Researchers have developed a tiny plastic robot, made of responsive polymers, that moves under the influence of light and magnetism. In the future, this wireless aquatic polyp should be able to attract and capture contaminant particles from the surrounding liquid or pick up and transport cells for analysis in diagnostic devices.
The mini robot is inspired by a coral polyp: a small, soft creature with tentacles that makes up the corals in the ocean. The stem of the living polyps makes a specific movement that creates a current to attract food particles. Subsequently, the tentacles grab the food particles floating by.
The wireless artificial polyp is 1 × 1 cm, has a stem that reacts to magnetism, and light-steered tentacles. Combining two different stimuli allows for complex shape changes and tasks to be performed. The tentacles move by shining light on them, so different wavelengths lead to different results; for example, the tentacles grab under the influence of UV light, while they release with blue light.
The device can grab and release objects underwater — a new feature of a light-guided package-delivery mini robot the researchers designed previously. The land-based robot couldn’t work underwater because the polymers making up that robot act through photothermal effects. The heat generated by the light fueled the robot, instead of the light itself. A new photomechanical polymer material was developed that moves under the influence of light only.
In addition to operating underwater, this new material can hold its deformation after being activated by light. While the photothermal material immediately returns to its original shape after the stimuli has been removed, the molecules in the photomechanical material actually take on a new state. This allows different stable shapes to be maintained for a longer period of time, controlling 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. By placing a rotating magnet underneath the robot, the stem circles around its axis, moving floating objects in the water towards the polyp.
The position of the tentacles (open, closed, or something in between) turned out to have an influence on the fluid flow. Computer simulations, with different tentacle positions, eventually helped to understand and get the movement of the stem exactly right.
An added advantage is that the robot operates independently from the composition of the surrounding liquid. The dominant stimuliresponsive material used for underwater applications (hydrogels) is sensitive for their environment. Hydrogels therefore behave differently in contaminated water. The robot works in the same way in saltwater or in water with contaminants. In the future, the polyp may be able to filter contaminants out of the water by catching them with its tentacles.