Biomedical Engineering Reference
In-Depth Information
Medullary cavity
Load
Electrode
(a)
(b)
FIGURE 9.9
(a) The geometry of the sample; (b) three-point test.
TABLE 9.2
Size of Samples
Span (mm)
Width (mm)
Height (mm)
85
4.0 ± 1.0
19 ± 3.0
of 10
10
Ω [29]. Then, the conductive silver adhesive (5001, SPI, United States)
was painted on both sides of each specimen as electrodes with dimensions
of 3 mm × 3 mm (Figure 9.9b). After the electrodes was painted, the samples
were kept in an environment with relative humidity of 52%-56% and tem-
perature of 22°C-25°C. The two electrodes were placed in the same axial
position and at the same mid-height from the neutral axes of the samples,
where the bone samples are subjected to both normal stress and shear stress.
9.4.2 Experimental Setup
The principle of the experimental setup was as follows [4]. It was noted that
the pair of electrodes and the bone tissue sandwiched between them were
equivalent to a capacitor; C was defined as its capacitance [29,30]. Once the
piezoelectric charge Q was induced by the load accumulating on the elec-
trodes, a corresponding piezovoltage V (V = CQ) could be observed. Because
piezovoltage is a linear function of piezocharge, the variation of the volt-
age is consistent with that of the charge. Based on this principle, Hou et al.
designed the experimental setup of the measurement system [4] as illustrated
in Figure 9.10. It can be seen from this figure that the electrode on the lateral
side facing the medullary cavity (Figure 9.9) was taken as zero potential (or
reference potential). The measured piezovoltage was input into a bioamplifier
