Biomedical Engineering Reference
In-Depth Information
oxygen on hepatocytes have been systematically investigated. The reported specific oxygen
uptake rate (OUR) for hepatocytes is around 1.0
mole/10
6
cells/hr, which is relatively high
for mammalian cells. Conversely, a much lower oxygen consumption rate of about
0.02
m
mole/10
6
cells/hr has been reported for rat bone marrow cells.
In addition to the supply requirements, the concentration of oxygen close to the cells
must be within a specific range. Oxygenation affects a variety of physiological processes,
ranging from cell attachment and spreading to growth and differentiation. An insufficient
concentration retards growth, while an excess concentration may be inhibitory or even
toxic. For instance, several studies have shown that the formation of hematopoietic cell
colonies in colony assays is significantly enhanced by using oxygen concentrations that
are 5 percent of saturation relative to air, and an optimal oxygen concentration for bioreactor
bone marrow cell culture has been shown to exist. The oxygen uptake rate of cells is thus an
important parameter in the design of cell culture and tissue engineering studies.
m
METABOLISM AND CELL SIGNALING
Typically, there is not a transport limitation for major nutrients, although cells can
respond to their local concentrations. The reason is that their concentrations can be much
higher than that of oxygen, especially for the nutrients consumed at high rates. Typical uptake
rates of glucose are on the order of 0.2
moles/million cells/hr, while the consumption rates of
amino acids are in the range of 0.1-0.5
m
moles per billion cells per hour. The transport and
uptake rates of growth factors face more serious transport limitations. The expected diffusional
response times are given in Figure 6.29.
m
1
device
oxygen
glucose
protein
virus/cells
4
2
0.1
4
2
0.01
microenvironment
4
100
μ
2
single cell
0.001
10
0
10
1
10
2
10
3
10
4
10
5
Time (sec)
minute
hour
day
FIGURE 6.29
The diffusional penetration lengths as a function of time for several classes of biomolecules.
