For the mature samples, the line scans also reveal increasing collagen content progressing from the articular surface to bone (Fig. 2), with significantly higher collagen detected in the deep zone, calcified cartilage, and bone compared with the surface zone cartilage. Both the calcified cartilage and bone contained significantly more collagen compared with the middle zone of cartilage. In contrast, no significant difference in relative collagen content was found among deep zone cartilage, calcified cartilage, and bone. The collagen fibrils of mature samples were highly oriented parallel to the articular surface in the surface zone and perpendicular to the calcified cartilage region in the deep zone, typical of articular cartilage structure (Fig. 2). In the calcified cartilage region, a relatively random collagen orientation was detected compared with the deep zone. With age, collagen orientation increased in the surface and deep zone regions of cartilage, and the mature samples also contained significantly more collagen compared with immature samples in both the surface and deep zones (Fig. 2). Similarly, a higher collagen content was also measured in the calcified cartilage and bone regions of mature samples compared with immature samples ( p < 0.05). Finally, both immature and mature samples exhibited little change in collagen content within the calcified cartilage region (Fig. 5