Breakthrough Bioengineered Blood Vessels Enter Clinical Trials

Humacyte, winner of a 2011 Popular Mechanics Breakthrough Award, is now testing its lab-grown blood vessels in a small group of human patients.

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It's been a busy year-and-a-half for bioengineer Laura Niklason and her partners at the biotech firm Humacyte. Since winning a 2011 Popular Mechanics Breakthrough Award, the team's lab-grown blood vessels were transplanted into primates for a six-month trial, where they were found to be safe. Now they're being tested in Poland in a small group of humans with kidney failure, and the FDA has just approved a similar trial in the U.S.

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Patients with kidney failure need to have their blood cleaned every week by a dialysis machine. That requires two big needles: One to draw blood out of the artery and a second to put the filtered blood back into a vein. But for the blood to flow through the dialysis machine quickly, doctors have to slightly rearrange the body's plumbing by linking up a vein and artery in the patient's forearm. The increased blood flow to the vein makes it larger and easier to prick with a needle.

Often, doctors must make the link using an artificial blood vessel made out of Teflon. Unfortunately, Teflon grafts are prone to infection, blood clotting, and immune rejection. On average, 40 percent of Teflon grafts fail within a year, says Niklason, a Yale University bioengineer and founder of Humacyte.

Humacyte's lab-grown blood vessels don't use synthetic materials. They rely on a biodegradable scaffolding of tiny fibers interwoven into the shape of the target blood vessel. The scientists seed the scaffold with blood vessel cells, then place it into a bioreactor for eight to ten weeks. Eventually the cells grow over the entire scaffold, building their own collagen matrix. The scaffolding later disintegrates, and the scientists wash away the cells (which would trigger an immune response if they entered the patient's body). What's left is a tubular collagen matrix—an all-natural, non-immunogenic blood vessel replacement.

"This collagen matrix graft was made by blood vessel cells, so it's sort of like the ideal home," Niklason says. "After it gets implanted, cells from the recipient actually repopulate it and turn it into a living vein."

So far the bioengineered blood vessels have succeeded in dogs and primates, where they were found to be durable and didn't cause the side effects of Teflon blood vessels. The U.S. trials—which commence next month—will test the safety of the artificial blood vessels in 20 human patients. If the trial goes well, Humacyte will move on to bigger, long-term studies to determine whether their blood vessels perform better than the alternatives.

Niklason couldn't say much about the preliminary results of the ongoing trial, but she says the team has gotten good feedback from patients.

"All of these patients have been on dialysis for a while, and they've all had multiple graft failures," Niklason says. When grafts fail, surgeons have to go in and replace the patient's graft or remove blood clots, neither of which is pleasant for the patients. "So we've had a few that are delighted that they have a shot with this new technology."

The bioengineered blood vessels have many potential applications beyond kidney dialysis, including bypass surgeries to get around clogged arteries. The collagen scaffolding system one day could help to build replacement intestines, airways, and other tubular structures in the body. If the trials continue to be successful, Niklason estimates the ready-made blood vessels could be FDA-approved by 2017.

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