We all know robots that are equipped with movable arms. They stand in factory halls, doing mechanical work and can be programmed. A single robot can be used to perform a variety of tasks.
Until today, miniature systems that transport tiny amounts of fluid through tiny capillaries had little association with such robots. Developed by researchers as an aid to laboratory analysis, these systems are known as microfluidics or lab-on-a-chip and generally make use of external pumps to move liquid across chips. Until now, it has been difficult to automate such systems, and chips have had to be custom designed and manufactured for each specific application.
Ultrasound needle vibrations
Now scientists, led by Professor Daniel Ahmed, combine 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 microbiotic and microfluidic applications and can also be used to automate such applications. Scientists reported this development in Nature Communications.
The device consists of a thin, tapered glass needle and a piezoelectric transducer that causes the needle to oscillate. Similar transducers are used in amplifiers, ultrasound, and professional dental cleaning equipment. ETH researchers can change the oscillation frequency of their glass needles. By dipping the needle into a liquid, it creates a three-dimensional pattern consisting of multiple swirls. Since this pattern depends on the oscillation frequency, it can be controlled accordingly.
Researchers have been able to use this to demonstrate many applications. First, they were able to mix together tiny droplets of highly viscous liquids. “The more viscous the liquids, the more difficult it is to mix,” explains Professor Ahmed. “However, our method is successful in doing this because it allows us to not only create a single vortex, but also to efficiently mix liquids using a complex three-dimensional pattern formed by multiple strong vortices.”
Second, the scientists were able to pump fluid through a small canal system by creating a specific pattern of vortices and placing the vibrating glass needle close to the canal wall.
Third, they successfully used their robot-assisted sonic device to trap microparticles in the liquid. This works because the particle’s size determines its reaction to sound waves. Relatively large particles move towards the vibrating glass needle, where they accumulate. The researchers show how this method can capture not only steric particles but also fish embryos. They believe it should also be able to capture biological cells in the fluid. “In the past, dealing with microscopic particles in three dimensions was always a challenge. Our microbiotic arm makes it easy,” says Ahmed.
“So far, developments in large conventional robotics and microfluidic applications have been done separately,” says Ahmed. “Our work helps bring the two approaches together.” As a result, future microfluidic systems can be designed similarly to existing robotic systems. An appropriately programmed single device will be able to handle a wide variety of tasks. “Mixing and pumping liquids, trapping particles – we can do it all with one device,” Ahmed says. This means that the microfluidic chips of tomorrow will no longer need to be developed specifically for each specific application. The researchers would then like to fuse several glass needles to create more complex swirl patterns in the fluids.
In addition to laboratory analysis, Ahmed can envision other applications for precision robotic weapons, such as sorting small objects. Arms can also be used in biotechnology as a way to insert DNA into individual cells. It should eventually be possible to employ them in additive manufacturing and 3D printing.