The way Cheerios stick together has inspired a new kind of robot

The same phenomena that let beetles float through puddles and cause Cheerios to cluster together they can be harnessed in your cereal bowl to make little mobile robots.

one of them Marangoni effectformed when a fluid with a lower surface tension spreads rapidly over the surface of a fluid with a higher surface tension. This effect is used Stenius beetles, which have evolved to wade through puddles by secreting a substance called stenusin, as well as soapy toy boats.

To investigate how engineers can use this, Jackson Wilt at Harvard University and his colleagues 3D printed round, plastic puffs about a centimeter in diameter. Inside each was an air chamber for buoyancy and a small fuel tank containing alcohol, which has a lower surface tension than water in concentrations ranging from 10 to 50 percent. The alcohol is gradually released from the puck, pushing it across the surface of the water.

The team used alcohol as fuel because it evaporates, unlike soap, which eventually contaminates the water and ruins the Marangoni effect. The stronger the alcohol, the better the result. “Beer would be pretty bad,” says Wilt. “Vodka is probably the best thing you could use. Absinthe… you’d have a lot of propulsion.” At top speeds, the robots moved 6 centimeters per second, and some experiments saw pucks being pushed for 500 seconds.

By printing pucks with more than one fuel outlet and gluing them together, the researchers could also create larger devices that drew sweeping curves or rotated on the spot. Using multiple pucks, researchers investigate the “Cheerios effect,” which is when cereal or other similar floating objects are collected. This is because they form a meniscus or curved surface in the fluid, and these surfaces are attracted to each other.

Wilt says 3D-printed devices could be useful in education to help students intuitively grasp concepts related to surface tension, but could also see applications in environmental or industrial processes if carefully designed to create more complex and elegant behavior.

For example, if there was a substance that needed to be dispersed in an environment that could also serve as a suitable fuel, the robots would automatically spread it. “Let’s say you have a body of water where you need to release a chemical, and you want to distribute it more evenly, or you have some chemical process where you need to accumulate the material over time,” says Wilt. “I think there’s very interesting behavior here.”