b2815 Tissue Engineering and Nanotheranostics “9.61x6.69”36 Tissue Engineering and Nanotheranostics
The samples were initially loaded to 5 N prior to the cyclic tests,
and 5–30 N (Cycle 1) was considered as the normal physiological load-
ing range, whereas 5–60 N (Cycle 2) was taken as the physiological
loading limit. Cycle 3 was also carried out between 5 N and 30 N. The
stiffness was calculated as the slope of loading curve of the 10th cycle.^13
Results from cyclic testing show that the stiffness increased with suc-
cessive loading cycles, which suggests strain hardening in the material
(Table 1). A considerable increase in C1 and C2 values is visible for all
three directions, hinting at the possibility of strain hardening at the
physiological loading limit, experienced during extreme pressure varia-
tion.^13 Studying the effects of cyclic loading after exposure to phos-
phate buffered saline (at 37°C) for time of intended implantation
would provide a more accurate understanding of the stiffness response
and strain hardening of the polymer.
Failure tests were conducted on three samples from each of the
three directions, where each sample was elongated to failure at
1 mm/s using a 1 kN load cell (Fig. 5).^13 The stiffest response was
unveiled by samples loaded in 90° direction, whereas the 0° direction
proved to be the most compliant. Results of failure tests clearly high-
light the anisotropic variation of the meshes, which needs to be exam-
ined in greater detail by biaxial tests.^13
In totality, Li and coworkers did an excellent job of failure analy-
sis and cyclic testing for patches, to mimic real-time conditions. As
the abdominal pressures carry weightage while designing a patch for
hernia repair, similarly the patches used for fetal surgeries need to be
designed taking into account the growth of the fetus. The patch
should have optimal elastic properties to accommodate radial stretch-
ing due to fetal growth over a period of few months.
Table 1. Stiffness values for cyclic testing in 0°, 45° and 90° directions.Direction Stiffness C1 (MPa) Stiffness C2 (MPa) Stiffness C3 (MPa)
0° 14.17 21.72 20.05
45° 17.47 26.62 25.75
90° 21.23 26.19 26.43