For durability, it’s hard to match human heart muscle. The heart’s muscle tissue takes wear and tear well enough to circulate 200 million liters of blood in 80 years. That is, unless a blockage deprives the tissue of oxygen, killing part of the perfect pumping machine with potentially fatal results for its owner. Now, researchers from MIT and Harvard Medical School have taken a first step toward creating patches for dead heart tissue. Eventually, they hope to be able to grow patches from patients’ own cells.

The scientists reported that they grew pieces of living, beating heart tissue from a few cells culled from rats. “Our ultimate idea is to be able to build a patch that could replace…damaged tissue and keep the mechanism working,” says Gordana Vunjak-Novakovic, a researcher in the Harvard-MIT Division of Health Sciences and Technology who worked on the project with postdoc Milica Radisic, the paper’s lead author.

The patent-pending process involves growing rat heart tissue on a scaffold of collagen, a fibrous protein. After the researchers cover the structure with rat cells, they immerse it in a bath of nutrients. The scaffold slowly disintegrates as the heart cells begin to form connections, taking on a structure of their own.

One of the team’s most significant discoveries is that the developing cells are erratic and uncoördinated unless coached by an electric shock. In an embryo, nascent heart cells begin to contract when shocked periodically by the body’s pacemaker, the sinoatrial node. Over time, the contractions become more coördinated, and the heart is able to pump blood effectively. The team replicated sinoatrial-node pulses by using a pacemaker. After eight days of preparation, their collection of cells developed into a solid piece of twitching tissue.

The researchers are now trying to determine how to effectively transplant these pieces of tissue into host rats. Human tissue patches are also in the works. The team has been attempting to build human patches using adult stem cells for more than a year, and they began using embryonic stem cells at the end of last year. Their ultimate goal is to build patches from a patient’s own cells, so that the repair tissue will always be compatible with the patient’s immune system and won’t carry diseases the patient doesn’t already have.

Another application might pop up before then. For example, the tissue samples may provide an ideal way to pretest new heart medications, says Frederick Schoen, a Harvard University professor of pathology who participated in the study. “One of the commonly overlooked benefits of this type of tissue engineering is that it will allow us to screen on a lab bench what could be too expensive or dangerous to screen in the human body,” he says.