Researchers say they’ve developed a 3-D bioprinter that can create artificial body parts with ready-made channels for getting nutrients and oxygen to the implanted cells. If the technology can be perfected, the device could solve one of the biggest obstacles to creating 3D-printed organs: how to nourish masses of manufactured tissue.

“It can fabricate stable, human-scale tissue of any shape,” Anthony Atala, director of the Wake Forest Institute for Regenerative Medicine in North Carolina, said in a news release. “With further development, this technology could potentially be used to print living tissue and organ structures for surgical implantation.”

Atala and his colleagues describe their experiments with the bioprinter, known as the Integrated Tissue-Organ Printing System or ITOP, in a study published today by Nature Biotechnology.

Bioprinting involves taking cells from a donor, culturing them, putting them into a water-based gel, and then depositing the gel around a biodegradable polymer structure that anchors the cells in place. Atala and other researchers have developed methods to bioprint artificial skin and bladders. But there’s a limit: Since the bioprinted tissue lacks blood vessels, it can’t be made any thicker than 200 micrometers, which is about the width of a human hair.

Several teams of researchers, including the group at Wake Forest, have been working on techniques for growing thicker layers of tissue.

Atala’s ITOP bioprinter does it by spitting out different types of gel in a computer-controlled pattern, similar to how an inkjet printer spits out ink. The bioprinter builds microchannels into the polymer scaffolding for the manufactured tissue. During the early stages of growth, the microchannels serve the function of blood vessels, allowing liquid nutrients and dissolved oxygen to reach the bioprinted cells in the interior.

“Our results indicate that the bio-ink combination we used, combined with the microchannels, provides the right environment to keep the cells alive and to support cell and tissue growth,” Atala said.

After implantation, blood vessels replace the microchannels in a process known as vascularization.

In the latest tests of the technique, the researchers created a variety of constructs, including artificial ears, muscle fibers and jawbone fragments.

Human-sized ears were 3D-printed and then attached to mice, under the skin. In two months’ time, blood vessels and cartilage tissue formed in the bioprinted tissue. Artificial muscle fibers were implanted in rats. After two weeks, tests showed that the muscles were robust enough to support vascularization and nerve formation. And when jawbones were implanted in rats, researchers found that the implants formed vascularized bone tissue within five months.

Wake Forest’s bioprinting procedure has not yet been used in humans, but Atala and his colleagues see no reason why it shouldn’t work. One big benefit of the technique is that the replacement parts can be custom-printed to fit the recipient, based on computerized 3-D body scans.

The technology is meant to provide a new tool for mending battlefield or bomb injuries. And eventually it could open the way for the production of more complex organs, such as kidneys. The research was supported in part by grants from the Armed Forces Institute of Regenerative Medicine, the Telemedicine and Advanced Technology Research Center at the U.S. Army Medical Research and Material Command and the Defense Threat Reduction Agency.

In addition to Atala, the co-authors of the study in Nature Biotechnology, “A 3D Bioprinting System to Produce Human-Scale Tissue Constructs With Structural Integrity,” include Hyun-Wook Kang, Sang Jin Lee, Carlos Kengla and James Yoo.