STABILITY OF POLY (EPSILON-CAPROLACTON) NANOSPHERES IN STERILE AQUEOUS-MEDIA

Polyester nanoparticles have shown promising results in the ophthalmic area for optimization of the bioavailability of drugs. However, polye sters can undergo hydrolysis during storage in aqueous media and their degradation can be enhanced by micro-organisms. Poly (epsilon caprola cton) (PEG) nanospheres were formulated for an ophthalmic application, i.e. sterile, isotonic and containing a preservative. Their physical and chemical stabilities were studied during a 6-month storage at 25 a nd 40 degrees C. The influence of temperature, surfactant, viscosifian t addition, and buffered or non-buffered pH was evaluated. The physica l stability of nanospheres was followed by the study of visual appeara nce and mean particle size. The pH and tonicity of the suspensions, an d the molecular weight and crystallinity of PEC were additionally anal yzed to evaluate their chemical stability. The influence of surfactant s was observed only on the nanosphere physical stability. Better resul ts were obtained with Pluronic F127. The degradation of PEC was especi ally affected by pH and temperature. At 25 degrees C and pH 7, the var iation of polymer molecular weight was negligible. At 40 degrees C, th e hydrolysis rate increased with a loss of 50% of the initial molecula r weight after 6 months in pH 7 buffer, and 60% in non-buffered pH 7 m edium. Finally, the mean particle size of all nanospheres remained unc hanged throughout this study.