This time-lapse image shows how two types of cells—which were tagged with fluorescent dye—organize themselves into a functioning capillary networks within 72 hours.

RICE (US) — A newly discovered way to grow blood vessels could be a game changer for efforts to grow replacement tissues and organs in the lab.

“The inability to grow blood-vessel networks—or vasculature—in lab-grown tissues is the leading problem in regenerative medicine today,” says lead co-author Jennifer West, a bioengineering professor at Rice University. “If you don’t have blood supply, you cannot make a tissue structure that is thicker than a couple hundred microns.”

As its base material, researchers chose polyethylene glycol (PEG), a nontoxic plastic that’s widely used in medical devices and food. They modified the PEG to mimic the body’s extracellular matrix—the network of proteins and polysaccharides that make up a substantial portion of most tissues. Details are reported in the journal Acta Biomaterialia.

The team, which included researchers from the Baylor College of Medicine, combined the modified PEG with two kinds of cells—both of which are needed for blood-vessel formation. Using light that locks the PEG polymer strands into a solid gel, they created soft hydrogels that contained living cells and growth factors.

They then filmed the hydrogels for 72 hours. By tagging each type of cell with a different colored fluorescent marker, the team was able to watch as the cells gradually formed capillaries throughout the soft, plastic gel.

To test these new vascular networks, the team implanted the hydrogels into the corneas of mice, where no natural vasculature exists. After injecting a dye into the mice’s bloodstream, the researchers confirmed normal blood flow in the newly grown capillaries.

The research was supported by the National Science Foundation and the National Institutes of Health.

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