The devices could give scientists a better tool for understanding healthy and diseased heart tissue, specifically how the precise arrangement of cells is necessary for the heart to function properly, says Kenneth Chien, director of the Massachusetts General Hospital Cardiovascular Research Center. Eventually, the devices could be used to screen drugs for effectiveness and toxicity by giving researchers an easy way to measure how a drug alters heart-muscle function.

Several other researchers have used heart muscle for powering devices. Earlier this week, for example, researchers in South Korea reported engineering a tiny heart-muscle-powered crablike device that "crawled" for 10 days. That work was reported in the journal Chemical Science.

But the Harvard muscle-power machines are larger and have the potential to be used in a wide variety of devices, says Bob Dennis, a professor of biomedical engineering at the University of North Carolina and North Carolina State University. What distinguishes Parker and Feinberg's work, he says, is the fact that it isn't a one-off prototype but a method that can be further developed for practical uses.