Research on articular cartilage has been one of the major on-going projects since Dr. Suh started his professional career in biomedical engineering. He loves articular cartilage not only because it plays an important role in our daily life and a damaged cartilage can cause a devastating impact on one's life, but because he believes small white cartilage of chicken bone at KFC is so crunchy and tasty.

Normal Cartilage (Click to Enlarge)

Articular cartilage is a thin white soft tissue covering the bony end inside the articulating joints (or diarthrodial joints) of our body. By the presence of a thick viscous fluid (or synovial fluid) layer inside the joint, articular cartilage produces a wonderful lubrication mechanism with almost zero friction, which helps us articulate our joints during daily activities. In addition, articular cartilage is also capable of dissipating the mechanical energy so that the joint structure is protected from any harmful damage by an impact force.

While cartilage tissue is surprisingly resilient in response to a mechanical force, it also is remarkably durable. This natural bearing material can remain healthy and functional for one full life span of a person provided the tissue is properly managed. Once damaged, however, the cartilage has limited or no ability to heal and often undergoes degenerative pathological changes. Complete understanding of the mechanisms and natural history of cartilage injuries, and the healing and regeneration of injured cartilage is lacking.

Articular cartilage contains collagen fibrils embedded in a hydrophilic gel made of various disaccharide polymer chains, called glycosaminoglycan (GAG). The most abundant GAGs found in articular cartilage include chondroitin sulfate, dermatan sulfate, keratan sulfate, and hyarulonic acid. In articular cartilage, these GAG molecules are usually present in association with protein, forming large aggregated macromolecule called proteoglycan (PG) monomer which has an appearance of bottle brush shape. The proteoglycan monomers are then attached to the hyaluronic acid chain to form amorphous gel (Figure).

Figure of Cartilage Schematic (Click to Enlarge)

In a hydrated environment at physiological pH, the GAG molecules aggregated in proteoglycan become negatively charged, and these high negative charges create electrostatic repulsive forces between the molecules. It is electrostatic repulsive force which is responsible for the marked compressive stiffness of articular cartilage. Interstitial water is abundant and imparts an important physical properties of articular cartilage. It is involved in providing several important biomechanical functions of the tissue not only through binding of water to the hydrophilic GAG molecules, but also through the Donnan osmotic swelling phenomenon and the relative motion between the interstitial water and the porous matrix.

The TCL has been investigating articular cartilage damage, healing mechanisms, and current experimental and clinical techniques to promote healing of damaged cartilage. Although a few successful clinical outcomes have been reported, current surgical treatments are widely believed to have a limited ability to completely restore the characteristics of hyaline cartilage. Nonetheless, recent experimental studies have shown that the successful repair of a clinically significant articular cartilage injury may be possible. Therapies could include a combination of growth factors, gene therapy, cell technologies, and autologous osteochondral transplantation. The further study to develop these techniques and define their clinical value is the primary focus of the TCL.

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