ATLANTA — In search of better spare parts, scientists for the first time have grown heart valves from scratch in a test tube, then shown that they work like nature's own, at least in animals, researchers said Sunday.
The approach, called tissue engineering, is intended to create a fresh source of heart valves to replace those that wear out or are faulty from birth. Using the recipient's own cells, researchers hope to construct valves that will grow along with young recipients and work without blood-thinning drugs.
So far, the experiments have been conducted on lambs with the valves grown at Children's Hospital in Boston by Dr. Simon Hoerstrup, who spoke at the annual scientific meeting of the American Heart Assn.
"What's exciting is the possibility of making valves that are exactly like our own. That's the potential here," commented Dr. Valentin M. Fuster of Mt. Sinai Medical Center in New York City.
Heart valves open and shut so that blood will flow in only one direction through the heart. When valves deteriorate or leak, surgeons replace them with mechanical valves or valves taken from other animals. Neither kind is ideal.
The animal valves tend to wear out, so they must be replaced. And the mechanical ones, while more durable, can trigger the development of blood clots, so recipients must take blood-thinning drugs that can cause unwanted bleeding.
Young patients with heart defects currently must undergo several potentially life-threatening valve replacement operations as their hearts outgrow their mechanical valves.
The test-tube valves appear to answer the problem, but it probably will be five years or more before they will be ready for human use, Hoerstrup said.
The scientists start by removing cells from one of the lamb's arteries and growing a mass of the cells in a test tube. Next, they use biodegradable polymers to create a scaffolding in the shape of a valve. Then they attach the cells to the form.
Within two weeks in a nutrient-rich culture, the cells multiply and completely envelop the scaffolding, which then decays.
Past attempts to make working valves the same way have failed because the valves, while they looked normal, were too weak to withstand the pressure of pumping blood. This time, the researchers devised a way to give the valve the strength of a normal one.
Six animals have had the new valves for about five months. That is not long enough to evaluate how the valves will hold up over a lifetime, Hoerstrup said.