3D-printed swimming microrobots can sense and remove toxins

Nanoparticles enable them to be self-propelled, chemically powered, and magnetically steered; could also be used for targeted drug delivery
August 26, 2015

3D-printed microfish contain functional nanoparticles that enable them to be self-propelled, chemically powered and magnetically steered. The microfish are also capable of removing and sensing toxins. (credit: J. Warner, UC San Diego Jacobs School of Engineering)

A new kind of fish-shaped microrobots called “microfish” can swim around efficiently in liquids, are chemically powered by hydrogen peroxide, and magnetically controlled. They will inspire a new generation of “smart” microrobots that have diverse capabilities such as detoxification, sensing, and directed drug delivery, said nanoengineers at the University of California, San Diego.

To manufacture the microfish, the researchers used an innovative 3D printing technology they developed, with numerous improvements over other methods traditionally employed to create microrobots, such as microjet engines, microdrillers, and microrockets.

Most of these microrobots are incapable of performing more sophisticated tasks because they feature simple mechanical designs — such as spherical or cylindrical structures — and are made of homogeneous inorganic materials.

The research, led by Professors Shaochen Chen and Joseph Wang of the NanoEngineering Department at the UC San Diego, was published in the Aug. 12 issue of the journal Advanced Materials.

A microrobotic toxin scavenger

Platinum nanoparticles in the tail of the fish achieve propulsion via reaction with hydrogen peroxide; iron oxide nanoparticles are loaded into the head of the fish for magnetic control (credit: W. Zhu and J. Li, UC San Diego Jacobs School of Engineering)

The nanoengineers were able to easily add functional nanoparticles into certain parts of the microfish 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.

“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.

As a proof-of-concept demonstration, the researchers incorporated toxin-neutralizing polydiacetylene (PDA) nanoparticles throughout the bodies of the microfish to neutralize harmful pore-forming toxins such as the ones found in bee venom.

The researchers noted that the powerful swimming of the microfish in solution greatly enhanced their ability to clean up toxins.

When the PDA nanoparticles bind with toxin molecules, they become fluorescent and emit red-colored light. The team was able to monitor the detoxification ability of the microfish by the intensity of their red glow. “The neat thing about this experiment is that it shows how the microfish can doubly serve as detoxification systems and as toxin sensors,” said Zhu.

“Another exciting possibility we could explore is to encapsulate medicines inside the microfish and use them for directed drug delivery,” said Jinxing Li, the other co-first author of the study and a nanoengineering Ph.D. student in Wang’s research group.

3D-printing microrobots

Schematic illustration of the μCOP method to fabricate microfish. (Left) UV light illuminates mirrors, generating an optical pattern specified by the control computer. The pattern is projected through optics onto the photosensitive monomer solution to fabricate the fish layer-by-layer. (Right) 3D microscopy image of an array of printed microfish. Scale bar, 100 micrometers. (credit: Wei Zhu et al./Advanced Materials)

The new microfish fabrication method is based on a rapid, high-resolution 3D printing technology called microscale continuous optical printing (μCOP) developed in Chen’s lab, offering speed, scalability, precision, and flexibility.

The key component of the μCOP technology is a digital micromirror array device (DMD) chip, which contains approximately two million micromirrors. Each micromirror is individually controlled to project UV light in the desired pattern (in this case, a fish shape) onto a photosensitive material, which solidifies upon exposure to UV light. The microfish are constructed one layer at a time, allowing each set of functional nanoparticles to be “printed” into specific parts of the fish bodies.

Fluorescent images demonstrating the detoxification capability of microfish containing encapsulated PDA nanoparticles (credit: Wei Zhu et al./Advanced Materials)

Within seconds, the researchers can print an array containing hundreds of microfish, each measuring 120 microns long and 30 microns thick. This process also does not require the use of harsh chemicals. Because the μCOP technology is digitized, the researchers could easily experiment with different designs for their microfish, including shark and manta ray shapes. They could also build microrobots in based on other biological organisms, such as birds, said Zhu.

“This method has made it easier for us to test different designs for these microrobots and to test different nanoparticles to insert new functional elements into these tiny structures. It’s my personal hope to further this research to eventually develop surgical microrobots that operate safer and with more precision,” said Li.


Abstract of 3D-Printed Artificial Microfish

Hydrogel microfish featuring biomimetic structures, locomotive capabilities, and functionalized nanoparticles are engineered using a rapid 3D printing platform: microscale continuous ­optical printing (μCOP). The 3D-printed ­microfish exhibit chemically powered and magnetically guided propulsion, as well as highly efficient detoxification capabilities that highlight the technical versatility of this platform for engineering advanced functional microswimmers for diverse biomedical applications.