Eccentric magnetic microcapsules for orientation-specific and dual stimuli-responsive drug release
In this paper, we fabricated uniform polydimethylsiloxane (PDMS) magnetic microcapsules with eccentric internal structures and employed them as a novel delivery system for orientation-specific and dual stimuli-responsive controlled drug release. These eccentric microcapsules contained Fe3O4 nanoparticles in their inner cores. Because of the paramagnetic Fe3O4 nanoparticles, the eccentric microcapsules could be accurately moved by a magnetic field, leading to the precise control of the microcapsule locations. Also, due to the eccentric structures of the magnetic microcapsules, the capsules exhibited a non-uniform magnetic property; the capsules could be aligned by magnetic fields with their thin walls facing the magnet, resulting in a precise orientation-specific control of the microcapsules. More interestingly, the eccentric magnetic microcapsules demonstrated a dual stimuli-responsive controlled release of inclusions involving a sustained release under ultrasound and an intense release under laser stimulation. Furthermore, we studied the efficacy of doxorubicin (DOX) release from the microcapsules regulated by laser stimulation by performing in vitro cell tests with and without an applied magnetic field. The cell tests showed that the orientation-specific control of the microcapsules under a magnetic field (when the thin walls of the eccentric microcapsules were oriented towards the cell) improved the efficacy of the drug released from the microcapsules. The results suggested that our eccentric magnetic microcapsules hold all the properties needed for a site-specific, orientation-specific and dual stimuli-responsive delivery system, demonstrating a great potential application for multifunctional controlled drug release.