These novel polymer fibers could be used as muscle-like structures in robots. Image: Penn State University/The University of Texas at Austin.
These novel polymer fibers could be used as muscle-like structures in robots. Image: Penn State University/The University of Texas at Austin.

Mimicking the human body, specifically the actuators that control muscle movement, is of immense interest around the globe. In recent years, it has led to many innovations for improving robotics, prosthetic limbs and more, but creating these actuators typically involves complex processes, with expensive and hard-to-find materials.

Researchers at the University of Texas at Austin and Penn State University have now created a new type of fiber that can perform like a muscle actuator, in many ways better than other options that exist today. And, most importantly, these muscle-like fibers are simple to make and recycle.

In a paper in Nature Nano, the researchers showed that the fibers, which they initially discovered while working on another project, are more efficient and flexible, and better able to handle increased strain, than what's out there today. These fibers could be used for a variety of applications, including medicine and robotics.

“You can basically build a limb from these fibers 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 the University of Texas at Austin’s Cockrell School of 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. Another potential application, the researchers say, could be as a sort of ‘self-closing bandage’ for use in surgical procedures, which would naturally degrade inside the body once the wound heals.

“Actuators are any material that will change or deform under any external stimuli, like parts of a machine that will contract, bend or expand,” explained Robert Hickey, assistant professor of materials science and engineering at Penn State and corresponding author of 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 fiber material is known as a block co-polymer. Creating it only requires putting the polymer in a solvent and then adding water. One part of the polymer is hydrophilic (attracted to water), while the other part is hydrophobic (resistant to water). The hydrophobic parts of the polymer group together to shield themselves from the water, creating the structure of the fiber.

Similar existing fibers require an electric current to stimulate the reactions that bond the parts together. This chemical cross-linking is harder to make happen than the mechanical reactions that produce the researchers' new fiber, where the parts take care of most of the work themselves. Another added bonus is it is simple to reverse the process and return the pieces of the fiber to their original states.

"The ease of making these fibers 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.

The researchers found that their fibers were 75% more efficient in terms of converting energy to movement, and able to handle 80% more strain and rotate with more speed and force, than current actuators. The fibers can also stretch to more than 900% of their length before they break.

The discovery of these fibers came about while the researchers were working on something else. They were trying to use these polymers to make membranes for water filtration, but the structures they made were too long for membranes. The resulting fibers stretched out to five times their original length and held that length. The researchers noticed that these characteristics were similar to muscle tissue, so they decided to shift the focus of their research.

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

This story is adapted from material from the University of Texas at Austin, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.