Steering Colloids using Chemical Gradients

Dynamically programmable colloidal materials (DPCMs) are an emerging class of materials that change their structure based on external stimuli. With the correct programming, DPCMs could be influenced to organize into arbitrary structures currently unattainable, with applications in photonics, tissue engineering, and nanorobotics. However, realizing such applications requires spatiotemporal control of colloids to a combined precision and scale that is currently unattainable. Inspired by the complex feedback of non-equilibrium chemical signals in biological systems, it has been suggested that colloids can be controlled using internal chemical feedback loops. By combining chemical feedback with a previous method of steering colloids with an electric field, we have devised a new technique for steering individual colloidal particles using externally applied chemical gradients. Our simulations use model predictive control to steer particles on various trajectories using a chemical solute gradient. We also present a new method of "stakeholder control", in which a chemically active particle is used to move other nonreactive particles into desired locations. This new method solves some of the problems of scale-up that arise from chemical gradient control.