"The cells know what to do," Putnam said. "You can take these things and mix them and put them in an animal. Literally, it's as easy as a simple injection and over a few days, they spontaneously form new vessels and the animals' own vasculature connects to them."
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: lung fibroblasts, adult stem cells from fat and adult stem cells from bone marrow. 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 the lung fibroblasts produced immature, misshapen human capillaries that leaked. They could tell because the tracer dye pooled in the tissue around the new vessels. On the other hand, the solutions with both types of adult stem cells gave rise to robust human capillaries that kept blood and dye inside them.
The paper notes that one popular method biomedical engineers use to check the success of their effortscounting blood vesselsmight not be an ideal measure. The adult stem cell solutions produced fewer blood vessels th
|Contact: Nicole Casal Moore|
University of Michigan