This dissertation studies the thermodynamic and structural properties of aqueous dispersions of ionic microgels ? soft colloidal particles composed of cross-linked polymer gels that swell in a good solvent. Starting from a coarse-grained model of microgel particles, we perform computer simulations and theoretical calculations using two complementary implementations of Poisson- Boltzmann (PB) theory. Within the framework of a cell model, the nonlinear PB equation is exactly solved and used to compute counterion distributions and osmotic pressures. By varying the free energy with respect to microgel size, we obtain exact statistical mechanical relations for the electrostatic component of the single-particle osmotic pressure. Explicit results are presented for equilibrium swelling ratios of charged microcapsules and of charged cylindrical and spherical microgels with fixed charge uniformly distributed over the surface or volume of the particle. Molecular dynamics simulations validate the theoretical findings. In the second method, within a one-component model framework, based on a linear-response approximation for effective electro- static interactions, we develop Monte Carlo (MC) simulations to compute the equilibrium swelling ratio, bulk osmotic pressure, radial distribution function, and static structure factor. Results presented in this dissertation demonstrate that swelling of ionic microgels increases with increasing microgel charge and decreases with increasing concentration of salt and microgels. In addition, results demonstrate that the microion distributions and osmotic pressure determine equilibrium swelling of microgels. Cell model predictions for bulk osmotic pressure agree well with data from MC simulations of the one-component model. The MC simulations also provide access to structural properties and to swelling behavior of microgels in highly concentrated suspensions. Taken together, results obtained in this work provide insight into factors of importance for practical use of microgels as drug delivery systems, in tissue engineering, and for other biomedical applications.

No description available.

Bio-interface topography strongly affects the nature and efficiency of interactions with living cells and biological molecules, making hydrogels decorated with micro and nanostructures an attractive choice for a wide range of biomedical applications. Despite the distinct advantages of protein hydrogels, literature in the field has disproportionately focused on synthetic polymers to the point that most methods are inherently incompatible with proteins and heat-sensitive molecules. We report the development of multiple biomolecule-friendly technologies to construct microstructured protein and bacteriophage (bacterial virus) hydrogels. Firstly, ordered and sphericity-controllable microbumps were obtained on the surface of protein hydrogels using polystyrene microporous templates. Addition of protein nanogels resulted in the hierarchical nano-on-micro morphology on the microbumps, exhibiting bacterial repellency 100 times stronger than a flat hydrogel surface. The developed microstructures are therefore especially suitable for antifouling applications. The microstructures created on protein hydrogels paved the way for applying honeycomb template on proteinous bacterial viruses. We developed a high-throughput method to manufacture isolated, homogenous, pure and hybrid phage microgels. The crosslinked phages in each phage-exclusive microgel self-organized and exhibited a highly-aligned nanofibrous texture. Sprays of hybrid microgels loaded with potent virulent phage effectively reduced heavy loads of multidrug resistant Escherichia coli O157:H7 on food products by 6 logs. / Thesis / Doctor of Philosophy (PhD) / Bacteriophages (bacterial viruses), also known as phages, are natural bacteria predators. These viruses act as direct missiles, each phage targeting limited groups of bacteria. In addition, phages are an endless resource for self-propagating nanoparticles that can be used as building blocks for new material. I developed a platform for manufacturing a large quantity of microscale beads made of millions of phages. These micro-beads can be sprayed on fresh produce and meat to remove bacterial contamination (with the added benefit of not affecting taste or smell). I also printed phages on substrates, like an ink. The printed phage ink evolved into a patented technology for designing phage coatings on surfaces with very high surface area, like the small structures on our fingers. This phage coating was successfully used to test the existence of bacteria in liquids.

