B. Murienne - Master Project Thesis - Infoscience - EPFL

4.8 Stretcher calibration
The last step before being able to perform a complete experiment including staining,
imaging, pacing and stretching of the cardiomyocytes was the calibration of the stretchers (see
Materials and methods section). Curves representing the percentage stretch versus the degree of
rotation of the screw-top for both the short and the long axis of the stretchers were obtained, one
of them is shown in Figure 31. The relationship between the percentage stretch and the degree of
rotation of the screw-top appeared to be linear, as expected.
percentage stretch (%)
25
20
15
10
5
-5
S1 short axis 1
S1 long axis 1
S1 short axis 2
S1 long axis 2
S1 short axis 3
S1 long axis 3
S1 short axis 4
S1 long axis 4
Calibration stretcher 1
42
R 2 = 0.9809
R 2 = 0.9928
0
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
angle (degree)
Figure 31. Rotation of the screw-top versus percentage stretch for the long axis (red regression curve) and short
axis (blue regression curve) of stretcher 1.
The stretch applied with such an elliptical stretcher design is homogeneous, except at 2 mm of the
indenter ring [18], anisotropic and is transferred from the substrate to the adherent cells [30].
Finally, a 4%:10% stretch ratio was used in order to be close to the 10%:5% stretch ratio found in
the literature and usually used for cells [18; 47].
4.9 Optical mapping experiments
After all the steps described above were completed, the optical mapping experiments
could finally be performed. The main goal of these experiments was to study the changes in APD
and CV values, in response to anisotropic stretch, in micropatterned cardiomyocyte monolayers.
In these experiments, the cardiomyocytes were cultured either without antibiotics or with
different concentrations of streptomycin. About 10% stretch was applied along the cardiomyocyte