A precision arm for miniature robots

We all know robots equipped with movable arms. They stand in the factory halls, perform mechanical work and can be scheduled. A robot can be used to perform a variety of tasks.

Until now, miniature systems that deliver small amounts of liquid through tiny capillaries have had little relevance to such robots. Developed by researchers to facilitate laboratory testing, these systems are known as microfluidics or lab-on-a-chip and typically use external pumps to move fluid through the chips. Currently, these systems are difficult to automate and chips have to be custom designed and manufactured for each specific application.

Oscillations of the ultrasound needle

Scientists led by ETH Professor Daniel Ahmed are now combining conventional robotics and microfluidics. They have developed a device that uses ultrasound and can be attached to a robotic arm. It is suitable for performing a wide range of tasks in microrobotics and microfluidics applications and can also be used to automate such applications. Scientists report this development in Nature of Communication.

The device includes a thin, sharp glass needle and a piezoelectric transducer that oscillates the needle. Similar transducers are used in loudspeakers, ultrasound imaging, and professional dental cleaning equipment. ETH researchers can vary the frequency of oscillation of their glass needle. By immersing the needle in a liquid, they create a three-dimensional pattern consisting of several swirls. Since this pattern depends on the frequency of oscillation, it can be controlled accordingly.

Researchers have used it to demonstrate several applications. First, they were able to mix small droplets of very viscous liquids. “The more viscous liquids are, the harder it is to mix them,” Professor Ahmed said. “However, our method succeeds in doing this because it not only allows us to create a single vortex, but also effectively mixes fluids using a complex three-dimensional pattern made up of many strong vortices. ยป

Second, the scientists were able to pump fluids through a system of mini-channels by creating a specific pattern of vortices and placing an oscillating glass needle near the channel wall.

Third, they were able to use their robot-assisted acoustic device to trap fine particles in the fluid. It works because the size of a particle determines how it reacts to sound waves. The relatively large particles move toward the oscillating glass needle, where they accumulate. The researchers showed how this method captures not only inanimate particles but also fish embryos. They think it should also capture the biological cells in the liquid. “In the past, manipulating microscopic particles in three dimensions has always been a challenge. Our microrobotic arm makes it easier,” Ahmed said.

“Until now, advances in large-scale conventional robotics and microfluidics applications have been achieved separately,” Ahmed said. “Our work helps to combine the two approaches. As a result, future microfluidic systems can be designed similarly to current robotic systems. A single properly programmed device will be able to handle various other tasks. “Mixing and pumping liquids and trapping particles – we can do everything in one device,” Ahmed said. This means that tomorrow’s microfluidic chips will no longer need to be tailored for each specific application.The researchers want to combine several glass needles to create more complex vortex patterns in liquids.

In addition to lab testing, Ahmed can see other applications for microrobotic arms, such as sorting small objects. Weapons can also be used in biotechnology as a means of introducing DNA into individual cells. Eventually, they could potentially be used in additive manufacturing and 3D printing.

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