Scientists from the University of California at San Diego developed a new 3D printing method to print tiny fish-like robots that are able to detect and remove toxins from liquids. The microfish are powered by hydrogen peroxide and are magnetically controlled.

Professors Shaochen Chen and Joseph Wang of the NanoEngineering Department at UC San Diego described their new microrobots in the journals Advanced Materials. The researchers hope that these proof-of-concept synthetic microfish will inspire a new generation of smart microrobots that have diverse capabilities such as detoxification, sensing and directed drug delivery.

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“We have developed an entirely new method to engineer nature-inspired microscopic swimmers that have complex geometric structures and are smaller than the width of a human hair. With this method, we can easily integrate different functions inside these tiny robotic swimmers for a broad spectrum of applications,” said the co-first author Wei Zhu, a nanoengineering Ph.D. student in Chen’s research group at the Jacobs School of Engineering at UC San Diego.

The new microfish fabrication method is based on a rapid, high-resolution 3D printing technology called microscale continuous optical printing, which was developed in Chen’s lab. “This is a scanless and continuous printing method developed in the lab. It is about 1,000 times faster than a traditional printer with microscale printing resolution”, wrote Chen in an email.

3D‐Printed Artificial Microfish

Within seconds, the researchers can print an array containing hundreds of microfish, each measuring 120 microns long and 30 microns thick. This process does not require the use of harsh chemicals. Because the technology is digitized, the researchers could easily experiment with different designs for their microfish, including shark and manta ray shapes. The researchers are also planning to work on other biology-inspired shapes such as birds.

The greatest breakthrough in this research project was integrating nanotechnology with 3D printing, which allowed for a much more sophisticated design than traditional mircorobots that moved with the help of microjet engines, microdriller and microrockets. Most of the existing robots have relatively simple shapes and are unable to perform complex tasks. By combining nanotechnology and 3D printing, the researchers from UC San Diego were able to insert functional nanoparticles into certain parts of the microfish’s bodies. They installed platinum nanoparticles in the tails, which react with hydrogen peroxide to propel the microfish forward, and magnetic iron oxide nanoparticles in the heads, which allowed them to be steered with magnets.

3D‐Printed Artificial Microfish

In a second step, the researchers loaded the microfish’s bodies with polydiacetylene (PDA) nanoparticles, which capture harmful pore-forming toxins such as the ones found in bee venom. When the PDA nanoparticles bound with toxin molecules, they emitted red-colored light. The team was thus able to monitor the detoxification ability of the microfish by the intensity of their red glow. It became apparent that the fish’s ability to swim fast through the toxin-filled liquid also enhanced their ability to clean up the venom.

So far, the research has aimed at developing and testing the new 3D printing method as a proof-of-concept. But the scientists have practical applications in mind: One is to use microfish that swim in a patient’s blood to deliver medication in places where it is most needed. The other is to eventually develop surgical microrobots that operate safer and with more precision than current methods allow.