Unique among the human body's larger organs, the liver has a remarkable ability to recover from injury. An individual can lose a big chunk of it in an accident or during surgery, but as long as at least a quarter of the organ remains intact and generally free of scars, it can grow back to its full size and function. Alas, this capacity for self-regeneration does not hold for other body parts. A salamander can regrow its tail, but a person cannot regain an amputated leg or renew sections of the brain lost to Alzheimer's disease. For this feat, humans need help—and that is the promise of an emerging field of research called regenerative medicine.

Stem cells—progenitor cells that can give rise to a variety of tissues—play an important role in this endeavor. Scientists are learning how to mix a hodgepodge of sugar molecules, proteins and fibers to create an environment in which the stem cells can develop into replacement tissue. As the following stories show, investigators have made strides in replacing damaged heart tissue and rebuilding muscle. They are also in the early stages of developing new nerve cells. Some of these advances could emerge from the lab as treatments in a few years, or they may take decades, or they may ultimately fail. Here are a few of the most promising ones.

The Future of Medicine Special Report

A Change of Heart: Stem Cells May Transform Treatment for Heart Failure
Stem cells may transform the way doctors treat heart failure

Doctors Repair Soldiers' Wounds with Biological Scaffolding Material
Regrowing muscles, tendons and even organs may be possible using nature's own adhesive

Use for 3-D Printers: Creating Internal Blood Vessels for Kidneys, Livers, Other Large Organs
To build large organs that work properly, researchers need to find a way to lace them with blood vessels

Neural Stem Cell Transplants May One Day Help Parkinson's Patients, Others
Neurodegenerative disorders devastate the brain, but doctors hope one day to replace lost cells