Hydrogel: Soft yet strong material keeps its shape after being run over by a car

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A gel with similar properties to shatterproof glass could have applications in soft robots and prosthetics

Physics



25 November 2021

A new gel rapidly returns to its original shape after being severely squashed

Zehuan Huang, University of Cambridge

A soft gel made of 80 per cent water has similar properties to shatterproof glass and can withstand being run over by a car 16 times without lasting deformation. The material could be useful for a range of applications including soft robots, prosthetics and wearable devices.

Hydrated polymer networks, or hydrogels, that have been made before are soft and stretchable, with rubber-like properties. But under high compression, these gels fail to bounce back to their original shape.

Now Oren Scherman and his colleagues at the University of Cambridge have created a soft and compression-resistant gel that can rapidly return to its original shape within a couple of minutes, even after being repeatedly squished by a car weighing 1200 kilograms.

“This work breaks through the boundaries of what was deemed possible,” says Richard Hoogenboom at Ghent University in Belgium, who wasn’t involved in the study. Polymer networks are usually either strong or deformable, while this gel combines both properties to make deformable, strong and tough glass-like materials, he says.

The gel contains a polymer made of two types of “guest” molecules – a perfluorophenyl and a phenyl – that sit inside barrel-shaped “host” molecules called cucurbiturils. The guest molecules are cross-linked to each other inside the hosts, forming a lattice network.

As the cross links are formed through attraction between opposite charges, they constantly unbind and reform. Scherman and his colleagues suspected that making the cross links last longer before dissociating could increase the resistance of the hydrogel to compression.

To test this idea, the researchers modified the structure of the phenyl guest molecules in the network to make them more water-repellent, which increased the time before cross links fell apart. They produced a range of gels, from rubber-like to glass-like.

“This new class of materials holds significant promise in a wide range of applications including cartilage replacement, electronic skins, prosthetic limbs, wearable devices as well as soft robotics,” says Scherman.

Journal reference: Nature Materials, DOI: 10.1038/s41563-021-01124-x

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