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We have investigated a series of molecular and polymeric approaches for generating adherent thin films that impart anti-fouling characteristics to oxide surfaces. These films incorporate oligo- or poly(ethylene glycol) moieties that are expressed in high density in the near-surface region. In our molecular approach, oligo(ethylene glycol)-terminated n-alkyl-trichlorosilanes, RO(CH₂CH₂O)₃(CH₂)₁₁SiCl₃, have been designed so to spontaneously adsorb onto oxide surfaces and produce densely packed films. Another strategy uses a surface initiated polymerization to generate reactive anchored polymer chains that are then chemically modified to incorporate oligo(ethylene glycol) units. Lastly, a comb copolymer comprising a poly(acrylic acid) backbone and different grafting ratios of a linear poly(ethylene oxide-r-propylene oxide) chain has been prepared that adsorbs onto surfaces and forms a poly(ethylene glycol)-exposing film in single step. These surface coatings provide varying levels of protein and cellular resistance that can be related to molecular-scale elements of their surface structure. / Singapore-MIT Alliance (SMA)

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Prepainted metal sheets being environment friendly and cost effective as compared to postpainted metal sheets, are widely used in construction, packaging, transportation and automotive industries. One of the key requirements for prepainted coatings is to retain its surface quality and properties during forming process. During forming process, major surface damage occurs when the coated sheet is bent and un-bent around the die corner. To reduce surface damage of coatings, proper control of the parameters during forming and detail study of the surface conditions is required. In the present study, influence of forming parameters such as die radius, lubrication and specimen material are investigated. The influence of these parameters on friction, surface damage and properties of polymer coatings are evaluated. Experiment set-up is built to conduct bending under tension test. This test gives a better way to evaluate coating performance, as it closely simulates the die region of real forming process and considers bending effects. Experimental results show increase in friction and surface damage with decrease in die radius. Moreover, with decrease in die radius hardness of the coating decreases and strain in the specimen increases. Lubrication has some effect on coefficient of friction, but the influence is not as significant as that of die radius. This is attributed to the fact that, the polymer coating itself acts as a solid lubricant in the test. Material effect was studied, polypropylene coating being the softer material compared to PVDF coating shows more surface damage in the form of scratches. Numerical simulations were performed using Finite Element Analysis package (FEA) Abaqus. A 2D model was built, exploiting the plane strain condition for bending under tension test. Numerical simulations indicate that maximum contact pressure and von Mises stress are concentrated at the beginning of the drawing edge. Apart from the location, the value of contact pressure was higher for smaller die radius. Thus, experiments help in studying the effect of forming parameters on coating performance and numerical simulations provide more insight into the critical areas where stresses are high. Numerical simulations also provide a scope to study the effect of material and geometric parameters on performance of coatings without running experiments.

This work investigates the feasibility of the use of plasma spray deposition as a method of producing high performance polymer coatings. The work concentrates on the understanding of the processing of the plasma spraying of polymers, the behaviour of polymeric materials during deposition, and the study of process-structure-properties relationships. Processing modelling for the three stages of the evolution of a polymer deposit (droplet-splat-coating) has been carried out using heat transfer theory. A theoretical model is proposed which consists of three parts: the first part predicts the temperature profile of in-flight particles within plasma jet, the second part predicts the cooling of isolated splats impacting on a substrate and the third part, the heat transfer through the coating thickness. The heat transfer analysis predicts that the development of large temperature gradients within the particle is a general characteristics of polymers during plasma spraying. This causes difficulties for polymer particles to be effectively molten within the plasma jet without decomposition. The theoretical calculations have predicted the effect of processing parameters on the temperature, the degree of melting and decomposition of in-flight polymer particles. With the aid of the model, the conditions for the preparation of high integrity thermoplastic deposits have been established by the control of the plasma arc power, plasma spraying distance, feedstock powder injection, torch traverse speed and feedstock particle size. The optimal deposition conditions are designed to produce effective particle melting in the plasma, extensive flow on impact, and minimal thermal degradation. The experimental work on optimizing processing parameters has confirmed the theoretical predictions. Examination of polymer coating structures reveals that the major defects are unmelted particles, cracks and pores. Five major categories of pores have been classified. It also revealed a significant loss in crystallinity and the presence of a minor metastable phase in the plasma deposited polyamide coatings due to rapid solidification. The study has indicated that the molecular weight of a polymer plays an important role on the splat flow and coating structure. Under non-optimal deposition condition, substantial thermal degradation occurred for which a chain scission mechanism is proposed for plasma deposited polyamide coatings. There are difficulties in achieving cross-linking during plasma spray deposition of thermosets. The theoretical calculations predict that adequate cross-linking is unlikely in a coating deposited under normal conditions, but preheating the substrate to above the cross-linking temperature improves the degree of cross-linking of the coatings substantially. In addition, the coating thickness has a major effect on the degree of cross-linking of thermosets. The calculations also predict that lowering the thermal conductivity by applying a thermal barrier undercoat and using a faster curing agent to reduce time required for the cross-linking reaction can improve the degree of cross-linking of thermoset deposits. The experimental results for the degree of cross-linking and wear resistance confirmed these predictions.

