Tiny Robot Could Clean Particles From Water and Transport Cells

Researchers at Eindhoven University of Technology have developed a tiny plastic robot that can be used to attract and capture particles in the water. It could also be used to transport cells for analysis in diagnostic devices.

The research was published in the journal PNAS.

The Robot

The tiny robot is made of responsive polymers that can be controlled by light and magnetism. Also termed “wireless aquatic polyp,” it is inspired by a coral polyp in nature, which is present in coral reefs and has tentacles.

In the real-world, living polyps can make a specific movement with their stem in order to create a current that attracts food particles.

According to doctoral candidate Marina Pilz Da Cunha, “I was inspired by the motion of these coral polyps, especially their ability to interact with the environment through self-made currents.”

The newly developed artificial polyp is 1 by 1 cm, with the stem reacting to magnetism and the tentacles being controlled by light. 

“Combining two different stimuli is rare since it requires delicate material preparation and assembly, but it is interesting for creating untethered robots because it allows for complex shape changes and tasks to be performed,” says Pilz Da Cunha.

In order to control the tentacles, light is shone on them with different wavelengths. With the use of UV light, the tentacles ‘grab,’ and while under blue light, they ‘release.’

Underwater

The artificial polyp is capable of grabbing and releasing objects underwater. The new robot is an advancement from the light-guided package delivery mini-robot that was presented by the researchers earlier in the year. 

The land-based robot was not able to operate underwater, since the polymers act through photothermal effects. In contrast to the underwater model, the land-based one used energy from the heat that was generated from the light, rather than the light itself.

“Heat dissipates in water, which makes it impossible to steer the robot underwater,” Pilz Da Cunha said.

With this information, the researchers developed a photomechanical polymer material capable of being controlled by light only, no heat. 

Another major development with this new robot is that it can hold its deformation after being activated by light. After the stimuli is removed, the photothermal material returns to its original shape, but the molecules in the photomechanical material take on a new state. Because of this, different stable shapes can be maintained for longer periods of time.

“That helps control the gripper arm; once something has been captured, the robot can keep holding it until it is addressed by light once again to release it,” says Pilz Da Cunha.

Attracting Particles

A rotating magnet is located underneath the robot which allows the stem to circle around the axis.

According to Pilz Da Cunha, “It was therefore possible to actually move floating objects in the water towards the polyp, in our case oil droplets.”

The fluid flow can be changed by the position of the tentacles.

“Computer simulations, with different tentacle positions, eventually helped us to understand and get the movement of the stem exactly right. And to ‘attract’ the oil droplets towards the tentacles,” says Pilz Da Cunha.

The robot can operate no matter what the surrounding liquid is. This runs counter to the hydrogels that are often used for underwater applications, which are sensitive to the environment. 

“Our robot also works in the same way in salt water, or water with contaminants out of the water by catching them with its tentacles,” says Pilz Da Cunha. 

The researchers are now working on getting various different polyps to collaborate, with the possibility of one polyp passing a package to another. They are also working on swimming robots that could be used for biomedical applications.