Faculty Sponsor's Department(s):
Hydrogels are present in a huge variety of consumer products, including contact lenses and wound dressings. In order to improve these types of products, we aim to understand how manipulation of their structure changes diffusive properties. Because hydrogels also exhibit promise as a vehicle for triggered delivery of macromolecules, we decided to study how changes in the external environment (e.g. temperature, pH) can trigger release of cargo. For our tests, we used hydrogels polymerized from poly(ethylene glycol) diacrylate (PEGDA) because they are cost-effective, biocompatible, and commonly studied. We investigated how different pH conditions affect the diffusivity, as a result of changes in structure, of PEGDA hydrogels co-polymerized with pH responsive polymers. To do this, we co-polymerized PEGDA hydrogels with protonable co-monomers, then soaked each hydrogel in solutions of varying pH that contained fluorophores. The diffusion coefficient of the fluorophore in the hydrogel was measured using Fluorescence Recovery After Photobleaching (FRAP), and compared to the coefficients of the same hydrogel compositions at neutral pH. Previous work shows that hydrogel swelling can be controlled, depending on co-monomer, by pH. Therefore, we hypothesize these gels will yield much higher diffusion coefficients than unswelled gels in neutral pH. If diffusion coefficients increase as expected, they will serve as an indication that the pH-induced swelling significantly changes the microscopic structure of the hydrogels. Alternatively, small differences in diffusion coefficients will indicate that the local microscopic structure does not change enough to significantly impact diffusivity, thus requiring different methods to trigger release of cargo.