Scientists Create Blood Vessels, Capillaries for Lab-Grown Tissues

Researchers have overcome one of the major hurdles on the path to growing transplantable tissue in the lab: they have found a way to grow the blood vessels and capillaries needed to keep tissues alive.

The new research, conducted by investigators from Rice University (Houston, TX, USA) and Baylor College of Medicine (BCM; Houston, TX, USA), is available online, and it was published in the January 2011 issue of the journal Acta Biomaterialia. "The inability to grow blood-vessel network --or vasculature--in lab-grown tissues is the leading problem in regenerative medicine today,” said lead coauthor Dr. Jennifer West, department chair, and professor of bioengineering at Rice. "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, a team of researchers led by Dr. West and BCM molecular physiologist Dr. Mary Dickinson chose polyethylene glycol (PEG), a nontoxic plastic that is widely used in medical devices and food. Building on 10 years of research in Dr. West's lab, the scientists modified the PEG to mimic the body's extracellular matrix--the network of proteins and polysaccharides that comprise a considerable portion of most tissues.

Drs. 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 scientists were able to see as the cells gradually formed capillaries throughout the soft, plastic gel.

To assess these new vascular networks, the researchers 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 major development, conducted by Dr. West and graduate student Joseph Hoffmann, in November 2010, involved the generation of a new technique called two-photon lithography, an ultrasensitive method of using light to create intricate three-dimensional (3D) 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 research, also in collaboration with the Dickinson lab at BCM, Dr. West and her colleagues plan to use the technique to grow blood vessels in predetermined patterns.

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Baylor College of Medicine