FIGURE 1.

Gradient schematic illustrating the different zones of OC tissue and their specific functions. Reproduced with permission from (Khanarian et al., 2014). While the OC tissue is made up of articular cartilage (including the superficial zone, the middle zone, the deep zone, and the calcified cartilage) and subchondral bone, each of these tissues is heterogeneous. Especially in the articular cartilage, each zone within varies in cell size, number, and orientation as well as collagen fiber size, type, and orientation.