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<p>Conformal coating is a promising method of encapsulating therapeutic cells for immunoprotection during implantation in the human body. Therapeutic cells can include donor-derived primary cells, genetically modified lab lines, or stem-cell derived cells, that can express an enzyme or hormone needed by the recipient. Layer-by-Layer (LbL) assembly, a common method for conformal coating, uses sequential deposition of alternating layers of positively and negatively charged polymers. This permits the preparation of small capsules with thin walls that maximize metabolic exchange while protecting cells from the hosts’ immune system. The current work describes the use of auto crosslinking synthetic polyelectrolytes to coat the surface of individual living yeast cells. It is proposed that such crosslinked coatings will provide greater protection than existing, non-crosslinked ones.</p> <p>The thesis also introduces new reactive polyanions formed by copolymerization of N-acryloxysuccinimide and acrylic acid (AA) using both free radical and photo induced radical polymerization. The resulting reactive polyanions bind under physiological conditions to poly-l-lysine coated calcium alginate hydrogel beads and spontaneously crosslink with the polyamine to form covalent networks of interest for long-term therapeutic cell encapsulation.</p> / Master of Science (MSc)

<p>Silicones exhibit a fundamentally hydrophobic character. While the incorporation of hydrophilic surface moieties can be achieved by a variety of means, normally surface reversion leads to rapid recovery of hydrophobic surfaces. We were interested to learn if the hydrophobic character of silicones could be manifested on organic polymers and, moreover, if different degrees of wetting of organic surfaces could controlled by simultaneous use of more than one hydrophilic entity.</p> <p>Herein, we present a method to control the hardness and wettability of methacrylate polymers with the addition of ACR A008-UP, a polymerizable, acrylate-based trisiloxane surfactant. Surface wettabilities were determined through the use of contact angle measurements, and the hardness modulus is determined through the use of a Shore OO durometer. The wettability and the hardness of the polymers were controlled by varying the ratio of surfactant to methacrylate monomers. As the proportion of surfactant monomer increased, the hardness of the copolymers was depressed. In a similar fashion, as the proportion of surfactant increased, the copolymer surfaces became increasingly wettable. However, at a certain threshold concentration the wettability decreased once again, which is ascribed to the formation of a hydrophobic brush at higher concentrations. The wettability and hardness of the polymers, and the stability of the trisiloxanes on the surface will be discussed.</p> / Master of Science (MSc)

<p>In recent years, cellulose nanocrystals (CNCs) isolated from natural cellulosic sources through an acid hydrolysis treatment have garnered significant interest in both academia and industry. CNCs have attracted attention not only because they stem from an abundant, renewable resource and are biodegradable, but also because of their low density, light weight, high aspect ratio, high tensile strength and a specific Young’s modulus comparable to steel and Kevlar. These properties make CNCs ideal for use as reinforcing agents in nanocomposites, as well as stabilizing agents in foams and gels. However, due to the high surface area and hydrophilic nature of CNCs, unmodified nanocrystals are difficult to disperse in non-polar materials. The lack of interfacial compatibility between components causes CNCs to agglomerate and thus their incorporation into conventional polymer matrices has been challenging at best, and unsatisfactory in most cases.</p> <p>In this work, CNCs have been rendered pH and temperature-responsive by surface-initiated graft polymerization of 4-vinylpyridine and <em>N</em>-isopropylacrylamide, respectively, using ceric (IV) ammonium nitrate as the initiator. The resultant suspensions of poly(4-vinylpyridine)-grafted cellulose nanocrystals (P4VP-<em>g</em>-CNCs) and poly(<em>N</em>-isopropylacrylamide)-grafted cellulose nanocrystals (PNIPAM-<em>g</em>-CNCs) show reversible hydrophilic to hydrophobic responses with changes in pH and temperature, respectively. The presence of grafted polymer and the tunable hydrophilic/hydrophobic properties were characterized via Fourier transform infrared spectroscopy, elemental analysis, electrophoretic mobility, mass spectrometry, transmittance spectroscopy, contact angle measurements, thermal analysis and various microscopies.</p> <p>The intention of this work has been to shift towards more industrially viable surface modification routes for CNCs by using a one-pot, water-based synthesis to produce a low cost and functional nanomaterial. Moreover, sonication is used throughout the polymerization reaction to avoid particle aggregation and ensure that individual CNCs are surface-functionalized. As a result, reproducible and uniform material properties have been measured in both suspensions and films of modified CNCs. The responsive nature of P4VP-<em>g</em>-CNCs and PNIPAM-<em>g</em>-CNCs may offer new applications for cellulose nanocrystals in hydrophobic nanocomposites, biomedical devices, as clarifying agents, and in industrial separation processes.</p> / Master of Applied Science (MASc)

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