Manta Ray Magic: How Nature’s Grace Is Revolutionizing Robotics and Water Filtration

This robot is capable of diving and resurfacing as well. Rapid flapping produces robust downward waves that propel the robot upwards, while slower flapping generates gentler upward waves, allowing it to descend further. (Mantas actually sink if they decrease their speed.) It also demonstrated the ability to retrieve a payload from the bottom of a tank and bring it back to the surface.

Dining on the move

As manta rays function as massive mobile water filters, researchers from MIT turned to them and other mobula rays (a category that encompasses mantas and devil rays) for ideas when seeking potential enhancements for industrial water filters.

Mantas feed by keeping their mouths open while swimming. Positioned at the base of each side of a manta’s mouth are structures called mouthplates, resembling dashboard air conditioning units. When water flows in, plankton particles that are too large to pass through the plates bounce deeper into the manta’s body cavity, eventually settling in its stomach. Gills extract oxygen from the water that exits, allowing the manta to breathe.

The MIT research team showed particular interest in mobula rays as they believed these creatures achieved an excellent balance between rapidly allowing water in for respiration while maintaining highly selective structures that prevent most plankton from escaping back into the water. To engineer a filter that closely mimics a mobula ray, the team utilized 3D printing to create plates that were subsequently bonded together, forming narrow gaps between them. Particles unable to pass through were instead directed into a waste reservoir.

With slow pumping, water and finer particles flowed out of the filter. When the pumping was accelerated, the water generated a vortex in each gap, permitting water to pass but not particles. The team discovered that this is the mechanism behind mobula rays’ success as filter feeders. They must be adept at determining the right swimming speed to ensure they can breathe while simultaneously securing an optimal quantity of plankton into their mouths.

The team believes that integrating vortex activity will “broaden the conventional design of [industrial] filters,” as mentioned in a study recently published in PNAS.

Manta rays may appear extraterrestrial, but there is nothing science-fictional about how they leverage physics to gain advantages, from powerful swimming to effective (and simultaneous) feeding and respiration. Occasionally, nature provides the most innovative technological advancements.

Science Advances, 2024. DOI: 10.1126/sciadv.adq4222

PNAS, 2024. DOI:  10.1073/pnas.241001812