Polymeric coatings are being used in a growing number of applications, contributing to protection against weather conditions and localized corrosion, reducing the friction and erosion wear on the substrate. In this study, various polypropylene (PP) coatings were applied onto steel substrates by compression molding. Chemical modification of PP has been performed to increase its adhesion to metallic surfaces by grafting of maleic anhydride (MAH) onto PP in the presence of dicumyl peroxide (DCP). Influence of different concentrations of MAH and DCP on the properties of resulting materials have been examined. The coated steel samples are characterized by scanning electron microscopy (SEM), shear adhesion testing, FTIR and tribometry. The coatings with 3 wt. % MAH have shown the maximum adhesion strength due to maximum amount of grafting. The wear rates increased with increasing the amount of MAH due to simultaneous increase in un-reacted MAH.

For a lay summary of the thesis presented in a 1-minute video format, visit the following link: https://www.youtube.com/watch?v=VhLzt_tEz-s / It is projected that, by 2030, 8% of all adults in the world will have diabetes mellitus and treatment will account for 10% of the total healthcare budget in many countries. Polymeric biomaterial research has led to the design of robust polymer hydrogel capsules to develop curative cell-based therapies for chronic disorders such as diabetes mellitus. Encapsulation of insulin-producing beta cells within synthetic, semi-permeable polymer hydrogels can avoid host immune rejection including fibrotic responses, and thus holds the promise of a long-term curative treatment of this disease. There is a paucity of literature regarding methods available for standardized in vitro screening of synthetic polymer hydrogel capsules to predict host responses in vivo. Thus, the focus of this thesis was to design in vitro assays able to screen for subsequent in vivo fibrotic responses. Two dimensional (‘2D’) (cell attachment to thin film hydrogel coatings) and three dimensional (‘3D’) (cell attachment and protein adsorption to hydrogel capsules) in vitro experiments were designed and tested in an iterative process to assess fibrotic responses to a diverse group of polymer hydrogels. Cell attachment assays included fibroblast (NIH 3T3) and macrophage (RAW 264.7) cell lines, and protein adsorption assays included proteins used to model fibrosis including fibrinogen and lysozyme. For some formulations, in vitro assays were compared with in vivo data on pericapsular cellular overgrowth (PCO) after being implanted into mice. A binomial logistic regression model was designed and validated to assess whether the ‘3D’ in vitro assays correlated with in vivo PCO responses. It was found that the RAW 264.7 cell attachment assay was significantly correlated with PCO outcomes in vivo, demonstrating for the first time a simple, cost-effective, and rapid in vitro cell-based approach to screen and select capsules with lower fibrotic potential to be further tested in animals. / Thesis / Master of Health Sciences (MSc) / In North America, one in eleven adults, or about 415 million people, have diabetes. It is projected that by 2030, around 8% of the world population will be diagnosed with this disease. A common form of treatment is through the frequent injection of insulin, but this is costly, requires multiple daily interventions, and cannot prevent regular excursions from the ideal blood glucose range. Cell-based therapies have a lot of promise in treating several chronic diseases including diabetes. Donor and stem-cell derived islets can be implanted into patients with type 1 diabetes and have been shown to function for over a year, albeit at the price of systematic immune suppression. Alternatively, cells that produce insulin can be placed inside immune-evasive capsules and implanted, potentially providing continuous blood glucose regulation without the need for daily insulin injections. However, this novel form of treatment is limited by the encapsulated cells’ survival once implanted. Cell survival can be affected by the body’s response to a foreign body (the capsule), causing deposition of protein or cells on the capsule surface which can limit the oxygen supply to cells in the capsule and the ability of insulin to leave the capsule in a timely fashion. The goal of this project is to develop assays to screen new capsule formulations. This can advance research by using capsules more readily accepted by the body, leading to a more promising and long-term treatment of diabetes.

