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Nereis virens, a sand worm, may not be the most attractive creature on the planet, but the strength, stability, and mechanical performance of its jaw inspired a new material that adapts to changing environments.

The soft, gel-like material developed by engineers at Massachusetts Institute of Technology could be used to control the movements of soft robots.

Researchers studying the jaw of Nereis discovered it’s made mostly of a soft protein material with the consistency of gelatin. Despite this wobbly structure, its strength has a hardness ranging between 0.4 and 0.8 gigapascals (GPa), similar to that of human dentin.

“It’s quite remarkable that this soft protein material, with a consistency akin to Jell-O, can be as strong as calcified minerals that are found in human dentin and harder materials such as bones,” says Markus J. Buehler, the McAfee Professor of Engineering, head of MIT’s Department of Civil and Environmental Engineering, and head author of a paper published recently in ACS Nano on the topic.

At the molecular level, researchers noticed the jaw contains metal-coordinated crosslinks, the presence of which provides a network of strong material that also makes the molecular bond more dynamic and responsive to changing conditions. At the macroscopic level, the metal-protein bonds result in an expansion/contraction behavior, the researchers found.

Photo Credit: Massachusetts Institute of Technology

Buehler, CEE research scientists Zhao Qin and Francisco Martin-Martinez, and former PhD student Chia-Ching Chou worked with the Air Force Research Lab, which had already conducted a study into protein structure, to create a multiscale model that can predict the mechanical behavior of materials that contain this protein in various environments.

The researchers used this model to design, test, and visualize how different molecular networks change and adapt to various pH levels, taking into account the biological and mechanical properties. The predictive model was able to explain how the pH sensitive materials change shape and behave, as well as demonstrate how the material both changes form and reverts to its original shape once pH levels change.

“These atomistic simulations help us to visualize the atomic arrangements and molecular conformations that underlay the mechanical performance of these materials,” says Martin-Martinez.

The pH- and ion-sensitive material can respond and react to its environment, and it could prove to be particularly helpful for active control of motion or deformation of actuators for soft robotics and sensors without using an external power supply or complex electronic controlling devices. It might also be used to build autonomous structures, the researchers say.

“The ability of dramatically altering the material properties, by changing its hierarchical structure, starting at the chemical level, offers exciting new opportunities to tune the material, and to build upon the natural material design towards new engineering applications,” says Buehler.

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