Repair of Osteochondral Lesions - Engineered Bone: Tissue Engineering Intelligence Unit - page 176

Figure 4. Repair of large osteochondral defects in adult rabbits by implantation of an osteochondral com-
posite, consisting of a layer of engineered cartilage combined with an osteoconductive support (Collagraft). 116
After 6 weeks (A), the original shape of the engineered cartilage (ec) was still preserved, on top of the
Collagraft material (cg). After 6 months (B), the engineered cartilage remodelled into a cartilaginous surface,
matching the thickness of native rabbit cartilage, and new trabecular bone. A clear tidemark was separating
the trabecular bone (C, von Kossa stain) and the cartilage surface (D, type II collagen immunostain). Scale
bar = 2 mm (A, B) or 0.2 mm (C, D).
osteochondral defects in adult rabbits. The result could be explained by the fact that the func-
tional extracellular matrix of the engineered cartilage layer not only provided a protective mi-
lieu for the embedded chondrocytes, but also served as a mechanical and electrochemical signal
transducer that conducted various joint stimuli to the chondrocytes. This approach therefore
deserves further extension to a human cell source.
Future Directions
In this chapter, we have reviewed some of the several approaches currently used or under
investigation to repair cartilage injuries. The last section describes what we believe to be key
challenges for the development of new procedures, which may predictably restore large osteo-
chondral lesions.
Generation of Cartilage Grafts Using Human Cells
As compared to the current procedures, implantation of structurally and mechanically func-
tional cartilage tissues would allow easier graft fixation, early recovering of joint functionality
and reduced mechanical discontinuity, which in turn might account for improved durability of
the repair (see section “Engineering Functional Cartilage Grafts”). Preformed cartilage could
ultimately be combined with osteoconductive materials in order to generate osteochondral
grafts (see section “Engineering Osteochondral Composite Tissues”). Despite all the recent
progresses made in ex vivo synthesis of cartilage, a reproducible generation of uniform carti-
laginous tissues of predefined size starting from adult human cells has not yet been achieved.