Tiny jellyfish robots made of ferrofluid can be controlled with light

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.