1) Thermodynamic drive - For every circuit through the blood stream, the nanobot would be exposed to inner and outer temperatures - maybe 98.6 degF in the lungs and 95 degF in the capillaries at the skin. The "bio-activated bellows" could be a material designed to change phases from crystalline to liquid between those temperatures, thus expanding and contracting as it travels through the body.
2) Pressure drive - When the nanobot gets pumped out of the heart, it would be squeezed in the flow at a higher pressure. The "bio-activated bellows" could be a gas-filled membrane that contracts onto the piezoelectric when it cycles through the heart chambers.
CATEGORY: Nanotechnology / Medicine / Biological