Magnetophoresis, the directed motion of magnetic objects up a magnetic field gradient, can be used to steer magnetic colloidal particles and shuttle them to target locations. This can be used to deliver therapeutics to a target location in the body or to gather and transportt molecules for diagnostic analysis or disposal. This requires magnetic particles to move through complex,  porous materials --  membranes, gels, tissue, vessels. However, the magnetic fields that steer/propel colloids magnetophoretically also drive particle aggregation through dipole-dipole attractions. If the particle aggregates grow larger than the characteristic pore size of the material around their destination, steric effects prevent the particles from navigating to their targets.

We are currently investigating magnetic navigation strategies that use time-varying magnetic fields to suppress aggregation during magnetophoresis and enhance navigation of particles through porous media. Key questions are how to relate optimal control protocols to geometric features of porous environment and colloidal particles, thermodynamic interactions among particles and the enviroment, and biomechanical properties of the viscoelastic  material particles are navigating.