Hydrogel nanoparticles and assemblies for bioapplications
Gaulding, Jeffrey Clinton
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Hydrogels are cross-linked networks of highly hydrophilic polymer chains. When reduced to colloidal dimensions, particles of this sort are termed “microgels�? and both discrete particles and ensembles have intriguing properties. Microgels can be made to be susceptible to numerous environmental stimuli, such as temperature and pH. The resultant changes in the network hydration lead to characteristic swelling responses which can have great impact on properties of the gel network such as the porosity, hydrophilicity, stiffness, or particle-particle packing. The multitude of responsive stimuli; the architectural versatility of discrete particles; and the variety of particle ensembles have made the study of microgels and their assemblies a very rich field. Primarily due to their physiological softness and the aforementioned versatility, responsive microgels are of great interest as a material to address the daunting challenges facing the next generation of healthcare. This dissertation describes investigations into hydrogel nanoparticles and assemblies thereof, with the goals of expanding their utility in applications such as drug delivery and non-fouling interfaces through the development of novel materials to both extend their synthetic versatility and to probe their underlying properties. Physiologically-relevant degradable cross-linking within microgels is studied, though the incorporation of hydrolytically degradable or reduction-responsive cross-links. More complex structures are demonstrated for both types of cross-linking as synthetic and architectural control enables additional functional microgel designs. Microgel assemblies, particularly thin films, have been demonstrated to have numerous desirable properties for biological applications, such as reduced cell attachment, drug delivery, and self-healing capabilities. This dissertation includes additional fundamental studies of microgel films, both in their synthesis, such as methods for depositing films onto colloidal substrates, and in their application, as investigations into the origins and critical factors for self-healing films. Further, the cell-resistant properties of microgel multilayers are studied and evidence suggests that the viscoelastic or mobile character of the films is likely the main factor that directs cell adhesion. The work in this dissertation serves to both expand our toolset with regard to the functional synthesis of microgels and assemblies and to improve our fundamental understanding of phenomena of interest for a variety of potential applications. Both of these should serve to allow the enormous potential of hydrogel nanoparticles and their assemblies to be more efficiently tapped for a wide range of applications in the field of biomaterials.