The photomechanical effect is the change in the shape of a material when it is exposed to light. The photomechanical effect was first documented by Alexander Graham Bell in 1880. More recently, Uchino demonstrated that a photostrictive material could be used as legs in the construction of a miniature optically-powered "walker."
The most common mechanism of the photomechanical effect is light-induced heating.
References
Photomechanical effect Wikipedia(Text) CC BY-SA