A plug of 3D bioprinted cartilage on top of a plug of bone and cartilage, both of which sit in a bath of nutrient media. Photo: Ozbolat, Penn State.
A plug of 3D bioprinted cartilage on top of a plug of bone and cartilage, both of which sit in a bath of nutrient media. Photo: Ozbolat, Penn State.

A novel 3D bioprinting process that uses strands of cow cartilage as ink may one day create cartilage patches for worn out joints, according to a team of engineers from Penn State. The engineers report their results in a paper in Scientific Reports.

"Our goal is to create tissue that can be used to replace large amounts of worn out tissue or design patches," said Ibrahim Ozbolat, associate professor of engineering science and mechanics. "Those who have osteoarthritis in their joints suffer a lot. We need a new alternative treatment for this."

Cartilage is a good tissue to target for bioprinting because it is made up of only one type of cell and has no blood vessels within the tissue. It also cannot repair itself: once cartilage is damaged, it remains damaged.

Previous attempts at growing artificial cartilage embedded cells in a hydrogel, a substance composed of polymer chains and about 90% water that is used as a scaffold to grow the tissue.

"Hydrogels don't allow cells to grow as normal," explained Ozbolat, who is also a member of the Penn State Huck Institutes of the Life Sciences. "The hydrogel confines the cells and doesn't allow them to communicate as they do in native tissues." This leads to tissues lacking sufficient mechanical integrity, while natural degradation of the hydrogel can produce toxic compounds that are detrimental to cell growth.

By taking advantage of 3D bioprinting, Ozbolat and his research team have now developed a method to produce larger scale tissues without the need for a scaffold at all. Their method involves creating a tiny tube, just a few hundredths of an inch in diameter, from alginate, an algae extract. They then inject cartilage cells into these tubes, allowing the cells to grow for about a week and adhere to each other to form a strand. Because the cells do not stick to the alginate, the strand of cartilage can easily be extracted from the tube.

The researchers then use these cartilage strands as a substitute for ink in a 3D printing process. Using a specially-designed prototype nozzle that can hold and feed the cartilage strands, the 3D printer lays down rows of cartilage strands in any pattern the researchers choose. After about half an hour, the cartilage patch self-adheres sufficiently for it to be moved to a petri dish, where it is placed in nutrient media to allow it to further integrate into a single piece of tissue. Eventually, the strands fuse together.

"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."

The artificial cartilage produced by the team is very similar to native cow cartilage. Its mechanical properties are inferior to those of natural cartilage, but better than the cartilage made using hydrogel scaffolding. Natural cartilage forms with pressure from the joints, and Ozbolat thinks that applying mechanical pressure to the artificial cartilage should improve its mechanical properties.

If this process is eventually applied to human patients, each individual would probably have to supply their own cartilage to avoid tissue rejection.

This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.