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The actuator, which could be used in manufacturing or medical applications, was developed by researchers at Postech in South Korea.
The research team led by Professor Dong Sung Kim, Dr Andrew Choi and Hyeonseok Han was inspired by the mutable collagenous tissue (MCT) of sea cucumbers. The body of a sea cucumber is made of MCT, which allows it to harden or soften according to the surrounding environment.
The creatures have a bumpy, oblong shape, which is soft but stiffens quickly when touched. They can shrink or stretch to several metres, and their original shape can be recovered with the regulation of water uptake even after they die and shrivel up.
The elastic modulus of sea cucumbers can change up to 10 times in just a few seconds, to quickly squeeze through crevices or inflate to threaten predators. The change is induced by formation or destruction of hydrogen bonds in collagenous tissues, by controlling chemical regulators.
Existing soft actuators are limited in their applications due to fragility and slow speed, the researchers said. Inspired by the sea cucumbers, they designed a ‘programmable’ alternative.
The new actuator is based on the bulk PNIPAAm hydrogel, which changes very flexibly and shows an actuation force 200-times (2N) greater and 300-times (0.3s) faster than the conventional soft actuators that use water as an energy source – even underwater at 80°C temperature. The team also demonstrated that the actuator was robust enough to restore its original shape even when subjected to 300% of its tensile strain.
The gripping devices could be integrated into industrial robots, or in surgical tools to lift and hold human tissue during operations and wound closures.
“The soft robot activates when it comes in contact with moisture, and is flexible and deformable to easily adapt to various environments,” said Professor Kim. “This newly developed hydrogel actuator is very powerful and actuates quickly to enable operation – even in places without electricity – by using chemical energy.”
The research was published in Journal of Materials Chemistry A.
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