Probing the Elasticity of Calcified Cartilage Zone Using Nano-Indentation

Objective. The aim of this study was to measure the elastic modulus of calcified cartilage zone (CCZ) from different locations of human knee joints. Methods. Osteochondral specimens were collected from 5 locations including medial/lateral tibial plateau, medial/lateral femoral condyles, and patella of 6 donors with no knee diseases or injuries. Nano-indentation was used to measure the stiffness of CCZ and subchondral bone. Results. The elastic modulus of CCZ was 208.6 +/- 39.7 MPa in the vertical direction, and 178.3 +/- 35.9 MPa in the horizontal direction. Compared with non-calcified cartilage zone and subchondral bone, CCZ was about 10 times stiffer than the former, yet about 60 times softer than the latter. The average stiffness of CCZ also varied between locations, with CCZ from medial tibia plateau having the greatest stiffness. Conclusions. Our study reported the average stiffness of CCZ in the human knee joints, and revealed the site-dependent stiffness of CCZ. These findings would provide useful reference in the construction of tissue engineered osteochondral scaffold with CCZ layer.