Biomedical Engineering Reference
In-Depth Information
Fig. 6
Characteristic stress and strain data versus degradation time in non-degraded samples
(
T
5-34 days): (
a
) Maximum stress,
σ
max
, and correspond-
ing strain,
ε
max
, versus degradation time; (
b
)Stress
σ
20 %
,i
of the five initial loading cycles (
i
=
0 days) and degraded samples (
T
=
=
1
to 5) and the final loading (
i
6) versus degradation time; (
c
) Ratio of stress at 20 % strain of final
loading to stress at 20 % strain of first cycle,
σ
20 %
,
6
/σ
20 %
,
1
, versus degradation time
=
Figure
7
shows the elastic modulus,
E
ε,i
, plotted against strain
ε
for the first
and sixth loading for all degradation time points
T
. During the first cycle, the
elastic modulus exhibited an initial increase with increasing strain but decreased
after reaching a maximum between
ε
=
4 and 8 %, irrespective of the degrada-
tion period. However, a steady increase of elastic modulus with increasing strain
was typically observed during the sixth loading. Overall, the key values of the
elastic modulus for the first loading were
E
0%
,
1
=
0
.
48
±
0
.
35 MPa,
E
8%
,
1
=
±
0
.
22 MPa and
E
18 %
,
1
=
±
0
.
92
0
.
67
0
.
29 MPa compared to the values during
the sixth loading of
E
0%
,
6
=
0
.
19
±
0
.
19 MPa,
E
8%
,
6
=
0
.
58
±
0
.
35 MPa and
E
18 %
,
6
=
0
.
42 MPa (all values are grand means over all degradation time
points). The maximum elastic modulus during the first and sixth loading,
E
max
,
1
and
E
max
,
6
, respectively, is provided in Table
1
for scaffolds prior to degradation
and for different degradation times points
T
1
.
1
±
5 to 34 days.
2D FFT analysis conducted on SEM micrographs of degraded samples revealed
no difference in fibre alignment between the non-degraded and degraded scaffold.
The fibre surfaces of scaffold samples after 14 and 34 days degradation prior to
mechanical testing are shown in Fig.
8
(a, b). Comparison with micrographs in
Fig.
1
(e, f) indicated that there were no visible differences in surface morphology
between degraded and non-degraded fibres. Figure
8
(c-f) provides scanning elec-
=
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