We studied PLA-microcrystalline cellulose composites, focusing on the effects of processing, particle size and surface modification. The thermal and mechanical properties of these PLA based composites were studied and the effect of cellulose addition on PLA degradation was analyzed. For our system, the degradation rate was found to depend on initial sample crystallinity, pH of the degradation media and cellulose content of the composite. Composites were prepared using solution processing and melt mixing methods. The processing methods influenced the polymer's ability to crystallize affecting the mechanical properties. Isothermal crystallization studies carried out to study the kinetics of crystallization showed melt processed samples to have lower half time for crystallization and higher value for the Avrami exponent. The crystallization rate of PLA was also found to depend on surface chemical composition of cellulose particles and the particle size. Influence of filler surface modification on the composite properties was studied via grafting of lactic acid and polylactic acid to cellulose particles and the effect of filler size was studied using hydrolyzed microcrystalline cellulose particles. A simple esterification reaction that required no external catalyst was used for surface modification of cellulose particles. Surface modification of cellulose particles enhanced the static and dynamic mechanical properties of the composite samples due to improvement in the PLA-cellulose compatibility that resulted in better interfacial interactions. The utility of cellulose, available from a renewable resource, as an effective reinforcement for PLA is demonstrated.

Biomimetic materials that recapitulate the complex mechanical and biochemical cues in load-bearing tissues are of significant interest in regenerative medicine and tissue engineering applications. Several investigators have endeavored to not only emulate the mechanical properties of the vasculature, but to also mimic the biologic responsiveness of the blood vessel in creating vascular substitutes. Previous studies in our lab generated the elastin-like protein polymer LysB10, which was designed with the capability of physical and chemical crosslinks, and was shown to display a range of elastomeric properties that more closely matched those of the native artery. While extensive validation of the mechanical properties of elastin-mimetic polymers has demonstrated their functionality in a number of tissue engineering applications, limited cell growth on the surfaces of the polymers has motivated further optimization for biological interaction. Recent biologically-inspired surface strategies have focused on functionalizing material surfaces with extracellular matrix molecules and bioactive motifs in order to encourage integrin-mediated cellular responses that trigger precise intracellular signaling processes, while limiting nonspecific biomaterial interactions. Consequently, this dissertation addresses three approaches to modulating cellular behavior on elastin-mimetic analogs with the goal of promoting vascular wall healing and tissue regeneration: genetic engineering of elastin-like protein polymers (ELPs) with cell-binding domains, biofunctionalization of elastin-like protein polymers via chemoselective ligation of bioactive ligands, and incorporation of matrix protein fibronectin for engineering of cell-seeded multilamellar collagen-reinforced elastin-like constructs. The synthesis of recombinant elastin-like protein polymers that integrate biologic functions of the extracellular matrix provides a novel design strategy for generating clinically durable vascular substitutes. Ultimately, the synthesis of model protein networks provides new insights into the relationship between molecular architecture, biomimetic ligand presentation, and associated cellular responses at the cell-material interface. Understanding how each of these design parameters affects cell response will contribute significantly to the rational engineering of bioactive materials. Potential applications for polymer blends with enhanced mechanical and biological properties include surface coatings on vascular grafts and stents, as well as composite materials for tissue engineered scaffolds and vascular substitutes.

