New 3D Printing Method Creates Complex Living Tissue Constructs

A new 3D printing method developed by Wyss Institute Core Faculty member Jennifer Lewis, Ph.D., and her team uses multiple print heads and customized “inks” to create intricately patterned 3D tissue constructs and tiny blood vessels. This new bio-printing method represents a major step toward a longstanding goal of tissue engineers: creating human tissue constructs realistic enough to test drug safety and effectiveness.

This method, reported in a Wyss Institute press release, also represents an early but significant step toward building fully functional replacements for injured or diseased tissue that can be designed from CAT scan data using computer-aided design (CAD), printed in 3D at the push of a button, and used by surgeons to repair or replace damaged tissue.

“This is the foundational step toward creating 3D living tissue,” said Lewis senior author of the study, who is a Core Faculty Member of the Wyss Institute for Biologically Inspired Engineering at Harvard University, and the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences. Lewis and her team, including lead author David Kolesky, reported the results in the journal Advanced Materials on February 18, 2014.

Tissue engineers have tried for years to produce lab-grown vascularized human tissues robust enough to serve as replacements for damaged human tissue. Others have printed human tissue before, but they have been limited to thin slices of tissue about a third as thick as a dime. When scientists try to print thicker layers of tissue, cells on the interior starve for oxygen and nutrients, and have no good way of removing carbon dioxide and other waste, so they suffocate and die. Kolesky and Lewis set out to mimic nature by permeating tissue with a network of tiny, thin-walled blood vessels that nourish tissue and remove waste.

To print 3D tissue constructs with a predefined pattern, the researchers needed functional inks with useful biological properties, so they developed “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 the team developed a third ink with an unusual property: it melts as it cools rather than as it warms. This allowed the scientists to first print an interconnected network of filaments, melt them by chilling the material and suctioning the liquid out to create a network of hollow tubes.

Lewis and her team are now focused on creating functional 3D tissues that are realistic enough to screen for safety and effectiveness. “That’s where the immediate potential for impact is,” Lewis said.