Quantification of tympanic membrane elasticity parameters from in situ point indentation measurements: validation and...

Correct quantitative parameters to describe tympanic membrane elasticity are an important input for realistic modeling of middle ear mechanics. In the past, several attempts have been made to determine tympanic membrane elasticity from tensile experiments on cut-out strips. The strains and stresses in such experiments may be far out of the physiologically relevant range and the elasticity parameters are only partially determined. We developed a setup to determine tympanic membrane elasticity in situ, using a combination of point micro-indentation and Moiré profilometry. The measuring method was tested on latex phantom models of the tympanic membrane, and our results show that the correct parameters can be determined. These parameters were calculated by finite element simulation of the indentation experiment and parameter optimization routines. When the apparatus was used for rabbit tympanic membranes, Moiré profilometry showed that there is no measurable displacement of the manubrium during the small indentations. This result greatly simplifies boundary conditions, as we may regard both the annulus and the manubrium as fixed without having to rely on fixation interventions. The technique allows us to determine linear elastic material parameters of a tympanic membrane in situ. In this way our method takes into account the complex geometry of the membrane, and parameters are obtained in a physiologically relevant range of strain.