Engineers have tested a design for synthetic grafts that mimics the active wrinkling of natural arteries, a movement that helps to reduce the risk of thrombosis.
Surgeons often use grafts made of Dacron or Teflon to redirect blood flow from blocked blood vessels during bypass surgery. They would prefer to harvest veins directly from patients for the grafts, but the procedure can often be dangerous, time consuming, and painful. While synthetic grafts are a viable alternative, they tend to clot more frequently than autologous veins that are taken from another area of a patient’s body. The clotting can lead to thrombosis, an obstruction of the blood vessels that can cause pain and swelling.
Now, engineers at the University of Pittsburgh have tested a proof-of-concept design for synthetic grafts that mimics the active wrinkling of natural arteries, a movement that helps to reduce the risk of thrombosis.
“There is a great need for improved synthetic vascular grafts,” said Edith Tzeng, M.D., a surgeon at the university’s School of Medicine. “If we could come up with a better graft, it might replace the need to use autologous vein, shorten the length of surgery, and reduce morbidity associated with vein harvest.”
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But that better graft needs to be able to avoid fouling, in which unwanted material accumulates and eventually blocks the pathway, leading to thrombosis.
The surface of natural arteries have a unique biomechanical property: They actively wrinkle in response to blood pressure, said Sachin Velankar, a chemical engineer at Pitt’s Swanson School of Engineering. He wondered if a synthetic graft with a similar dynamic topography could help prevent clots.
“There are circumstances where the arteries need to expand so blood can flow more freely,” he said. “That expansion can only be accommodated without damaging the artery if the artery can wrinkle and then smooth out. We hypothesized that this wrinkling also perhaps helps keep the surface free of clots, preventing thrombosis.”
The researchers created a model simulation to test their hypothesis. They found materials that transition between wrinkled and smooth do help to avoid fouling and blockages. The study, recently published in Science Direct, offers proof that careful engineering can result in the development of more successful synthetic graft products, Velankar said.
“We need a soft yet strong rubber-like tube that can expand and contract by about 10% with just a very small change in blood pressure,” he said. “It would have to be soft enough to suture but durable enough not to rip. And it needs to be biocompatible but last a long time. There are many constraints that you have to balance to create this.”
The researchers recently received a three-year grant from the National Science Foundation to continue their investigations into the biomechanics of active wrinkling. They are also doing some “good old-fashioned engineering” to come up with an appropriate prototype for synthetic vascular grafts with the founding of a new company, Aruga Technologies, Velankar said. Some of their current goals include optimizing the fabrication of grafts with hemocompatible materials and improving the manufacturing and production process. Once that is done, they can move on to in vivo experimentation.
“This idea isn’t just something that can help with synthetic grafts,” Velankar said. “It’s for any solution that requires soft folding. If we can come up with a purely mechanical approach, or one that works with chemical strategies, it could be very, very useful.”
Tzeng agreed. “Today, current synthetic grafts work well in large caliber arterial reconstructions such as in the aorta,” she said. “But we are reluctant to use these grafts in bypasses to arteries below the knee where the vessels are much smaller. Thus, if this kind of graft modification can reduce the risk of thrombosis, it would greatly impact patient outcomes by simplifying the operation and reducing complications.”
Kayt Sukel is an independent writer.
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