Employing nanobots to patrol the blood vessels of the human body and repair damage along the way is still a couple decades away, at least, but doctors are already employing small robots that patients can swallow to perform remote surgeries. Some of these robots are even capable of being swallowed as separate components and then re-assembling themselves in the gut, as the below video shows:
Tiny robots that measure only a few millimeters or less may be used for a number of medical procedures, including injecting stem cells or gene therapy directly into hard-to-reach areas, taking photos and tissue samples, cleaning shunts that drain fluid from the brain, and more.