Designing autonomously motile gels that follow complex paths

Abstract

Using theory and simulation, we determine the effect of light on the motion of polymer gels undergoing the Belousov–Zhabotinsky (BZ) reaction. The BZ gels undergo rhythmic mechanical oscillations in response to the periodic reduction and oxidation of ruthenium catalysts that are grafted to the polymer network. The Ru-catalyzed BZ reaction is photosensitive, with light of a certain wavelength suppressing the oscillations within the gel. We exploit this property to control the self-sustained motion of millimeter-sized BZ gel “worms”. By tailoring the arrangement of illuminated and non-illuminated regions, we direct the movement of these worms along complex paths, guiding them to bend, reorient and turn. In particular, these gels can make both 90° and U-turns. Notably, the path and the direction of the gel's motion can be dynamically and remotely reconfigured (as opposed to being fixed, for example, by a pattern on an underlying surface). Hence, our findings can be utilized to design intelligent, autonomously moving “soft robots” that can be reprogrammed “on demand” to move to a specific target location and to remain at this location for a chosen period of time.