Forming Self-rotating Pinwheels from Assemblies of Oscillating Gels

By using computational modeling, we show that millimeter-sized polymer gels undergoing the self-oscillating Belousov-Zhabotinsky (BZ) reaction not only respond to a chemical signal from the surrounding solution, but also emit this signal and thus, multiple neighboring gel pieces can spontaneously self-aggregate into macroscopic objects. We also show that the gels' coordinated motion can be regulated by light, allowing us to achieve selective self-aggregation and control over the shape of the gel aggregates, as well as reconfiguration of the entire structure. We find that the aggregated gel pieces can rotate as a unit. For example, four millimeter-sized gels can associate into a structure that resembles a pinwheel and then undergo spontaneous, autonomous rotation. With eight gel pieces, the system can form two pinwheels, which communicate and coordinate their motion. Notably, this communication can be controlled with light. In particular, light can be used to translate the pinwheels and to control the relative rotation of two such clusters. These findings reveal a new route for creating dynamically reconfigurable materials using self-oscillating BZ gels where reconfiguration is achieved by using auto-chemotatic behavior of the gels, and also applying external light.