Tiny Objects Coated in Special Magnetic Material Walk, Crawl, and Roll

The objects could be used for biomedical applications.
Fabienne Lang
Two objects that can now crawl and rollCityU Research/YouTube

A swarm of mini robots may soon be crawling, walking, and rolling through parts of your body for biomedical reasons. 

A team of researchers led by a scientist at the City University of Hong Kong (CityU) has developed a novel magnetic coating that enables little objects to act like millirobots by shifting in different ways across different surfaces.

The coating is also biocompatible and can disintegrate into powder if required. This discovery could prove useful for biomedical applications, such as specific drug delivery or catheter insertion. 

Their study was published in Science Robotics on November 18. 


The CityU team constructed millirobots — insect-sized robots — by applying a magnetic coating. These mini bots can more easily adapt to different environments that are required for biomedical applications and exploration in the human body

The M-spray, as Dr. Shen Yajing and his team have called it, is a glue-like spray that coats objects and turns them into moving robots. 

"Our idea is that by putting on this ‘magnetic coat’, we can turn any objects into a robot and control their locomotion. The M-spray we developed can stick on the targeted object and ‘activate’ the object when driven by a magnetic field," explained Dr. Shen, lead researcher and Associate Professor of the Department of Biomedical Engineering at CityU. 

Tiny Objects Coated in Special Magnetic Material Walk, Crawl, and Roll
The tiny objects the team turned into millirobots using its M-spray. Source: City University of Hong Kong

The M-spray is made up of polyvinyl alcohol (PVA) gluten, and iron particles, and can stick to both rough and smooth surfaces. The objects maintain their original form and size as the coating is only 0.1 - 0.25 mm thick.

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The spray is then magnetized with either one or a number of magnetization directions, leading the objects to roll, crawl, or walk in the desired direction and pattern. 

What's even more special about the team's creation is that it can be reprogrammed at will. For example, the millirobots can change from "a faster 3D caterpillar movement in a spacious environment to a slower 2D concertina movement for passing through a narrow gap," as the researchers point out. Something invaluable when trying to get through tricky passages in our body.

Another important feature the M-spray offers is that it can disintegrate into powders on command, which means it can then be absorbed or excreted by the body without causing any harm. 

The team has so far tested its millirobots on rabbits, delivering drugs to specific areas in the stomach. The coating was then disintegrated.

"We hope this construction strategy can contribute to the development and application of millirobots in different fields, such as active transportation, moveable sensor, and devices, particularly for the tasks in limited space," said Dr. Shen.

Take a look at the millirobots in action below:

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