Polymers for biodegradable medical devices XI. Microencapsulation studies: characterization of hydrocortisone-loaded poly-hydroxybutyrate-hydroxyvalerate microspheres

Abstract

Hydrocortisone-loaded monolithic microspheres were prepared, using a single emulsion solvent evaporation process, from a range of poly-beta-hydroxybutyrate-hydroxyvalerate copolymers in which both molecular weight and hydroxyvalerate content were varied. Many similarities were observed in the effects of process parameters and co-polymer composition on the morphologies of the microspheres, and the morphologies of microcapsules prepared (and previously reported) by a double emulsion process. The yields of the single emulsion process were generally superior to those of the double emulsion process, although these were adversely affected by hydrocortisone incorporation as the molecular weight of the copolymer was reduced. The predominant effect of hydrocortisone incorporation was on polymer morphology, characterized by the appearance of small surface pores; an effect which increased with increasing drug loading. Changes in polymer molecular weight, copolymer composition and process temperature, together with the incorporation of polycaprolactone in the form of a solvent blend, enabled microspheres with a range of morphologies to be produced providing the potential for control of drug release.