Electrothermal actuation of the spiral coil from Fig. 3. When heated, the coil shortens until it inverts through its center and begins extending in the opposite direction. This process reverses when cooled.
Carter S. Haines, Na Li, Geoffrey M. Spinks, Ali E. Aliev, Jiangtao Di, and Ray H. Baughman
PNAS. 2016. 113:11709-11716 DOI: 10.1073/pnas.1605273113