University of Minnesota researchers have bioengineered blood vessels with the potential to grow and continue developing after being placed inside people.

Kristopher Sturgis

Updated October 3, 2016

University of Minnesota researchers say they were able to bioengineer blood vessels in a lab from a postnatal donor's skin cells, generating vessel-like tubes that can be implanted into human beings when needed.

The study was led by Robert Tranquillo, professor of biomedical engineering at the University of Minnesota, who told university news that this discovery could be the first of its kind, and could have a significant impact on children who suffer from heart defects.

"This might be the first time we have an 'off-the-shelf' material that doctors can implant in a patient," he said. "In the future, this could potentially mean one surgery, instead of five or more surgeries that some children with heart defects have before adulthood."

To create the material itself, Tranquillo and his colleagues combined sheep skin cells in a gelatinous material known as fibrin. They mixed the materials in the form of a tube before rhythmically injecting in nutrients for cell growth using a bioreactor. The bioreactor was also used to strengthen and fortify the tube, and became a key component that enabled the bioartificial vessels to become even stronger than native arteries.

After the vessel was created, the group then used special detergents to wash away all of the sheep cells so that only a cell-free matrix remained.

"When first implanted, our vascular graft is a rather poor approximation to a natural artery. It is a tube of cell-produced collagen and other proteins that possesses stiffness and strength like a natural artery, but it contains little elastin, which normally provides for elastic recoil when blood pulses through, and it has no cells (which we removed, by design), therefore, no  endothelial cells on the inner surface that normally prevent clotting," Tranquillo said.

Tranquillo and his team decided to test the vessel by implanting it in three different lambs to replace part of their pulmonary artery. Upon implantation the lamb's cells began to grow around the vessel, allowing the vessel to grow together with the lamb's tissue into adulthood.

Tranquillo says that this was key for the success of the implanted vessels, as the repopulating of the cells around the vessel graft is what will enable them to grow with the recipient. He was also quick to note that this could be the perfect combination of tissue engineering and regenerative medicine, as they were able to successfully grow tissue in a lab before implanting it, and watching it grow and become a part of the living tissue in the body.

As the sheep continued to grow, the blood vessel graft continued to grow with it. At 50 weeks old, the vessel had increased 56% in diameter, and the amount of blood that could be pumped through the vessel had more than tripled. The group also noted that no evidence of adverse effects such as clotting, vessel narrowing, or calcification could be found.

Tranquillo said that "after the nearly one year implantation in the growing lambs, we observed not only an increase in graft diameter equal to the adjacent artery, but maintenance of strength, presence of substantial organized elastin formed from cells that repopulated the collagenous matrix, and an endothelium--all features consistent with a natural artery."

"If these results occur following implantation of our 'off-the-shelf' vascular graft in children who require 'replumbing' of the heart to repair congenital heart defects, they may require only a single open heart surgery in contrast to the multiple surgeries now required to replace the current vascular grafts that do not grow with larger grafts every few years. That would spare the children and families an incredible amount of anguish and greatly reduce health care costs," Tranquillo added.

Creating bioengineered structures that can boost regenerative processes isn't necessarily a new area of research. Last year researchers from the Medical College of Wisconsin developed a new technology comprised of biodegradable microrods that release peptides with regenerative properties that can repair and restore tissue and organ function. Tranquillo and his colleagues hope that their new bioengineered blood vessels could be another building block for regenerative medicine, and perhaps usher in new discoveries.

As for the next steps for the group, Tranquillo says they hope to begin speaking with doctors to get a better idea on how to gain approval from FDA for human clinical trials. In the meantime, the group plans to continue to explore the efficacy of the artificial vessels to improve the success of implantation, and prepare for eventual human trials. 

Kristopher Sturgis is a contributor to Qmed.

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[Image courtesy of University of Minnesota]