|M.Sc Student||Ovadia Maya|
|Subject||Hydrogel-Based Porous Polymers via Emulsion Templating|
|Department||Department of Materials Science and Engineering||Supervisor||Professor Michael Silverstein|
|Full Thesis text|
This work describes the synthesis of emulsion-templated highly porous polyHIPE hydrogels. Hydrogels, hydrophilic polymers with three dimensional network structures that undergo extensive swelling in water, are sensitive to their environment (temperature, pH, ionic strength). Natural hydrogels from renewable resources have advantageous biocompatibility compared to synthetic hydrogels. PolyHIPEs are highly porous emulsion-templated polymers synthesized in high internal phase emulsions (HIPEs), emulsions with dispersed phase volume fractions greater than 0.74. PolyHIPEs, with unique porous structures that absorb large quantities of liquids through capillary action, seem especially suitable for the development of highly porous hydrogels. Using ionic monomers, monomers for lower critical solution temperature (LCST) polymers, and natural polymers in hydrogel polyHIPEs should affect their porous structures and properties.
The objectives of this research were to synthesize novel hydrogel-based polyHIPEs using various types of monomers (including non-ionic, ionic, and LCST-producing) and using natural renewable resource polymers and to investigate their synthesis-structure-property relationships. The densities, porous morphologies (scanning electron microscopy), mechanical properties (uniaxial compression), thermal transitions (differential scanning calorimetry) and water uptakes of these hydrogel polyHIPEs were characterized and a model was developed to describe polyHIPE void swelling.
PolyHIPEs based on copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) exhibited pH-sensitive and salt-concentration-sensitive water uptakes. The water uptake mechanism changed from Fickian to anomalous as the pH increased, with a maximum equilibrium water uptake of 1800%. The equilibrium water uptake decreased as the salt solution concentration increased and was not significantly affected by the ionic strength. PolyHIPEs based on copolymers of HEMA, N-isopropylacrylamide (NiPAAm), and N,N’-methylenebisacrylamide (MBAM) exhibited LCSTs at 40°C, around 8°C higher than PNiPAAm's owing to the MBAM crosslinking. Combined-network hydrogel polyHIPEs containing either gelatin or alginate, natural renewable resources polymers, were successfully synthesized within a PHEMA-based polyHIPE using a two-stage sequential polymerization procedure, filling the voids and the interconnecting holes. Combined-network hydrogel polyHIPEs containing gelatin were also synthesized using a one-stage simultaneous polymerization. The gelatin phase-separated prior to HEMA polymerization, yielding an assembly of PHEMA-coated gelatin spheres. A polyurea polyHIPE, based on the reaction between an aqueous alginate solution in the internal phase with isocyanate in the external phase, exhibited millimeter-scale "craters" (CO2 is generated as a by-product) and 5 µm scale voids within the walls between the craters. This research has conclusively demonstrated that a large number of hydrogel polyHIPEs with very different porous structures and very different properties can be synthesized through emulsion templating.