Abstract

Using simulation and theory, we demonstrate how nanoparticles can be harnessed to regulate the interaction between two initially stationary microcapsules on a surface and promote the self-propelled motion of these capsules along the substrate. The first microcapsule, the “signaling” capsule, encases nanoparticles, which diffuse from the interior of this carrier and into the surrounding solution; the second capsule is the “target” capsule, which is initially devoid of particles. Nanoparticles released from the signaling capsule modify the underlying substrate, and thereby initiate the motion of the target capsule. The latter motion activates hydrodynamic interactions, which trigger the signaling capsule to follow the target. The continued release of the nanoparticles sustains the motion of both capsules. In effect, the system constitutes a synthetic analogue of biological cell signaling and our findings can shed light on fundamental physical forces that control interactions between cells. Our findings can also yield guidelines for manipulating the interactions of synthetic microcapsules in microfluidic devices. In the second study, we use computational modeling to investigate how an applied mechanical pressure can be harnessed to initiate traveling chemical waves in polymer gels undergoing the Belousov-Zhabotinsky (BZ) reaction. We uncover a rich dynamic behavior, isolating systems where the applied pressure induces chemical oscillations in an initially non-oscillatory system. We also pinpoint a scenario where the compression induces both oscillations and the autonomous rotation of the entire sample. Such BZ gels can potentially be used to fabricate touch-sensitive sensors and membranes, as well as self-reinforcing materials.