Magnetic drug targeting has been explored by an in vitro study of the deposition of polyvinyl alcohol (PVA) coated magnetic carrier nanoparticles (MCNPs) in a tube under the influence of an externally applied magnetic field. Experiments and simulations show a steady decrease in the retention of MCNPs with increasing flow rate and weaker magnetic field strength. The retention of MCNPs has been significantly influenced by the fluid flow behaviour resulting from the position and shape of the magnet, magnetic properties and size of the MCNPs, and the magnetic field strength. Under strong magnetic fields, the MCNPs tend to creep along the wall of the tube and undergo high shear before reaching the targeted region. These results highlight the importance of choosing the region of MCNP injection, magnetic field strength and, the magnetic properties and size of the MCNPs to minimize the loss of the drug.

We report a controlled migration of an iron nanoparticle (FeNP) coated polymer micromotor. The otherwise diffusive motion of the motor was meticulously directed through an in situ pH-gradient and an external magnetic field. The self-propulsion owing to the asymmetric catalytic decomposition of peroxide fuel was directed through a pH gradient imposed across the motor-surface, while the magnetic field induced an external control on the movement and the speed of the motor. Interestingly, the sole influence of the pH gradient could move the motor as high as ∼25 body lengths per second, which was further magnified by the external assistance from the magnetic field. Applying a magnetic field against the pH directed motion helped in the quantitative experimental estimation of the force-field required to arrest the chemotactic migration. The influence of the coupled internal and external fields could halt, steer or reverse the direction the motor inside a microchannel, rotate the motor around a target, and deliver the motor to a cluster of cells. This study showcases a multimodal chemical–magnetic field regulated migration of micro-machines for sensing, transport, and delivery inside a fluidic environment.