Biomedical Engineering Reference
In-Depth Information
9.4.2
EIS
Figure 9.5A and B
show the Nyquist plots for the bare Ti6Al4V and the TiO
2
nanoparticle-coated Ti6Al4V
alloy in NaCl solution, respectively. The Nyquist plots for the bare Ti6Al4V shows arc-shape, which indi-
cated that the electrochemical corrosion process of bare Ti6Al4V in NaCl solution is an electron-transfer
controlled process. Compared to the bare Ti6Al4V, straight-lines were observed in the Nyquist plots for
TiO
2
nanoparticle-coated Ti6Al4V (
Figure 9.5B
), which indicate that the corrosion process is mass trans-
port (diffusion) controlled. This is different from the bare Ti6Al4V which is an electron-transfer controlled
process.
Bode plots for bare Ti6Al4V and TiO
2
nanoparticle-coated Ti6Al4V are shown in
Figure 9.5C
and D
. It is found that the maximum phase angles of both bare Ti6Al4V and TiO
2
nanoparticle-coated
Ti6Al4V are less than 90° and
n
values are less than 1. However, the shapes of the phase angle plots
are quite different. According to the proposed EIS model, the electrochemical interface of bare Ti6Al4V
in solutions can be described as the equivalent circuit, as shown in
Figure 9.5E
. The impedance data
obtained for bare Ti6Al4V are simulated by a simple R (QR) circuit wherein
R
s
is the solution resistance,
in series with the constant phase element (CPE or Q) and in parallel with the
R
p
, i.e., a simple Randles
equivalent circuit. After the Ti6Al4V substrates were coated with TiO
2
nanoparticles, the modified elec-
trical equivalent circuit (
Figure 9.5F
) used to simulate the measured data were somewhat different from
that used for bare Ti6Al4V (
Figure 9.5E
). Using this oxide layer coating approach,
R
s
corresponds to
the solution resistance,
R
pl
to the resistance of the outer porous layer,
Q
pl
to the capacitance of the outer
porous layer,
R
bl
to the resistance of the barrier layer, and
Q
bl
to the capacitance of the barrier layer. It
is reasonable to introduce an “outer porous layer” to this model due to the nanostructured TiO
2
particle
deposition as well as the formation of oxide layer during the electrochemical corrosion process.
9.5
CONCLUSIONS
Nanoscale modification can alter the chemistry and/or topography of the implant surface. Different
methods have been described to modify or to enhance titanium substrates with nanoscale features.
Such changes alter the implant surface interaction with ions, biomolecules, and cells. These interac-
tions can favorably influence molecular and cellular activities and alter the process of osseointegra-
tion. In this chapter, a nanoscale modification of TiO
2
nanoparticle-coated Ti6Al4V was introduced
in detail. From the results mentioned above, it can be concluded that the TiO
2
nanoparticle-coated-
Ti6Al4V is more corrosion resistant than the bare Ti6Al4V in the simulated biofluids. Furthermore,
Raman microspectroscopy, as a powerful technique to distinguish different crystalline phases by
using Raman mapping spectroscopically, was also discussed. The results show that the temperature
affects anatase to rutile transformation.
References
[1] E.P. Lautenschlager, P. Monaghan, Titanium and titanium alloys as dental materials, Int. Dent. J. 43 (3)
(1993) 245.
[2] R.R. Wang, A. Fenton, Titanium for prosthodontic applications: a review of the literature, Quintessence Int.
27 (6) (1996) 401.
