A rotary engine harnesses energy from evaporation to drive a miniature car. (Ozgur Sahin, Columbia University)

Biological systems are known to convert energy generated from the evaporation of water confined within nanoscale compartments into muscle-like mechanical work in response to changes in environmental humidity. Recently, scientists designed shape-changing engineered composites of bacterial spores and a polymer that used an evaporation-driven process to power locomotion and generate electricity.

By harvesting the energy from water evaporation in the environment, researchers demonstrated self-sustained power generation from engines placed at air-water interfaces —powering a light source and moving a miniature car forward. These evaporation-driven engines could power robotic systems, sensor, devices, and machinery.