Swiss scientists invent eco-friendly robot made from fish food

By Stephen Beech

A new eco-friendly aquatic robot is made from fish food.

The edible machine utilizes biodegradable fuel and surface tension to zip around the water’s surface.

It creates a safe and nutritious alternative to environmental monitoring devices made from artificial polymers and electronics, say Swiss scientists.

They explained that the boat-shaped robot takes advantage of the same phenomenon – the Marangoni effect – used by some aquatic insects to propel themselves across the surface of water.

A chemical reaction inside a tiny detachable chamber produces carbon dioxide gas, which in turn enters a fuel channel, forcing the fuel out.

The sudden reduction in water surface tension caused by the ejected fuel then propels the robot forward.

This clever design is not only effective, allowing the robots to move freely around the surface of the water for several minutes, but also entirely non-toxic and biodegradable.

The Swiss team explained that the components of the triggering chemical reaction - citric acid and sodium bicarbonate - are the same ones used in a typical school science experiment involving a volcano.

And the "fuel" is propylene glycol - a liquid commonly found in skin care products.

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Shuhang Zhang, of the Swiss Federal Technology Institute of Lausanne (EPFL), said: “While the development of miniature swimming robots for natural environments has progressed rapidly, these typically rely on plastics, batteries, and other electronics, which pose challenges for mass deployment in sensitive ecosystems.

“In this work, we show how those materials can be replaced by completely biodegradable and edible components.”

He says the robot, described in the journal Nature Communications, is designed to be not only harmless to aquatic fauna, but even beneficial.

To add strength and rigidity to the outer structure, which is about five centimetres (two inches) long, the research team used fish food with a 30% higher protein content and 8% lower fat content than commercial pellets.

PhD student Mr Zhang said: "The device can therefore act as nourishment for aquatic wildlife at the end of its lifetime, just as animals do."

The EPFL team envisions the robots being deployed in large numbers.

They say each device would be equipped with biodegradable sensors for collecting environmental data such as water acidity, temperature, pollutants, and the presence of microorganisms, which could be read out after collection or by remote sensing.

Rather than controlling precisely the directional movement of the robots, the team has fabricated "left turning" and "right turning" variants by altering the fuel channel’s asymmetric design.

The level of control is all that is needed to disperse the robots across the water’s surface, and their pseudo-random movements mimic those of insects, making them ideal vessels for delivering nutrients or medication to fish.

Team leader Professor Dario Floreano, of EPFL's School of Engineering, added: “The replacement of electronic waste with biodegradable materials is the subject of intensive study, but edible materials with targeted nutritional profiles and function have barely been considered, and open up a world of opportunities for human and animal health."