Biomedical Engineering Reference
In-Depth Information
To examine the effects of H
2
O
2
on the phenotype of endothelial cells H
2
O
2
was added for 24 h to HDMEC growing on PS and Ti6Al4V alloy. 0.5 mM
H
2
O
2
did not induce marked changes in the phenotype of HDMEC on PS
(Fig.
4.4
). The cells retained their spindle-like shape, organised alignment and
the degree of confluence. HDMEC grown on Ti6Al4V alloy appeared to be more
in fl uenced by H
2
O
2
. The alignment of the cells became more disordered, most
of the cells lost the spindle-like shape and appeared rounded, and the amount
and the size of the gaps in the cell monolayer increased. In general this points to
the higher toxicity of H
2
O
2
to HDMEC grown on Ti6Al4V alloy, compared to
HDMEC on PS.
As already mentioned, H
2
O
2
can induce oxidative stress in endothelial cells
by promoting ROS formation. This is achieved by several mechanisms, includ-
ing activation of ROS production by mitochondria, NADPH oxidases, xanthine
oxidase, uncoupled eNOS, etc. [
6
] . H
2
O
2
in the cell can also undergo the Fenton
reaction in the presence of metal ions, resulting in the formation of highly toxic
hydroxyl radicals. Using the DCF-assay higher levels of ROS was observed in
endothelial cells grown on Ti6Al4V alloy 1 h after H
2
O
2
addition compared to
the cells on PS [
87
]. DCF is the resulting oxidation product from DCDHF,
which is oxidised by peroxyl radical, peroxynitrite and also H
2
O
2
[
25
] .
Therefore, increases in DCF-fluorescence can be explained through oxidation
by H
2
O
2
, which enters the cell. However, since the H
2
O
2
concentration remain-
ing in the medium 1 h after its addition is nearly similar on both materials the
higher DCF-fluorescence in cells grown on Ti6Al4V alloy might reflect further
ROS production. One possible explanation for this could be the formation of
ROS due to the reactivity of H
2
O
2
with the TiO
2
layer. A study by Lee et al. [
44
]
showed that
·
OH were formed during the interaction of TiO
2
and H
2
O
2
in vitro,
while UV-irradiated TiO
2
reacting with H
2
O
2
could produce
·
O
2
−. Other stud-
ies, on the contrary, demonstrate no formation of
·
OH in the reaction between
H
2
O
2
and TiO
2
[
84,
85
]. Tengvall et al. suggested that a Ti-peroxy gel is formed
as a result of the interaction of Ti with H
2
O
2
[
85
]. This gel is believed to trap
·
O
2
− [
84
]. Interestingly, in the absence of serum, Ti-peroxy gels could decrease
ROS production by activated leukocytes [
43
]. Opposite effects of Ti-peroxy gel
were also reported. Thus, while the TiO
2
layer was acting as a scavenger for
·
OH, the Ti-peroxy gel could amplify detrimental effects of
·
OH on ECM pro-
teins, as well as cause these effects alone in vitro [
83
]. High amounts of H
2
O
2
are needed to produce Ti-peroxy gel in vitro. Such conditions are probably
unachievable in vivo, although the formation of Ti-peroxy gel and trapping of
radicals could hypothetically contribute to the tissue reactions to the implant
over longer time periods. This may also be a reason for a relatively better per-
formance of Ti materials compared to other metal materials. However, higher
ROS formation in HDMEC on Ti6Al4V alloy shown in this study favours the
interaction of H
2
O
2
with the TiO
2
layer on the alloy surface. It is also known
that traces of iron are present in titanium alloys (according to ASTM F136
Ti6Al4V is allowed to have up to 0.2 % Fe). The presence of iron in titanium
Search WWH ::
Custom Search