Most of us are familiar with robots with movable arms. These machines are usually in factory settings and are capable of performing a variety of mechanical tasks. They can be programmed to perform a number of functions, and a robot can perform several tasks. Until now, robots equipped with movable arms have had limited connections to microfluidic systems that transport tiny amounts of fluid through delicate capillaries. Known as microfluidics or lab-on-a-chip, these systems were created by researchers to aid lab analysis and typically rely on external pumps to circulate fluid between chips. However, such systems were difficult to automate, and chips had to be specifically designed and manufactured for each application.

Vibration of ultrasound needle

Scientists led by ETH Professor Daniel Ahmed are now combining traditional robots and microfluidics. They have developed a device that uses ultrasound and can be attached to a robotic arm. It is suitable for a wide variety of tasks in microrobotic and microfluidic applications and can be used to automate such applications. The scientists reported this development in Nature Communications.

The device consists of a thin, pointed glass needle and a piezoelectric transducer that causes the needle to oscillate. Similar transducers are used in loudspeakers, ultrasound imaging, and professional dental cleaning equipment. ETH researchers can change the vibration frequency of glass needles. By immersing the needle in the liquid, they create a three-dimensional model of several vortices. Since this circuit depends on the oscillation frequency, it can be controlled accordingly.

Researchers were able to use it to demonstrate various applications. First, they succeeded in mixing small droplets of high-viscosity liquids. “The more viscous the liquids are, the harder it is to mix them,” explains Professor Ahmed. “However, our method achieves this because it allows us to not only create a single vortex, but also efficiently mix liquids using a complex three-dimensional model made up of several powerful vortices.”

Second, the scientists were able to pump fluids through a system of mini-channels by creating a custom vortex pattern and placing an oscillating glass needle close to the canal wall.

Third, they were able to use their robotic acoustic devices to capture tiny particles found in the liquid. This works because the particle’s size determines its response to sound waves. Relatively large particles move towards the oscillating glass needle, where they accumulate. The researchers showed that this method can capture not only non-living particles, but also fish embryos. They believe it should also be able to capture biological cells in the liquid. “Manipulating microscopic particles in three dimensions has always been a challenge in the past. Our micro robotic arm makes it easy,” says Ahmed.

“So far, major advances in conventional robotics and microfluidic applications have been made separately,” says Ahmed. “Our work helps bring the two approaches together.” As a result, the microfluidic systems of the future can be designed similarly to the robotic systems of today. A single device programmed accordingly can perform a variety of tasks. “We can do it all with one device for mixing and pumping liquids and capturing particles,” says Ahmed. This means that tomorrow’s microfluidic chips will no longer need to be custom-designed for every particular application. The researchers then want to join multiple glass needles to create even more complex swirl patterns in liquids.

Beyond laboratory analysis, Ahmed can envision other applications such as sorting small objects for micro robotic arms. Possibly hands could also be used in biotechnology as a way to inject DNA into individual cells. Eventually, they can be used in additive manufacturing and 3D printing.