts a combination of pH-responsiveness (stimulated pore opening) and structural integrity to resulting capsules. We have further demonstrated the first double Pickering emulsion templated capsules in which interfacial polymerization was carried out at both emulsion interfaces, yielding a capsule with two composite shells, composed of polyurethane and silica particles, and characterized the transport of a model cargo through the capsules walls as well as the capsules' mechanical properties.

Concrete, a composite material consisting of aggregates bound together with cement paste, is the most widely used construction material. Concrete is relatively cheap, very versatile and has excellent compressive strength. However, its tensile strength is limited and for this reason steel rebars are often added to create reinforced concrete (RC). Cracking inevitably occurs in all RC materials and associated structures due to a variety of mechanical and environmental actions. The generation of tiny microcracks within concrete facilitates the flow of potentially aggressive fluids that can corrode the embedded steel rebars and, in extreme cases, lead to premature structural failure. Concrete, along with all cement-based materials, does possess some inherent self-healing capacity and is able to heal certain-size cracks autogenously. This self-healing capability is very limited and therefore researchers have attempted to improve upon it by using a variety of techniques. In particular, the use of engineered additions for autonomic self-healing has gained significant interest in the past two decades. An example is the addition of microcapsules that disperse throughout the hardened material subsequently providing reservoirs of healing agents. When cracks arise within the material, they rupture the embedded microcapsules causing a release of their contents into the crack volume. The released material then reacts to provide filling, sealing and healing of the crack. The primary aim of this research project was to investigate the autonomic self-healing performance of concrete containing microencapsulated sodium silicate. The effect of microcapsule addition on the fresh, hardened and self-healing properties of cement, mortar and concrete were all explored. Self-healing was monitored using a variety of techniques and results reveal the increased self-healing ability of microcapsule-containing cementitious materials as well as the efficacy of sodium silicate as a healing agent. Furthermore, the self-healing concrete field trial displays the great potential for microcapsules to be incorporated into large-scale self-healing concrete applications.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

La déformation des cellules végétales durant leur croissance génère des formes anisotropes variées. L'enveloppe des cellules en croissance, appelée paroi primaire végétales, est une couche fine, flexible et extensible, faite d'un réseau de microfibrilles de cellulose reliées entre elles par des hémicellulose qui ont une extension directionnelle. Le but de ce travail est d'élaborer des microcapsules biomimétiques possédant une structure similaire à la paroi primaire et d'étudier leur déformation sous une contrainte mécanique. Pour cela, nous avons utilisé les fortes interactions entre les nanocristaux de cellulose (sous-unités des microfibrilles) et les xyloglucanes (hémicellulose la plus répandue) déjà utilisée pour construire des multicouches plan [1]. Pour reproduire la géométrie des cellules, nous avons fabriqué des microcapsules multicouches à partir de nanocristaux de cellulose et de xyloglucanes, en combinant une émulsion d'huile dans l'eau, de dimension de 20µm environ, avec un dépôt couche par couche conduisant à des capsules biomimétiques. La régularité du dépôt de couche a été suivit par un marquage fluorescent sélectif, l'épaisseur et l'organisation de la paroi ont été caractérisées en microscopie électronique. Par séchage et évaporation du coeur d'huile, les capsules ainsi dégonflées présentent diverses formes révélées par des reconstructions 3D à partir de coupes de microscopie confocale. La relation entre les formes obtenus, les dimensions caractéristiques et les propriétés mécaniques de la paroi a été étudiée [2]. Le contrôle de la taille et de l'épaisseur de la capsule permet d'explorer diverses situations de déformations. [1] B. Jean*, L. Heux, F. Dubreuil, G. Chambat & F. Cousin, Non-electrostatic building of biomimetic cellulose-xyloglucan multilayers, Langmuir, 25(7), 3920-3923 (2009) [2] C. Quilliet, C. Zoldesi, C. Riera, A. van Blaaderen, and A. Imhof Anisotropic colloids through non-trivial buckling Eur. Phys. J. E, 27, 13{20} (2008) / The deformation of plant cells during their growth can generate various anisotropic shapes. The envelop of the growing cells, also called primary wall of plants, is a thin, flexible and extensible layer made of a network of cellulose microfibrils linked by hemicellulose tethers, that can have directional extension. The goal of this work is to elaborate biomimetic microcapsules with structures similar to the plant primary walls and explore their deformation under mechanical stress. For that purpose, we took advantage of the strong interaction of cellulose nanocrystals (the microfibrils sub-elements) with xyloglucan (the most common hemicellulose) already used to build planar multilayer systems [1]. In order to reproduce the cell geometry, we successfully build multilayered microcapsules from cellulose nanocrystals and xyloglucans, by combining oil in water emulsions with dimensions around 20 µm with layer-by-layer deposit, leading to biomimetic microcapsules. The regularity of the layer deposition has been followed by selective fluorescent tagging and the wall thickness and organization was characterized by electron microscopy. Upon drying and evaporation of the oily core, the deflated microcapsules exhibited various shapes as revealed by 3D reconstruction from confocal microscopy slices. We have investigate the relationships between the obtained shapes in relation to the characteristic dimensions and the mechanical properties of the wall [2]. The control of the capsule size and thickness allows exploring various situations in terms of deformation behavior. [1] B. Jean*, L. Heux, F. Dubreuil, G. Chambat & F. Cousin, Non-electrostatic building of biomimetic cellulose-xyloglucan multilayers, Langmuir, 25(7), 3920-3923 (2009) [2] C. Quilliet, C. Zoldesi, C. Riera, A. van Blaaderen, and A. Imhof Anisotropic colloids through non-trivial buckling Eur. Phys. J. E, 27, 13{20} (2008)