Biomedical Engineering Reference
In-Depth Information
4.6
Cathodic Half-Reaction of Corrosion as the Possible
Source of Oxidative Stress on Ti6Al4V Alloy
Only very few studies have addressed the problem of the cathodic partial reaction of
corrosion simulation in vitro to investigate its effects on the cells involved in the
implant integration process. It was found in electrochemical studies that oxygen
reduction reactions, the main event during cathodic partial reaction of corrosion,
can lead to the formation of H 2 O 2 on TiO 2 surfaces [ 8, 9 ] .
The study by Mentus et al. [ 59 ] provided evidence that this process is driven by
a pH-dependent transition from 2e to 4e reduction of oxygen on anodically formed
TiO 2 in an electrochemical cell that led to the formation of H 2 O 2 and other oxygen
radicals as intermediate products. It also showed that oxygen reduction reactions
can occur on TiO 2 at any pH value without any particular activation.
To examine the effects of cathodic polarisation products on cellular functions an
experimental set-up was developed in which Ti6Al4V discs with cultivated cells
were cathodically polarised by applying electrical current to the system [ 39 ] . It was
demonstrated that endothelial cells grown on Ti6Al4V alloy display the reduction
of metabolic activity with increasing current densities applied to Ti6Al4V samples
[ 88 ]. This was in agreement with lower metabolic activity of HDMEC grown on
Ti6Al4V compared to the cells on PS and the further decrease induced by H 2 O 2 .
While lower charge densities (current density per square of metal surface) had no
visible effects, higher charge densities induced adverse effects (Fig. 4.7 ).
160
1 h
140
24 h
120
72 h
100
80
60
40
20
0
0
250
500
750
Charge density (mC/cm 2 )
Fig. 4.7 The effect of cathodical partial reaction of corrosion on viability of HDMEC. Metabolic
activity of HDMEC on Ti6Al4V was measured with MTS conversion assay after Ti6Al4V cathodi-
cal polarisation for 1, 24 or 72. Dependency of MTS conversion in HDMEC on charge density
applied to Ti6Al4V (untreated HDMEC are set as 100 %)
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