Functions of Cartilage

Human synovial joints are covered by articular cartilage to withstand physiological loading over a lifetime. It provides a smooth load-bearing surface to reduce friction and acts as shock-absorbing tissue. In the lower limbs, articular cartilage sustains physiological stresses estimated to be in the range of 1-6 MPa during level walking. However, these stresses increase up to and beyond 10 MPa with activities [62, 63]. Lubricin, a glycoprotein abundant in cartilage and synovial fluid, has multiple functions in articulating joints and tendons that include the protection of surfaces and the control of synovial cell growth [64]. The mechanical properties of articular cartilage include the response of cartilage in frictional, compressive, shear, and tensile loading. Cartilage is resilient and displays viscoelastic properties [65]. Besides, costal cartilage can attach ribs to the sternum.

Biomechanical Properties and Mechanobiology of the Articular Chondrocyte

The mechanical function of articular cartilage largely depends on the composition and structural integrity of the cartilage matrix produced by chondrocytes. The articular chondrocyte lives in a dynamic mechanical environment that is a complex combination of compression, hydrostatic pressure, osmotic stress, shear stress, and tensile stretch. The mechanical signals are transmitted through the complex network of the ECM, pericellular matrix, cytoskeleton, and nucleus of chondrocytes. Chondrocytes respond to these mechanical stimuli by altering gene expression and metabolism [66]. The precise mechanism that govern development of chondrocytes is still unknown, so future research is needed to decipher which signaling pathways are mainly affected by mechanical loads.

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