<p>The interactions of microgel based adhesives with cellulose were studied by peel test of cellulose laminates and tensile test of handsheets. The objective of this project was to create design rules for microgel based adhesives so as to improve the wet paper strength. Colloidal microgel based adhesives were formed by coating carboxylated poly(Nisopropylacrylamide) (PNIPAM) microgels with polyvinylamine (PVAm). The characterization of the microgel base adhesives were performed by electrophoretic mobilities, dynamic light scattering, and potentiometric titration. The microgel based adhesives were pH sensitive and their swelling behaviour was related to the composition of PVAm in the microgels. The maximum amount of PVAm binding to microgels depends on the location of charges in the microgels and the molecular weight of PVAm. The binding process of PVAm to microgels was monitored by quartz crystal microbalance measurements. It is proposed that the binding of PVAm to microgels is controlled by the rate of initial attachment of PVAm and the rate of reconfiguration of PVAm on the microgels. The microgel based adhesives were laminated between oxidized cellulose films and the wet adhesion of microgel based adhesives with cellulose was studied by a 90° peel test. The wet delamination force was measured as a function of PVAm content, PVAm molecular weight, coverage of adhesives on cellulose films, size of adhesives, stiffness of adhesives and the roughness of cellulose films. The wet adhesion of microgel based adhesives with cellulose increased with PVAm content in the microgels, and decreased with microgel stiffness. The molecular weight of PVAm did not influence the performance of adhesives. The effect of microgel size on wet adhesion with cellulose was related to the roughness of cellulose films. Larger microgels did fill the voids between rough cellulose films to create more contact area with these films resulting in higher wet adhesion. By contrast, for smooth cellulose films, the size of microgels didn’t affect the wet adhesion. Finally, this basic research was extended to a practical situation. The microgel based adhesives were added to unbeaten, bleached softwood pulp to prepare handsheets and their ability to enhance wet paper strength was evaluated by tensile test. The wet paper strength increased with PVAm content of the microgels. For linear PVAm, high molecular weight PVAm was more effective as a wet strength adhesive while for PVAm coated microgels, the molecular weight was not significant for wet paper strength. With the aid of PVAm coating, solid carboxylated polystyrene particles improved the wet paper strength. However the wet strength of paper treated with PVAm coated microgels was larger than that treated with PVAm coated polystyrene by a factor of 2.</p> / Doctor of Philosophy (PhD)

Ce travail de thèse porte sur l’élaboration de microgels biocompatibles et multi-stimulables à base de méthacrylate d’oligo(éthylène glycol) et de nanoparticules d’oxyde de fer. Des microgels sensibles au pH, à la température et au champ magnétique ont été élaborés au cours de cette étude via une stratégie multi-étape partant de : 1. la synthèse et la caractérisation de microgels pH- et thermosensibles à base d’oligo(éthylène glycol), 2. l'élaboration de microgels hybrides par imprégnation de nanoparticules magnétiques au sein des microgels d’oligo(éthylène glycol). L’étude de la synthèse des microgels et de leurs propriétés physico-chimiques a permis de mettre en avant l’effet important de la structure interne des microgels sur leurs propriétés de gonflement/contraction. La caractérisation des microgels hybrides a mis en évidence l’importance des fonctions acide carboxylique réparties de manière homogène au sein des microgels, le tout permettant d’encapsuler efficacement et de manière homogène des nanoparticules magnétiques tout en préservant les propriétés colloïdales et thermo-stimulables des microgels hybrides. Enfin des films structurés constitués de multicouches de microgels ont ainsi pu être élaborés via un procédé simple de séchage de dispersion aqueuse de microgels. Une étude prospective des propriétés optique et mécanoélectrique de films auto-assemblés de microgels d’oligo(éthylène glycol) hybride et non hybride par évaporation de solvant a permis de mettre en évidence le rôle positif des groupements ioniques issus des fonctions carboxylates sur le potentiel électrique induit lors de la compression des films. / Smart polymer materials can provide wide range of options to induce advanced functional features and relevant surface properties in one material. This all-in-one concept is of great interest for applications that require several simultaneous treatments such as cosmetic application. Herein, we aim to develop oligo(ethylene glycol)-based biocompatible multiresponsive microgels that could both interact on the skin as smart drug delivery system (DDS) while fulfilling advanced properties such as surface protection, mechanical and optical properties. Specifically, aqueous dispersed microgels responsive to pH, temperature and magnetic field were synthesized via multi-step strategy: 1. The synthesis and characterization of pH- and thermo-responsive oligo(ethylene glycol)-based microgels by precipitation polymerization, 2. The encapsulation of pre-formed magnetic nanoparticles via adsorption of the nanoparticles into the multiresponsive microgels. The effect of the microgel microstructure on their pH- and thermo-responsive properties were highlighted thanks to a rational investigation of the crosslink density and acid-functional units distribution within the microgels. Oligo(ethylene glycol)-based microgels with homogeneous distribution of both acid-functional unit and crosslinker allowed the synthesis of highly pH-and thermo-responsive microgels. The hybrid microgels prepared by straightforward encapsulation of pre-formed magnetic nanoparticles were characterized. The homogeneous microstructure of the initial stimuli-responsive biocompatible microgels plays a crucial role for the design of unique well-defined ethylene glycol-based thermoresponsive hybrid microgels. Thus, robust monodisperse thermoresponsive magnetic microgels were produced, exhibiting both a constant value of the swelling-to-collapse transition temperature and good colloidal stability whatever the NPs content. These smart microgels can spontaneously form a transparent film with perfect arrangement of the microgels by simple solvent evaporation process. The characterization of the optical and mechanoelectrical properties of the self-assembled microgel films were performed. We highlighted that the presence of anionic charges inside the microgels emphasizes the mechanoelectrical effect of the films.

