Physics of in vitro magnetofection. Effect of magnetic transport and redistribution of nanoparticles

•Magnetically-assisted gen-transfection on B92 cells under controlled geometry.•Time and magnetic field dependency of transfection efficiency.•Effect of magnetic force on the geometry of magnetic nanoparticles redistribution.•Magnetic carriers are concentrated in disk- or ring-shaped regions.•Relevant results to improve the efficiency of in vitro and in vivo magnetofection. A comprehensive study of relevant aspects of the physics behind in vitro magnetic assisted transfection, or magnetofection is presented. Magnetofection experiments were performed as a function of culture-magnet distance for a fixed time of 30 min, as a function of time for a fixed separation of about 1 mm, and under special geometries chosen to elucidate the relative effects of gravitational and magnetic forces. It is shown that under appropriate conditions, in vitro magnetofection can be performed with almost equal easiness in any desired space direction, even against gravity. Redistribution of magnetic nanoparticles in a colloid, with an initial uniform distribution, was studied with the same experimental setup used in magnetofection experiments, as a function of time, and as a function of culture-magnet relative position. It was found that magnetic nanoparticles tend to arrange into concentrated regions with ring or circle shapes, and that final distribution depends strongly on relative position. Cellular uptake of magnetic nanoparticles was estimated for standard magnetofection and for no applied magnetic field experiments. A consistent description of results is given by comparing magnetofection efficiency, nanoparticles uptake and redistribution experiments. The results presented here constitute novel information that will contribute to gaining deeper understanding of how magnetofection proceeds and how can be improved. They impact directly on in vivo procedures, providing conceptual tools to optimize setup geometry and magnetic field application time.