Quercetin microspheres by solvent evaporation: preparation, characterization and release behavior

Quercetin (Q) gastro-resistant microspheres were successfully prepared by solvent evaporation method using cellulose acetate phthalate (C-A-P), cellulose acetate propionate (CAP), or their mixtures in different ratios as matrices. The formulation and preparation conditions (stirring speed, polymer concentration, drug-to-polymer ratio, temperature) were optimized to obtain high encapsulation efficiency and production yield. The prepared microspheres were submitted to several chemical–physical analyses (light scattering, fluorescence and scanning electron microscopy, X-ray diffractometry, calorimetry, infrared spectroscopy), to obtain information about particle size distribution, drug loading, and morphology. Moreover, their release properties were investigated performing in vitro dissolution studies with a pH change method. The release tests evidenced that all samples exhibit a fairly gastro-resistance with a typical biphasic drug release trend, due to the pH-dependent solubility of the enteric polymers used as matrices. Moreover, the total amount of released quercetin strictly depends on the system composition, increasing with the C-A-P percentage in the formulation to such an extent that it is about complete (∼ 90%) in the case of C-A-P microspheres.