Tissue Engineering and Regenerative Medicine Strategies for the Treatment of Osteochondral Lesions - 3D Multiscale Physiological Human - page 27

Table 2.1 Mechanical
properties of articular
cartilage and bone [ 24 ]

Tissue Tensile strength (MPa) Modulus (MPa)

Articular cartilage 11-35 3.7-400

Trabecular bone 0.1-30 10-2000

Cortical bone 47-133 5500-20000

cartilage the water content is above the normal condition [ 8 ]. The increase in the
water content causes cartilage to become softer and more permeable [ 23 ].
Table 2.1 presents indicative range of values of the mechanical properties of ar-
ticular cartilage and bone from [ 24 ]. The values vary depending on many conditions
including loading direction, the anatomical location, age and health of donors [ 24 ].
The biomechanical properties of the tissues relate to the structure of and interactions
in the collagen network. Collagens are proteins that interact with cells and affect cell
functioning such as adhesion, growth and differentiation [ 22 ]. Collagens constitute
10-20% of the weight of the cartilage. Collagen type II is the major component of
cartilage that gives tensile strength, and it is the predominant collagen type repre-
senting 90-95% of the collagen content. Other collagen types present in the articular
cartilage are VI, IX, X and XI [ 8 ]. Collagen type II is a sign for differentiated chon-
drocytes, while collagen type I, which is not found in articular cartilage, is a sign for
fibrocartilage as a result of chondrocyte dedifferentiation to fibroblast [ 18 ]. PGs take
up 10-20% of the cartilage weight and give compressive strength [ 8 ]. PGs consist
of a protein core to which glycosaminoglycans (GAGs) are attached [ 18 ]. PGs can
help matrix stabilization by binding to other macromolecules and also may affect the
cell function by binding to growth factors [ 19 ].
Articular cartilage is a four-layered structure: (i) the superficial layer, (ii) the
intermediate or transitional layer, (iii) the deep layer, and (iv) the calcified layer
that is separated from the deep layer with the 3D border called tidemark. These
layers differ in cellularity, cell morphology, concentration of PGs, collagen fibril
content and orientation, water content, and thickness [ 8 ]. Figure 2.3 illustrates an
OC tissue with distinct layers of articular cartilage and subchondral bone. Articular
cartilage is a highly organized tissue and possesses a particular cellular andmolecular
structure [ 18 ]. Thus, it is obvious that the properties of the cartilage matrix cannot
be achieved just by combining the components of the ECM in right concentrations.
Chondrocytes are in charge of the synthesis, organization and maintenance of the
ECM in the articular cartilage. Therefore, in response to a damage in the cartilage
matrix, the local chondrocytes detect the changes occurring within the matrix and
determine the new needs of the matrix. Subsequently, the chondrocytes will give
the needed response, synthesizing the required components in right amounts, and
assemble and organize them in the matrix [ 7 , 19 ].