Actuation and visualization of a magnetically coated swimmer with magnetic particle imaging

The untethered actuation of milli- and microdevices is of great interest for a variety of medical applications. A millimeter sized swimmer is shown, which is 3D-printed and coated with magnetic nanoparticles. The coating has to fulfill two requirements: First, it must have a high magnetic moment in order to show a strong reaction to a magnetic field for good actuation performance. Second, it has to be suitable for magnetic particle imaging (MPI). MPI is an emerging medical imaging technique, based on the nonlinear response of superparamagnetic nanoparticles to oscillating magnetic fields. It is aimed at dual use of an MPI scanner: for both actuation and visualization. When applying rotating homogeneous magnetic fields, the swimmer performs an axial movement due to its shape and the viscosity of the surrounding medium. These fields can be generated with an MPI scanner. The swimmer dynamics have been observed and a maximum swimming velocity of 6 mm/s at a rotation frequency of the magnetic field of 10 Hz was found. The experiments are performed with a commercially available preclinical MPI scanner. It is shown, that the swimmer is suitable to be imaged with MPI. Furthermore, sequentially acquired images of a moving swimmer are shown. For this, the MPI scanner was alternately driven in imaging and actuation mode.