Fibre actuator shows potential for robotics

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Researchers in the US have created a new type of fibre that performs like a muscle actuator, an advance with potential applications in robotics and prosthetic limbs.

Fibres developed at developed at The University of Texas at Austin and Penn State University can be used as muscle-like structures in robots
Fibres developed at developed at The University of Texas at Austin and Penn State University can be used as muscle-like structures in robots - Penn State University / The University of Texas at Austin

These muscle-like fibres, developed by a team from The University of Texas at Austin and Penn State University, are reportedly simple to make and recycle.

In a new paper published in Nature Nano, the researchers showed that these fibres are more efficient, flexible and able to handle increased strain compared to existing solutions.

“You can basically build a limb from these fibres in a robot that responds to stimuli and returns power, instead of using a mechanical motor to do this, and that’s good because then it will have a softer touch,” said Manish Kumar, an associate professor in UT Autsin’s Cockrell School of Engineering’s Department of Civil, Architectural and Environmental Engineering and one of the lead authors of the paper.

This kind of robotic arm could be used in an assistive exoskeleton to help people with weak arms regain movement and strength. The team added that another potential application could be a form of "self-closing bandage" that could be used in surgical procedures and naturally degrade inside the body once the wound heals.

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“Actuators are any material that will change or deform under any external stimuli, like parts of a machine that will contract, bend, or expand,” said Robert Hickey, assistant professor of materials science and engineering at Penn State and corresponding author on the paper. “And for technologies like robotics, we need to develop soft, lightweight versions of these materials that can basically act as artificial muscles. Our work is really about finding a new way to do this.”

The fibre material is a block co-polymer and creating it requires putting the polymer in a solvent and adding water. One part of the polymer is hydrophilic, while the other part is hydrophobic. The hydrophobic parts of the polymer group together to shield themselves from the water, creating the structure of the fibre.

Similar existing fibres require an electric current to stimulate the reactions that bond parts together. This chemical cross-linking is harder to make happen, compared to the researchers' new fibre, which is a mechanical reaction. According to UT Austin, it is simple to reverse the process and return the pieces of the fibre to their original states.

"The ease of making these fibres from the polymer and their recyclability are very important, and it's an aspect that much of the other complicated artificial muscle research doesn't cover," Kumar said in a statement.

The researchers found their fibres were 75 per cent more efficient in terms of converting energy to movement, able to handle 80 per cent more strain and could rotate with more speed and force than current actuators. Furthermore, it can stretch to over 900 per cent of its length before it breaks.

The researchers next plan to learn more about the structural changes of the polymer and improve some of the actuation properties, including energy density and speed. They also may use this same design technique to create actuators that respond to different stimuli, such as light.