An anonymous reader writes to mention a Wired article about the first surgical nanobot developed for practical use. No wider that two human hairs, the machine is intended to swim through arteries and the digestive tract, and can perform surgical procedures in spaces no bigger than 250 microns. The article also addresses safety concerns; the bot will swim upstream from blood flow, so if something goes wrong it can be retrieved on its way back. Likewise, for the most delicate procedures it can be fitted with a tether, to ensure it doesn't get lost. From the article: "The tiny robot, small enough to pass through the heart and other organs, will be inserted using a syringe. Guided by remote control, it will swim to a site within the body to perform a series of tasks, then return to the point of entry where it can be extracted, again by syringe. For example, the microrobot might deliver a payload of expandable glue to the site of a damaged cranial artery -- a procedure typically fraught with risk because posterior human brain arteries lay behind a complicated set of bends at the base of the skull beyond the reach of all but the most flexible catheters."