Three Dimensional Aggregation of Magnetic Particles

A. Pai, D. Ho, A. Hajimiri

Magnetic drug delivery is a promising therapeutic because of magnetic fields’ ability to permeate unperturbed in human tissue. One of the long-standing challenges in magnetic drug delivery is the inability to generate 3D aggregation non-invasively within the interior of the body. Earnshaw’s theorem, which proves the impossibility of creating an energetic minimum in a curl-free and divergence-free field such as a magnetic field. However, one of the assumptions of Earnshaw’s theorem is a static field. Here we show that it is possible to utilize a dynamically changing field and a dissipative force such as the drag, which is generally present, to create a stable aggregation point for magnetic particles. We also introduce a theoretical framework for designing the suitable magnetic fields for controlling a given magnetic particle in a particular fluid. This framework enables accurate determination of the necessary parameters for aggregation across a wide variety of magnetic particles and across multiple biologically-relevant fluids. By coating magnetic particles with desired therapeutic agents or attaching them to cells, a new class of treatment methodologies can be created in therapies such as targeted drug delivery and cell-based therapies. By dynamically changing the aggregation point, agents can also be guided along a particular path in the body. This technique of using dissipative forces to create a stable 3D aggregation point for particles could possibly be extended to a broad range of applications such as microscopic and macroscopic manipulation, robotics, guided self-assembly, magnetic plasma confinement, tissue engineering, and ion traps for quantum computers.