Video: This walking gel inches along like a looper caterpillar

A chemical gel that can walk like an inchworm, or looper caterpillar has been demonstrated in a Japanese robotics lab.

The video above shows the material in action. It was created in the Shuji Hashimoto applied physics laboratory at Waseda University, Tokyo.

Shingo Maeda and colleagues made the colour-changing, motile gel by combining polymers that change in size depending on their chemical environment. This is based on an oscillating chemical reaction called the Belousov–Zhabotinsky (BZ) reaction. The result is an autonomous material that moves without electronic stimulation.

The BZ reaction is one of a class of chemical systems in which the concentration of one or more compounds periodically increases and decreases. As well as producing stunning patterns (video), it can even be used to perform calculations using a dish containing the pulsing patterns as a chemical brain.


Force amplifier

Polymers used in the gel shrink and grow in response to ruthenium bipyridine ions, alternately losing and gaining electrons in the cyclical reaction. That effect has been known for some time, but hasn’t been used to make a self-locomoting material on such a scale before, says Maeda.

“In previous work, the displacement of the mechanical oscillation of the gel was very small in comparison with the gel size,” he told New Scientist.

Maeda and colleagues created a gel that magnifies the small changes in size by building tension into it. That produces its curved shape as well as amplifying the material’s response to the oscillating reaction inside itself.

The gel shown in the video above is able to move thanks to a notched surface. But Maeda is now working on a new version that lies flat on a normal surface and moves using a peristaltic motion, like an earthworm or snail.

Lab worm

Like the inchworm, this incarnation of the gel will still be limited to the lab bench, but these experiments demonstrate the potential of using oscillating chemical systems like the BZ reaction for tasks engineers usually achieve using electronics, says Maeda.

“Mechanical systems need complex fabricated circuits or external control devices because the mechanical motion is driven by on-off switching of external signals,” he explains.

By comparison, chemical systems can be “self organised” and generate their own control and mechanical signals from within, he says. Those abilities could be used to make some components of a future robot, while more conventional engineering is used for the parts for which only electronics will do.

Journal reference: Advanced Robotics (DOi: 10.1109/IROS.2007.4399392)