Biomedical Engineering Reference
In-Depth Information
TABLE 11.2. Release Test of B io - S i C (mg/l)
Element
SBF
Beech
Sapelly
Eucalyplus
Al
0.014
0.007
0.005
0.004
Ca
93
104
97.8
86.4
Cu
0.01
0.375
0.097
0.166
F e
<
0.005
<
0.005
<
0.005
<
0.005
P
37.1
32.4
33.8
32.3
S
4.62
6.33
5.3
4.5
Si
0.369
5.76
4.69
0.829
T i
< 0.005
< 0.005
< 0.005
< 0.005
2004 ]. The elements identifi ed by both techniques are marked in grey. The mea-
surements reveal the majority presence of Si and C. Small amounts of Ca were
found in all samples and, in some cases, Al, Cu and Na. Other trace elements were
also identifi ed in very low concentrations.
The biocompatible behaviour of this material has been tested by soaking the
SiC ceramics in Simulated Body Fluid. Table 11.2 shows the ICP-MS analyses of
the SBF fl uids after one-week immersion of the Bio-SiC materials [González,
2004]. The SBF element concentrations used as reference values are also shown.
Only weak signals related to the release of Si and Cu until reaching concentration
values in the order of ppm were observed. Most of the elements remain unchanged
within experimental error. Therefore, it can be concluded that no important dis-
solution rate of these materials is observed and no adverse physiological effects
in the body are expected.
The biomorphic SiC selected to be used as medical implant must have
microstructural features similar to the ones of the cortical bones. In particular it
will be important and adequate partial pore orientation and porous continuity;
suffi cient pore volume (typically 50% to 70%); micropores of approximately
10
μ
m in diameter for cell adhesion; macropores with diameters larger than
100
m for cell penetration, tissue ingrowth, and vascularisation [Gauthier 1998,
Black 1998]. The bimodal hard woods microstructures are very promising because
they can fulfi l these requirements, in particular the beech, sapelly and eucalyptus
precursors.
μ
11.3.3 Reaction-Formation Mechanisms
Molten Si infi ltrates into the porous preform by effect of the capillary pressure
[Bhagat, 1994 ; Gern, 1997 ; Greil, 2001 ; Sangsuwan, 1999 ]. Jurin ' s law establishes
that the maximum height a liquid can penetrate inside a capillary is:
2
σθ
ρ
cos
h
=
(11.3)
max
rg
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