Biomedical Engineering Reference
In-Depth Information
and
in vitro
models is that the
in vivo
study is a fully dynamic system,
with body fluids constantly being replenished and the pH of the micro-
environment being much closer to the ambient. The culture medium in
the static
in vitro
model will show a significant change in pH, usually
increasing to about 9 or 10 for a borate glass, which would be toxic to
cells. The ionic concentration of the medium can also be significantly
altered depending on the ratio of glass to media used [7]. Therefore,
in vitro
testing is much more effective in evaluating chemically inert
materials, where the pH and the culture medium content do not change
significantly. Bioreactor systems comprising fluid flow may improve
in
vitro
tests in the near future.
The problem is illustrated in Figure 6.3, which shows the total DNA
of a bone cell line present after four days of growth in cell culture. Static
culture is compared to dynamic culture, although here dynamic culture
was a rocking motion to stimulate movement of ions rather than fluid
flow. An increase in total DNA is an indication of an increase in the
number of active cells. The data show that even rocking the culture had
a significant effect in changing the results. In static culture, the increasing
Static
Dynamic
100
80
**
*
60
**
40
**
20
0
45S5
45S5-B1 45S5-B2
Glass type
45S5-B3
Figure 6.3
Total DNA of bone cells exposed to bioactive glasses in static and
dynamic culture after four days for: silicate-based 45S5 Bioglass; two borosilicate
glasses, 45S5-B1 (one-third of the silica replaced with borate) and 45S5-B2 (two-
thirds of the silica replaced by borate); and a borate glass, 45S5-B3. The * and
** indicate statistically significant differences compared to 45S5 Bioglass. (Data
acquired from Ref. [7].)
