The ability to print human tissue will revolutionize healthcare. Using 3D printing techniques to generate custom human tissues will enable new treatments for a wide variety of ailments and injuries, including arthritis, bone fractures and heart disease.

Until now, the challenge has been combining the strength and fluid characteristics needed for 3D printing with the special requirements to support living cells, particularly at a scale large enough to generate full-sized human tissue.

But researchers in the Department of Biomedical Engineering at Texas A&M University have created a new solution that could solve these problems and support 3D printing of human-scale tissue.

Akhilesh K. Gaharwar, assistant professor in the Department of Biomedical Engineering, said his laboratory has developed a new “bioink” that can print taller, stronger and more complex structures, bringing us closer to printing anatomical-scale tissues.

"Bioprinting requires materials that can flow through a nozzle like a liquid, but solidifies almost as soon as they're deposited. Developing materials that can do this and keep cells alive at the same time has been a big challenge for researchers in this field," said David Chimene, graduate student in Gaharwar’s lab and lead author of the project. "We found a way to combine two of the latest bioink reinforcement techniques, nano-reinforcement and ionic covalent entanglement, into an even more effective reinforcement that results in much stronger structures."

When bioinks solidify they form a watery polymer network called a hydrogel, which provides a water-rich environment similar to the human body, keeping living cells happy.

Ionic covalent entanglement reinforced bioinks contain two separate polymer networks that work together to strengthen the hydrogel. Gaharwar’s lab uses nanoengineering to create an ever-stronger hydrogel bioink called, "nanoengineered ionic-covalent entanglement” (NICE).

In NICE bioinks, the ICE bioink is reinforced again using nanoparticles called 2D nanoclays, which are shaped like tiny plates a few dozen nanometers wide and only a few atoms thick. This incredible thinness grants nanoclays the unusual property of having a surface area of over 900 square meters per gram (more than one-fifth of an acre), which enables even small amounts of nanoclays to interact with nearly every polymer in the bioink.

"Nanoclays work like trillions of tiny weak magnets that hold the bioink together," Gaharwar said. "These linkages are disrupted when the bioink flows out of the printer, but re-form in seconds after the ink stops moving, effectively turning the ink back into a solid."

This technique has allowed the lab to produce full-scale, cell-friendly reconstructions of human body parts, including ears, blood vessels, cartilage and even bone segments.

The next step for NICE bioinks will be determining how cells remodel the printed structures over time.

"Printing human-scale structures is a huge step forward," says Roland Kaunas, co-investigator in the study. "But it's still only half the battle. We still need to make sure we can direct the cells inside to recreate the tissue we want."

The NICE bioinks are still in their developmental stages, but in vivo experimentation is set to start soon. These tests will help the Gaharwar lab tweak their bioinks to maximize regenerative potential, and the researchers are optimistic that their cell-friendly ingredients will pay off.

The study is funded by National Institute of Science Division of Chemical, Bioengineering, Environmental, and Transport Systems.