Fiber Actuator Developed Using Nanoscale Materials to Stimulate Muscle Structure, Function

A research team recently developed a two-step process to make fiber actuators that emulate the structure of muscle fibers, excelling in numerous aspects compared to other existing actuators, including efficiency, actuation strain, and mechanical properties.

A Phys.org report said that according to a Penn State-led of researchers who discovered the process, Inspired by the muscles' structure, an innovative new strategy for making fiber actuators could result in advances in "robotics, prosthetics, and smart clothing."

According to assistant professor of materials science and engineering Robert Hickey from Penn State, actuators are any material that will either "change or deform under any external stimuli," such as parts of a machine that will contract, expand or bend.

He also said, for technologies such as robotics, there's a need to develop soft, lightweight versions of such materials that can function as artificial muscles. The professor added, that their work is about discovering an approach to do this.

Fibers Made of Hydrogel

Hickey explained that this is a big field, and there is a lot of interesting research out there, although it has been focused on engineering materials to optimize properties.

What's making their work exciting, he continued, is they focus on the link between chemistry, structure, and property.

The professor previously headed a team that produced self-assembling, nanostructured hydrogel materials. Hydrogels are networks of polymers that can swell and hold large amounts of water while keeping their structure.

In this new study published in Nature Nanotechnology, the researchers discovered that fibers made of this hydrogel material could stretch many times their original length when hydrated and harden and lock in the elongated shape when they get dried in the extended state.

Mirroring or Mimicking Natural Muscle

Adding water to heat enables the material to return to its original size, making it potential for use as an actuator, explained the researchers.

Hickey said they began to recognize these fibers were contracting and displaying some fascinating properties. He added that when they began to characterize the structure, they realized some fundamentally interesting stuff was going on.

More so, they began to recognize that in several ways, the structure of these mirrored or mimicked natural muscle.

The study investigators explained that the materials comprise highly aligned nanoscale structures with substituting crystalline and amorphous domains, resembling the ordered and strained pattern of mammalian skeletal muscles.

Organized at the Nanometer Scale

A similar Research News report said the exceptional stretching properties of the hydrogels are an outcome of the combination of rigid amorphous nanoscale domains and micrometer-scale pores filled with water.

Moreover, when the hydrogels are stretched, they're snapping like a rubber band. If the stretch fibers become dry in the extended state, the polymer network will crystallize, locking in the fibers' elongated form.

Hickey explained that they think one of the main reasons for these exceptional properties is that the fibers are very accurately organized at the nanometer scale, similar to a human muscle's sarcomere.

He also said that what's going on is that there's a uniform contraction. Such amorphous domains are all organized accurately along with the fiber, which means they are contracting in a single direction, giving rise to such an ability to return to that original state.

Application of Heat or Water

Applying water or heat to the stretched materials melts the crystals and enables the material to return to its original form.

The researchers said that when stretched to five times its original length, the material can go back to within 80 percent of its size and can do this over numerous cycles without any decline in performance.

The fact that two different stimuli, which include heat and water, can be used to stimulate actuation, Hickey said, opens up twice the possibilities of materials made with this approach.

Lastly, he explained that a single stimulus stimulates most actuators. More so, dual stimuli open up the versatility of the materials.

Related information about muscle fiber actuator is shown on Reborn Bionics' YouTube video below:

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