File under disgusting/interesting: Scientists have designed a new type of nanobot that could swim through your bodily fluids by mimicking the motion of scallops in the ocean.
Since nanobots are designed to be tiny, there's not really room for electronics to make them swim. You can use magnets, but they don't work well if you want to put more than one nanobot in the body at a time. That's why it's important to make a nanobot that can swim on its own.
Many nanobots have been tested with the idea that they'd move through Newtonian fluid, like water. And while our bodies are largely made of water, most of the fluids and tissues inside of us (blood, mucus, sputum, Synovial fluid) are non-Newtonian. They're more viscous and you can't move through them in the same way. That's why these scallop-shaped bots (created with a 3D printer in a lab at the Max Planck Institute for Intelligent Systems in Germany) are so notable: they have been designed specifically to move through and probe our bodies in a way that makes sense, without motors or batteries.
The ones from this design get their power from magnets, but it's just a magnetic field, so it doesn't pull them along the way a direct magnet system would. IEEE Spectrum noted that the scallopbots could be customised to work with a large array of power sources, including "piezoelectrics, bimetal strips, shape memory alloys, or heat or light-actuated polymers."
This is just a concept, and there's no one specific application that anyone's focusing on, yet. But the possibilities are wide-ranging. You could have nanobots surfing your eyeball goo to correct vision, or monitoring your joint fluid to make sure Crossfit isn't about to murder your kneecaps. [Nature Communications via IEEESpectrum via I almost barfed writing this]