Scientists build blood vessels large and small

Blood vessels may seem like straightforward pipes, especially when compared to organs such as the heart or the liver. But they are critical, complicated infrastructure, and replacing or replicating them poses an important challenge in modern-day medicine — and for futuristic attempts to build organs from scratch.

At one end of the spectrum are large arteries and veins. Blood vessel grafts are used in cardiac bypass surgery and in dialysis treatment, and doctors and patients could benefit from a readily available supply of veins and arteries.

At the opposite extreme are the tiny beds of capillaries, which nourish organs and will be an essential part of efforts to replace and repair damaged tissue.

“All the scales are important, whether you’re talking about an aorta or down to a 10-micron diameter [microscopic] capillary,’’ said Jeffrey Borenstein, director of the biomedical engineering center at Draper Laboratory in Cambridge. Borenstein is working on building intricate capillary networks using techniques akin to those used to print circuits on silicon wafers.

In work published in February in the journal Science Translational Medicine, Yale University researchers attacked the larger scale.

Doctors routinely take blood vessels from one part of a patient’s body, using them to make a bypass around a diseased artery, but that is not always easy.

“I can remember being an anesthesiologist in the cardiac surgery room and watching surgeons hunt around, sometimes desperately,’’ looking for a blood vessel, said Dr. Laura Niklason, a professor of anesthesiology and biomedical engineering at Yale and senior author of the new research.

Niklason and colleagues took cells from human donors and grew them on tubular, trellis-like scaffolds. The scaffolds degraded, leaving behind blood vessels. Then researchers washed away the cells to reveal a matrix structure that was successfully implanted in animals. A North Carolina company, Humacyte Inc., is developing the technology, with plans to begin clinical testing in dialysis patients within a year.

Borenstein’s team has been working on a technique to print silicon wafers with the intricate blood vessel networks. Researchers use the chips as molds to imprint the capillary networks on plastic sheets, which are stacked up to make a 3-D structure.

Recently, his group received a National Institutes of Health grant to use the synthesized capillary networks to mimic the gas exchange that the lungs facilitate through breathing, on a chip. Initially, the approach will be aimed at developing a better way to help premature infants with severe respiratory failure get oxygen into their blood, and ultimately Borenstein hopes that such technology could help people who suffer from acute lung injury and chronic lung disease.

Not all the approaches are focused on building blood vessels from scratch. At Harvard University, David Mooney, a professor of bioengineering, is harnessing the body’s natural ability to grow new blood vessels. Mooney finds ways to control the release of substances that can spur or inhibit the growth of new blood vessels.

While the more immediate goal is to help patients with cardiovascular disease, Mooney noted that the grand vision of regenerative medicine — growing or engineering new organs and tissues — will depend on the ability to create networks of essential blood vessels.

Leon Bellan, a postdoctoral researcher at MIT, is engineering blood vessels, inspired by a carnival confection.

Bellan works with nanofibers and often found himself drawing on analogies to explain them to nonscientists — comparing the tiny fibers to Silly String, Cheez Whiz, or cotton candy. He began to wonder about the dimensions of strings of sugar in cotton candy.

Using a pink cotton candy machine inscribed with the warning “Do Not Eat,’’ he has been investigating the question. Bellan starts by making cotton candy and then uses the spun sugar as a mold — pouring an epoxy material around it that hardens. Then, he dissolves the cotton candy (in scientific terms, the “sacrificial sugar structure’’), leaving behind fine channels that resemble a network of capillaries.

Now, he is trying to create the artificial blood vessels in a gelatinous material that more accurately mimics the body.

“What’s nice about this technique is that it’s inherently three-dimensional,’’ Bellan said.

And, he added, “it makes the lab smell nice.’’