Biomedical Engineering Reference
In-Depth Information
Dynamics
Temporal aspects of the cellular microenvironment also are critical to obtaining desired
cell phenotype and function. The microenvironment is highly dynamic and displays a
multitude of time constants. Some of the key dynamic processes are described following.
OXYGENATION
Generally, mammalian cells do not consume oxygen rapidly compared to microorganisms,
but their uptake rate is large compared to the amount of oxygen available at any given time
in blood or in culture media (Table 6.12). At 37
C, air-saturated aqueous media contain only
about 0.21 mM oxygen per liter. Mammalian cells consume oxygen at a rate in the range of
0.05-0.5
mol/10
6
cells/hr. With tissue cellularities of 500 million cells per cc, these oxygen
uptake rates call for volumetric oxygen delivery rates of 25 to 250
m
mol oxygen/cc/hour.
This rate needs to be balanced with the volumetric perfusion rates of tissues and the oxygen
concentration in blood.
Metabolically active tissues and cell cultures, even at relatively low cell densities, quickly
deplete the available oxygen. For instance, at cell densities of 10
6
cells/ml, oxygen is
depleted in most tissues in about 0.4 to 4 hours. Oxygen thus must be continually supplied.
To date, a number of primary cell types (e.g., hepatocytes, keratinocytes, chondrocytes, and
hematopoietic cells) have been grown ex vivo for the purpose of cell therapy. The effects of
m
TABLE 6.12 Measured Oxygen-Demand Rates of
Human Cells in Culture
mol O
2
/10
6
cells/h
Human
m
HeLa
0.1-0.0047
HLM (liver)
0.37
LIR (liver)
0.30
AM-57 (amnion)
0.045-0.13
Skin fibroblast
0.064
Detroit 6 (bone marrow)
0.43
Conjunctiva
0.28
Leukemia MCN
0.22
Lymphoblastoid (namalioa)
0.053
Lung
0.24
Intestine
0.40
Diploid embryo WI-38
0.15
MAF-E
0.38
FS-4
0.05
