New York, Nov 29 (IANS): Researchers have developed a functioning artificial human heart muscle large enough to patch over damage typically seen in patients who have suffered a heart attack.

Unlike some human organs, the heart cannot regenerate itself after a heart attack. The dead muscle is often replaced by scar tissue that can no longer transmit electrical signals or contract, both of which are necessary for smooth and forceful heartbeats.

The end result is a disease commonly referred to as heart failure that affects over 12 million patients worldwide.

The heart patch developed by biomedical engineers at Duke University in the US takes a major step toward the goal of repairing dead heart muscle in human patients.

"Right now, virtually all existing therapies are aimed at reducing the symptoms from the damage that's already been done to the heart, but no approaches have been able to replace the muscle that's lost, because once it's dead, it does not grow back on its own," said Ilya Shadrin, first author on the study published online in the journal Nature Communications.

"This is a way that we could replace lost muscle with tissue made outside the body," Shadrin added.

For heart patches to work, it must be large enough to cover the affected tissue. It must also be just as strong and electrically active as the native heart tissue, or else the discrepancy could cause improper beating of the heart.

"Creating individual cardiac muscle cells is pretty commonplace, but people have been focused on growing miniature tissues for drug development," Nenad Bursac, Professor of Biomedical Engineering at Duke, said.

"Scaling it up to this size is something that has never been done and it required a lot of engineering ingenuity," Bursac said.

The cells for the heart patch were grown from human pluripotent stem cells -- the cells that can become any type of cell in the body.

Tests showed that the heart muscle in the patch was fully functional, with electrical, mechanical and structural properties that resemble those of a normal, healthy adult heart.

"This is extremely difficult to do, as the larger the tissue that is grown, the harder it is to maintain the same properties throughout it," said Bursac.

"Equally challenging has been making the tissues mature to adult strength on a fast timescale of five weeks while achieving properties that typically take years of normal human development," Bursac added.

The researchers showed that these cardiac patches survive, become vascularised and maintain their function when implanted onto mouse and rat hearts.

For a heart patch to ever actually replace the work of dead cardiac muscle in human patients, however, it would need to be much thicker than the tissue grown in this study.

The researchers said they were working on making it possible.