Assuming the nanorobot isn't tethered or designed to float passively through the bloodstream, it will need a means of propulsion to get around the body. Because it may have to travel against the flow of blood, the propulsion system has to be relatively strong for its size. Another important consideration is the safety of the patient -- the system must be able to move the nanorobot around without causing damage to the host.
Some scientists are looking at the world of microscopic organisms for inspiration. Paramecium move through their environment using tiny tail-like limbs called cilia. By vibrating the cilia, the paramecium can swim in any direction. Similar to cilia are flagella, which are longer tail structures. Organisms whip flagella around in different ways to move around.
Nanorobot designers sometimes look at microscopic organisms for propulsion inspiration, like the flagellum on this e-coli cell.
Other devices sound even more exotic. One would use capacitors to generate magnetic fields that would pull conductive fluids through one end of an electromagnetic pump and shoot it out the back end. The nanorobot would move around like a jet airplane. Miniaturized jet pumps could even use blood plasma to push the nanorobot forward, though, unlike the electromagnetic pump, there would need to be moving parts.
Another potential way nanorobots could move around is by using a vibrating membrane. By alternately tightening and relaxing tension on a membrane, a nanorobot could generate small amounts of thrust. On the nanoscale, this thrust could be significant enough to act as a viable source of motion.
In the next section, we'll look at the tools nanorobots might carry to fulfill their medical missions.