3D printing organs, complete with blood vessels, takes a big step forward

Unresolved challenges can be lost among reports of breakthroughs in regenerative medicine. While many researchers have found ways to grow organ tissues in vitro, they have had not succeeded at growing full-size organs in large part because they haven’t figured out how to produce blood vessels that feed the organ tissue.
Earlier this year, Harvard materials scientist Jennifer Lewis devised a way to coax 3D printers into printing the tiny empty spaces as a part of a tissue mockup that consists of several different materials and cell types.
“This is the foundational step toward creating 3D living tissue,” Lewis said in a news release.
To create a simplified version of tissue complete with blood vessels, Lewis’s team filled a printer with tiny print-heads with several different “inks.” One consisted of extracellular matrix, the biological material that knits cells into tissues; another contained both extracellular matrix and living cells.
A third ink traced out the vessels. This ink was designed to melt when it cools, rather than warms. (All of the inks are designed to be printed at room temperature.)
They printed an interlace of the inks that included a maze of “vessels.” Then they chilled the material and siphoned out the melted blood vessel ink, leaving hollow tubes in its wake. The researchers then injected endothelial cells into the tubes, and the cells formed a lining for the tubes, making them capable of carrying liquid.
A network of blood vessels, besides being essential for any prospective transplant organ, would allow researchers to make thicker organ stand-ins to use to test drugs in the lab. Vasculature would also allow tissues to live longer, making room for better tests.