Titanium and titanium alloys are frequently used for implants in bone contact. In some cases (diabetis, osteoporosis) there are requirements for improved osseointegration. Initial reactions after surgery show an important influence on the long time stability of the implants. Newer studies focus on the surface composition of the implants in particular the modification with biological components. Collagen is the main component of bone and is therefore an interesting substance for the base modification of titanium implants. The aim of the work was to investigate the adsorptive immobilisation of collagen type I on titanium surfaces. The influence of different adsorption parameters was studied. Several modified surfaces were characterized in matters of immobilized collagen amount, stability, change of conformation and influence on cell behavior. / Titanimplantate werden aufgrund ihrer ausgezeichneten Volumen- und Oberflächeneigenschaften seit vielen Jahren mit großem Erfolg als Implantatmaterialien im Knochenkontakt eingesetzt. Für bestimmte Patientengruppen, u.a. Diabetiker oder Patienten mit osteoporotischem Knochen, ist ein weitergehend verbessertes Einheilverhalten der Implantate anstrebenswert. Entscheidende Bedeutung für den Einheilprozess sowie für die Langzeitstabilität wird der initialen Reaktion des Körpers unmittelbar nach Implantation zugemessen. Neben zahlreichen Ansätzen, durch Modifizierung der chemischen und morphologischen Eigenschaften der Oberfläche in die Reaktionen des Körpers einzugreifen, rückt in neueren Studien zunehmend die Immobilisierung biologischer Komponenten (Proteine, Peptide, Wachstumsfaktoren) in den Mittelpunkt der Betrachtungen. Die Einbeziehung von Kollagen als Hauptbestandteil der organischen Knochenmatrix stellt daher eine interessante Grundmodifikation dar. Das Ziel dieser Arbeit bestand darin, zu untersuchen, inwieweit durch eine adsorptive Immobilisierung von Kollagen eine stabile und funktionale Beschichtung von Titanoxidoberflächen erzielt werden kann. Da sowohl Tropokollagen als auch fibrilläres Kollagen prinzipiell zur Beschichtung von Titanoberflächen eingesetzt werden können, wurde das Adsorptionsverhalten beider Kollagenformen in bezug auf verschiedene Lösungsparameter untersucht und ausgewählte Zustände hinsichtlich ihrer Stabilität und der Erhaltung der biologischen Funktionalität charakterisiert.

Die Immobilisierung von Oligo(ethylenglykol)-derivaten an Oberflächen von Metallen ist ein viel versprechender Ansatz, um unspezifische Adsorptionen von Proteinen, Bakterien und Zellen zu minimieren bzw. zu verhindern. Im Mittelpunkt der Arbeit stand die Entwicklung, Darstellung, Charakterisierung sowie Applikation maßgeschneiderter, self-assembly-fähiger Moleküle, die gezielt auf TiO2- und nicht auf SiO2-Oberflächen anbinden. Die resultierenden Monoschichten (SAMs) wiesen eine Biokompatibilität sowie Biofunktionalität auf. Dazu wurden neue bisher noch nicht beschriebene Moleküle entwickelt, die auf einer Kombination von funktionalisierten Oligo(ethylenglykol)-Einheiten mit Monoalkylphosphorsäure- und Alkylphosphonsäurederivaten basieren. Diese Verbindungen konnten durch die Anwendung der Self-Assembly-Technik erfolgreich aus wässriger Lösung auf TiO2-Substrate adsorbiert werden. Die hergestellten, ultradünnen monomolekularen Schichten wurden mit verschiedenen analytischen Methoden, wie Spektroskopische Ellipsometrie, winkelabhängiger XPS und SPR-Spektroskopie charakterisiert. Durch eine gezielte Anbindung an TiO2-Oberflächen und einer stabilen Ausbildung von SAMs konnten sowohl die unspezifische Proteinadsorption zurückgedrängt bzw. verhindert, als auch eine spezifische Anbindung von ausgewählten Proteinen realisiert werden. / The surface immobilization of oligo (ethylene glycol) on metals is a promising approach to minimize or prevent non-specific adsorption of proteins, bacteria and cells. The aim of this work was the design, preparation, characterization and application of tailor-made, self-assembly molecules, which are able to adsorbed selectively on TiO2 surfaces but not on SiO2. The resulting self-assembled monolayers (SAMs) had a biocompatibility and bio functionality. For this purpose new molecules have been developed, which are not described in the literature. These compounds are derivatives of monoalkyl phosphoric acids or alkyl phosphonic acids and contain a terminal functional oligo (ethylene glycol) unit. The compounds were assembled on the TiO2-surface by self-assembly technique from aqueous solution. The adsorbed layers were characterized by different analytical tools, like angle resolved XPS, spectroscopic ellipsometry and SPR-spectroscopy. The selective adsorption of SAMs on TiO2-surfaces and the formation of stable SAMs make it possible to prevent or minimize non specific protein adsorption and also to bind selected proteins via specific surface reactions.

