Gastro-resistant encapsulation of amorphous solid dispersions containing darunavir by coaxial electrospraying

The relatively simple technique of coaxial electrospraying allows to produce core-shell microparticles with potentially high encapsulation efficiencies. In this study, amorphous solid dispersions of a hydroxypropyl methylcellulose or polyvinlypyrrolidone based polymer matrix containing the active pharmaceutical ingredient darunavir were coated with a gastro-resistant shell polymer that does not dissolve at lower pH present in the stomach, but only later at a higher pH in the small intestine. A multitude of shell polymers were tested with the aim to identify a material that limits the drug release to less than 10% after two hours at a pH of 1 to comply with the European Pharmacopoeia regarding gastro-resistant formulations. In parallel, the core-shell structure of the particles was determined with confocal imaging and their surface morphology with SEM imaging. While the structural analysis revealed significant differences between the different formulations, all investigated shell polymers exhibited a burst drug release followed by a slow release for the remainder of a two hour period. Ultimately, the shell copolymer poly(methacrylic acid-co-methyl methacrylate), in particular for a monomer ratio 1/2, resulted consistently in darunavir release below the 10% upper limit compared to the other tested polymers, where such low releases were inaccessible. Further investigation of this shell polymer revealed that both the monomer ratio of methacrylic acid to methyl methacrylate in the copolymer and the utilized solvent are determining factors in the release performance of the final particles.