MIT researchers have developed a bio-inspired gel material to control the motion or deformation of soft robotics and sensory actuators without using any external power supply or complex electronic controlling devices.
The protein material was designed and modeled on the jaw of the Nereis virens, a type of sand worm that flawlessly adapts to changing environments.
The new material expands and contracts into different geometric patterns depending on the ions and pH levels in the environment. When the conditions change again, the material reverts back to its original shape. This makes it particularly useful for smart composite materials with tunable mechanics and self-powered roboticists that use pH value and ion condition to change the material stiffness or generate functional deformations.
In order to create bio-inspired materials that can be used for soft robotics, sensors, and other uses, engineers and scientists at MIT’s Laboratory for Atomistic and Molecular Mechanics (LAMM) and the Air Force Research Lab (AFRL) needed to first understand how these materials form in the Nereis worm, and how they ultimately behave in various environments.
AFRL experimentally synthesized a hydrogel, a gel-like material made mostly of water, which is composed of recombinant Nvjp-1 protein responsible for the structural stability and impressive mechanical performance of the Nereis jaw.
The Nereis jaw is mostly made of organic matter, meaning it is a soft protein material with a consistency similar to gelatin. In spite of this, its strength, which has been reported to have a hardness ranging between 0.4 and 0.8 gigapascals (GPa), is similar to that of harder materials like human dentin.
Combining the protein structural studies from AFRL with the molecular understanding from LAMM, Markus J. Buehler – Head of the Department of Civil and Environmental Engineering (CEE), Martin-Martinez, CEE Research Scientist Zhao Qin, and former PhD student Chia-Ching Chou, created a multiscale model that is able to predict the mechanical behavior of materials that contain this protein in various environments.
Using the predictive model, the research team found that the material not only changes form, but it also reverts back to its original shape when the pH levels change. At the molecular level, histidine amino acids present in the protein bind strongly to the ions in the environment. This very local chemical reaction between amino acids and metal ions has an effect in the overall conformation of the protein at a larger scale.
“Changing the pH or changing the ions is like flipping a switch. You switch it on or off, depending on what environment you select, and the hydrogel expands or contracts” said Martin-Martinez.
Image and content credits: Allison Dougherty/MIT