Ibuprofen-loaded ethylcellulose microspheres: release studies and analysis of the matrix structure through the Higuchi model

The following work deals with ibuprofen-loaded ethylcellulose microspheres. The drug exists either in a state of molecular dispersion or in crystalline form, depending on the encapsulation ratio. The in vitro release profiles have been studied and the Higuchi model applied to the experimental results. With an appropriate treatment of the results, it has been shown that the surface crystals responsible for the observed burst effect are really encapsulated by the polymer. The calculation of the tortuosity factor clearly shows that the release kinetics are controlled by the hydrophobicity of ethylcellulose and the geometry of the porous volume resulting from the dissolution of ibuprofen crystals. It thus appears that crystals are probably differently distributed in the matrix depending on the microsphere size.