Two Harvard scientists have built a transparent, artificial “muscle” that uses electrical charges carried by ions, not electrons, to produce sounds.

In a video press release, the two postdoctoral fellows—Christoph Keplinger, a fellow in chemistry and chemical biology, and Jeong-Yun Sun, a fellow at the School of Engineering and Applied Sciences—demonstrated how their speaker can play classical tunes.

Keplinger, who along with Sun was a co-lead author on an article on the project published last month in the journal Science, said that although the speaker is a modern technology, the inspiration for the research stemmed from basic biology.

The speaker is made of rubber membrane sandwiched between layers of gel. Exploring the research field of stretchable electronics, the scientists aimed to overcome some of the disadvantages of their chosen technology, ionic conductors.

“People have used ionics first, and then because of semiconductors and the computer, people began to use electronics,” Sun said. “Using soft actuators, we are going back to ionics again, or iontronics.”

In a related review also published in Science, John A. Rogers, professor of materials science and engineering at the University of Illinois at Urbana-Champaign, wrote that these actuator technologies are “promising and remarkably simple.”

Philipp J. M. Rothemund, a SEAS research assistant who worked with Keplinger and Sun on the project, said that the speaker has much promise for future application.

“We have shown two things: it is highly transparent and it is very fast, meaning we can make the lens itself the electronic part,” Rothemund said. “We can make the car window or the front of your iPhone a loudspeaker.”

Beyond novel applications for entertainment, the invention may eventually be used to save human lives.

Keplinger said that ionic conductors are “easily made biocompatible,” meaning they can be integrated into a living system.

The speaker, he said, provides a foundation for future developments in intervention surgery.

“The artificial muscle actually outperforms natural muscles,” Keplinger said. “They are stronger, faster, and more efficient.”

—Staff writer Fatima N. Mirza can be reached at fatima.mirza@thecrimson.com. Follow her on Twitter @fatimanmirza.