Directing the behavior of active, self-oscillating gels with light

In the biological realm, light can act as a powerful stimulus, promoting both positive and negative phototaxis. Using computational modeling, we attempt to design systems that display analogous biomimetic behavior by exhibiting directed, autonomous motion in response to light. We specifically focus on polymer gels that undergo the oscillating Belousov-Zhabotinsky (BZ) reaction and thus manifest periodic chemomechanical pulsations, which can be modulated with light. Reviewing our recent computational studies, we describe how long, rectangular samples of BZ gels, or "worms", can perform self-sustained movement and via a distinct form of negative phototaxis migrate along complex paths under nonuniform illumination. When the ends of multiple rectangular BZ gels are anchored to a surface, the dynamic behavior of the cilia-like layer can be tuned by light to resemble the motion of a keyboard. With BZ gel pieces that move freely on a surface, we show that these gels exhibit autochemotaxis and, thereby, can self-organize in response to self-generated chemical signals. These examples illustrate that BZ gels constitute optimal materials for creating millimeter-sized soft robots whose self-sustained movement can be regulated through the use of light. © 2014 American Chemical Society.