[Analysis of the breakage process during the measurement of the mechanical strength of guinea pig tympanic membranes].

We analyzed the breakage process of the tympanic membrane in relation to the material mechanics, using the microtesting system which we have reported previously. 111 fresh tympanic membranes from 56 guinea pigs were used. We calculated the stress-strain curve from the load-displacement curve which was obtained in this experiment. In addition, we observed the morphological changes during the breakage process of the tympanic membrane using optical microscope and scanning electron microscope (SEM). We observed multiple notches (small peaks) on the stress-strain curve. The first notch was considered to correspond to the elastic limit of the tympanic membrane. This first notch appeared at the point when the stress was 4.86 MPa and the strain was 0.10. Comparing the stress-strain curve to morphological changes, this notch in the stress-strain curve appeared when the stress suddenly decreased due to a slit on the tympanic membrane. The elastic modulus of the fresh tympanic membrane of guinea pigs was calculated as 5.71 x 10(-2)mN/microns 2. The maximal stress was 18.5 MPa and this value represented the maximal strength of the radial fiber bundles. From these results, we can speculate that from a mechanical point of view, the tympanic membrane of the guinea pig is a combined material consisting of the radial fiber bundles and circular fibers and that at the site of mechanical injury both fibers strengthened their interactions with each other.