Abstract: The movement of magnetically responsive nanoparticles through a membrane is significantly enhanced by using a varying magnetic field gradient. The magnetic field varies in intensity and/or direction and can be achieved by mechanically varying the position of a magnet with respect to the membrane, or by oscillating the strength of one or more electromagnets.

Abstract: A system for introducing a bioactive substance into a target cell within a body. The bioactive substance is transported to the target cell using a superparamagnetic nanoparticle and a controllable magnetic field generator that is capable of moving the nanoparticle to the target cell through the body in three dimensions. The nanoparticle may be covered with a biocompatible shell that forms a covalent bond with the bioactive substance. In an alternative embodiment, the bioactive substance and a plurality of nanoparticles are supported by a bioerodable matrix that forms a nanosphere. The nanosphere may be moved into the target cell using an external magnetic field that is controllable to move the nanosphere in three dimensions through the body and the bioactive substance is released from the nanosphere once inside the target cell.