(144g) Organohydrogels From Thermogelling, Photocurable Nanoemulsions: Formulation, Properties, and Applications

Hydrogels are attractive biocompatible materials due to their ability to immobilize, transport, and deliver soluble therapeutics and macromolecules. Conversely, organogels are rapidly emerging as an alternative for storage and delivery of hydrophobic species. Combining the useful properties of both types of materials, we have discovered a novel class of ?organohydrogels? based on nanoemulsions composed of a simple oil dispersed in a photopolymerizable aqueous phase containing functionalized polyethylene gycols (PEGs). This presentation explores the colloidal properties, microstructure, and rheology of these nanoemulsions toward the design of functional materials for pharmaceuticals and therapeutics. The nanoemulsions are prepared by high-pressure homogenization, yielding nanodroplets with low polydispersity (< 20%) with sizes ranging from 30-300 nm. The resulting dispersion exhibits thermoreversible gelation at elevated temperatures to form a viscoelastic solid, whose mechanical properties can be tuned over a wide range through a number of physicochemical conditions, including temperature, volume fraction of droplets, and PEG molecular weight. Small angle neutron scattering (SANS) measurements reveal that this gelation is due to the formation of a fractal-like network of droplets, similar to a colloidal gel, induced by effective inter-droplet attractions. We hypothesize that these interactions are mediated by the self-assembly of functionalized PEGs at the oil-water interface, and demonstrate that these interactions can be tuned by changing the PEG functionality, resulting in further ability to tune the structure and rheology of the resulting organohydrogel. Furthermore, the ability of photopolymerization to ?lock in? the gelled network at any point throughout the gelation process holds potential for developing organohydrogels with highly controllable nanostructure. Finally, we demonstrate the utility of these materials through the synthesis of organohydrogel colloids for the simultaneous encapsulation and release of hydrophilic and hydrophobic compounds.