The Geeky Mind

When old food packaging, discarded toys, and other plastic waste break down into tiny microplastics, cleaning them from oceans and waterways becomes even more challenging. These tiny plastic particles, which measure 5 millimeters or less, also attract bacteria, including harmful pathogens. In a study published in ACS Nano, researchers detail how swarms of microscopic robots (microrobots) can capture both plastic bits and bacteria from water. After cleaning, the robots can be decontaminated and reused.

The small size of microplastics not only makes them hard to clean up but also poses a threat to wildlife. Animals can ingest these particles, potentially harming themselves and passing the plastics up the food chain to humans. Although the full health effects on humans are still unclear, the fact that microplastics attract bacteria, including disease-causing pathogens, is a significant concern.

To tackle this dual problem, Martin Pumera and his team developed microscale robotic systems that work together like natural swarms, such as schools of fish. The robots were constructed by linking strands of a positively charged polymer to magnetic microparticles, which move in response to a magnetic field. These polymer strands attract both plastic particles and microbes.

Each microrobot measures just 2.8 micrometers in diameter. When exposed to a rotating magnetic field, the robots swarm together. By adjusting the number of robots in these clusters, the researchers could control the swarm’s movement and speed.
In lab tests, the team simulated an environment with microplastics and bacteria by adding fluorescent polystyrene beads (1 micrometer wide) and Pseudomonas aeruginosa bacteria, which can cause pneumonia and other infections, to a water tank. The microrobots were then added to the tank and exposed to a rotating magnetic field for 30 minutes, switching it on and off every 10 seconds. At the highest concentration tested, 7.5 milligrams per milliliter, the microrobots captured about 80% of the bacteria and significantly reduced the number of free plastic beads.

After the experiment, the robots were collected using a permanent magnet and the bacteria were detached with ultrasound. The removed microbes were then disinfected with ultraviolet radiation. Even after reuse, the decontaminated robots continued to capture plastic and microbes, though in smaller amounts.

This innovative microrobotic system offers a promising solution for cleaning water of both plastic and bacterial contaminants, the researchers conclude.