Atlant’s Column: Army of Micro-Robots

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Welcome to the section on which explores, analyzes and explains fascinating microscopical structures.

This picture shows how doctors will fight cancer cells, bacteria or viruses in the future. What appears to be lined up lollipops, are in fact micro-robots. They are only half a millimetre in diameter. At the moment they are still fixed with two short arms on a silicon plate. But as soon as the laser cuts them off, they are ready for their first mission.

Text by science writer Atlant Bieri
Photography by Martin Oeggerli

The micro robots were created in the Institute of Robotics and Intelligent Systems of the ETH Zurich. Professor Bradley Nelson and his PhD student Hsi-Wen Tung specially designed them for locomotion in liquid media. Their potential application area is the interior of an eye, the blood stream or any other body region with enough liquid for their locomotion. There, they can steer directly towards a cancer or a bacterial infection and make a pinpoint delivery of the drugs they carry.

Their drive system is simple and sophisticated at the same time. The robots at the rear two rows for example consist of two cobalt-nickel bricks (white). Two springs made of plastic polymer (yellow) at both sides keep them apart. This is the engine. The fuel comes from an artificial electromagnetic field. If the field is turned on, the cobalt-nickel bricks are magnetised and start to attract one another. If the field is turned off, they immediately lose their attraction and the spring pushes them apart again.

One single such cycle is not enough, however, to accelerate the robot. Therefore, the field is turned on and off two thousand times per second. This means that the two bricks move back and forth two thousand times in every second. Through this oscillation, the micro-robots move forward with an astonishing 13 millimetres per second. The physician can tell them to move left or right by changing the direction of the magnetic field. The micro-robot behave like compass needles and adjust themselves along the field lines. Thus they follow every command.


Remote 3D-Locomotion to Enable Targeted Drug Delivery

To transport a package with drugs, they only need to touch it. Immediately, the naturally occurring adhesion force (see Van der Waals Force) binds the package to the micro-robot. It is the same force that makes a water droplet adhere to the tip of a finger. If the physician wants to unload the package, he makes the robot perform a pirouette. The resulting shear force is greater than the adhesion force and the package is released.

Unfortunately, the micro-robots are not yet quite ready for the application in our body. All the disc-shaped types shown here can only move in two dimensions. The three-dimensional space is still out of reach for them. Therefore, the hopes of the researchers lie with the next generation. Their prototypes are waiting in the front row for their first tests. With their metal head and a tail made of plastic they resemble sperms. The head starts to spin in the oscillating magnetic field. This turns the tail into a propeller and drives the micro-robot ahead.

Inspired by Nature

A group of bacteria has evolved the helical shape million years ago (see yellow bacteria in circular cut-out). Scientists believe it is an adaptation to move through water or body fluid more easily compared to bacteria with globular- or rod-like shape. In this case, the shape of helical bacteria has served Professor Nelson and his team as a source of inspiration for the development of the three dimensional micro-robots. If you want to join a scientific exploration into the territory of the world’s most famous helical-shaped bacteria Helicobacter pylori, please feel free to continue reading David versus Goliath – or how a tiny pathogen winds up the elaborate human DNA repair system.

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Continue reading Atlant’s Column: Flying Submarine, May 2012, or go back to the archive