Magnetically driven artificial propellers have potential applications in biomedicine, targeted drug delivery, and microfluidics. Applied magnetic fields drive polarizable particles in a fluid medium, and these particles presumably could transport “cargo” without degrading the fluid or the surrounding systems.

Fernando Martinez-Pedrero and Pietro Tierno, Universidad de Barcelona, Spain, demonstrated a method for assembling, manipulating, and propelling large two-dimensional ensembles of monodisperse paramagnetic colloidal particles. These “magnetic carpets” trapped, transported, and released yeast cells and silica microspheres.

The carpets self-assembled in the presence of an applied magnetic field and were propelled using a rotating field in the (x,z) plane coupled with an oscillating component in the y direction. Steering is achieved by momentarily stopping the propulsion, inducing a rotation of the carpet, and restoring the field with different phases and frequencies along the x and y directions. The researchers demonstrated two ways to steer the carpet around obstacles. The magnetic clusters immediately disintegrate when the field is removed.
This efficient control of cargo transportation and the ability to surpass obstacles gives it great potential towards development of multifunctional smart microdevices.

• Magnetic Propulsion of Self-Assembled Colloidal Carpets: Efficient Cargo Transport via a Conveyor-Belt Effect,
  Fernando Martinez-Pedrero, Pietro Tierno,
  Phys. Rev. Applied 2015.
  DOI: 10.1103/PhysRevApplied.3.051003