Artificial Blood Vessels Grown in Polyethylene Glycol Hydrogels

Researchers from Rice University and Baylor College of Medicine have developed a method to grow blood vessels in a laboratory. The investigators used biomimetic polyethylene glycol hydrogels embedded with a growth factor called BB (PDGF-BB) to spur angiogenesis, and are now working on a way to guide the formation of vasculature for specific applications.

As its base material, a team of researchers led by West and BCM molecular physiologist Mary Dickinson chose polyethylene glycol (PEG), a nontoxic plastic that’s widely used in medical devices and food. Building on 10 years of research in West’s lab, the scientists 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.
West, Dickinson, Rice graduate student Jennifer Saik, Rice undergraduate Emily Watkins and Rice-BCM graduate student Daniel Gould 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. After that, they 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.
Another key advance, published by West and graduate student Joseph Hoffmann in November, involved the creation of a new technique called “two-photon lithography,” an ultrasensitive way of using light to create intricate three-dimensional patterns within the soft PEG hydrogels. West said the patterning technique allows the engineers to exert a fine level of control over where cells move and grow. In follow-up experiments, also in collaboration with the Dickinson lab at BCM, West and her team plan to use the technique to grow blood vessels in predetermined patterns.

Time-lapse image showing how two types of cells (tagged red and green) organize themselves into a functioning capillary networks within 72 hours: