These self-repairing robot fish can gobble up microplastics from our seas

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Scientists at Sichuan University in China have created fish-like swimming robots with a twist: These light-activated robots have the potential to rid us of the growing microplastic pollution in our waterways.

The little fish robots. Picture credits: Adapted from Nano Letters 2022

Plastic is everywhere. Plastic waste has become a serious threat to our environment and in particular to the seas and oceans, where it accumulates releasing toxic chemicals and killing millions of animals every year. To make matters worse, we have learned in recent years about the threats of microplastics, pieces of plastic smaller than 5cm.

The problem is so severe that our oceans today may contain more microplastics than fish and unfortunately this harmful material is now entering our bodies. Microplastics are also extremely difficult to clean because they are so small. Researchers are therefore increasingly looking for innovative ways to get rid of microplastics.

A team of researchers began to wonder if it was possible to entrust robots with the collection of microplastics in aquatic environments. They have now developed fast-swimming fish robots, each of which is around 15mm in size. These tiny, self-propelled robots can absorb polystyrene microplastics from aquatic environments and transport them to different locations. Here is a glimpse of this enticing technology.

The science behind fish-bots

Scientists have also created robots to solve the problem of plastic waste in the past, but most of these experiments involved the use of soft robots. However, due to various reasons, soft robots were often damaged and stopped working after some time. Therefore, they could not be used to carry out long campaigns to clean up microplastics in water bodies.

These new robo-fish, on the other hand, are made from nanosheets that have similar physical properties to mother-of-pearl – a strong, durable and flexible material obtained from hard clam shells, also known as mother-of-pearl. The researchers modeled the structure of mother-of-pearl to create durable robotic fish. They combined a variant of two-dimensional graphene and mixed it with a type of sugar molecules and prepared nanosheets to build the robot.

While explaining the importance of mother-of-pearl, the study’s lead author and professor at the Polymer Research Institute of Sichuan University, Xinxing Zhang, said ZME Science:

“Here, inspired by mother-of-pearl, we have developed a durable soft robot with the integration of versatile locomotion and microplastic processing function by a self-assembled bionic gradient structure. Mother-of-pearl also has strong properties mechanics with high inorganic filling, so instead of making an artificial mother of pearl, we just modeled the structure of the mother of pearl.

A mixture of polyurethane latex was then added to the nanosheet material and this solution gave rise to robotic fish capable of healing themselves and withstanding the various challenges of aquatic environments. Unlike other soft bots, fish bots can continue microplastic harvesting operations even if damaged, thanks to their self-healing ability. Additionally, they can swim at a speed of 2.67 body lengths per second (15 x 2.67 = 40.07 mm per second), making them the fastest microplastics collection robot to date. according to the researchers.

Zhang added:

“The swimming speed of our robots exceeds that of previously reported soft swimmers while exhibiting comparable body weight and the speed of living neuston and nekton.” He further added, “The breaking and rearranging of dynamic hydrogen bonds enables healing capacity at the molecular level and improves extensibility.”

Potential and limits of small fish robots

The tiny robots move using infrared light. Light rays facilitate heat transfer between graphene nanosheets and lead to volumetric changes causing movement. This is why they are also called light-activated fishing robots. Their size, speed and strength allow them to work in complex and harsh aquatic environments where no other man-made machine could be used.

Picture credits: Miles Hardacre/Unsplash

These tiny machines could therefore play an important role in removing microplastics from our water bodies. However, the researchers point out that robotic fish still need to overcome various limitations before they can be used in the real world. Currently, soft robots only incorporate the function of directionally collecting microplastics from the water surface and regulating its size. All these functions need to be optimized and improved before large-scale application.

Professor Zhang and his team are currently working on a new material that could detect microplastic contaminants underwater and share live data online.

The study is published in the journal Nano-letters.

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