Fig. 1: A library of magnetic active swarms.
From: Active generation and magnetic actuation of microrobotic swarms in bio-fluids
a Paramagnetic nanoparticle vortex-like swarm can be generated using rotating magnetic fields, and the merging of fluidic vortices is the main reason for the generation20. b Magnetic microparticles arrange into an aster on liquid–liquid interface, which is mainly due to the self-induced circular standing wave19. c A snake-like pattern is formed by magnetic microparticles on liquid–air interface actuated by an oscillating field28. d A circular pattern formed by rotating helical swimmers29. e Paramagnetic nanoparticles form reconfigurable ribbon-like swarms actuated by oscillating magnetic fields21. f By combining magnetic fields and ultrasound fields, superparamagnetic particles can assemble with each other due to dipole-dipole interaction under a rotating magnetic field30. g Manipulation and propulsion of magnetic colloidal carpets realised by applying conical oscillating magnetic fields31. h Chain-like structure formed by rolling hematite colloids32. i Actuation of helical nano-swimmers in vitreous humour33. j A swarm of artificial bacterial flagella can be navigated in vivo, in the peritoneal cavity of a mouse by applying rotating magnetic fields7. The experimental planes of a–h are X–Y planes. For i, j the swimmers perform 3D locomotion, and the rotating plane of the magnetic field changes with the desired moving direction.