This work describes the results of experimental study of the flow of soft objects (microgels) through microchannels. This work was carried with the intention of building a fundamental biophysical model for the flow of neutrophil cells in microcirculatory system. In Chapter 1 we give a summary of the literature describing the flow of cells and “model cells” in microchannels. Paramount to this we developed methods to modify microchannels fabricated in poly(dimethyl siloxane) (PDMS). Originally, these microchannels could not be used to mimic biological microenvironments because they are hydrophobic and have rectangular cross-sections. We designed a method to create durable protein coatings in PDMS microchannels, as outlined in Chapter 3. Surface modification of the channels was accomplished by a two-step approach which included (i) the site-specific photografting of a layer of poly(acrylamide) (PAAm) to the PDMS surface and (ii) the bioconjugation of PAAm with the desired protein. This method is compatible with different channel geometries and it exhibits excellent longevity under shear stresses up to 1 dyn/cm. The modification was proven to be successful for various proteins of various molecular weights and does not affect protein activity. The microchannels were further modified by modifying the cross-sections in order to replicate cardiovascular flow conditions. In our work, we transformed the rectangular cross-sections into circular corss-sections. Microchannels were modified by polymerizing a liquid silicone oligomer around a gas stream coaxially introduced into the channel, as outlined in Chapter 3. We demonstrated the ability to control the diameter of circular cross-sections of microchannels. The flow behaviour of microgels in microchannels was studied in a series of experiments aimed at studying microgel flow (i) under electrostatic interactions (Chapter 4), (ii) binding of proteins attached to the microgel and the microchannel (Chapter 5) and (iii) under the conditions of varying channel geometry (Chapter 6). This work overall present’s new methods to study the flow of soft objects such as cells, in the confined geometries of microchannels. Using these methods, variables can be independently probed and analyzed.

No description available.

Cellulose is one of the most abundant biopolymers found in nature. Cellulose based derivatives have a number of advantages including recyclability, reproducibility, biocompatibility, biodegradability, cost effectiveness and availability in a wide variety of forms. Due to the benefits of cellulose based systems, this research study was aimed at developing novel cellulosic nanoparticles with potential pharmaceutical and personal care applications. Two different cellulosic systems were evaluated, each with its own benefits and proposed applications. The first project involves the synthesis and characterization of polyampholyte nanoparticles composed of chitosan and carboxymethyl cellulose (CMC), a cellulosic ether. EDC carbodiimide chemistry and inverse microemulsion technique was used to produce crosslinked nanoparticles. Chitosan and carboxymethyl cellulose provide amine and carboxylic acid functionality to the nanoparticles thereby making them pH responsive. Chitosan and carboxymethyl cellulose also make the nanoparticles biodegradable and biocompatible, making them suitable candidates for pharmaceutical applications. The synthesis was then extended to chitosan and modified methyl cellulose microgel system. The prime reason for using methyl cellulose was to introduce thermo-responsive characteristics to the microgel system. Methyl cellulose was modified by carboxymethylation to introduce carboxylic acid functionality, and the chitosan-modified methyl cellulose microgel system was found to be pH as well as temperature responsive. Several techniques were used to characterize the two microgel systems, for e.g. potentiometric and conductometric titrations, dynamic light scattering and zeta potential measurements. FTIR along with potentiometric and conductometric titration was used to confirm the carboxymethylation of methyl cellulose. For both systems, polyampholytic behaviour was observed in a pH range of 4-9. The microgels showed swelling at low and high pH values and deswelling at isoelectric point (IEP). Zeta potential values confirmed the presence of positive charges on the microgel at low pH, negative charges at high pH and neutral charge at the IEP. For chitosan-modified methyl cellulose microgel system, temperature dependent behaviour was observed with dynamic light scattering. The second research project involved the study of binding interaction between nanocrystalline cellulose (NCC) and an oppositely charged surfactant tetradecyl trimethyl ammonium bromide (TTAB). NCC is a crystalline form of cellulose obtained from natural sources like wood, cotton or animal sources. These rodlike nanocrystals prepared by acid hydrolysis of native cellulose possess negatively charged surface. The interaction between negatively charged NCC and cationic TTAB surfactant was examined and it was observed that in the presence of TTAB, aqueous suspensions of NCC became unstable and phase separated. A study of this kind is imperative since NCC suspensions are proposed to be used in personal care applications (such as shampoos and conditioners) which also consist of surfactant formulations. Therefore, NCC suspensions would not be useful for applications that employ an oppositely charged surfactant. In order to prevent destabilization, poly (ethylene glycol) methacrylate (PEGMA) chains were grafted on the NCC surface to prevent the phase separation in presence of a cationic surfactant. Grafting was carried out using the free radical approach. The NCC-TTAB polymer surfactant interactions were studied via isothermal titration calorimetry (ITC), surface tensiometry, conductivity measurements, phase separation and zeta potential measurements. The major forces involve in these systems are electrostatic and hydrophobic interactions. ITC and surface tension results confirmed two kinds of interactions: (i) electrostatically driven NCC-TTAB complexes formed in the bulk and at the interface and (ii) hydrophobically driven TTAB micellization on the NCC rods. Conductivity and surface tension results confirmed that the critical micelle concentration of TTAB (CMCTTAB) shifted to higher values in the presence of NCC. Phase separation measurements allowed us to identify the formation of large aggregates or hydrophobic flocs depending on the TTAB concentration. Formation of NCC-TTAB complexes in aqueous solutions was confirmed by a charge reversal from negative to positive charge on the NCC rods. The effect of electrolyte in shielding the negative charges on the NCC was observed from ITC, surface tensiometry and phase separation experiments. Several mechanisms have been proposed to explain the above results. Grafting of PEGMA on the NCC surface was confirmed using FTIR and ITC experiments. In phase separation experiments NCC-g-PEGMA samples showed greater stability in the presence of TTAB compared to unmodified NCC. By comparing ITC and phase separation results, an optimum grafting ratio (PEGMA : NCC) for steric stabilization was also proposed.

