Researchers at the University of Freiburg’s livMatS Cluster of Excellence have succeeded in developing an artificial muscle solely on the basis of natural proteins. The autonomous contractions of the material can be controlled with the help of pH and temperature changes.
In the past, scientists have already taken natural proteins as a basis for developing artificial muscle systems and built them into miniscule molecular machines or into polymers. However, it has not yet been possible to develop synthetic muscle materials that are entirely bio-based and move autonomously with the help of chemical energy.
The new artificial muscles are made of elastin, a natural fibrous protein that also occurs in humans that gives tissues like skin and blood vessels their elasticity. Following the model of this protein, the Freiburg research team developed two elastin-like proteins, one of which responds to fluctuations in pH, while the other response to changes in temperature. They then combined the two proteins by means of photochemical cross-linking to form a bilayered material. This allowed the team to flexibly shape the material and set the direction of its movement.
The resulting artificial muscle powered by sodium sulfite could be made to move rhythmically thanks to an oscillating chemical reaction, in which the pH changes in cycles due to a special linkage of several reactions. The researchers were also able to switch the contractions on and off with the help of temperature changes: The oscillating chemical reaction started at a temperature of around 20-degrees Celsius, and the material began to make rhythmic movements.
In the process, it was possible to program certain states for the material to assume and to reset them again with another stimulus. The scientists thus achieved a simple system for implementing learning and forgetting at the material level.
“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,” explains Schiller. “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 artificial muscle is still a prototype. Researchers believe that the high biocompatibility of the material and the possibility of adjusting its composition to match particular tissue could pave the way for future applications in reconstructive medicine, prosthetics, pharmaceutics, or soft robotics.