MIT engineers at the David H. Koch Institute for Integrative Cancer Research have created a polymer film that generates energy using water vapor. The film makes use of two different polymers: a hard but flexible layer matrix and a soft gel that expands when it comes in contact with moisture. Together, the film contracts it comes in contact with water, causing the material to curl up. When the wet surface is exposed to air, the moisture is released and the cycle repeats, as shown in the video below. MIT News explains that the polymer could be used as an actuator to control robotic limbs, or act as a generator when paired with a piezoelectric material that converts mechanical stress into electricity. The energy created by the film can be used to power small sensors or nanoelectronics without the need for batteries.