Progress in regenerative medicine has been coming fast and furious in recent months: scientists are now using far-out tissue engineering techniques to restore liver function in mice, regrow human muscle, and even implant bioengineered blood vessels into ailing patients. Now, a team at the University of Pittsburgh has managed to grow human heart tissue that can beat autonomously in a petri dish — an exciting step towards devising transplantable replacement organs.

The group, who reported their progress in the journal Nature Communications, used induced pluripotent stem cells (iPS cells) to accomplish the feat. These mature human cells are first "reprogrammed" to an embryonic state, before being spurred to develop into a specialized type of cell. In this instance, iPS cells derived from human skin were induced to become multipotential cardiovascular progenitor (MCP) cells — basically heart cells that can further differentiate into three varieties of highly specialized cells required for cardiovascular function.

A functional organ capable of beating on its own

From there, scientists transplanted the cells onto a mouse heart that had been completely stripped — turning the organ into what's known as a "scaffold." Over a period of weeks, the transplanted human cells proliferated and differentiated, rebuilding the scaffold into a functional organ capable of beating on its own. Right now, the heart tissue contracts at a rate of 40 to 50 beats per minute (on-par with a human's resting heart rate) but needs to be further refined before it's capable of beating strongly enough to distribute blood, or speeding up and slowing down when necessary.

This isn't the first time that scientists have managed to engineer heart tissue — in recent years, other teams have created lab-grown beating rat hearts and even human heart tissue. The latter breakthrough, however, relied on embryonic stem cells, which can't be derived from a specific patient for subsequent, personalized transplant the way this new technique allows.

A full-sized, fully functional replacement human heart is, of course, several years off. But in the near future, scientists hope to develop personalized "patches" of human heart muscle to repair damaged organs, and hope to see their technique used to more accurately study the effects of new pharmaceuticals to treat cardiovascular ailments.