Scientists have found a new way of growing artificial arteries almost from scratch, and make them much stronger than previously developed artificial vessels. The approach, described in today's Science, may be of great help in coronary bypass surgery.
To replace clogged coronary arteries, surgeons can often use blood vessels from the patient's own leg or chest. But sometimes this is impossible--for instance, when the patient has already undergone one such operation and doesn't have any suitable blood vessels left. Attempts to grow blood vessels from scratch have had mixed success. Last January, Canadian researchers reported growing smooth muscle and fibroblast cells as sheets, then wrapping them in successive layers around a pipette and lining them with endothelial cells. But when stitched into animals, the resulting arteries leaked blood, and many plugged up with clots within a week.
A team led by biomedical engineer Robert Langer from the Massachusetts Institute of Technology in Cambridge, Massachusetts, grew its blood vessels on tubes of polyglycolic acid, under conditions designed to mimic those encountered by a newly formed artery in the body. First, they treated the acid polymer with sodium hydroxide, to create water-loving hydroxyl groups that enable more cells to attach. Next they drizzled smooth muscle cells from cows onto the tube-shaped scaffold and inserted a pliable piece of silicon into the interior. The tubing was hooked up to a pump, which pulsed 165 times a minute to mimic the pulsing pressure on a developing embryonic artery. After 8 weeks, the researchers coated the inside of the vessels with endothelial cells. "To me the most novel thing [about this study] is the idea of using a bioreactor that beats like a heart," says Langer.
The pulsing made the tissue stronger because it increased the cells' production of collagen, a tough protein found in connective tissue. The pulsed blood vessels had walls that were twice as thick as nonpulsed vessels; they could withstand sutures without tearing. When the researchers took cells from tiny arterial biopsies of miniature pigs, grew vessels, and used them to replace an artery in the same animals' legs, the engineered arteries lasted more than 3 weeks without clogging, whereas arteries grown without pulsing clogged.
The results are "really astounding," says cardiovascular surgeon Timothy Gardner of the University of Pennsylvania School of Medicine, who is chair of the surgery council of the American Heart Association. "If this works out," he adds, "it will be a major development in cardiovascular surgery."