In this thesis, fluid characteristics and sampling efficiency of high molecular weight cut-off microdialysis are presented, with the aim of improving the understanding of microdialysis sampling mechanisms and its performance regarding extraction efficiency of biological fluid and biomarkers. Microdialysis is a well-established clinical sampling tool for monitoring small biomarkers such as lactate and glucose. In recent years, interest has raised in using high molecular weight cut-off microdialysis to sample macro molecules such as neuropeptides, cytokines and proteins. However, with the increase of the membrane pore size, high molecular weight cut-off microdialysis exhibits drawbacks such like unstable catheter performance, imbalanced fluid recovery, low and unstable molecule extraction efficiency, etc. But still, the fluid characteristics of high molecular weight cut-off microdialysis is rarely studied, and the clinical or in vitro molecule sampling efficiency from recent studies vary from each other and are difficult to compare.   Therefore, in this thesis three aspects of high molecular weight cut-off microdialysis have been explored. The first, the fluid characteristics of large pore microdialysis has been investigated, theoretically and experimentally. The results suggest that the experimental fluid recovery is in consistency with its theoretical formula. The second, the macromolecule transport behaviour has been visualized and semi-quantified, using an in vitro test system and fluorescence imaging. The third, two in vitro tests have been done to mimic in vivo cerebrospinal fluid sampling under pressurization, using native and differently surface modified catheters. As results, individual protein/peptide extraction efficiencies were achieved, using targeted mass spectrometry analysis. In summary, a theory system of the fluid characteristics of high molecular weight cut-off microdialysis has been built and testified; Macromolecular transport of microdialysis catheter has been visualized; In vivo biomolecules sampling has been simulated by well-defined in vitro studies; Individual biomolecular extraction efficiency has been shown; Different surface modifications of microdialysis catheter have been investigated. It was found that, improved sampling performance can be achieved, in terms of balanced fluid recovery and controlled protein extraction efficiency.

This thesis focuses on the use of surface modifiers to tune the properties of both metals and metal oxides. Particular attention is given to examine the modification of transparent conducting oxides (TCOs) including indium tin oxide and zinc oxide both through the use of phosphonic acids as well as organic and metal-organic dopants. In this thesis a variety of known and new phosphonic acids are synthesized. A subset of these molecules are then used to probe the relationship between the ability of a phosphonic acid to tune the work function of ITO and how that interrelates with the coverage and molecular orientation of the modifier on the surface. Experimental techniques including XPS, UPS, and NEXAFS are coupled with theoretical DFT calculations in order to more closely examine this relationship. Literature surrounding the modification of zinc oxide with phosphonic acids is not as prevalent as that found for the modification of ITO. Thus, effort is placed on attempting to determine optimal modification conditions for phosphonic acids on zinc oxide. As zinc oxide is already a low work function metal oxide, modifiers were synthesized in an attempt to further decrease the work function of this substrate in an effort to minimize the barrier to carrier collection/injection. Etching of the substrate by phosphonic acids is also examined. In a related technique, n- and p-dopants are used to modify the surfaces of ITO, zinc oxide, and gold and it was found that the work function can be drastically altered, to approximately 3.3 – 3.6 eV for all three of the substrates examined. Surface reactions are straightforward to conduct typically taking only 60 s to achieve this change in work function.

The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram]/cm2), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling. / text

