Scientists have created tiny disk-shaped particles that can swim on their own when hit with light, akin to microscopic robots that move through a special liquid without any external motors or propellers.

Published in Advanced Functional Materials, the work shows how these artificial swimmers could one day be used to deliver cargo in a variety of fluidic situations, with potential applications in drug delivery, water pollutant clean-up, or the creation of new types of smart materials that change their properties on command.

“The essential new principles we discovered—how to make microscopic objects swim on command using simple materials that undergo phase transitions when exposed to controllable energy sources—pave the way for applications that range from design of responsive fluids, controlled drug delivery, and new classes of sensors, to name a few,” explained lead researcher Juan de Pablo.

Currently the Executive Vice President for Global Science and Technology at NYU and Executive Dean of the NYU Tandon School of Engineering, de Pablo conducted this research in collaboration with postdoctoral researchers and faculty at the Pritzker School of Molecular Engineering at the University of Chicago, the Paulson School of Engineering at Harvard University, and the Universidad Autonoma of San Luis Potosi, in Mexico.

The research team designed tiny flat disks about 200 micrometers across, which is roughly twice the width of a human hair. These structures are made from dried food dye and propylene glycol, creating solid disks with bumpy surfaces that are essential for swimming.

When placed in a nematic liquid crystal (the same material used in LCD screens) and hit with a green LED light, the disks start swimming on their own. The food dye absorbs the light and converts it to heat, warming up the liquid crystal around the disk. This causes the organized liquid crystal molecules (normally lined up like soldiers in formation) to “melt” and become jumbled and disorganized, creating an imbalance that pushes the disk forward.

Depending on temperature and light brightness, the disks behave differently. Under the right conditions, they achieve sustained swimming at speeds of about half a micrometer per second, which is notable for something this tiny.

The most spectacular results happen when the disks can move in three dimensions. As they swim, they create beautiful flower-like patterns of light visible under a microscope. These patterns evolve from simple 4-petaled shapes to intricate 12-petaled designs as the light gets brighter.

“The platelet lifts due to an incompatibility between the liquid crystal’s preferred molecular orientation at different surfaces,” said de Pablo. “This creates an uneven elastic response that literally pushes one side of the platelet upward.”

What distinguishes this discovery is how different it is from other swimming methods. Unlike bacteria that use whip-like tails or other artificial swimmers that need expensive chemical reactions, these disks create movement using a simple melting transition, cheap materials and basic LED lights. Plus, they have perfect on/off control: When light is turned off, they stop swimming immediately.

This research taps into the growing field of “active matter,” which are materials that can harvest energy from their surroundings and turn it into movement. While these specific disks rely on light and heat to change the extent of order in a liquid crystal, the principles could be adapted to create swimmers in other types of liquid or solid media, powered by light or body heat, for example.