Researchers have developed artificial blood vessels that are derived from human cells but appear to have long shelf lives and are unlikely to provoke an immune response. Such vessels could someday prove valuable to patients undergoing heart-bypass operations, dialysis, or other procedures in which portions of blood vessels, or vascular grafts, may be needed.
In a typical bypass operation, surgeons take veins from a patient’s leg and use them to reroute blood around blocked arteries. But suitable veins can be hard to find, especially in patients who have had previous bypass surgeries or are obese or diabetic. “I’ve spent a lot of time in the OR watching surgeons dig around in a patient’s leg and try to find suitable vessels,” says Laura Niklason, the lead researcher on the new technology and an anesthesiologist and biomedical engineer at Yale University. In heart-bypass surgery, typically “it’s the leg incision, more than the chest incision, that causes patients problems.”
Now, Niklason and her team have developed a potential alternative in which donor cells are used to create a collagen matrix but are then removed, so the final product is acellular.
“It’s an incredibly important and creative approach,” says Robert Langer, a renowned engineer and Institute Professor at MIT. “She’s taking advantage of some of the things cells can do” while ending up with an acellular material. (Niklason was a fellow in Langer’s lab from 1995 to 1998.)
Niklason developed the new vessels under the auspices of a company called Humacyte, which she founded in 2004. She and her team took cells from a tissue bank and placed them on biodegradable scaffolds, which had been shaped into tubes of different diameters. The cells laid down collagen matrices as they grew. After roughly eight weeks, the team washed the cells away, leaving behind tubes made of acellular material. In theory, if the grafts are implanted in humans, they should be repopulated by the patients’ own endothelial cells, which would reduce the likelihood of clots. But it is not yet clear how the grafts will behave in humans.
This material is likely to be compatible with the body and with blood because it is derived from human cells. But it will probably not provoke an immune response because it is acellular. It is also likely to last much longer on the shelf than a cellular product would.
So far, Niklason has created and studied the properties of these vessel substitutes using cells from dogs, pigs, and humans. But she has only implanted them in animals. “She still has to prove this in a human,” says Robert Nerem, director of the Parker H. Petit Institute for Bioengineering and Bioscience at the Georgia Institute of Technology. “Having said that, I consider what she’s doing to be very exciting.”
Synthetic materials like Teflon and Dacron have also been used in bypass operations, but they’re only helpful for large vessels like the aorta. They do not work for narrower vessels like the coronary arteries because at smaller diameters they readily cause blood clots.