Modeling magnetic microcapsules that crawl in microchannels

Using computational modeling, we probe how to design microfluidic systems in which magnetic microcapsules could autonomously crawl along channel walls. The polymeric microcapsules are fluid-filled elastic shells with embedded superparamagnetic nanoparticles and, thereby, can be controlled by external magnetic fields. We show that when a magnetic force circulates normal to a sticky microchannel wall, capsules can propel in a steady, autonomous manner. The unidirectional capsule propulsion is facilitated by hydrodynamic interactions between the capsules and channel walls, and is most effective when the magnitudes of magnetic and adhesive forces are equal to each other. Furthermore, the propulsion efficiency is greater for compliant capsules. Our findings could be useful for designing novel microfluidic devices where mobile magnetic microcapsules could be harnessed as microscale transport vehicles.