UCLA advances development of artificial muscle

LOS ANGELES—Materials scientists from the University of California, Los Angeles (UCLA), in collaboration with research institute SRI International, have developed a new material and manufacturing process for creating artificial muscles that are "stronger and more flexible than their biological counterparts."

To create the artificial muscle, the researchers worked with dielectric elastomers (DE), which are lightweight materials with high elastic energy density that offer optimal flexibility and toughness.

Dielectric elastomers are electroactive polymers, which are natural or synthetic substances composed of large molecules that can change in size or shape when stimulated by an electric field, UCLA said in a statement July 7.

The materials can be used as actuators, enabling machines to operate by transforming electric energy into mechanical work.

Most dielectric elastomers are made of either acrylic or silicone, both of which have certain drawbacks.

While traditional acrylic DEs can achieve high actuation strain, they require pre-stretching and lack flexibility. Silicones are easier to make, but they cannot withstand high strain, according to UCLA.

"Creating an artificial muscle to enable work and detect force and touch has been one of the grand challenges of science and engineering," said Qibing Pei, a professor of materials science and engineering at the UCLA Samueli School of Engineering.

Utilizing commercially available chemicals and employing an ultraviolet (UV) light curing process, the UCLA-led research team created an improved acrylic-based material that is "more pliable, tunable and simpler to scale without losing its strength and endurance."

The acrylic acid, according to UCLA, enables more hydrogen bonds to form, thereby making the material more movable.

In addition, the researchers also adjusted the crosslinking between polymer chains, enabling the elastomers to be softer and more flexible.

The resulting "thin, processable, high-performance" dielectric elastomer film, or PHDE, was then sandwiched between two electrodes to convert electrical energy into motion as an actuator.

According to UCLA, each PHDE film is as thin and light as a piece of human hair, about 35 micrometers in thickness.

Once multiple layers are stacked together, they become a miniature electric motor that can act like muscle tissue and produce enough energy to power motion for small robots or sensors.

The researchers have made stacks of PHDE films varying from four to 50 layers.

"This flexible, versatile and efficient actuator could open the gates for artificial muscles in new generations of robots, or in sensors and wearable tech that can more accurately mimic or even improve humanlike motion and capabilities," Qibing Pei said.

Artificial muscles fitted with PHDE actuators are claimed to be able to generate more megapascals of force than biological muscles.

They also demonstrate three to 10 times more flexibility than natural muscles, according to the researchers.

Multilayered soft films are usually manufactured via a "wet" process that involves depositing and curing liquid resin.

But that process can result in uneven layers, which make for a poor-performing actuator.

For this reason, up to now, many actuators have only been successful with single layer DE films.

The UCLA research, however, involves a "dry" process by which the films are layered using a blade and then UV-cured to harden, making the layers uniform.

This increases the actuator's energy output so that the device can support more complex movements.

"The simplified process, along with the flexible and durable nature of the PHDE, allows for the manufacture of new soft actuators capable of bending to jump, like spider legs, or winding up and spinning," the statement said.

The researchers have also demonstrated the PHDE actuator's ability to toss a pea-sized ball 20 times heavier than the PHDE films.