A tiny underwater robot being developed at the University of Eindhoven may someday catch water contaminants with its tentacles.

The proof-of-concept technology gets its grabbing ability by imitating the maneuvers of a small, soft sea creature: the coral polyp.

A living polyp attracts food particles through the movement of its stem, which creates a magnetic-like current.

The University of Eindhoven robot, created by doctoral candidate Marina Pilz Da Cunha, takes a similar approach to finding underwater objects.

A rotating magnet underneath the robot sends the stem circling around its axis. As you can see in the video below, the spinning motion from the 1 x 1-cm artificial polyp creates a water current that brings the oil droplet into the robot's tentacles.

The robot is made from a photomechanical polymer material that moves under the influence of light and only light — not heat. UV light initiates the grabbing mechanism; blue light, by contrast, opens the tentacles to release the droplet.

"Once something has been captured, the robot can keep holding it until it is addressed by light once again to release it," said Pilz Da Cunha in a recent news release from the university .

Because the tiny robot operates in a variety of conditions, including salt water and contaminated water, the polyp technology has the potential to support applications like filtering or cell transport for medical diagnostics.

In a short, edited interview with Tech Briefs below, Pilz Da Cunha explains how the robot's motion may inspire future designs beyond the ocean.

Tech Briefs: Why a polyp? What inspired this design?

Marina Pilz Da Cunha: We were inspired by the way coral polyps interact with their environment. Even though they are surface-attached, they can manipulate the water by creating self-made currents to aid their survival. Further inspiration was the soft and flexible design of coral polyps. Essentially consisting of a flexible stem and flexible arms and tentacles, polyps can move in a variety of ways having ample freedom of motion.

Tech Briefs: How is the design different from traditional aquatic robots?

photo of Doctoral candidate Marina Pilz Da Cunha
Doctoral candidate Marina Pilz Da Cunha

Marina Pilz Da Cunha: The greatest distinction of our artificial coral polyp is its soft nature, being fully composed of polymers, and the lack of wires or onboard electrical control units to actuate the device. Our artificial polyp is an assembly of two different stimuli-responsive materials: a magnetic-responsive rubber stem and light-responsive liquid crystal polymers which make up its tentacles. The ability to control the polyp’s actuation from outside an enclosed environment gives the design great freedom.

Tech Briefs: How are these robots powered?

Marina Pilz Da Cunha: The polyp is attached to a surface and when under the influence of a rotating magnetic field, the magnetic-responsive stem will undergo a rotating deformation. This motion results in the generation of an attractive flow which can guide suspended targets towards the artificial polyp. Once the targets are within reach of the polyp’s tentacles, light is used to activate the liquid crystal polymer to bend, enclosing the passing target in its grasp.

Tech Briefs: For applications, where is the light coming from that will activate the robot’s ability to grab and release objects?

Marina Pilz Da Cunha: In our demonstration the light is coming from outside the water. The only important requirement is that the light source is located above the polyp, as the light-responsive polymers will bend towards the light.

Tech Briefs: Will the robot have trouble in situations with less light?

Marina Pilz Da Cunha: The grasping mechanism might be hampered if there is less light. But in our case we use artificial light of which the intensity can be tuned.

Tech Briefs: What kinds of applications do you envision with this kind of robot? What can be grabbed?

Marina Pilz Da Cunha: The present study serves as a proof of concept to demonstrate the potential of actuator assemblies in the performance of wirelessly controlled tasks in an aquatic environment. The design concept can be further explored in biomedical applications in which polyps would handle cells, or in microfluidic applications which require the separation of particles or pollutants in a liquid. Further work may allow for the creating of polyp arrays which can work together to attract larger targets and pass them between each other. Multiple polyps will also generate more complex flows in the fluid.

Tech Briefs: Can you take us through your most recent test, and what you were able to demonstrate?

Marina Pilz Da Cunha: In the current work, we demonstrate how a single polyp, present in an enclosed environment, can generate sufficient attractive flow through magnetic actuation of its stem, to attract oil droplets suspended in the liquid. Subsequent activation by UV light can trigger the tentacles to trap the target within its grip. The release of such targets is then triggered by exposing the tentacles to blue light.

In the current study, we also demonstrate that the polyp tentacles are also active when the liquid contains contaminants such as salt for example, something that would hamper the activity of other stimuli-responsive materials such as hydrogels.

Overall, we demonstrate that the soft artificial polyp can be triggered to perform tasks underwater, namely attraction and grasping of suspended targets, without the need for complex external setups or wires. The soft robot presents an example of how the motion of different stimuli-responsive materials can be harnessed in assemblies to perform useful tasks and serves as an inspiration for future designs.

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