Designing autonomously motile gels that follow complex paths

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 degrees 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.