Putting new parts to the test

James Chow (left) and Lee Sierad (right) work on the vascular bioreactor for testing artery scaffolds, using the Patewood facility. Photo by Craig Mahaffey.

Lee Sierad likes to cook, so if it takes a while to launch the business he’s planning, he could always find a job in a restaurant somewhere. In high school, he worked his way up from dishwasher to line cook, so he knows his way around the kitchen. But the business he’d really like to start would design and build bioreactors, devices that could simulate conditions in the body and help bioengineers regenerate and test replacement parts. In a way, a bioreactor is a kind of test kitchen for tissues designed to help people heal.

Sierad, who is in his final year of work on a Ph.D. in bioengineering, built his first bioreactor as part of his master’s project, working with Dan Simionescu in the Biocompatibility and Tissue Regeneration Laboratories.

“It’s a system to pump fluid through a heart valve, the way it works in the body,” Sierad says. With its chambers, pumps, and valves, the bioreactor can simulate blood flow, and the pressures and rhythms of a beating heart.

But Sierad isn’t just testing new heart valves; he makes them. With guidance from Dr. Chris Wright, a cardiac surgeon with the Greenville Health System, Sierad tailors heart valves taken from pigs, removes their cells, and mounts a cell-free, scaffold-like matrix in the bioreactor, where he can seed the matrix with stem cells and kick-start their transformation into new tissue.

“Doctor Wright gives me a lot of input on the end requirements of what our replacement valve should look like,” Sierad says. “That’s extremely valuable, because we’re researchers, and we don’t have much idea what goes on in an operating room.”

The heart valves have performed like champs in the bioreactor, and the team is ready for tests in large animals. Sierad and Simionescu, collaborating with surgeons in Romania, are implanting the heart valves in sheep. Large-animal studies of this kind are a necessary step before trials in human patients.

“That’s a big hurdle, and we’ve made good progress on it,” Sierad says.

Meanwhile, Sierad is concentrating on another part of the circulatory system, the aorta, a heavy-duty artery that distributes oxygen-rich blood to the body. Because it is so strong and thick, the aorta presents special problems for tissue regeneration. For one thing, itís tricky to remove all the pig cells hidden deep inside its layers.

“Aortic tissue has fifty to a hundred layers of elastin,” Sierad says, “and those layers are so tightly woven together that they prevent the solution from reaching the structure.” Working with Laine Shaw, a senior in bioengineering, Sierad has developed a specialized system to target different portions of the aortic group and perfuse fluid through them to remove the cells.

“Laine has done a tremendous job developing the device,” Sierad says. “That’s a huge advantage for us, to be able to build the devices and understand the mechanical engineering—fluid dynamics, pressure, and all the other aspects—it’s a lot of engineering.”

This kind of technical problem solving appeals to him, but so does the potential to help people heal. The culture of the lab and collaborations with surgeons such as Chris Wright keep everybody thinking about the patients.

“If we are able to do this then people who are on the organ-transplant list, who are just waiting, will have another option for extending their lives,” Sierad says. “That’s the whole reason I got into bioengineering in the first place, rather than say, aerospace engineering. I could really make a difference in people’s lives, rather than just make their flight smoother.”

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