Biomedical Engineering Reference
In-Depth Information
Table 7.2-4 Representative examples of high-density bone cell cultivation within 3-D scaffolds
Cell type
Pore size
(mm)
Pore
volume
(%)
Scaffold
thickness
(mm)
Cell
density
(cells/ml)
Observation
a
Rat marrow
300-500
90
1.9
Maximum osseous penetration of 240
82
m
m (day 56)
a
Rat calvaria
150-300
90
1.9
Maximum osseous penetration of 220
40
m
m (day 56)
a
500-710
90
1.9
Maximum osseous penetration of 190
40
m
m (day 56)
9.5 10
7
SaOS-2
187
30
2.5
Preferrential cell growth on scaffold
exterior (day 7)
300-500
b
5.8
b
10
6
c
Rat marrow
78
6
Preferrential cell growth on scaffold
exterior (day 7)
Notes
Refer to the original work for the references.
a
Values of cell density within the scaffold could not be determined from the reference.
b
An average pore diameter of 400 mm was assumed to facilitate model calculations.
c
Reported values for cell and scaffold void volume of 3.5 10
6
and 0.60 cm
2
were used to determine cell density (cells/ml).
and mechanical stimulation, but the basic steps of cell-
culturing processing, regardless of 2-D and 3-D cultures,
involve sufficient nutrient transfer throughout the cul-
ture medium and sufficient removal of waste products
from around the cells. Other important parameters that
must be monitored are oxygen concentration and pH of
the culture medium, as changing these parameters can
have a positive or negative effect on the cell growth.
The spatial organization of cells provides cell-cell
adhesion cues that are important in directing numerous
biological functions, such as embryonic tissue develop-
ment, organ formation, and tissue regeneration. This
spatial organization is necessary for the preservation of
vital cell-cell interactions as well as cell phenotype.
7.2.6.2.1 Serum
As mentioned above, reaction of tissue-engineered con-
structs requires the
in vitro
propagation of human cells to
increase cell numbers. The
in vitro
cell growth can be
stimulated by supplementation of the growth medium
with serum. So far, culture techniques have required the
use of xenobiotic material
7.2.6.2 Cell seeding
Seeding cells into porous scaffolds using autologous or
xenogeneic serum is generally the first step of tissue
engineering. Achieving the optimal cell density and de-
sired cell distribution in scaffolds is a major goal of cell
seeding technologies in tissue engineering. General
seeding requirements for 3-D scaffolds include (a) high
yield to maximize the utilization of donor cells, (b) high
kinetic rate to minimize time in suspension for anchorage-
dependent cells, (c) specially uniform distribution of
attached cells to provide basis for uniform tissue re-
generation, (d) high initial construct cellularity to en-
hance the rate of tissue development, and (e) appropriate
nutrient and oxygen supply to maintain cell viability
during the seeding procedure. Efficiency of cell seeding is
usually low and in many cases cells are found close to the
surface of the scaffold, but not in the interior. In addi-
tion, time-consuming, costly, and physiologically stress-
ful cell seeding and tissue assembly techniques would
become limiting factors in the development of clinically
useful tissue-engineered products.
fetal calf serum (FCS). The
bovine serum has been used as a rich source of mitogens
for cell proliferation. However, there is a risk of viral and/
or prion disease transmission when bovine serum is used
in clinical cell culture. To reduce the risk of disease
transmission, it is preferable to culture cells under
completely defined culture conditions, without any xe-
nobiotic or donor cell material. The ideal medium is one
that contains no xenobiotic products and in which any
mitogens present are recombinant.
The choice of medium for the culture of autologous
cells for clinical use may be at the discretion of the
consultant medical doctors in many countries. Green's
medium that has been in use for some 20 years for cul-
ture of skin cells for patients with burn injuries con-
tains xenobiotic materials. Serum for clinical use
must be sourced from countries such as New Zealand
or Australia, where BSE has not been found to occur. In
d
