Chiang Mai Journal of Science

A method for the formation of polymer-lipid nanoparticles (Astosomes) is described. These lipid-based structures have been shown to be capable of being loaded with hydrophobic compounds. A range of dyes (oil red O, rhodamine B, basic fuchsin and fluorescein sodium salt) differing in structure were used as surrogate compounds for drugs in order to characterize the factors that affect incorporation and release. The incorporation methodology allowed each of these compounds, which were widely different in chemical structure, to be incorporated into the polymer-lipid complexes prior to polymerization with hydrogel-forming monomers. The surface behaviour of the complexes under compression, measured using a Langmuir trough, proved to be a useful method of characterizing them in both non-loaded and loaded forms. These loaded polymer-lipid nanoparticles were then encapsulated into hydrogels to give optically clear hydrophilic polymer matrices. Poly(hydroxyethyl methacrylate-co-methacrylic acid), poly(HEMA-co-MAA), hydrogel matrixes were prepared by the redox polymerization of HEMA and MAA monomers using ethylene glycol dimethacrylate as cross-linking agent and Oxone and ascorbic acid as initiators. The release studies of model drugs delivered from hydrogels were carried out in phosphate buffers of pH 7.4 and pH 9.2 and were determined by fluorimetry. The extents of release were dependent on the partition coefficients and the ionization of the drugs, the release medium and the degree of hydrogel swelling. Results indicate that the loaded hydrogels can deliver model drugs at a slow rate for a long period and offer a useful technology for the development of therapeutic contact lenses with long-term controlled drug release characteristics. This would be of particular value in the case of the new generation of lenses which can be worn continuously for 30 consecutive day and night period.