Asymmetrical magnetic microbeads transform into micro-robots

These findings were recently published in EPJ E by Gabi Steinbach from the Chemnitz University of Technology, Germany, and colleagues at the Helmholtz-Zentrum Dresden-Rossendorf. It is part of a topical issue entitled "Nonequilibrium Collective Dynamics in Condensed and Biological Matter." The observed effects were exploited in a lab-on-a-chip application in which microscopic systems perform tasks in response to a changing external magnetic field.

Initially, the authors experimentally investigated large assemblies of these microbeads with an optical microscope. They then performed numerical simulations based on a simple model featuring off-centred magnetic dipoles, and performed a detailed comparison of both experimental and simulation approaches. Under an oscillating field, the particles continuously revert back to standard magnetic behaviour where the North magnetic poles of particles point towards other particles' South poles; and this behaviour has been confirmed for as few as two particles.

The authors concluded that the interactions between the off-centred dipoles with the changing external magnetic field transform larger particle clusters into different configurations. For example, they found that staggered bead chains continuously expand to spontaneously form linear chains. This could be harnessed, for instance, to create a zipper-style micro-muscle on a chip; here a staggered chain repeatedly expands and contracts depending on the intensity of the applied field.