Oscillating Membranes: Controlling Autonomous Shape-transforming Sheets*

Imposing residual stresses on thin structures is an established mechanism to induce global shape changes. Living organisms have mastered the dynamic control of these residual stresses to induce shape transformation and locomotion. By comparison, man-made implementations are rudimentary. Here we present the first autonomously shape-shifting soft sheets and show that these have the potential to achieve the locomotive capabilities of living organisms. The sheets are made of a gel that shrinks and swells in response to the phase of an oscillatory chemical (Belousov-Zhabotinsky) reaction. Propagating reaction-diffusion waves of the reaction induce localized shrinking or swelling of the gel resulting in time-periodic global shape changes, for example flapping. We present the computational tools and experimental protocols needed to control this system, principally the relationship between the curvature of the sheet and the reaction phase, and optical imprinting of the wave pattern. This quantitative control marks an important step towards the realization of autonomous soft machines.

IL, R. Deegan, and E. Sharon, Phys. Rev. Lett. 125, 178001 (2020)