E-beam irradiation and UV photocrosslinking of microemulsion-laden poly(N-vinyl-2-pyrrolidone) hydrogels for "in situ" encapsulation of volatile hydrophobic compounds

Gelled microemulsions are the subject of considerable scientific and commercial interest. Many efforts are currently devoted to improving their toxicological profile and functioning as biocompatible diffusion barrier for the controlled delivery of hydrophobic compounds. In the present investigation, a non-ionic polymeric surfactant was chosen to generate an oil-in-water microemulsion of a model fragrance in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). The microemulsion was then subjected to either electron-beam or UV-irradiation to induce free-radical crosslinking of PVP at low temperature and in the absence of crosslinking agents, catalysts and initiators. Irradiation conditions with the two irradiation sources have been purposely selected to generate PVP hydrogels with similar appearances and mechanical spectra. Despite the macroscopic analogies, specific features are imparted to the two families of hydrogels by the two different irradiation methodologies. A description of the microstructure of both pure PVP and microemulsion-laden hydrogels is given starting from the dynamic light scattering (DLS) characterization of the liquid (unirradiated) formulations, followed by the study the hydrogels' dynamic mechanical, solubility and swelling properties, FTIR analysis of the water insoluble fractions, DLS measurements and cytotoxicity studies.