Scientists at Eidgenössische Technische Hochschule Zürich have developed an ultrasound device suitable for performing a wide range of tasks in micro-robotic and micro-fluidic applications that can be attached to a robotic arm.
The device is comprised of a thin, pointed glass needle and a piezoelectric transducer – similar to those used in loudspeakers, ultrasound imaging and professional dental cleaning equipment – that causes the needle to oscillate. The researchers can vary the oscillation frequency of the glass needle. By dipping it into a liquid, they can create a three-dimensional pattern composed of multiple vortices. Since this pattern depends on the oscillation frequency, it can be controlled accordingly.
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The researchers were able to use this to demonstrate several applications. First, they were able to mix tiny droplets of highly viscous liquids. ‘The more viscous liquids are, the more difficult it is to mix them,’ explained Professor Daniel Ahmed. ‘However, our method succeeds in doing this because it allows us to not only create a single vortex, but to also efficiently mix the liquids using a complex three-dimensional pattern composed of multiple strong vortices.’
Second, the scientists were able to pump fluids through a mini-channel system by creating a specific pattern of vortices and placing the oscillating glass needle close to the channel wall.
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Third, they succeeded in using their robot-assisted acoustic device to trap fine particles present in the fluid. This works because a particle’s size determines its reaction to the sound waves. Relatively large particles move towards the oscillating glass needle, where they accumulate. The researchers demonstrated how this method can capture not only inanimate particles but also fish embryos. They believe that the device should also be capable of capturing biological cells in the fluid. ‘In the past, manipulating microscopic particles in three dimensions was always challenging. Our micro-robotic arm makes it easy,’ Ahmed said.
‘Until now, advancements in large, conventional robotics and microfluidic applications have been made separately,’ Ahmed continued. ‘Our work helps to bring the two approaches together.’
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As a result, future microfluidic systems could be designed similarly to today’s robotic systems. An appropriately programmed single device would be able to handle a variety of tasks. ‘Mixing and pumping liquids and trapping particles – we can do it all with one device,’ Ahmed said. This means that tomorrow’s microfluidic chips will no longer have to be custom-developed for each specific application. The researchers would next like to combine several glass needles to create even more complex vortex patterns in liquids.
In addition to laboratory analysis, Ahmed envisages using micro-robotic arms for a range of other applications, including sorting tiny objects. The arms could also conceivably be used in biotechnology as a way of introducing DNA into individual cells and it should ultimately be possible to employ them in additive manufacturing and 3D printing.
The research has been published in Nature Communications.