To print 3D tissue constructs with a predefined pattern, the researchers needed functional inks with useful biological properties, so they developed several "bio-inks" tissue-friendly inks containing key ingredients of living tissues. One ink contained extracellular matrix, the biological material that knits cells into tissues. A second ink contained both extracellular matrix and living cells.
To create blood vessels, they developed a third ink with an unusual property: it melts as it is cools, rather than as it warms. This allowed the scientists to first print an interconnected network of filaments, then melt them by chilling the material and suction the liquid out to create a network of hollow tubes, or vessels.
The Harvard team then road-tested the method to assess its power and versatility. They printed 3D tissue constructs with a variety of architectures, culminating in an intricately patterned construct containing blood vessels and three different types of cells a structure approaching the complexity of solid tissues.
Moreover, when they injected human endothelial cells into the vascular network, those cells regrew the blood-vessel lining. Keeping cells alive and growing in the tissue construct represents an important step toward printing human tissues. "Ideally, we want biology to do as much of the job of as possible," Lewis said.
Lewis and her team are now focused on creating functional 3D tissues that are realistic enough to screen drugs for safety and effectiveness. "That's where the immediate potential for impact is," Lewis said.
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|Contact: Dan Ferber|
Wyss Institute for Biologically Inspired Engineering at Harvard