While significant progress has been made in the treatment and management of cancer, challenges remain because of the complexity and the heterogeneous nature of the disease. The improvement that has been seen in survival rates reflects advancements not only in treatment, but also in early stage detection and diagnostics for certain cancers. In particular, early stage detection and treatment of cancer before it has metastasized to other organs has resulted in a dramatic improvement in patient survival rates. One area of research that has shown considerable promise in further advancing diagnostics and early cancer detection is nanotechnology. Specifically, semiconductor and metal nanoparticles have great potential to provide advanced technology platforms for ultrasensitive and multiplexed detection of disease markers and probe disease on the molecular level. Because they are in the same size regime as biological molecules, these nanoparticles exhibit unique interactions with proteins, nucleic acids and other biomarkers of interest for detecting and diagnosing disease. However, high-quality nanoparticles are often unsuited for use in complex biological environments because of their coatings and surface chemistry. In this work, we describe the design and development of polymer-coated nanoparticle imaging agents for use in blood, cell and tissue diagnostic applications. Low-molecular weight, amphiphilic polymers capable of noncovalent interactions with nanoparticle surface ligands and the aqueous environment were synthesized and characterized for use in nanoparticle coating applications. We demonstrate that the hydrophobic and hydrophilic interactions between the nanoparticle surface, the amphiphilic polymer and the aqueous solvent were able to drive the coating and water solubilization of quantum dots. Novel nanoparticle synthetic techniques were also developed using the amphiphilic polymers in a one-pot method to make high quality semiconductor and gold nanoparticles and stabilize and encapsulate the particles for transfer into water. Using the polymer functional groups as multidentate ligands, nanoparticles were synthesized with a high degree of size control and increased stability. In addition, by performing the synthesis in a noncoordinating amphiphilic solvent such as polyethylene glycol, nanoparticles were immediately transferred to water with the excess polymer forming a water soluble coating. Next, nanoparticle surface charge and how it relates to the nonspecific binding of nanoparticles in cells, tissues and other complex biological samples was studied. We have found that highly charged (negative and positive) particles exhibit significant nonspecific binding to biomolecules and other cellular components in biological environments. By reducing the surface charge through the incorporation of hydroxyl functional groups, we have nearly eliminated the nonspecific binding of quantum dots in blood, cells and tissues. Moreover, through crosslinking and altering the surface chemistry of the polymer-coated quantum dots, we have increased the stability of the nanoparticles while maintaining a small hydrodynamic size. Finally, we have investigated the use of the low-binding, hydroxyl quantum dots in tissue staining applications, where nonspecific binding presents a considerable challenge to detection sensitivity and specificity. A number of biomolecule conjugation techniques were examined for the coupling of quantum dots to antibody targeting molecules and preliminary staining experiments were performed.

Doctor of Philosophy / Department of Chemistry / Peter M.A. Sherwood / This dissertation will examine the fabrication of different phosphorus containing films and their use as corrosion preventative films and adhesion materials between polymers and metal and metal alloys. Orthophosphate films are used in several metals and metal alloys to prevent corrosion and promote adhesion between paints or polymers and metal substrates. One key component is to examine the use of different phosphorus containing acids that might lead to phosphorus containing films which would compliment the mainly orthophosphate films currently in use. The objectives of this study are to see if it is possible to fabricate different phosphorus containing films, use them to adhere polymers to metal and metal alloys, and test the phosphorus containing films’ and polymer films’ corrosion protection properties. The thermoplastic resin, Poly(ether ketone ketone), or PEKK was found to adhere well to different phosphorus containing films and protect the underlying layers from oxidation in 4-D water. The phosphorus containing films were created by electrochemical deposition in different 5 M phosphorus containing acids. The metal or metal alloy was abraded to remove the native oxide and treated in the electrochemical cell. The second, separate polymer films were created by dip coating the metal or metal alloy in a polymer solution. The film thickness in both cases was controlled to be less than 100Å to ensure that the underlying metal or metal alloy could be detected. The surface chemical analysis was collected using X-ray photoelectron spectroscopy, or XPS. Core level and valence band XPS were used to distinguish the differences in the chemistry at the surfaces. The valence band XPS spectra were interpreted using spectra generated by multiple scattered wave calculations and band structure calculations. In the cases were more than one film was present subtraction and addition spectrum were used to interpret the chemistry in the interface region of the films.