Biomedical Engineering Reference
In-Depth Information
Figure 3. Bioreactors for the application of physical forces to engineered cartilage tissues. In the rotating wall
vessel system (A), the rotational speed is adjusted so that the drag force of the medium (Fd) is balanced by
the centrifugal (Fc) and gravitational (Fg) forces. The constructs are thus maintained in a tumble-slide
regime and the resulting dynamic laminar flow enhances the production and accumulation of cartilaginous
extracellular matrix. 107 Specific culture chambers (B) have been developed for the application of direct
deformation to engineered constructs. 123 Chambers include wells to allocate tissue constructs (I), a mag-
netic bar for medium stirring (II), an inlet/outlet port for medium change (III), a cover lid to maintain
sterility (IV), and micrometer screws to accurately establish the contact position between the plungers and
each specimen (V).
addition, the method is mostly suited to fiber meshes as opposed to porous foams. The design
of bioreactors providing the possibility of scaffold perfusion with a cell suspension in alternate
directions has the potential to yield a more homogeneous seeding on a variety of scaffolds. 106
Once the cells are associated with the scaffold, cell-polymer constructs can be cultured in
bioreactors applying specific regimes of fluid flow. It was previously shown that dynamic (rather
than steady) and laminar (rather than turbulent) flow patterns were associated with rapid in
vitro assembly of functional cartilaginous matrix containing glycosaminoglycans and type II
collagen by articular chondrocytes cultured on biodegradable scaffolds 107 (Fig. 3A). Such find-
ings could be explained by the fact that dynamic laminar flow generated by rotating wall vessels
provided efficient mass transfer at limited shear stress levels, which was essential to promote/
maintain cell differentiation, synthesis and retention of extracellular matrix macromolecules.
Tissue engineering bioreactors can also expose developing cartilage constructs to specific
physical stimuli that may be beneficial for tissue growth and maturation (Fig. 3B). Enhanced
chondrogenesis and cartilage formation were reported upon stimulation of (i) cartilaginous
nodules by intermittent motion of medium in roller bottles, 108 (ii) gel-immobilised chondrocytes
 
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