Cow cartilage used to 3D-print patches for worn joints

Washington, June 29

Scientists have developed a new 3D-printing process that uses strands of cow cartilage as bioink, an advance that may help create tissue patches for worn out joints in arthritis patients.

Cartilage is a good tissue to target for scale-up bioprinting because it is made up of only one cell type and has no blood vessels within the tissue. The tissue that cannot repair itself. Once cartilage is damaged, it remains damaged.

"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 at Pennsylvania State University in the US.

"Those who have osteoarthritis in their joints suffer a lot. We need a new alternative treatment for this," Ozbolat said.

Previous attempts at growing cartilage began with cells embedded in a hydrogel - a substance composed of polymer chains and about 90 per cent water - that is

used as a scaffold to grow the tissue.

"Hydrogels don't allow cells to grow as normal. The hydrogel confines the cells and doesn't allow them to communicate as they do in native tissues," said Ozbolat. This leads to tissues that do not have sufficient mechanical integrity. Degradation of the hydrogel also can produce toxic compounds that are detrimental to cell growth.

Researchers developed a method to produce larger scale tissues without using a scaffold. They created a tiny - from three to five hundredths of an inch in diameter - tube made of alginate, an algae extract.
They inject cartilage cells into the tube and allow them to grow for about a week and adhere to each other.
Since cells do not stick to alginate, they can remove the tube and are left with a strand of cartilage. The cartilage strand substitutes for ink in the 3D printing process.
Using a specially designed prototype nozzle that can hold and feed the cartilage strand, 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 enough to move to a petri dish. The researchers put the patch in nutrient media to allow it to further integrate into a single piece of tissue. Eventually the strands fully attach and fuse together.

"Because there is no scaffolding, the process of printing the cartilage is scalable, so the patches can be made bigger as well," said Ozbolat.

"We can mimic real articular cartilage by printing strands vertically and then horizontally to mimic the natural architecture," he said.

The artificial cartilage produced by the team is very similar to native cow cartilage.

However, the mechanical properties are inferior to those of natural cartilage, but better than the cartilage that is made using hydrogel scaffolding.

The findings were published in the journal Scientific Reports. — PTI