Stem cell-based cartilage regeneration: Biological strategies, engineering innovations, and clinical translation

Figure 1 Structural differences between normal and degenerated articular cartilage. A and B: Schematic representation of healthy (A) and osteoarthritis-affected (B) articular cartilage. Normal cartilage is composed of four zones-superficial, middle, deep, and calcified-organized above the subchondral bone and enriched in collagen type II and aggrecan. In osteoarthritis, progressive matrix degradation, fissures, loss of chondrocytes, and elevated expression of matrix metalloproteinases and aggrecanases (a disintegrin and metalloproteinase with thrombospondin motifs) result in biomechanical failure and tissue degeneration. MMPs: Matrix metalloproteinases; ADAMTs: A disintegrin and metalloproteinase with thrombospondin motifs.