Fluorescent nanotubes in PHEMA hydrogels: Visualizing aggregation and distribution by confocal fluorescence microscopy

In this work, physical hydrogels of poly(2-hydroxyethyl methacrylate) loaded with fluorescein-labelled halloysite nanoparticles were synthesized. The nanoparticles were first functionalized with amino groups and subsequently labelled with fluorescein isothiocyanate (FITC). Hydrogels were then synthesized by in situ polymerization using different contents of halloysite. The thermal properties of the resulting hydrogels were studied by differential scanning calorimetry and thermogravimetric analysis, the mechanical properties were examined by dynamic mechanical analysis, and the distribution of nanoparticles was determined by confocal microscopy. The results indicated that the addition of nanoparticles lowered the glass transition and decomposition temperatures of the hydrogels. Mechanical tests showed that the addition of 0.5 wt% nanoparticles led to an increase in the compression and relaxation moduli and a decrease in the relaxation time when the polymer was subjected to stress relaxation assays. Finally, the two-and three-dimensional distributions of nanoparticles in the hydrogel were examined by confocal microscopy and showed the formation of agglomerates with sizes in the range of 1-30 mu m, where larger agglomerates formed with larger contents of nanoparticles, which was correlated to the measured mechanical properties.