Scientists have figured out how to print artificial versions of the body’s complex vascular networks, which mimic our natural passageways for blood, air, lymph, and other vital fluids, reports Popular Mechanics.

“One of the biggest road blocks to generating functional tissue replacements has been our inability to print the complex vasculature that can supply nutrients to densely populated tissues,” says Jordan Miller, assistant professor of bioengineering at Rice’s Brown School of Engineering, who helped lead the team, in a press statement.

Creating functional tissue replacements is a high scientific priority because of its potential impact on organ donations. The crisis of organ shortages is a long-lasting one; around 114,000 people are on transplant waiting lists in the United States alone. Even after a successful transplant, patients have to take immune-suppressing drugs to prevent organ rejection for the foreseeable future. Bioprinting organs could play an important role in reducing both problems.

“Tissue engineering has struggled with this for a generation,” says Kelly Stevens of the University of Washington, who led the team of bioengineers with Miller, in the press statement. “With this work, we can now better ask, ‘If we can print tissues that look and now even breathe more like the healthy tissues in our bodies, will they also then functionally behave more like those tissues?’ This is an important question, because how well a bioprinted tissue functions will affect how successful it will be as a therapy.”