This dissertation has focused on i) optimizing charge transfer rates at indium-tinoxide (ITO) electrodes, and ii) characterization of the supramolecular structure and properties of ultra thin surface modifier films on modified electrodes for various device applications. Commercial ITO surfaces were modified using conducting polymer thin film architectures with and without various chemical activation procedures. Ferrocene derivatives were used as redox probes, which showed dramatic changes in electron transfer rate as the SA-PANI/PAA layers were added to the ITO surface. Highest rates of electron transfer were observed for DMFc, whose oxidation potential coincides with the potential region where these SA-PANI/PAA films reach their optimal electroactivity. Apparent heterogeneous electron transfer rate constants, kS, measured voltammetrically, were ca.10 x higher for SA-PANI/PAA films on ITO, versus clean ITO substrates. These films also showed linear potentiometric responses with retention of the ITO transparency with the capability to create smoothest films using an aqueous deposition protocol, which proved important in other applications. ITO electrodes were also modified via chemisorption of carboxy functionalized EDOTCA and electropolymerization of PEDOTCA/PEDOT copolymers, when properly optimized for thickness and structure, enhance voltammetrically determined electron transfer rates (kS) to solution probe molecules, such as dimethylferrocene (DMFc). Values of kS ≥ 0.4 cm•sec⁻¹, were determined, approaching rates seen on clean gold surfaces. ITO activation combined with formation of these co-polymer films has the effect of enhancing the electroactive fraction of electrode surface, versus a non-activated, unmodified ITO electrode, which acts as a “blocked” electrode. The electroactivity and spectroelectrochemistry of these films helped to resolve the electron transfer rate mechanism and enabled the construction of models in combination with AFM, XPS, UPS and RAIRS studies. The surface topography, structure, composition, work function and contact angle, also revealed other desirable properties for molecular electronic devices. The carboxylic functionality of the EDOTCA molecule adds more desirable properties compared to normal PEDOT films, such as favoring the deposition of smooth films, increasing the optical contrast, participating in hydrogen-bonding, chemisorption to oxide surface, self-doping and providing a linker for incorporation of different functional groups, new molecules, or nanoparticles. Periodic sub-micron electrode arrays can be created using micro-contact printing and electropolymerization. The sinusoidal modulation of the refractive index of such confined conducting polymer nanostructures or nanoparticle stripes allows efficient visible light diffraction. The modulation of the diffraction efficiency at PANI and PEDOT gratings in the presence of an analytical stimulus such as pH or potential demonstrate the sensing capability at these surfaces. The template stripped gold surfaces that are being developed in our lab demonstrate several advantages over commercially available evaporated gold films especially for nanoscale surface modification.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Superparamagnetic iron oxide (Fe3O4 and γ-Fe2O3) nanoparticles (IONPs) are of great in-terest as a diagnostic and/or therapeutic aid. Several IONPs with biocompatible polymer coatings have been approved for clinical use, as MRI contrast agents. IONPs conjugated to targeting ligands and therapeutic agents are being investigated for targeted drug deliv-ery applications. The superparamagnetic properties of IONPs are also helpful for magnetic field assisted localization to specific target sites and for in situ MRI applications. This thesis primarily focuses on the synthesis and surface modifications (with biocompatible polymers including dextran, poly(ethylene glycol) (PEG), dextran, poly(ethyl methacry-late) (PEMA), poly(hydroxyethyl methacrylate) (PHEMA), etc.) of IONPs. The IONPs were prepared following the classical co-precipitation method and a novel reduction-hydrolysis method. Initial studies used bovine serum albumin (BSA) to examine the ca-pabilities of polymer coated IONP to deliver a model protein therapeutic. Gel migration studies using BSA physisorbed onto polymer coated IONP under gradient magnetic field of an MRI showed that the IONPs had limited control in transporting the protein. Cova-lent linking of therapeutics to IONP core can improve the time window of formers con-trollability using magnetic field. To facilitate covalent conjugations, functional silane coated IONPs (with surface amino and carboxylic acid) were prepared as general precur-sors. The utility of silane coated IONPs for bioconjugations was demonstrated by cova-lently linking PEG diacid through surface amino groups and by linking of BSA through surface carboxylic acid groups. The biocompatibility of the IONPs synthesized following the novel reduction-hydrolysis method were assessed in vitro on cell culture models using toxicity assays. The versatile reduction-hydrolysis method was further extended, as a general method to prepare several early transition metal oxide NPs (manganese oxide (Mn3O4), cobalt oxide (Co3O4), nickel/nickel oxide (Ni/NiO), copper/copper oxide (Cu/Cu2O) and zinc oxide (ZnO) NPs), silica nanoparticles with surface IONPs, and iron/iron oxide nanosheets.