Hydrogels are water-swellable cross-linked polymeric networks that are capable of incorporating a variety of functionalities and responsivities. The stable colloidal form of a hydrogel is known as a microgel and ranges in size from the nano- to the micrometer scale. Microgels can exhibit similar properties to hydrogels, but the colloidal size of the microgel creates differences in their responsive behavior, such as faster reaction kinetics, as compared to their macrogel counterpart. Microgels have been explored for a broad range of applications, either as individual entities or within large scale assemblies. Although these materials have shown a great deal of utility and versatility, microgels have also demonstrated a great deal of complexity due to the fact that they exhibit both polymeric and colloidal properties. This so-called polymer/colloid duality creates intricacies in characterizing the behavior of these materials, especially when coupled with an oppositely charged component within multilayered assemblies. In this dissertation, work is focused primarily on building a greater fundamental understanding of microgels and their behavior within large scale assemblies. This is done through the development of new characterization techniques or through a direct visualization of the interactions of microgels with their surrounding environment with emphasis on their interaction with an oppositely charged linear polyelectrolyte. From these studies, a more developed fundamental understanding of microgels and their assembly into complex structures is obtained, and these findings will aide in the development of future applications of microgel assemblies.

Hydrogels, which are polymeric cross-linked networks that swell in aqueous environments, are versatile materials that can contain a variety of chemical functionalities, mechanical properties, and topographical features. Microgels are the stable colloidal form of hydrogel materials that range in size from approximately 100 nm to a few microns in diameter. While they also can exhibit similar properties to those of macrogels, microgels can be used as building blocks in a bottom-up approach to assemble films of higher complexity. In this dissertation, work is focused on understanding the assembly and behavior of microgel thin films as non-fouling surfaces, centrifugally deposited materials, self-healing coatings, and degradable constructs. Non-fouling films were assembled using PEG cross-linked microgels to reduce non-specific protein adsorption and mitigate cellular adhesion. These constructs were assembled in a polyelectrolyte multi-layered fashion, of alternating anionic microgels and cationic linear polymer, to effectively block the substrate from the biological environment and consequently exhibited control over cellular adhesion with the surface. The utility and application of these non-fouling microgel coatings on functional implants was also explored. Centrifugal deposition was used to rapidly generate non-fouling microgel multi-layered interfaces on planar surfaces, and upon closer inspection of the microgel monolayers, it was found that the centrifugally deposited films contained closer-packed microgel assemblies with microgels of smaller footprint size, compared to microgels that are passively adsorbed to the surface. Microgels that are centrifugally deposited may adopt a higher energy chain conformation than passively adsorbed microgels, and this higher energy chain conformation may translate into the multi-layered materials. Nonetheless, the centrifugally deposited non-fouling microgel multi-layered films were found to effectively block macrophage adhesion. Films were also assembled in a polyelectrolyte fashion on soft substrates, and were observed to become significantly damaged under mechanical manipulation (poking, bending, or stretching), but then self-heal upon addition of water. By altering the building blocks of the polyelectrolyte multi-layered films, such as the molecular weight of the polycation between microgel layers or by using anionic rigid spheres as the particle in the assembly, changes in the observed film damage suggest that particle-linear polymer interpenetration and polyvalency likely play an important role in the strength and integrity of the microgel thin films. Fluorescently-labeled microgels were also used to interrogate how the films reorganize in the lateral direction, and these early studies suggest that the microgel multi-layered films reorganize when damaged and also possibly when they are undamaged and simply incubated in an aqueous environment. Additional studies were also conducted on microgels synthesized with a hydrolyzable cross-linker, and by supporting these degradable constructs on substrates, detailed single-particle morphological changes during erosion could be interrogated in complex media such as serum. This work, as a collection, demonstrates the ability to obtain information about microgel thin film assemblies and their behavior using microscopy techniques such as ambient and in liquid atomic force microscopy, brightfield optical microscopy, and fluorescence microscopy. The observations made here illustrate how microgels can be used to fabrication thin films that can be utilized in biological applications (non-fouling, self-healing, and erodable constructs), and how different deposition methods (centrifugal deposition and polyelectrolyte multi-layers) can dictate their behavior.