Nanoengineers 3D print microscopic fish that do more than swim

Microfish Cover
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. Image credit: J. Warner, UC San Diego Jacobs School of Engineering.

Nanoengineers at the University of California, San Diego fabricated a multipurpose fish-shaped microrobots, called microfish that can swim in a solution containing hydrogen peroxide and can be magnetically controlled, using an innovative 3D printing technology.

The research, led by Professors Shaochen Chen and Joseph Wang of the NanoEngineering Department at the UC San Diego, combined Chen’s 3D printing technology with Wang’s expertise in microrobots to custom-build microfish.

The team was able to easily add platinum nanoparticles in the tails of the microfish, which react with hydrogen peroxide to propel the microfish forward, and magnetic iron oxide nanoparticles in the heads, which helped in steering with magnets.

schematic microfish functionalization
Platinum nanoparticles are first loaded into the tail of the fish for propulsion via reaction with hydrogen peroxide. Next, iron oxide nanoparticles are loaded into the head of the fish for magnetic control. Image credit: W. Zhu and J. Li, UC San Diego Jacobs School of Engineering.

As a proof-of-concept demonstration, the researchers mixed in polydiacetylene (PDA) nanoparticles, which capture harmful pore-forming toxins, such as the ones found in bee venom, throughout the body of the microfish and found that the powerful swimming of the microfish in solution greatly enhanced their ability to clean up toxins.

When the PDA bind with toxin molecules, they become fluorescent and emit red-colored light, which enabled the team to monitor the detoxification ability of the microfish by the intensity of their red glow. Hence, the microfish can doubly serve as detoxification systems and as toxin sensors. The team also plan to encapsulate medicines inside the microfish and use them for directed drug delivery.

The microfish is fabricated using a rapid, high-resolution 3D printing technology called microscale continuous optical printing (μCOP), developed in Chen’s lab, which offers speed, scalability, precision and flexibility. The researchers can print an array containing hundreds of microfish, each measuring 120 microns long and 30 microns thick within seconds.

μCOP is digitized and avoids harsh chemicals, which allows printing of different designs including shark and manta ray shapes or even other biological organisms such as birds.

The key component of μCOP is a digital micromirror array device (DMD) chip containing approximately two million micromirrors, each individually controlled to project UV light in the desired pattern onto a photosensitive material that solidifies on exposure to UV light.

The microfish are built using a photosensitive material one layer at a time, allowing each set of functional nanoparticles to be “printed” into specific parts of the fish bodies.

This method helped the team to test different designs and to insert new functional elements into these tiny structures. The research might also develop surgical microrobots that operate safer and with more precision.