One of the major obstacles to growing new organs — replacement hearts, lungs and kidneys — is the difficulty researchers face in building blood vessels that keep the tissues alive, but new findings from U-M could help overcome this roadblock.
“It’s not just enough to make a piece of tissue that functions like your desired target,” said Andrew Putnam, associate professor of biomedical engineering. “If you don’t nourish it with blood by vascularizing it, it’s only going to be as big as the head of a pen.
“But we need a heart that’s this big,” he added, holding up his fist.
More immediately, doctors and researchers believe figuring out how to grow working blood vessels might offer treatments for diseases that affect the circulatory system, such as diabetes. Perhaps the right drug or injection could save patients’ feet from amputation.
Putnam and his colleagues have revealed why one of the leading approaches to building blood vessels isn’t consistently working: It’s making leaky tubes. They also demonstrated how adult stem cells could solve this problem. A paper on the findings is published online in Tissue Engineering Part A, and will appear in a forthcoming print edition.
Today, biomedical researchers are taking two main approaches to growing new capillaries, the smallest blood vessels and those responsible for exchanging oxygen, carbon dioxide and nutrients between blood and muscles or organs.
One group of researchers is developing drug compounds that would signal existing vessels to branch into new tributaries. These compounds — generally protein growth factors — mimic how cancerous tumor cells recruit blood vessels.
The other group, which includes the U-M team, is using a cell-based method. This technique involves injecting cells within a scaffolding carrier near the spot where new capillaries are wanted.
But it turns out these vessels don’t always thrive. The U-M team aimed to figure out why. In reading previously published findings, Putnam noticed that researchers used “a mishmash of support cells,” and the field had paid little attention to which ones work best. So that’s where he and his colleagues focused.
In their experiments, they mixed three recipes of blood vessel starter solutions, each with a different commonly used supporting cell type. They also made a version with no supporting cells at all.
They injected each solution under the skin of mice, and allowed the new blood vessels to form over a period of two weeks. At various points in time, they injected a tracer dye into the animals’ circulation to help them see how well the engineered capillaries held blood, and whether they were connected to the animals’ existing vessel networks.
The researchers found that the solution with no support cells and the one with lung fibroblasts produced immature, misshapen human capillaries that leaked. On the other hand, solutions with both types of adult stem cells gave rise to robust human capillaries that kept blood and dye inside them.
Karen Simpson, student financial assistant, Student Financial Services, on the increase in technology in her 35 years at U-M: “When I first came here we were typing student checks on typewriters. Now, everything is very modernized, very streamlined.”
“Crazy for You,” 7:30 p.m. April 18, 8 p.m. April 19-20 and 2 p.m. April 21, Power Center for the Performing Arts.