Engineering news
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.
Nanoengineers at the University of California, San Diego, have manufactured multipurpose fish-shaped microrobots, or “microfish”, that swim around efficiently in liquids, are chemically powered by hydrogen peroxide and magnetically controlled.
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, researchers said.
The research team, led by professors Shaochen Chen and Joseph Wang of the NanoEngineering Department at the UC San Diego, was able to custom-build microfish by adding 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. The microfish are also capable of removing and sensing toxins.
Wei Zhu, nanoengineering Ph.D. student in Chen's research group at the Jacobs School of Engineering at UC San Diego and co-first author of the study, said: "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.”
The technique used to fabricate the microfish improves upon previous methods traditionally employed to create microrobots that use various locomotion mechanisms, such as microjet engines, microdrillers and microrockets to swim. Most of these microrobots are incapable of performing more sophisticated tasks because they feature simple designs - such as spherical or cylindrical structures - and are made of homogeneous inorganic materials.
The new microfish fabrication method is based on a rapid, high-resolution 3D printing technology called microscale continuous optical printing (μCOP), which was developed in Chen's lab. Using the μCOP technology means that 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 digitised, the researchers could easily experiment with different designs for their microfish, including shark and manta ray shapes.
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.
Jinxing Li, the co-first author of the study and nanoengineering Ph.D. student in Wang's research group, said: "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.”
As a proof-of-concept demonstration, the researchers incorporated toxin-neutralizing nanoparticles throughout the bodies of the microfish. Specifically, the researchers mixed in polydiacetylene (PDA) nanoparticles, which capture 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.
Jinxing Li, co-author of the study, added: “Another exciting possibility we could explore is to encapsulate medicines inside the microfish and use them for directed drug delivery."