Measurement of the mechanical properties of the tympanic membrane with a microtension tester.

The mechanical properties of guinea pig and human tympanic membranes were measured by a microtension tester newly developed by us. Guinea pig tympanic membranes were tested under various conditions. When the tensile rate was 4.17 x 10(-4) m.sec-1 fresh specimens were 8.8 times stronger for a tension applied parallel to the radial fibres than for that applied at a right angle to them. No difference in tensile strength was seen when the tension was applied at a right angle to the radial fibres. When the tensile direction was parallel to the radial fibres, the posterior part was stronger than the anterior part. Two human tympanic membranes were measured under formalin fixation. The measured values were calculated into those of the fresh specimens based on the results of the guinea pig material. The adjusted values for fresh human specimens were 2.56 kgf.mm-2 at a right angle to the radial fibres and 3.28 kgf.mm-2 parallel to them. Applying the thin cylinder and shell theory, the breakage pressure of the human tympanic membrane was calculated to be 1.02-22.4 atmospheric pressure.