Evaluation of highly-water soluble drug physical state in biodegradable microcapsules

Abstract

Microencapsulation of highly water soluble pharmaceuticals (solubility more than mg/ml) especially if high drug loading is required (more than 50%) is a big challenge. Biodegradable poly(lactic acid) (PLLA) as coating material and polyvinyl alcohol as surfactant were found suitable for this purpose. Active substance was microencapsulated using slightly modified water-in-oil-in-water technique which involves dissolving of the drug in water and polymer in methylene chloride and forming an emulsion in water using a surfactant. Procedure of microencapsulation was followed by filtration and drying of product obtained. To evaluate the drug physical state in microcapsules powder X-Ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used. Differential scanning calorimetry analysis confirmed absence of any drug-polymer interaction. At the same time decrease of glass transition temperature (Tg) of microcapsules testify that molecularly dispersed drug is forming a true solution with a polymer. X-ray diffraction patterns showed the changes of polymer crystallinity during the encapsulation procedure as well as decrease of crystallinity of the drug. SEM investigations showed the morphology of obtained product and demonstrated the drug location inside the capsule. © 2008 Springer-Verlag.