Jellyfish-shaped robots made of magnetic ferrofluid can be controlled by light through an underwater obstacle course. Swarms of these soft robots could be useful for delivering chemicals throughout a liquid mixture or moving fluids through a lab-on-a-chip. Ferrofluid droplets are made of magnetic nanoparticles suspended in oil, and they can move across flat surfaces or change shape when coaxed in different directions by magnets. By immersing these droplets in water and exposing them to light, Mengmeng Sun at the Max Planck Institute for Intelligent Systems in Germany and his colleagues have now made them defy gravity. When ferrofluids absorb light – they are particularly good at that because they are dark – they heat up and any tiny bubbles within them expand.

Researchers have revealed the first ever liquid magnet that can stay magnetic even when changing its shape -- an attractive prospect for developing fluid robots. The liquid is made of nano-scale particles of metal floating in solution -- which normally would only behave as a magnet when in the presence of a magnetic field. But by using a special oil-polymer mixture, the team succeeded in jamming the particles so close together at the surface of the liquid that they can stay magnetic. The pioneering discovery changes our understand of magnetic materials and could find manifold practical applications in the future. Researchers have revealed the first ever liquid magnet that can stay magnetic even when changing its shape -- an attractive prospect for developing fluid robots. University of Massachusetts material scientist Thomas Russell and his colleagues spent seven years developing a simple method to transform so-called'paramagnetic ferrofluids' -- plain metal particles floating in a liquid -- into permanent magnets.

Not all magnets have to be solids – a new kind of liquid magnet may eventually help control wireless soft robots. Liquid magnets of a sort already exist. These ferrofluids are a mixture of a non-magnetic liquid and solid magnetic nanoparticles, but they only work when under the influence of an external magnetic field. Thomas Russell at the University of Massachusetts Amherst and his colleagues were able to turn a ferrofluid into a truly magnetic fluid that retains its magnetic properties.