A 3D bio-printing process has been demonstrated that uses strands of cow cartilage as substitute for ink and could lead to the development of cartilage patches for worn-out joints in humans.
"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 who worked on the project. "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 scale-up bio-printing because it is made up of only one cell type and has no blood vessels within the tissue. It is also a tissue that cannot repair itself. Once cartilage is damaged, it remains damaged.
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. This method proved ineffective as the resulting cartilage was too weak for its intended purpose.
Therefore, a different approach was taken which involved creating a tiny tube made of alginate, an algae extract.
Cartilage cells were then injected into the tube and allowed to grow for about a week. As 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.
"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. Although the mechanical properties are still inferior to those of natural cartilage, they are an improvement on earlier attempts using the hydrogel scaffolding.
Natural cartilage forms with pressure from the joints, and Ozbolat thinks that mechanical pressure on the artificial cartilage could improve its mechanical properties.
If this process is eventually applied to human cartilage, each individual treated could supply their own source material to avoid tissue rejection such as existing cartilage or stem cells differentiated into cartilage cells.
In February, scientists at Wake Forest Baptist Medical Centre in North Carolina demonstrated a 3D printer that can print human flesh in order to replace injured or diseased tissue.