Scientists develop durable material for flexible artificial muscles

4×5 inch film made from 10 layers of processable, high performance dielectric elastomers (PHDE) stacked together with 20 actuators. Credit: Soft Materials Research Laboratory/UCLA

Materials scientists at UCLA and colleagues at the nonprofit research institute SRI International have developed a new material and manufacturing process to create artificial muscles that are stronger and more flexible than their biological counterparts.

“Creating an artificial muscle that enables work and detects force and touch is one of the grand challenges of science and engineering,” said Qibing Pei, professor of materials science and engineering at the UCLA Samueli School of Engineering and corresponding author of the study , recently published in Science.

For a soft material to be considered for use as an artificial muscle, it must be able to output mechanical energy and remain viable under high stress conditions – meaning it does not easily lose its shape and strength after repeated work cycles. Although many materials are considered as contenders for making artificial muscles, dielectric elastomers (DE) – lightweight materials with high elastic energy density – are of particular interest due to their optimal flexibility and durability.

Video showing PHDE films and actuators undergoing testing. Credit: Soft Materials Research Laboratory/UCLA

Dielectric elastomers are electroactive polymers, which are natural or synthetic substances composed of large molecules that can change their size or shape when stimulated by an electric field. They can be used as actuators, allowing machines to operate by transforming electrical energy into mechanical work.

Most dielectric elastomers are made of acrylic or silicone, but both materials have drawbacks. While traditional acrylic DEs can achieve high actuation tension, they require pre-stretching and lack flexibility. Silicones are easier to make, but cannot withstand high loads.

Using commercially available chemicals and using an ultraviolet (UV) light curing process, the UCLA-led research team created an improved acrylic-based material that is more flexible, adjustable and easier to scale without losing its strength and endurance. While the acrylic acid allows more hydrogen bonds to form, thus making the material more mobile, the researchers also adjust the cross-linking between the polymer chains, allowing the elastomers to be softer and more flexible. The resulting thin, processable, high-performance dielectric elastomer film, or PHDE, is then sandwiched between two electrodes to convert electrical energy into motion as an actuator.

Each PHDE film is as thin and light as a piece of human hair, about 35 micrometers thick, and when multiple layers are stacked together, they become a miniature electric motor that can act like muscle tissue and produce enough energy to drive the movement of small robots or sensors. The researchers made stacks of PHDE films ranging from four to 50 layers.

“This flexible, versatile and efficient actuator could open the door to artificial muscles in new generations of robots or in sensors and wearable technologies that can more accurately mimic or even enhance human movements and abilities,” Pei said.

UCLA scientists develop durable material for flexible artificial muscles

A jumping robot with a diameter of about 1.2 centimeters, equipped with PHDE actuators. Credit: Soft Materials Research Laboratory/UCLA

Artificial muscles equipped with PHDE actuators can generate more megapascals of force than biological muscles and also demonstrate three to 10 times more flexibility than natural muscles.

Multilayer soft films are usually produced by a “wet” process, which involves the deposition and curing of a liquid resin. But this process can lead to uneven layers, resulting in poor actuator performance. For this reason, so far many actuators have only been successful with single-layer DE films.

The UCLA research involves a “dry” process in which the films are layered using a knife and then cured with ultraviolet rays to harden them, making the layers uniform. This increases the power output of the actuator so that the device can support more complex movements.

The simplified process, along with the flexible and durable nature of PHDE, enables the production of new soft actuators capable of bending to jump, like spider legs, or to coil and spin. The researchers also demonstrated the ability of the PHDE actuator to throw a pea-sized ball 20 times heavier than the PHDE films. The actuator can also expand and contract like a diaphragm when voltage is turned on and off, giving insight into how artificial muscles might be used in the future.

Advances could lead to soft robots with improved mobility and durability, and new wearable and haptic touch-sensing technologies. The manufacturing process can also be applied to other soft thin-film materials for applications including microfluidic technologies, tissue engineering or microfabrication.

A uniform nanocomposite dielectric elastomer for large-scale actuation

More info:
Ye Shi et al, Processable, High Performance Dielectric Elastomer and Multilayer Process, Science (2022). DOI: 10.1126/science.abn0099.

Courtesy of University of California, Los Angeles

Quote: Scientists develop durable material for flexible artificial muscles (2022, July 7) retrieved July 7, 2022, from

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