Biomedical Engineering Reference
In-Depth Information
more attention for cartilage implant applications since their architecture can be
matched to the distinct collagen orientation in cartilage. The alignment and
chondrogenic differentiation of bone marrow-derived human mesenchymal stem
cells were reported when such cells were cultured on oriented PCL scaffolds
[84±86]. For polysaccharide hydrogels, nanotechnology has also been used to
produce nanometer surface features to improve the interaction of such materials
with natural tissue. Alginate has also been fabricated into nanostructured
scaffolds [83]. As in bone tissue engineering, nano-HA and collagen have also
served as improved nanostructured hydrogel composites for cartilage
applications [87].
Natural collagen
Of course, natural materials have often been investigated for cartilage
replacements (such as collagen type II). Collagen (mostly type II) constitutes
50±80% of the dry weight of articular cartilage. There are 29 types of collagen in
humans, and most of collagen exists in connective tissue. Collagen (type II) is a
fibrous, insoluble, macromolecular protein secreted by chondrocytes, maintains
the mechanical integrity of connective tissue, and also provides adhesive quali-
ties towards chondrocytes and other macromolecules (such as proteogylcans)
[88±90]. It has high tensile strength, resistance to proteolysis, and weak
antigenicity due to the molecular arrangement of its fibrils. Previous studies
have demonstrated the ability to fabricate collagen type II into nanostructured
fibers with good mechanical properties (with a tangent modulus of
172:536:1MPa and an ultimate tensile strength of 3:30:3MPa compared
with a tangent modulus of natural articular cartilage of 5±30MPa and an
ultimate tensile strength of 9±18MPa) and suitable for chondrocyte seeding and
growth [91].
In the clinical and industrial world, collagen is one of the most successful
materials used today in regenerative medicine, especially in nanostructured
composites. Recently, a case study reported that a 46-year-old athletic patient
with a large degenerative chondral lesions of the medial femoral condyle,
trochlea and patella, was successfully treated by using a closing-wedge high
tibial osteotomy and implanting of a biomimetic nanostructured osteochondral
bioactive scaffold (commercialized by Fin-Ceramica SpA in Faenza, Italy). The
biomimetic nanostructured scaffold was composed of several layers of nano-HA
and collagen type I at different ratios (100% collagen at the top, 60% collagen
with 40% HA in the middle and 30% collagen with 70% HA at the bottom) to
mimic the transition zone between articular cartilage and subchondral bone (Fig.
9.11). After one year, the patient was pain-free, had full range of knee motion,
and had returned to his pre-operation level of athletic activity. Magnetic
resonance imaging (MRI) evaluation after 6 months showed a good restoration
of the articular surface, with minimal subchondral bone oedema (abnormal
