Robert L. Sah, MD, ScD
University of California, San Diego
Bioengineering Articular Cartilage and Synovial Joints (more ...)
Bioengineering Articular Cartilage and Synovial Joints (hide ...)
The synovial joint is the most common type of joint in the body. Such a joint consists of a synovium-lined cavity containing synovial fluid that separates articulating cartilage-covered bones. Often, such joints are functional for a lifetime, with the synovial fluid-bathed articular cartilage providing surfaces that are low-friction, wear-resistant, and load-bearing. In adults, damaged articular cartilage does not heal effectively after injury, and a common aging-associated malady is osteoarthritis with progressive cartilage deterioration.
The synovial fluid has high concentrations of lubricant molecules, facilitating low friction and low wear of articular cartilage. Boundary-mode friction tests and accelerated wear tests of articulating cartilage surfaces demonstrate these roles for synovial fluid. Lubricant molecule components of synovial fluid that lower friction in the boundary mode are proteoglycan-4 and hyaluronan. Such lubricant molecules can be synthesized by cartilage and synovium.
One structural feature of articular cartilage is the location and organization of the indwelling chondrocytes. Chondrocytes are present at a density that decreases with depth from the articular surface. The density of chondrocytes also decreases with normal aging. In osteoarthritis, brood clones can lead to a normalization of cell density, although the organization of cells within cartilage may remain deranged. Such cellular features of cartilage can be delineated by 3-D histological methods.
To fabricate and maintain whole biological joints ex vivo, an appropriate interaction of cartilage, synovium, and synovial fluid components appears critical. Mechanobiological effects and interactions in joints normally result in a high concentration of lubricant molecules, while providing for nutrient exchange. Dynamic compressive and shear loads applied to cartilage stimulate secretion of load-bearing matrix and friction-lowering lubricant, respectively. An inter-compartmental model highlights such interactions and can be used to select component parameters for testing fabricated joints ex vivo. A joint-scale bioreactor has been developed and shows the ability to maintain whole joints with viable articular cartilage that is responsive to its mechanical environment.
Founder Series, MRB III Lecture Hall (Room 1220)