Locomotion at low Reynolds number is a key physical mechanism  for microscopic living organisms, but has lots of technological applications like nanomachines and microrobots . Our last paper  proposes a tricky experiment for generating low Reynolds swimming of microscopic particles along a liquid-air interface.
First, identical soft ferromagnetic particles are placed on a liquid-air interface. Capillary attraction is prevented by applying a vertical magnetic field which provides a repulsive interaction between the particles. The balance of capillary attraction and magnetic repulsion creates a self-assembly  as shown in the front picture. These structures are then perturbed by applying an oscillating horizontal field. The resulting cooperative dance of the particles provides a net propulsion of the particles along the liquid surface (see trajectories on the picture below). The self-assembly is swimming ! See the movies below :
- Movie 1 – An efficient swimmer of N=3 beads.
- Movie 2 – The horizontal field is switched off. The swimmer is seen to stop its motion. Then the field is switched on but in another direction. The motion resumes but in a different pulsating mode (with a different swimming speed).
- Movie 3 – The complex motion of a swimming (pentagonal) assembly made of N=6 beads.
This work opens new perspectives in mesoscopic physics. The most important feature of our system is that both self-assembling and periodic deformations can be rescaled to smaller sizes.
 E.Lauga, Soft Matter 7, 3060 (2011)
 P.Tierno, R.Golestanian, I.Pagonabarraga, and F.Sagués, Phys. Rev. Lett. 101, 218304 (2008)
 G.Lumay, N.Obara, F.Weyer, N.Vandewalle, Soft Matter 9, 2420 (2013) – PDF
 N.Vandewalle et al., Phys. Rev. E 85, 041402 (2012) – PDF – Post