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Human articular cartilage is a remarkably resilient tissue that is exposed to approximately 10 million cycles of loading per year and in many instances provides normal function for as many as 8 decades. Articular cartilage provides the bearing surface that allows bony segments to glide and rotate against each other and cushions peak stresses associated with physical activity. Articular cartilage tissue is composed of approximately 70% water, 25% extracellular matrix proteins, and 5% cells. The concentration of macromolecules, primarily collagens and proteoglycans influences the mechanical properties of the tissue, as does the assembly and organization of these components into an ordered structure. The mechanical properties of cartilage are also influenced by the interaction of the porous extracellular matrix and the fluid occupying the pores. In normal healthy cartilage, a delicate balance exists between the synthesis and degradation of matrix components, so that homeostasis is maintained and continued mechanical performance of the tissue is ensured.