Biomedical Engineering Reference
In-Depth Information
Periosteal flap
taken from
medial tibia
Periosteal flap
sutured over lesion
Lesion
Biopsy of healthy
cartilage
Injection of
cultured chondrocytes
under flap into lesion
Enzymatic digestion
Cultivation for 11-21 days
(10-fold increase in number of cells)
Suspension of
2.6 × 10 6 - 5 × 10 6 cells
Trypsin treatment
FIGURE 6.7 Chondrocyte transplantation in the right femoral condyle. From [2].
embryonic stem cells to treat acute spinal cord injury. These therapies, while exciting and of
high potential, are still at a very early stage of development. From the tissue engineering
perspective, there are still many unanswered questions regarding the most appropriate cell
sources, mass transfer limitations, delivery methods, control of the microenvironment, inte-
gration with the host, and provision of an acceptable functional outcome.
6.1.4 Mechanisms Governing Tissues
Normal tissue functions can be used to define the engineering specifications of tissues
created in the lab. In addition, our understanding of biology can be used to control cell
function to generate tissues. Two important mechanisms that govern tissue dynamics are
the relationship between epithelial cells and mesenchymal cells, and stem cell and matura-
tional lineage biology. An understanding of these biological processes can inform the
design of engineered tissues. For example, the smallest physiological unit defines mass
transfer dimensions, while the number of cells required to replace the desired physiological
functions defines the overall dimensions of an engineered product. These numbers help set
overall design specifications and goals of the clinical device or engineered tissue.
The Epithelial-Mesenchymal Relationship
A fundamental paradigm defining tissues is the epithelial-mesenchymal relationship,
since many tissues are composed of a layer of epithelial cells bound onto a layer of mesen-
chymal cells (e.g., fibroblasts, smooth muscle cells, etc.), as shown in Figure 6.8. Normal
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