Designing self-propelled microcapsules for pick-up and delivery of microscopic cargo

Using computational modeling, we design a system of active polymeric microcapsules that pick-up, convey and drop-off a cargo between locations on a patterned surface. To create this system, we harness "signaling" and "target" capsules, which release nanoparticles into the surrounding solution. These nanoparticles bind to the underlying surface and thereby create adhesion gradients that trigger the spontaneous motion of the capsules. One signaling and two target capsules are found to form a stable triad, which can transport a cargo of four target capsules. Guided by an adhesive stripe on the surface, the triad and cargo form a "train" that moves autonomously along the substrate. The stripe is designed to encompass a small region with a lower adhesive strength. Through the aid of this patch, the triad can deposit its cargo and move on to potentially pick up a new payload at another location. Since the microcapsules can encase a wide variety of compounds, the system could provide an effective means of autonomously transporting a broad range of substances within microfluidic devices.