Researchers have developed a new type of artificial muscle that’s entirely made out of natural proteins. Responding to changes in its environment allows the muscle to flex on demand, which could make it useful for implants, prosthetics or robotics.

As promising a technology as artificial muscles have been, most of the time they’re still a bit too artificial, often made of plastics, nylon, rubber, waxy carbon nanotubes and the like. That might make them fine for robots, but natural proteins could make them more compatible for use inside the human body.

For the new study, researchers at the University of Freiburg created artificial muscles that are entirely “bio-based.” They’re made of elastin, a natural protein that gives tissues like skin and blood vessels their elasticity. From that starting point, the team made two variations of the protein that respond to different stimuli – fluctuations in temperature and acidity. These were then combined in layers to create a muscle that would flex in one direction in response to one stimulus, and in a different direction when the other stimulus is applied.

The end result was an artificial muscle powered by sodium sulfite, which could be made to move rhythmically thanks to an oscillating chemical reaction. This process could be kickstarted by setting the temperature to 20 °C (68 °F), then changes in the pH balance would cycle the muscle to contract back and forth. The cycle can be turned off again by changing the temperature. This makes the muscles fairly programmable by changing their structure, so that their movements can be set in a specific direction in response to a certain stimulus.

Along with potential applications in soft robotics or prosthetics, the team says this new type of artificial muscle is biocompatible, so it could be matched to specific tissues and used in the body for implants or reconstructive medicine.

“Since it is derived from the naturally occurring protein elastin and is produced by us through biotechnological means, our material is marked by a high sustainability that is also relevant for technical applications,” said Dr. Stefan Schiller, corresponding author of the study. “In the future, the material could be developed further to respond to other stimuli, such as the salt concentration in the environment, and to consume other energy sources, such as malate derived from biomass.”

The research was published in the journal Advanced Intelligent Systems.

Source: University of Freiburg