Soft robot powered by edible pneumatic battery and actuator

Using common kitchen ingredients such as citric acid and sodium bicarbonate, scientists have created an edible pneumatic battery and valve system to power soft robots.

Soft, biodegradable robots are used in various fields, such as environmental monitoring and targeted drug delivery, and are designed to completely disappear after performing their tasks. However, the main problem with them is that they rely on conventional batteries (such as lithium), which are toxic and non-biodegradable. And until now, no successful system has been developed that can provide repeated, self-sustained motion using only edible materials.

In a new paper published in the journal Advanced Science, researchers from Dario Floreano’s Laboratory of Intelligent Systems at EPFL in Switzerland describe how they developed a fully edible power source (battery), a valve system (controller), and an actuator (the robot’s muscle).

How the system works

The battery consists of two components: one containing citric acid, found in lemons, and the other containing powdered sodium bicarbonate (common baking soda). To generate power, the acid drips onto the baking soda, causing it to fizz safely and release pressurized carbon dioxide gas. This is the classic “volcano” chemical reaction seen in many college science lessons.

“The edible pneumatic battery described here relies on the chemical reaction of sodium bicarbonate and citric acid, yielding an energy source that is safe to eat, delivers fast actuation, is low cost, and has zero environmental impact,” wrote the researchers in their study.

The carbon dioxide gas flows into the edible actuator, which is made from soft, flexible gelatin. As gas pressure builds inside, the actuator bends. This bending is the robot’s movement.

When the pressure gets too high, it is released through a valve, which is a thin, circular gelatin shell with a slit. As the pressure drops, the valve closes automatically, allowing pressure to build up again from the battery to drive the next cycle of rhythmic movement. This continuous cycle results in self-sustained motion.

The system is highly programmable and scalable, allowing it to be finely tuned for specific missions. By adjusting the size of the opening through which the acid drips, the scientists can control the rate at which the gas is generated. This in turn influences how fast the robot moves.

Meanwhile, the number of repetitive movements can be controlled by varying the resistance to gas flow between the components. Additionally, the battery can be made in various sizes and operate for as little as 20 seconds or as long as 650 seconds.

Successful test

The researchers successfully demonstrated their technology in a lab setting that mimicked real-world use. They created a foot-triggered actuator that could be buried underground and activated when a wild animal, such as a boar, stepped on it.

The robot would then move repeatedly (mimicking live prey), attracting the wild animal to come closer. When it eats the robot, it will also consume its payload of nutrients or vaccines. No toxic waste would be left behind.

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