| Local variations in chemical concentration can be used to initiate and direct the self-sustained motion of microscopic objects. Using computational modeling, we design cell-like microcapsules and worm-like gels that generate such chemical gradients, sense these self-generated gradients and consequently, undergo autonomous movement. In the first example, “signaling” microcapsules release “agonist” nanoparticles, while “target” microcapsules release “antagonist” nanoparticles and the permeabilities of both capsule types depend on the local nanoparticle concentration in the surrounding solution. Additionally, the released nanoparticles can bind to the underlying substrate and thereby create adhesion gradients that propel the microcapsules to move. Due to these self-imposed gradients, the polymeric microcapsules can self-organize into various autonomously moving structures and exhibit ant-like tracking behavior. Our model provides a platform for integrating both the spatial and temporal behavior of assemblies of “artificial cells”, and allows us to design a rich variety of structures capable of exhibiting complex, cooperative behavior. In the second example, 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. The path and the direction of the gel’s motion can be dynamically and remotely reconfigured. Hence, our findings can be utilized to design autonomously moving ‘‘soft robots’’ that can be programmed to move to specific locations in microfluidic devices.
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