Biomedical Engineering Reference
In-Depth Information
10
8
6
4
2
0
0
4
8
12
16
Applied Normal Stress (Incipient) (kPa)
Figure 4.6
Yield locus and Mohr's circles of studied sodium
hyaluronate powder (measured at 24 °C). Determined parameters:
cohesion = 1.41 kPa; unconfined yield strength s
c
= 5.08 kPa;
major principal stress s
1
= 16.4 kPa; friction coefficient
ff
c
= 3.24;
angle of internal friction j = 31.9 °; and effective angle of internal
friction j
e
= 40.75°
4.4 Conclusions
For the sodium hyaluronate powder studied, the surface coverage
dependence of the surface energy was found to be dominated by the
dispersive energy part, thus indicating the low polarity character of
the material. For 0% coverage, 30 mJ/m
2
total surface energy was
found. The surface structure of the studied polymer powder was
found to be relatively inhomogeneous as reflected in the three-fold
higher energy content for the highest energy sites (at 0% surface
coverage) in comparison to the lowest energy sites as observed for
100% coverage (11.7 mJ/m
2
). The total surface energy distribution
ranged from 10 to 34 mJ/m
2
with a maximum at 18.5 mJ/m
2
.
The major component of the total surface energy with respect to the
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