Biomedical Engineering Reference
In-Depth Information
TABLE 6.2
Cell Numbers in Tissue Biology and Tissue Engineering: Orders of Magnitude
Cell numbers
in vivo
10
14
Whole body
10
9
-10
11
Human organ
10
2
-10
3
Functional subunit
Cell production
in vivo
2
30-50
10
15
Theoretical maximum from a single cell (Hayflick limit)
<
10
16
Myeloid blood cells produced over a lifetime
10
14
Small intestine epithelial cells produced over a lifetime
5
Cell production
ex vivo
10
7
-10
9
Requirements for a typical cellular therapy
Expansion potential
a
of human tissues
Hematopoietic cells
Mononuclear cells
10-fold
CD34 enriched
100-fold
10
6
-to10
7
-fold
Two or three antigen enrichment
10
3
-to10
4
-fold
T cells
Chondrocytes
10- to 20-fold
10
6
-fold
Muscle, dermal fibroblasts
>
a
Expansion potential refers to the number of cells that can be generated from a single cell in culture.
number of nephrons in the kidney is determined by the maximal clearance need of toxic
by-products and the clearance capability that each nephron possesses. These estimations
provide insight into tissue structure and function. The fundamental functional subunit
of most tissues contains only a few hundred cells, and in most cases this is a mixed-cell
population, since most organs have accessory cells that can be as much as 30 percent of
the total cell number. Further, as illustrated following, the tissue-type-specific cells may
be present at many stages of differentiation.
The nature of tissue microenvironments, along with cellular dynamics, communication,
and metabolic processes, must be understood in order to reconstitute tissue function
accurately. In addition, generating a therapeutic dose of cells requires a large number of
microenvironments. These microenvironments must be relatively similar to have all the
functional subunits perform in comparable fashions. Therefore, the design of cell culture
devices must provide uniformity in supporting factors, such as nutrient, oxygen, and
growth factor/hormone concentrations. These inputs must be reasonably homogeneous
down to 100
m distances. Below this size scale, nonuniformity would be expected and
in fact needed for proper functioning of tissue function subunits.
m
