Polymer could provide self-healing muscle for robots

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The highly stretchable new material could revolutionise robot ‘muscles’. – Zhenan Bao

A new polymer could provide “self-healing” muscles for robots, the Stanford University researchers who developed it say.

The material can repair damage, move in response to an electrical current and – most surprisingly – stretch to 100 times its own length, all at temperatures never before achieved by current polymers.

Polymer “muscles”, themselves are not new. There ability to stretch and compress are used in haptic feedback systems – which govern a robot’s sense of touch – and the movement of its appendages. But, until now, the problem has been that when damage occurs, such as tears or cuts, this often causes a failure of the whole muscle, which must then it must be replaced.

“Artificial muscles are typically very sensitive to defects and pinholes – they really affect their actuation performance,” said Zhenan Bao, whose work on the new material, was published in Nature Chemistry.

Her new material starts with a network of long polymer chains, made from the commonly used elastomer polydimethylsiloxane to provide strength against mechanical force.

Bao and her team then added molecules that either contain or bind to iron to form weak bonds that were found to be able to break apart and then reform instantaneously.

It is these weak bonds that allow the polymer to heal, sealing any breaks caused by stressing the sheet. 

They also make it possible for the sheet to be stretched to such an extreme degree – a property that came as an unexpected surprise to the materials scientists.

Bao and her team also found that the repair process was able to take place at room temperature. This is in stark contrast to current polymers, which either require heating or use hydrogen bonds that are susceptible to moisture in the air.

It is hoped that this new polymer will find its way into new self-healing robots and even electronic circuitry that could fix damage on its own.

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