A New Printing Method for Cartilage Tissue

Researchers continue to search for better methods of 3-D printing to build tissues, approaches capable of producing the correct structural properties in the resulting product. Cartilage is a challenge in particular, as while it is a comparatively simple tissue type and thus a good place to start, it has proven difficult to recreate the strength and resilience of naturally grown cartilage. So far the most promising line of work has involved recreating the stage of mesenchymal condensation, but this has not yet been widely adopted.

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. 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 percent 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." 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 have developed a method to produce larger scale tissues without using a scaffold. They create a tiny - from 3 to 5 one 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. Because 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.

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. Natural cartilage forms with pressure from the joints, and the researchers think that mechanical pressure on the artificial cartilage will improve the mechanical properties.

Link: http://news.psu.edu/story/415808/2016/06/27/research/3d-printing-produces-cartilage-strands-bioink

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