Hyaluronan-based microspheres as tools for drug delivery: a comparative study

The present paper describes the production of biodegradable microparticles using different hyaluronan polymers, such as native hyaluronan, the esterified derivative of hyaluronan Hyaff 11p50 (where 50% of the carboxy groups of hyaluronic acid are esterified with benzyl alcohol) and the autocross-linked polymer (ACP) internally esterified derivative of hyaluronan, by solvent evaporation and spray-drying methods. As model drugs cromolyn sodium salt, metronidazole and prednisolone hemisuccinate sodium salt were employed. The influence of polymer and preparation procedure has been evaluated on microparticle characteristics (i.e. morphology and encapsulation yield) and on the drug release profiles. The use of solvent evaporation method, a polymeric matrix constituted of Hyaff 11p50 3% (w/v), a dispersing phase constituted of 80 g of mineral oil (w/o ratio: 0.1), Span 85 0.1% (w/w) as stabilizer, and a stirring speed of 700 rpm resulted in the production of microspheres characterized by spherical shape, absence of aggregates, a mean diameter of 6.4 μm and a recovery of 90% (w/w). The production of drug containing microspheres led to an increase of mean diameter of microspheres and to high encapsulation yields. Moreover in vitro models have demonstrated that in all cases drugs were released from Hyaff 11p50 microspheres in a controlled fashion. Finally mathematical analysis of the drug release modalities has evidenced that drug release from Hyaff 11p50 microspheres is more consistent with kinetics of the diffusion rather than of the dissolution type.