Robot fish printed

C&I Issue 10, 2015

A novel method for 3D printing micro-sized robot fish may help realise a new generation of advanced microrobots. The process, developed by researchers in the US, uses a photosensitive polymer with added nanoparticles to provide functionality.

There are a number of ways of manufacturing micro-sized robots able to propel themselves through liquids. However, such approaches have typically been limited to constructing simple designs from uniform materials, which restricts the tasks such robots can perform.

In the current study, researchers from the University of California San Diego, US, report a simple method for creating more complicated micro-robots via ‘microscale continuous optical printing’ – to create the robots layer-by-layer from a photosensitive hydrogel of polyethylene glycol diacrylate (W. Zhu et al, doi: 10.1002/adma.201501372). When exposed to UV light, projected in the desired pattern by millions of independently-controlled micro-mirrors, each 100nm-thick layer is individually solidified from the gel.

The printing process is extremely rapid, producing an array of hundreds of microfish in seconds, and requires no harsh chemicals. Further, as the printing is based on a digital template, the micro-robot’s shapes can easily be adjusted to provide different configurations. In this study, for example, the researchers created robots shaped like various fish, sharks and manta rays.

‘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,’ says paper author Wei Zhu: ‘We can easily integrate different functions inside these tiny robotic swimmers for a broad spectrum of applications.’

This functionality comes from the addition of nanoparticles to each micro-robot during fabrication. As a demonstration, the researchers printed fish-shaped microrobots with three types of functional nanoparticles. Platinum nanoparticles were embedded in the tail of each microfish to provide propulsion – through a chemical reaction – when the microfish were placed in a solution of hydrogen peroxide. Iron oxide nanoparticles in the head of each robot allowed the researchers to guide them in particular directions by applying a magnetic field. Finally, polydiacetylene nanoparticles – which fluoresce when they capture harmful, pore-forming toxins – gave the microfish toxin-sensing and removal capabilities.

By altering the nanoparticles added, the researchers say, the robots could also be tailored for a variety of different tasks – including remote drug delivery, detoxification and in vivo sensing.

‘This is a potentially ground-breaking technology,’ comments Dave Cappelleri, a mechanical engineer from Purdue University, US. ‘Being able to 3D print targeted materials and functionality at the micro-scale, as is done here, opens up many possibilities in the microrobot design community.’

‘It is exciting to see the high degree of functionalisation,’ agrees Eric Diller, a micro-robotics expert from the University of Toronto. However, at such small scales, fish shapes are not ideal for chemically-propelled locomotion, he notes. ‘I suspect that a simple block shape would perform just as well.’

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