Biomedical Engineering Reference
In-Depth Information
Fig. 4.9
Evaluation of ROS
formation in HDMEC grown
on Ti6Al4V polarised for
24 h. ROS production was
assessed with the DCF assay
(DCF fl uorescence in
untreated cells was set as 1)
12
10
8
6
4
2
0
0
-2.5
-15
Current density (
μ
A/cm
2
)
higher current densities are applied. This could be excluded, since the current
densities used in this study were below oxygen diffusion current density, which is
approximately −30 mA/cm² in unstirred air-saturated aqueous electrolytes [
80
] .
Additionally, interactions of the electric field occurring during polarisation with
electric properties of cell membranes and electric field-induced changes in the
conformation of proteins absorbed to the polarised surface are poorly studied
phenomena and can also play their role in the reduction of cell viability in the
used model. Electric fields have been shown to direct cell migration during wound
healing processes [
100
] .
Interestingly, similar results were obtained in the same model of cathodic
polarisation with osteoblastic and macrophage cell lines. Cathodic polarisation
of Ti6Al4V alloy induced current density-dependent reduction in cellular meta-
bolic activity that coincided with increased ROS formation and changes in cell
morphology. While the reactions of osteoblasts were comparable to H
2
O
2
treat-
ment on Ti6Al4V alloy done in parallel, macrophages were more resistant to
H
2
O
2
[
39
] .
This in vitro model, which allows the exposure of cultivated cells to cathodic
corrosion products without distortive effects by anodic reactions/reaction products,
offers the possibility to study direct influence of ROS formed at the metal surface
on cellular viability and functions. Using current densities that induce production
of ROS amounts similar to the in vivo situation could deepen our knowledge about
the contribution of the cathodic partial reaction of corrosion to metal-induced
adverse tissue reactions. However, the origin and nature of oxidative stress at the
metal implant surface has to be considered as a multifactorial process, in which the
effects of H
2
O
2
and ROS formed on titanium alloy surface may be augmented by
ROS derived from inflammatory cells. The possibility of H
2
O
2
interaction with the
TiO
2
layer, leading to the formation of further ROS, makes the process even more
complicated. Upon debris formation damage to the TiO
2
layer occurs, which can
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