Back3D-printed microscopic fish that do much more than just swim
Nanoengineers were able to add functional nanoparticles into certain parts of the microfish bodies
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Mumbai: Three-dimensional or 3D printing technology has been around for almost three decades and is being used to make jewellery and toothbrushes, football boots, racing car parts, custom-designed cakes, guns, human organs, homes and plane parts, among others.
Recently, nanoengineers at the University of California, San Diego, have used this technology to manufacture a multipurpose fish-shaped microrobot they call microfish that swims efficiently in liquids. The current research, led by Professors Shaochen Chen and Joseph Wang of the NanoEngineering Department at the UC San Diego, was published in the 12 August issue of the journal Advanced Materials.
By combining Chen’s 3D printing technology with Wang’s expertise in microrobots, the team was able to build microfish that can do more than simply swim around when placed in a solution containing hydrogen peroxide. Nanoengineers were able to 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.
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 “powerful swimming" by the microfish in the solution greatly enhanced their ability to clean up toxins. When the PDA nanoparticles bind with toxin molecules, they become fluorescent and emit red-coloured light. The team was able to monitor the detoxification ability of the microfish through the intensity of the red glow. The microfish, thus, served as detoxification systems as well as toxin sensors.
The technique used to fabricate the microfish provides numerous improvements over other methods traditionally employed to create microrobots with various locomotion mechanisms such as microjet engines, microdrillers and microrockets—most of which 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 researchers said in a 26 August press statement.
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. The technology enables researchers to print an array containing hundreds of microfish, each measuring 120 microns long and 30 microns thick, in seconds. Also, this process 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.
“With our 3D printing technology, we are not limited to just fish shapes. We can rapidly build microrobots inspired by other biological organisms such as birds," said Zhu.
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 (ultraviolet) 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 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.
The researchers believe 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.
3D printing belongs to a class of techniques known as additive manufacturing, or building objects layer by layer.
The most common household 3D-printing process involves a “print head", which allows for any material to be extruded or squirted through a nozzle.
Others use a laser beam or glue to selectively fuse powdered plastic, metal or ceramic in layers. There are several additive processes, including selective laser sintering, direct metal-laser sintering, fused deposition modelling, stereolithography and laminated object manufacturing. All of them differ in the way layers are deposited to create the 3D objects.
But even as 3D printing technology is making great strides, the concept of 4D printing is evolving simultaneously. The concept that allows materials to “self-assemble" into 3D structures was initially proposed by Massachusetts Institute of Technology faculty member Skylar Tibbits in April 2013.
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