A new “bioprinting” technique uses droplets of “bioink” — clumps of cells a few hundred micrometers in diameter that behave just like a liquid.

This means that droplets placed next to one another will flow together and fuse, forming layers, rings or other shapes, depending on how they were deposited. To print 3D structures, the researchers alternate layers of supporting gel, dubbed “biopaper,” with the bioink droplets. To build tubes that could serve as blood vessels, for instance, they lay down successive rings containing muscle and endothelial cells, which line our arteries and veins. “We can print any desired structure, in principle,” said Gabor Forgacs, a biophysicist at the University of Missouri in Columbia.