Biomedical Engineering Reference
In-Depth Information
Based on these observations, which cell type would you expect to be the
fastest to align in the direction of shear when subjected to fluid shear stress?
Give a rationale for your answers (20 points).
A bioreactor has an oxygen mass transfer rate of (ka) of 8 hr
−1
. Hybridoma
cells are inoculated into the bioreactor at an initial viable cell density of
100,000 cells/mL. The cell doubling time is 18 hours. The head space in the
bioreactor contains 5%CO
2
/95% air. The oxygen consumption rate of cells is
5
7.23
10
−17
mol/ cell-s. Calculate the bulk oxygen concentration after 72 hours.
×
7.24
Cocultures of hepatocytes and fibroblasts have been used to build prototype
bioartificial livers. A series of tests to measure the effect of fibroblasts on the
expression of liver-specific functions by the hepatocytes was carried out.
10
6
cells) were seeded onto surfaces
A fixed number of hepatocytes (0.25
×
in circular patterns of a 490-
m diameter. A variable number of fibroblasts
were then seeded around the hepatocyte islands (fibroblasts will not attach on
top of the hepatocyte islands, but only on the free spaces in-between). To keep
the seeding density of fibroblasts (number of fibroblasts per unit area of free
space available in-between hepatocyte islands) constant, the total area used
for culturing the cells was decreased with decreasing fibroblast numbers ac-
cording to the table. The secretion rate of urea was measured for each culture
condition shown above, and the results found to fit a dose-response curve
which can be described by
μ
PN
P
=
P
KN
max
+
0
+
0.5
where
P
0
and
P
max
are the minimum and maximum urea secretion rates, re-
spectively,
N
is the number of fibroblasts, and
K
0.5
is the number of fibroblasts
to obtain a half-maximal response. For the hepatocyte-fibroblast system, the
parameter values are
P
0
=
23.7 mg/day,
P
max
=
230 mg/day, and
K
0.5
=
4.66
×
10
3
fibroblasts.
Experiment
A
B
C
Fibroblasts seeded
1.5 × 10
6
0.25 × 10
6
0.125 × 10
6
Center-to-center spacing
between hepatocyte islands
1,230
μ
m
650
μ
m
560
μ
m
(a) Estimate the culture area and the
P
value for each experiment shown in the
table above.
