Artificial muscle for soft robots can bend in sunlight

Robots aren't known for being light on their feet, but a new artificial muscle that can be powered by a sunbeam could change that. Researchers have developed a photoresponsive actuator - a gel-like material that bends when it is exposed to light.
Akira Harada at Osaka University in Japan and colleagues have developed a prototype that works in water. When hit with UV light at a wavelength of 365 nanometres it expands, bending and increasing in mass by taking on water. Visible light at a wavelength of 430 nm restores the muscle to its previous form. "The gel absorbs water like an expanding and contracting sponge," says Harada.
The muscles work via the interaction of two chemical compounds in the gel - azobendrine and cyclodextrin - which react differently under different light. The direction in which the gel bends can then be controlled by shining UV and visible light from various angles.
Light-activated muscles are likely to be most applicable in soft robots, which are built from materials such as gel or rubber and lack a skeletal frame. Existing examples tend to move pneumatically, but the need for an umbilical air hose keeps them tethered. Soft robots are also currently limited by their inability to carry heavy loads such as a battery.
By using light as an external power source, soft robots could be given a much greater range. Even sunlight could be used, says Harada.


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