A research team from Penn State University has developed a 3-D bioprinting process that uses strands of cow cartilage in the hopes of creating "patches" for worn out joints.

"Our goal is to create tissue that can be used to replace large amounts of worn out tissue or design patches," said Ibrahim T. Ozbolat, associate professor and a member of the Penn State Huck Institutes of the Life Sciences. “Those who have osteoarthritis in their joints suffer a lot. We need a new alternative treatment for this."

Cartilage was previously grown with cells embedded in a hydrogel—a substance composed of polymer chains and about 90 percent water. This was used as a scaffold to grow tissue, but the tissue did not have sufficient mechanical integrity and the hydrogel could produce toxic compounds.

The research team was able to develop larger scale tissues without using a scaffold by creating a tiny tube—from 0.03 to 0.05 in. in diameter—made of an algae extract called "alginate." They then inject the cartilage cells into the tube where they grow for about a week. The cells do not stick to alginate, so they can remove the tube to produce a strand of cartilage.

The cartilage strands can then replace the ink in the 3-D printer to build any pattern the researchers choose. The cartilage then self-adheres for an hour before being moved into a petri dish full of nutrients to help the cartilage grow into a single piece of tissue. The artificial cartilage produced is very similar to native cow cartilage. While mechanical properties are not as strong as natural cartilage, they are better than the cartilage that made via scaffolding.

"We can manufacture the strands in any length we want," said Ozbolat. "Because there is no scaffolding, the process of printing the cartilage is scalable, so the patches can be made bigger as well. We can mimic real articular cartilage by printing strands vertically and then horizontally to mimic the natural architecture."