An experiment with pig cells and a machine that mimics the pulse of the heart shows that new, living arteries can be grown in the laboratory to replace diseased vessels. It marks an important step in the developing field of making new body parts.
Dr. Laura A. Niklason of Duke University, leader of the research team that made the pig arteries, said that the vessels "are indistinguishable from the native structure. They are completely smooth, glistening structures inside and out."
Niklason, first author of a study that appears Friday in the journal Science, said that although the experiment used pigs, it demonstrated that it is fundamentally possible to grow new arteries to replace those that have become clogged or blocked by heart disease. She said engineered, living arteries may someday be used in human heart bypasses instead of the leg veins that doctors now use.
"This is proof that one can take a vessel from an adult animal, make an artery and then put it back in and have it work," said Niklason.
A number of labs are now experimenting with tissue culture techniques designed to grow new body parts. Some have grown ligaments, tendons, bone and even a new ear. But Niklason said her experiment was different because the incubation machine rhythmically pumped nutrients through the developing cells, imitating the pressures from a beating heart.
This pulsation, she said, increased the strength of the finished artery and made it last longer when it was transplanted. "This is the first tissue engineering in a lab system that tried to mimic the pulse in the human body," she said. "Other tissue engineering has been done in a static system where there was no real attempt to copy what is happening so far as the push and pull of pressure."
Dr. Charles A. Vacanti, director of the Center for Tissue Engineering at the University of Massachusetts Medical Center, said Niklason's work "is an important advance in tissue engineering."
Vacanti, whose work includes growing a new thumb bone for one patient, said that so much is unknown about how nature makes new tissue that "the best thing you can do is mimic the human body. She (Niklason) has demonstrated that that principal is true."
In her experiment, Niklason made a tube resembling an artery from a polymer material. This tube would eventually dissolve, but it acted as a scaffold for the developing tissue.
Niklason then removed a small segment of a neck artery from a pig and from this vessel took some smooth muscle cells.
The tube was placed in a machine that circulates a broth that includes cell nutrients and oxygen. The tube was then seeded with the smooth muscle cells. A pump sent pulses of nutrient through the tube, feeding the cells and causing them to grow new cells. After 10 weeks, a tube of smooth muscle cells had replaced the polymer.
Niklason then added endothelial cells, the tissue that lines arteries, and in just three days the inner surfaces were smoothly covered and the artery was complete.
Arteries made in this way were grafted into the pigs that donated the cells and Niklason said that the vessels "worked beautifully."
Some specimens made without the pulsing system failed after two weeks, but the arteries made with the pulsing "functioned like native vessels" for up to four weeks, she said.
Niklason said it will be years before she is ready to attempt to make human arteries, but she predicts that eventually doctors will use engineered vessels routinely as replacement parts when operating on ailing hearts.
Currently, surgeons must remove up to 24 inches of leg vein in order to find segments needed for heart bypass surgery. Often, the vein removal causes more complications for patients than does the heart bypass itself. Niklason said that to make an engineered artery might require only about an inch of vein, leaving the leg vessels essentially unaffected.