CARTILAGE 3D PRINTING - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 259

FIGURE 12.2
Macro and histology images of human cartilage: (a) photograph of a normal articular femoral knee joint; (b)
osteoarthritic femoral knee joint with several surface erosions (*); (c) histological Safranin O-fast green stained
section of normal cartilage with a smooth intact surface; and (d) osteoarthritic cartilage section with fibrillated
surface, lower cell density, reduced Safranin O staining, and cell cluster formation (inset). (Magnification C and
D = 10 × ).
Muir et al., 1970 ). Although the total collagen content in the DZ is lower than that in the other zones, the
collagen fibrils are of larger diameter and, similar to the cells that are commonly arranged into stacks or
columns, are oriented perpendicular to the articular surface ( Siczkowski and Watt, 1990 ) ( Figure 12.1 ).
Osteopontin is exclusively expressed in the DZ ( Pullig et al., 2000; Schnapper and Meyer, 2004 ).
Integration between articular cartilage and the much stiffer subchondral bone begins at the base of
the deep zone where a 5 m m thick undulating “tidemark” is observed, which marks the transition into a
layer of calcified cartilage (20-250 m m thick) containing perpendicular chondrocyte-derived collagen
type II fibers that become structurally cemented in the collagen type I osteoid produced by osteoblasts
( Hoemann et al., 2012; Orth et al., 2013 ) ( Figure 12.1 ). The calcified cartilage contains small cells
in a chondroid matrix that is characterized by increased mineral density speckled with apatitic salts
( Burr, 2004; Mow et al., 2012 ).
12.1.2 CARTILAGE INJURY, DISEASE, AND TREATMENT OPTIONS
Cartilage function is often compromised following acute or chronic injury or as part of the aging pro-
cess and eventually leading to tissue degeneration manifested as osteoarthritis (OA). Photographs and
histology images of normal and degenerated OA human articular cartilage are shown in Figure 12.2 .