Could shape-shifting elastomer 'transform the way mechanical devices work'?

Ambitious researchers behind a shape-shifting sheet with power density similar to natural muscles have claimed it “could transform the way that mechanical devices work”.

Announcing the research, the team from Harvard John A Paulson School of Engineering and Applied Sciences (Seas) asked: “What if we could mimic shape changes and movements found in nature?”

Natural systems can perform complex functions with soft components more directly than mechanical systems, which rely on linear or rotational movement with stiff components. For example, the researchers said, our eyes change focal point by simply contracting muscles to change the shape of the cornea. In contrast, cameras focus by moving solid lenses along a line, either manually or by autofocus.

In its quest to mimic natural movements, the team developed a method of changing the shape of a flat sheet of elastomer, using fast and reversible actuation. The changes are controllable by an applied voltage, and the sheet is reconfigurable to different shapes.

"We see this work as the first step in the development of a soft, shape shifting material that changes shape according to electrical control signals from a computer," said senior author David Clarke, materials professor at Seas.

"This is akin to the very first steps taken in the 1950s to create integrated circuits from silicon, replacing circuits made of discrete, individual components. Just as those integrated circuits were primitive compared to the capabilities of today's electronics, our devices have a simple but integrated three-dimensional architecture of electrical conductors and dielectrics, and demonstrate the elements of programmable reconfiguration, to create large and reversible shape changes."

The reconfigurable elastomer sheet is made up of multiple layers. Carbon nanotube-based electrodes of different shapes are incorporated between each layer. When a voltage is applied to these electrodes, a ‘spatially varying electric field’ is created inside the elastomer sheet that produces uneven changes in its material geometry, making it morph into a controllable three-dimensional shape.

Different sets of electrodes can be switched on independently, enabling different shapes based on which sets of electrodes are on and which ones are off.

"In addition to being reconfigurable and reversible, these shape-morphing actuations have a power density similar to that of natural muscles," said first author Ehsan Hajiesmaili, graduate student at Seas.

“This functionality could transform the way that mechanical devices work. There are examples of current devices that could make use of more sophisticated deformations to function more efficiently, such as optical mirrors and lenses. More importantly, this actuation method opens the door to novel devices that [were] deemed too complicated to pursue due to the complex deformations required, such as a shape-morphing aerofoil."

In the research, the team predicted the shapes that would appear given the electrode arrangement and applied voltage. Next, they hope to achieve desired shapes by selecting the best electrode design and required voltage.

The work was published in Nature Communications.