Biomedical Engineering Reference
In-Depth Information
Fig. 4.3
Dose response of
HDMEC grown on PS and
Ti6Al4V to H
2
O
2
treatment.
MTS conversion was
measured 24 h after H
2
O
2
addition (means ± SDs;
untreated control on PS set
as 100 %)
fi broblasts that H
2
O
2
concentrations between 0.12 and 0.4 mM led to growth arrest,
whereas higher H
2
O
2
concentrations induced cell death via apoptosis (0.5-1.0 mM)
or necrosis (5.0-10.0 mM) (reviewed in [
12
] ). Low H
2
O
2
concentrations (<0.05 mM)
were also shown to inhibit proliferation in endothelial cells [
14
] . The discrepancy
in cell number and proliferation ability of HDMEC on Ti6Al4V could possibly
be explained by the higher initial attachment of endothelial cells to Ti6Al4V alloy.
In fact, it was demonstrated that osteoblasts attach to Ti6Al4V alloy in higher
numbers compared to PS, which correlated with a better cell spreading [
79
] .
Another study, however, showed opposite results for epithelial cells [
77
] . The initially
higher number of HDMEC on Ti6Al4V could gradually be reduced as a result
of slower proliferation and possible higher cytotoxicity leading to the equal cell
numbers on Ti6Al4V and PS at the measurement time point.
The LDH-release cytotoxicity assay revealed a concentration-dependent increase
of LDH release from HDMEC after H
2
O
2
treatment [
87
]. The LDH release indicates
damage of the cell membrane, a characteristic feature of necrotic cell death.
Moreover, the LDH release was higher in cells grown on Ti6Al4V alloy compared
to those in contact with PS. Another indication for a higher degree of cytotoxicity,
the reduction of cellular metabolic activity (determined by the MTS viability assay
which mirrors the energy metabolic state, e.g. the development of NADH), was also
observed after H
2
O
2
treatment. While the H
2
O
2
concentrations tested did not induce
major changes in the metabolic activity of HDMEC grown on PS, they significantly
decreased MTS conversion in the cells grown on the Ti6Al4V alloy (Fig.
4.3
).
Importantly, even the basic MTS conversion rates (i.e. in cells not treated with
H
2
O
2
) were lower in the cells grown on Ti6Al4V alloy compared to the cells grown
on PS. It has been shown that oxidative stress induced by H
2
O
2
treatment can lead
to a rapid depletion of NADH and ATP due to an increased catabolic rate [
74
] . Thus,
the reduction of metabolic activity in cells grown on Ti6Al4V could be a result of
H
2
O
2
-induced oxidative stress. However, this does not explain the absence of metabolic
reduction of cells in contact with PS. It is possible that compensatory mechanisms
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