Inspired by the jelly-like jaw of a sea worm, researchers have developed a new material that becomes hard or flexible depending on the environment around it and can be used in soft robotics.

The researchers at the Massachusetts Institute of Technology looked at a sea worm called Nereis virens whose jaw has a texture similar to gelatin, but if the environment varies, the material — described in a study published in the journal ACS Nano — may adopt the hardness of dentin or human bones.

“The jaw of Nereis virens is composed of a protein that contains large amounts of histidine, an amino acid that interacts with the ions of the environment and makes it more or less flexible depending on the environment in which it finds itself,” said co-author of the paper Francisco Martín-Martínez.

“It’s a hydrogel made from a synthesized protein, similar to the one that makes up the jaw of this worm and which gives it structural stability and impressive mechanical performance. When we change the ions of the environment and the salt concentration, the material expands or contracts,” added Martín-Martínez.

The team found that at the molecular level, the structure of protein material is strengthened when the environment contains zinc ions and certain pH indexes. The Zinc ions create chemical bonds with the structure of the compound. These bonds are reversible, and can form or break at convenience, making the material more dynamic and flexible.

Martín-Martínez explained that the material’s ability to contract and expand makes it especially suited to creating devices that work as muscles for so-called soft robots, which are made of polymers.

It could also be used in the development of sensors that do not need to use external power supplies and control devices for complex electronic systems, he said.