Our muscles get stronger when put under stress and now robots could do the same, thanks to a soft gel that becomes harder when exposed to vibration.

Zhao Wang at the University of Chicago and his colleagues created the gel by embedding zinc oxide nanoparticles into a cellulose mixture. They then vibrated the material using a device designed to test car and aeroplane designs and found that the nanoparticles emitted an electrical charge, creating new links within the gel as the material turned into a polymer.

The team found that the strength of the material increased as it was shaken. The vibration-strengthened material maintained its shape when squashed with a press, but the untreated gel was deformed permanently, demonstrating that the gel had become up to 66 times stiffer from the vibrations.

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“When we exercise, we can certainly build up our muscles,” says Wang. “We want to mimic that process so when we exercise the artificial muscle it can increase its modulus, it’s stiffness.”

The team now aims to make the process reversible by trying to create bonds that will decay over time and also increase the hardness of material. It could then have a range of applications such as artificial robotic muscle that adapts to tasks and becomes stronger at performing repetitive motions, but could also lose strength and gain flexibility to better suit a new task, says Wang.

Journal reference: Nature Materials, DOI: 10.1038/s41563-021-00932-5