Advances in Materials Development of Responsive Photonic Crystal Hydrogels

We advanced the material development of our responsive photonic crystal hydrogels, which are utilized in our polymerized crystalline colloidal array (PCCA) technology. PCCA consist of a hydrogel network that embeds an array of monodisperse, highly-charged 100--200 nm polystyrene particles. The optical properties of the embedded array are such that it Bragg diffracts visible light. Responsive materials are fabricated by exploiting the volume-responsive nature of the hydrogel network, such that the material is functionalized to respond to a specific analyte of interest by actuating a volume change in the hydrogel, resulting in a change in the color of diffracted light. We prepared a new hydrogel system for the preparation of responsive PCCA based on the biocompatible and rehydratable polymer polyvinyl alcohol (PVA). This material can be reversibly dehydrated and rehydrated, without the use of fillers, while retaining the diffraction and swelling properties of polymerized crystalline colloidal arrays. This reversibility of rehydration of this new hydrogel material enables practical storage of hydrogel-based photonic crystal sensors in the dry state, which makes them much more useful for future commercial applications. We continued the development of our PCCA glucose sensing materials for application in monitoring relatively high glucose concentrations, such as found in blood. We modified our synthetic fabrication methodologies in order to increase the reproducibility of our sensing materials. We advanced our understanding of the sensing response by utilizing independently determined variables in our modeling of the PCCA diffraction response. We characterized our material's response dependence upon environmental variations and interferences. We completed the first quantitative study of how the mechanical properties of a swollen hydrogel depend upon the size of nonbonded embedded nanoparticles. We experimentally determined the dependence of the elastic shear storage modulus for our PCCA, as a function of embedded CCA size and prepolymerization conditions, and found that the modulus increases linearly with increasing CCA size due to interaction between the embedded nanoparticles and the hydrogel matrix. The effective hydrogel crosslink densities determined from these storage modulus values indicate that we can affect the responsivity of our photonic crystal materials by controlling the included nanoparticle size.