BBC has an article about swimming microbots that can swim through blood veins. Japanese scientists have created a tiny screw mechanism that can spin for swimming propulsion. These microbots can be injected into the body with a hypodermic needle and once inside a blood vein, the robot can be steered with the aid of 3D magnetism field and controller in any direction. The micro swimming bots can deliver drugs to specific parts of the body, burrow by screwing itself into tumors in seconds or poke a hot spike into cancerous tissues to kill them. They hope to create smaller versions that can get even into the smaller blood veins of the brain.