Constitutive Effects of Hydrolytic Degradation in Electro-Spun Polyester-Urethane Scaffolds for Soft Tissue Regeneration - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 55

Fig. 4 Cumulative loss of
mass, as a percentage of the
original sample mass at
T 0 days, versus the

degradation time

=

2.4 Physical Characterisation

The scaffold mass (Mettler Toledo XS105S analytical balance, Mettler Toledo,
Greifensee, Switzerland) did not change significantly due to degradation. Figure 4
shows the cumulative loss of mass as a percentage of the original sample mass at
T = 0 days. The largest loss of mass was observed between T = 5 and 10 days, in-

creasing from 0 . 04 0 . 45 %, while it remained at that level there-

after. (For all quantitative data, one-way ANOVA was performed when more than
two groups were compared by using Tukey HSD post-hoc analysis with p< 0 . 05
indicating statistical significance. Data are expressed as mean values

± 0 . 08 % to 0 . 54 ±

± standard

deviation.)
Tensile testing was performed on dry samples at room temperature on an In-
stron 5544 universal testing machine (Instron, Norwood, USA) using custom made
clamps. The width and length of the tensile test samples was 9 . 69

± 0 . 21 mm by

18 . 47 0 . 31 mm. The test protocol com-

prised five pre-cycles (0 to 20 % strain, 20 mm / min crosshead speed, data sampling
at 0.1 % strain intervals) and a final extension until complete failure (20 mm / min
crosshead speed data sampling at 0.1 % strain intervals). The data recorded were
maximum stress σ max and the associated strain ε max , the stress at the upper strain
limit of ε

± 2 . 62 mm and the gauge length was 10 . 40 ±

20 % of each load cycle, σ 20 % ,i , where i denotes the number of the
load cycle with i

=

= 1 to 5, and the stress at ε = 20 % of the final loading, σ 20 % ,i ,

with i 6. The change in stress associated with cycling was expressed as the ra-

tio, σ 20 % , 6 /σ 20 % , 1 , of the stress at ε

=

20 % during the final and the first loading.
The elastic modulus was determined as the slope of the stress-strain curves for the
first and the final loading at discrete strain values, E ε,i , where ε refers to the strain
value with ε

=

=

0, 4, 8, 12, 16 and 18 %, and i refers to the number of the loading

with i 1 and 6. After smoothing of the stress-strain data (moving average filter,

half-width: 3), the slope was calculated for the strain range [ ε −

=

0 . 1%]
and filtered (moving average filter, half-width: 5). This procedure resulted in elastic
modulus values averaged over a range of [ ε

0 . 1%, ε +

− 0 . 9%, ε + 0 . 9 %] for each discrete