American researchers have created smart 3D-printed fish-inspired micro-robots powered by hydrogen peroxide that can swim in liquids and perform a variety of tasks including toxin removal and drug delivery.
The magnetically-controlled micro-fish, the researchers said, offer several improvements compared to earlier swimming micro-robotic technology.
"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,” said Wei Zhu, a nanoengineering Ph.D. student at the Jacobs School of Engineering at UC San Diego and one of the authors of the invention described in the latest issue of the journal Advanced Materials.
“With this method, we can easily integrate different functions inside these tiny robotic swimmers for a broad spectrum of applications."
Previously developed fish-inspired micro-robots usually featured a rather cumbersome design with spherical and cylindrical structures, micro-jet engines, micro-drillers and micro-rockets.
While the earlier systems were usually made from homogeneous inorganic materials, the new micro-fish contain various nanoparticles to enhance functionality. Platinum nanoparticles in the tails react with hydrogen peroxide, propelling the micro-fish, while magnetic iron oxide nanoparticles in the heads allow the robots to be steered with magnets.
As a proof-of-concept demonstration, the researchers incorporated toxin-neutralizing nanoparticles throughout the bodies of the micro-fish that can capture harmful toxins such as those in bee venom.
In the experiment, researchers integrated polydiacetylene (PDA) nanoparticles into the fish and monitored how the micro-robots remove the toxins while swimming. When it binds toxin molecules, PDA becomes fluorescent and emits red light, allowing the researchers to easily monitor efficiency of the toxin removal.
"The neat thing about this experiment is that it shows how the micro-fish can doubly serve as detoxification systems and as toxin sensors," said Zhu.
The researchers said it might be possible to inject medicine into the micro-robots and use them for targeted drug delivery.
The new micro-fish fabrication method is based on a rapid, high-resolution 3D printing technology called micro-scale continuous optical printing (μCOP), which was developed in the laboratory of Professors Shaochen Chen.
The technique is fast, scalable, precise and flexible, allowing the engineers to print large amounts of micro-fish measuring only 120 by 30 microns. As the technology is fully digitised, the researchers were able to experiment with various shapes including shark and manta ray shapes.
"With our 3D printing technology, we are not limited to just fish shapes. We can rapidly build micro-robots inspired by other biological organisms such as birds," said Zhu.
The key component of the μCOP technology is a digital micro-mirror array device (DMD) chip, which contains approximately two million micro-mirrors. Each micro-mirror 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 micro-fish are built using a photosensitive material and are constructed one layer at a time, allowing each set of functional nanoparticles to be "printed" into specific parts of the fish bodies