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3-D Printing Technique Devised for Replacement Cartilage

Knee X-ray

(Akha, Wikimedia Commons)

28 June 2016. Biomedical engineers developed a process for directly printing replacement cartilage without the scaffolds needed in previous tissue engineering techniques. The team at Pennsylvania State University, led by engineering professor Ibrahim Ozbolat, describe their process in yesterday’s issue of the journal Scientific Reports.

Ozbolat and colleagues, from Penn State and University of Iowa where he was previously on the faculty, are seeking to simplify production of replacement cartilage tissue for people with osteoarthritis, or wear and tear on joints, and other cartilage damage. Once damaged, cartilage tissue does not grow back on its own. In addition, replacement cartilage not only needs to provide physical and structural support, but also the biological and cell signaling functions of original tissue.

Current tissue engineering methods for replacement cartilage require first creating a scaffold for the new tissue, usually from hydrogel, a material made up largely of water with polymer chains that provides a framework. Cartilage cells are then seeded on the hydrogel framework, where they proliferate and grow. “Hydrogels don’t allow cells to grow as normal,” says Ozbolat in a university statement. “The hydrogel confines the cells and doesn’t allow them to communicate as they do in native tissues.” Because of these limitations, adds Ozbolat, scaffold-grown tissue often lacks the needed mechanical properties and is susceptible to toxins from degrading hydrogel.

The researchers designed a process that produces new cartilage tissue directly with strands of cells that can be extruded through a 3-D printer. The cells are first cultured for 10 days inside thin tubes made of alginate, a biocompatible extract of algae used in wound healing, drug delivery, and tissue engineering. The cells adhere into strands that are easily removed from the alginate. The strands are thin enough to fit through a 3-D printer, with a specially-designed nozzle, and fabricated into tissue patches. The patches are then cultured further in nutrients where they self-assemble into replacement cartilage.

“We can manufacture the strands in any length we want,” notes Ozbolat. “Because there is no scaffolding, the process of printing the cartilage is scalable, so the patches can be made bigger as well.”

The Penn State team demonstrated the process in proof-of-concept tests with cartilage cells from cattle. The tests show the printed cartilage has biochemical and some mechanical properties similar to natural cartilage. The researchers also attached the printed cartilage to a cattle bone model. While superior to scaffold-grown cartilage, however, the replacement cartilage did not fully integrate with the bone, like original cartilage. The authors recommend a bio-compatible glue to improve adhesion.

Ozbolat tells more about 3-D printing of cartilage in the following video.

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