Light-induced self-assembly of active rectification devices

TL;DR

This paper demonstrates through computational modeling that active rectification devices can be self-assembled from motile particles using spatially modulated light, relying on irreversibility, symmetry breaking, and particle interactions.

Contribution

It introduces a novel mechanism for creating active rectification devices via light-controlled self-assembly from unstructured particle systems.

Findings

Rectification devices can be formed from motile particles using light patterns.

Spatial symmetry breaking and particle interactions are essential for rectification.

The approach enables programmable self-assembly of active devices.

Abstract

Self-propelled colloidal objects, such as motile bacteria or synthetic microswimmers, have microscopically irreversible individual dynamics - a feature they share with all living systems. The incoherent behaviour of individual swimmers can then be harnessed (or "rectified") by microfluidic devices that create systematic motions impossible in equilibrium. Examples include flow of rotor particles round a circuit, steady rotation of a gear wheel in a bacterial bath, and pumping of bacteria between chambers by "funnel gates". Here we present a computational proof-of-concept study, showing that such active rectification devices might be created directly from an unstructured "primordial soup" of motile particles, solely by using spatially modulated illumination to control their local propulsion speed. Alongside both microscopic irreversibility and speed modulation, our mechanism requires spatial symmetry breaking, such as a chevron light pattern, and strong interactions between particles, such as volume exclusion causing a collisional slow-down at high density. These four factors create a many-body rectification mechanism that generically differs from one-body microfluidic antecedents. Our work suggests that standard spatial-light-modulator technology might allow the programmable, light-induced self-assembly of active rectification devices from an unstructured particle bath.