Topologically controlled synthesis of active colloidal bipeds

TL;DR

This paper presents a method for synthesizing active colloidal bipeds with controlled length using topological magnetic field control, enabling precise assembly and autonomous movement of colloids.

Contribution

It introduces a topological magnetic control technique to produce and regulate active colloidal bipeds of specific lengths, advancing programmable colloidal assembly.

Findings

Successful synthesis of colloidal bipeds with defined lengths

Active bipeds can walk on patterned magnetic substrates

Controlled polymerization of colloids into bipeds achieved

Abstract

Topological growth control allows to produce a narrow distribution of outgrown colloidal rods with defined and adjustable length. We use an external magnetic field to assemble paramagnetic colloidal spheres into colloidal rods of a chosen length. The rods reside above ametamorphic hexagonalmagnetic pattern. The periodic repetition of specific loops of the orientation of an applied external field renders paramagnetic colloidal particles and their assemblies into active bipeds that walk on the pattern. The metamorphic patterns allow the robust and controlled polymerization of single colloids to bipeds of a desired length. The colloids are exposed to this fixed external control loop that causes multiple simultaneous responses: Small bipeds and single colloidal particles interpret the external magnetic loop as an order to walk toward the active zone, where they assemble and polymerize. Outgrown bipeds interpret the same loop as an order to walk away from the active zone. The topological transition occurs solely for the growing biped and nothing is changed in the environment nor in the magnetic control loop. As in many biological systems the decision of a biped that reached its outgrown length to walk away from the reaction site is made internally, not externally.