The goal of this thesis is to study the role of single particle elasticity in the overall behavior of particulate systems. For this purpose, we use microgel particles, which are crosslinked polymer networks immersed in a solvent. In these systems, the amount of cross-linker determines their elasticity and ultimately the stiffness of the particle. For a system of hard spheres, the phase behavior is solely determined by the volume fraction occupied by the particles. Based on the volume fraction, liquid, crystal and glassy phases are observed. Interestingly, microgel particles display a richer and fascinating set of different behaviors depending on the particle stiffness. Previous results obtained in our group show that for highly cross-linked microgels, the glass phase disappears and there are only liquid and crystalline phases. By contrast, preliminary measurements indicate that for ultrasoft microgel particles the system does not show any signature of crystalline or glassy phases. The system seems to remain liquid irrespective of volume fractions. In this Thesis, we will address this striking result using light scattering as well as rheology, in order to access both static and dynamic properties in a wide range of length and time scales. In addition, we will also perform additional studies using very stiff microgels and use their swelling capabilities to change the volume fraction. We will use hydrostatic pressure to change the miscibility of the polymer network and thus change the microgel size; the use of this external variable allows fast equilibration times and homogeneous changes throughout the sample. By using neutron scattering techniques, we study the structural and dynamical properties of the system in its different phases involved.

Detection of trace elements such as organic contaminants, explosive residues, and metal ions is an intellectually challenging task in science and engineering. It is also a topic of increasing importance due to its impact on society and the environment. Designing molecularly imprinted materials is one of the most promising approaches to explore sensing and detection applications. “Stimuli-sensitive” polymer materials are ideal candidates for these imprinted sensors as they are able to respond to changes in their environment and can be tailored by cross-linking the polymer chains. The responses can be amplified and transduced into measurable signals due to macromolecular properties provided by the use of a polymer. The purpose of the research in this project is to combine organic polymers with inorganic constituents to tailor the binding properties and the responses of the composite material for detection of metals ions in aqueous solutions. The research, here, is based on a thermally responsive polymer such as poly(Nisopropylacrylamide) (PNIPAM), which exhibits a well-known reversible volume phase transition in aqueous media around approximately 32°C. Combining cross-linked microgels formed from PNIPAM and its copolymers with gold nanoparticles (GNP) imparts the composite material with optical properties such as intense visible absorption due to the unique surface plasmon absorption of these small nanoparticles. The use of copolymers allows incorporation of functional groups, such as carboxylic acid, that are potential sites for binding metal ions. Cross-linking of the metal ion binding polymer imprints the metal ion in the PNIPAM microgel network. In this research, design of the composite material was investigated using copolymers of NIPAM and acrylic acid (AA), copolymers of NIPAM and glycidyl methacrylate (GMA), and interpenetrating networks of PNIPAM and PAA. A broad spectrum of polymerization conditions were studied such as changes in cross-linking density as well as changes in the synthetic procedure. Techniques such as turbidometry, ultraviolet visible spectroscopy (UV-VIS), transmission electron microscopy (TEM), and dynamic light scattering (DLS) were employed to characterize the microgels as well as their composites with GNP. Preliminary investigation of imprinting the microgels with heavy metal ions such as copper was also performed. The novel polymer-metal nanocomposites explored here will serve as an important contribution for the current ongoing research efforts in designing materials in the nano-scale capable of sensing and detecting metal ions in solution with high selectivity.