Biomedical Engineering Reference
In-Depth Information
1500
1400
1300
1200
300
Sample #1 (0.63x10
−
2
Pa)
200
Sample #2 (0.93x10
−
2
Pa)
100
Sample #4 (1.7x10
−
2
Pa)
Sample #5 (2.7x10
−
2
Pa)
0
20
30
40
50
60
70
80
90
2
(
°
)
FIGURE 19.47
XRD patterns of the as-deposited titanium oxide fi lms. (From Leng, Y.X. et al.,
Surf. Coat-
ing Tech
., 156, 295, 2002. With permission.)
parameters. The fi lms were subsequently annealed
in situ
at 700°C for 60 min and then 750°C
for 30 min at a base pressure of 1.5
10
-
3
Pa. The annealing apparatus comprised a resistively
×
heated quartz tube.
The fi lm is polycrystalline with coexisting Ti
2
+
, Ti
3
+
, and Ti
4
+
. The intensity of the (101) and
(110) diffraction peaks goes up while that of the (002) diffraction peak diminishes with increas-
ing oxygen partial pressure, as shown in Figure 19.47 [133]. Hence, Leng et al. [133] conclude that
the growth on the (110) plane parallel to the surface becomes more dominant at higher oxygen
partial pressure. The microhardness values obtained from TiO
2
shown in Figure 19.48 increase
with oxygen partial pressure between 0 and 1.7
10
-
2
Pa.
In vitro
blood compatibility investigation
indicates that the TiO
2
fi lm has longer clotting time, lower hemolytic rate, less amounts of adherent
platelets, less aggregation, and less pseudopodium of the adherent platelet [133].
In vivo
tests also
demonstrate that the TiO
2
fi lm has much better hemocompatibility than LTIC [179], as shown in
Figure 19.49.
To improve the mechanical properties, Leng et al. fabricate Ti
×
Ti-N duplex coatings
on biomedical titanium alloys by metal PIII and reactive plasma nitriding / oxidation [180]. The
presence of Ti
-
Ti-O/ Ti
-
-
Ti-O improves the blood compatibility and the main effect of Ti
-
Ti-N is to improve
the mechanical properties. Blood compatibility investigation reveals that the Ti
Ti-N duplex
coatings are better than LTIC. In addition, tantalum nitride fi lms with excellent mechanical and
biomedical properties have been synthesized using a similar method [181]. Chen et al. prepared tan-
talum-doped Ti
-
Ti-O/ Ti
-
Ti-N and obtained good mechanical property and blood compatibility results
[182]. Studies have shown that TiO
2
has good blood compatibility due to the n-type semiconductiv-
ity with a wider band gap of 3.2 eV, low surface energy, and low critical surface force. The good
surface physical properties preclude fi brinogen from denaturation and consequently prevent the
blood coagulation process [166,170,183,184]. The blood-biomaterial interfacial tension γ
s
.
blood
can
infl uence the denaturing or distortion of fi brinogen. Furthermore, the activation of fi brinogen on the
solid surface can be correlated with the electrochemical reaction between the protein and material
-
Ti-O/ Ti
-
