Durable material for artificial muscles

For a soft material to be used as artificial muscle, it must be able to produce mechanical energy and remain operative under conditions of high structural stress. In other words, it should not easily lose its shape and strength after repeated work cycles. Although many materials have been considered for making artificial muscles, dielectric elastomers, lightweight materials with high elastic energy density, have attracted particular interest due to their optimal flexibility and robustness.

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

Most dielectric elastomers are made from acrylic or silicone, but both materials have drawbacks. Although traditional acrylic dielectric elastomers can achieve high actuation stress, they require pre-stretching and lack flexibility. The silicone ones are easier to manufacture, but they do not withstand great stress.

Using commercially available chemicals and employing an ultraviolet light curing process, Qibing Pei’s team from the Samueli School of Engineering at the University of California, Los Angeles (UCLA) in the United States, has created an improved material. acrylic-based that is more flexible, more adjustable and easier to manufacture on a large scale and also does not lose strength or resistance. While acrylic acid allows more hydrogen bonds to form, making the material more mobile, the researchers also fine-tuned the crosslinking between polymer chains, allowing elastomers to be softer and more flexible. The resulting very thin and easily processable dielectric elastomer (PHDE) film is sandwiched between two electrodes to convert electrical energy into motion as an actuator.

Each PHDE film is about 35 micrometers thick. When multiple layers of PHDE are stacked, the whole becomes a miniature electric motor that can act like muscle tissue and produce enough energy to power small robots. The researchers have fabricated stacks of PHDE films with between 4 and 50 layers.

Artificial muscle film made of 10 layers of high-performance dielectric elastomer stacked with 20 actuators. (Photo: Soft Materials Research Lab/UCLA)

The resulting artificial muscles are stronger and more flexible than their biological counterparts, and lack the aforementioned limitations of artificial muscles made from other materials.

Pei and his colleagues expose the technical details of their achievement in the academic journal Science, under the title “A processable, high-performance dielectric elastomer and multilayering process.” (Font: NCYT by Amazings)