Bio-inspired controlled release through compression–relaxation cycles of microcapsules

The aim of microencapsulation is to achieve controllable and sustainable release at the desired site. Despite the many methods developed in recent years, there is still a need to advance the strategies for higher controllability and scalability. Taking inspiration from the heart, which pumps blood by continual contraction of muscles, we demonstrate a novel releasing method, in which the core release is controlled by the compression–relaxation cycles of microcapsules upon the application of a magnetic field. This idea is realized by embedding Fe3O4 particles into a polymer shell. When the magnetic field is applied, the Fe3O4 particles align along the field direction and stretch the shell, resulting in compression of the microcapsules and release of the core contents; the shape is restored after the field is removed. We demonstrated various release patterns by altering the strength of the magnetic field and the compression frequency. This release method provides repeated and pulsatile delivery, enhanced spreading distance and ejection speed, and is site specific and proactive, providing a new option for controlled release applications. A new drug-release method based on constricting magnetic microcapsules by applying a magnetic field has been developed by a team in China. The researchers, who are from the Chinese Academy of Sciences in Beijing, were inspired by the action of heart muscles pushing blood out from the heart. In a proof-of-principle study, they made the magnetic microcapsules by embedding Fe3O4 microparticles in polymer shells. On applying a magnetic field, the Fe3O4 particles aligned parallel to the field, causing the shells to elongate, thereby compressing the microcapsules so that they released their contents. When the field was removed, the microcapsules returned to their original shape. This method is highly controllable and permits repeated, pulsed delivery. Furthermore, it is site specific and provides greater delivery distance and speed than conventional drug delivery methods. A novel release mechanism of microcapsules is demonstrated, where the rate of core release can be solely controlled by magnetic field-induced deformation of microcapsules. Composite microcapsules are prepared with magnetic particles embedded in the polymer wall. It shows that the release rate is highly dependent on the strengths of the magnetic field and deformation frequency of the microcapsules.