Researchers at Columbia University are working on an incredibly reliable small scale energy source, water vapor to power small machines. The team is using bacteria spores that are great at absorbing water. When they absorb water, they swell and when they lose water, they contract, and they can do this repeatedly without breaking down. This movement, like that of a small muscle is what is being used by the team to power small engines.
The researchers glued billions of these spores on a plastic tape-like surface and then attached several pieces of the tape together. The result was a measurable difference between when the bacteria were swollen with water and when they were shrunken from water loss. They then began building small machines harnessing this movement. One machine is a set of shutters that lift as the “muscles” extend when wet and then close when the water evaporates. Another is a rotary engine that spins because only one side is exposed to the moist air that fuels the spores’ work. That engine is being used to drive a wheel in a toy car like device.