Other researchers are fighting the clotting problem in different ways, Elbert notes. “A lot of people are trying to make blood vessels by tissue engineering,” he says. Tissue engineers remove cells from a patient’s vessels, grow them on a porous tube, and nurture the structure until it’s strong enough to reimplant. Clots don’t clog these vessels because they’re lined with endothelial cells. “That works,” says Elbert. But growing a human blood vessel in a lab is slow and “incredibly expensive.” And the vessels can be fragile–blood flow can rip cells off, causing clotting. Others have tried making synthetic vessels out of clot-resistant materials. These are cheap and sturdy. And they resist clots for some time. But after several years, they can clog. Neither method has fully succeeded in animals.
Unlike other alternatives, Elbert says, vessels lined with his team’s material would be cheap, easy, durable, non-clotting, and non-immunogenic. So far, his gel has passed some initial tests in the laboratory. Endothelial cells migrate quickly on top of the gel. The cells stick to it, even inside a flow chamber, which simulates the shearing force of blood flow.
Elbert adds that his team’s gel may also help the body grow new vessel networks. Chicken-egg membranes treated with it grew new webs of vessels. “One could imagine putting the material next to the heart after a heart attack, allowing the lipid to diffuse into the heart wall and form new vessels that would help the heart survive,” he says.
“It’s way too early to know” how Elbert’s vessels or gel will perform in the human body, cautions Robert Langer, professor of chemical and biological engineering at MIT. Many formulations have looked promising in the lab, only to fail in animals, he says. “The key is animal studies, particularly pigs.”
Safety is also a concern, adds Omolola Eniola-Adefeso, assistant professor of chemical engineering at the University of Michigan. She worries that Elbert’s lipid, which sends many signals in the body, could disrupt normal body processes.
“One has to be extremely careful,” agrees Elbert. Large quantities of the lipid can suppress the immune system and trigger cell death. He plans to determine how much he can deliver to stimulate endothelial cells without overloading. Tests will begin in animals in 2007 and continue for at least four years, he says.
As for the clotting problem, “there are as many engineers working on it as there are bioengineering departments across the country,” says Eniola-Adefeso. So far, she says, Elbert’s “is the most promising approach.”