Micro- or even nano-robots could someday perform medical tasks in the human body, such as delivering drugs precisely to a target location, and researchers from the Max Planck Institute for Intelligent Systems in Stuttgart, Germany have taken a step towards this goal. They constructed swimming bodies that simultaneously meet two requirements: they are small enough to be used in bodily fluids or even individual cells, and they are able to navigate through complex biological fluids. Using 3D printing and micro-molding, the research team developed a kind of artificial scallop just a few hundred micrometers in diameter. To control their micro-swimmers, the researchers integrated tiny rare-earth magnets in the two scallop shells. This enables them to control how the scallop shells open and close - and ultimately how the device moves - by applying an external magnetic field. The micro-scallop does not swim in water, but can swim in most fluids and tissues found in the human body.