Designing chemical micromotors that communicate-A survey of experiments

Micromotors that communicate with their neighbors or with the environment are useful in a wide variety of applications, especially those involving complicated tasks that require coordination. A biomimetic strategy for achieving this goal is via chemical communication, where chemical signals released from one motor is transmitted through the medium and induce a specific response from a second motor. In this article, we review the recent experimental progress on this front. We first introduce three common strategies for releasing chemicals from a microscopic object, via diffusion, physical/chemical stimuli, or gated control, that form the cornerstone for designing communicating micromotors. We then review three levels of chemical communication of micromotors in order of ascending complexity, starting with cases where micromotors attract or repel inert tracers, to the unidirectional signal transmission between two motors of different types, and finally to the reciprocal (bidirectional) communication between two motors that often lead to higher-order assemblies. This review article ends with a perspective of the challenges and opportunities with communicating micromotors, which could inspire more sophisticated designs of in-depth communication between motors with different functions.