Mechanical properties of human tympanic membrane in the quasi-static regime from in situ point indentation measurements.
ABSTRACT The tympanic membrane is a key component of the human auditory apparatus. Good estimates of tympanic membrane mechanical properties are important to obtain realistic models of middle ear mechanics. Current literature values are almost all derived from direct mechanical tests on cut-out strips. For a biomedical specimen like the tympanic membrane, it is not always possible to harvest strips of uniform and manageable geometry and well-defined size suitable for such mechanical tests. In this work, elastic and viscoelastic properties of human tympanic membrane were determined through indentation testing on the tympanic membrane in situ. Indentation experiments were performed on three specimens with a custom-built apparatus that was also used in previously published works. Two types of indentation tests were performed on each specimen: (i) sinusoidal indentation at 0.2 Hz yielding the quasi-static Young's modulus and (ii) step indentation tests yielding viscoelastic properties in the quasi-static regime (0-20 Hz). In the cyclic indentation experiments (type i), the indentation depth and resulting needle force were recorded. The unloaded shape of the tympanic membrane and the membrane thickness were measured and used to create a specimen-specific finite element model of the experiment. The Young's modulus was then found through optimization of the error between model and experimental data; the values that were found for the three different samples are 2.1 MPa, 4.4 MPa and 2.3 MPa. A sensitivity analysis showed that these values are very sensitive to the thickness used in the models. In the step indentation tests (type ii), force relaxation was measured during 120 s and the relaxation curves were fitted with a 5 parameter Maxwell viscoelastic model. The relaxation curves in the time domain were transformed to complex moduli in the frequency domain, yielding viscoelastic properties in the quasi-static regime only.
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ABSTRACT: The full-field thickness distribution, three-dimensional surface model and general morphological data of six human tympanic membranes are presented. Cross-sectional images were taken perpendicular through the membranes using a high-resolution optical coherence tomography setup. Five normal membranes and one membrane containing a pathological site are included in this study. The thickness varies strongly across each membrane, and a great deal of inter-specimen variability can be seen in the measurement results, though all membranes show similar features in their respective relative thickness distributions. Mean thickness values across the pars tensa ranged between 79 and 97 μm; all membranes were thinnest in the central region between umbo and annular ring (50-70 μm), and thickness increased steeply over a small distance to approximately 100-120 μm when moving from the central region either towards the peripheral rim of the pars tensa or towards the manubrium. Furthermore, a local thickening was noticed in the antero-inferior quadrant of the membranes, and a strong linear correlation was observed between inferior-posterior length and mean thickness of the membrane. These features were combined into a single three-dimensional model to form an averaged representation of the human tympanic membrane. 3D reconstruction of the pathological tympanic membrane shows a structural atrophy with retraction pocket in the inferior portion of the pars tensa. The change of form at the pathological site of the membrane corresponds well with the decreased thickness values that can be measured there.Journal of the Association for Research in Otolaryngology 05/2013; · 2.95 Impact Factor
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ABSTRACT: The human tympanic membrane (TM) transfers sound in the ear canal into the mechanical vibration of the ossicles in the middle ear. The dynamic properties of TM directly affect the middle ear transfer function. The static or quasi-static mechanical properties of TM were reported in the literature, but the dynamic properties of TM over the auditory frequency range are very limited. In this paper, a new method was developed to measure the dynamic properties of human TM using the Dynamic-Mechanical Analyzer (DMA). The test was conducted at the frequency range of 1-40 Hz at three different temperatures: 5, 25, and 37 °C. The frequency-temperature superposition was applied to extend the testing frequency range to a much higher level (at least 3800 Hz). The generalized linear solid model was employed to describe the constitutive relation of the TM. The storage modulus E' and the loss modulus E″ were obtained from 11 specimens. The mean storage modulus was 15.1 MPa at 1 Hz and 27.6 MPa at 3800 Hz. The mean loss modulus was 0.28 MPa at 1 Hz and 4.1 MPa at 3800 Hz. The results show that the frequency-temperature superposition is a feasible approach to study the dynamic properties of the ear soft tissues. The dynamic properties of human TM obtained in this study provide a better description of the damping behavior of ear tissues. The properties can be transferred into the finite element model of the human ear to replace the Rayleigh type damping. The data reported here contribute to the biomechanics of the middle ear and improve the accuracy of the FE model for the human ear.Annals of Biomedical Engineering 07/2012; · 3.23 Impact Factor
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ABSTRACT: A new anatomically-accurate Finite Element (FE) model of the tympanic membrane (TM) and malleus was combined with measurements of the sound-induced motion of the TM surface and the bony manubrium, in an isolated TM–malleus preparation. Using the results, we were able to address two issues related to how sound is coupled to the ossicular chain: (i) Estimate the viscous damping within the tympanic membrane itself, the presence of which may help smooth the broadband response of a potentially highly resonant TM, and (ii) Investigate the function of a peculiar feature of human middle-ear anatomy, the thin mucosal epithelial fold that couples the mid part of the human manubrium to the TM. Sound induced motions of the surface of ex vivo human eardrums and mallei were measured with stroboscopic holography, which yields maps of the amplitude and phase of the displacement of the entire membrane surface at selected frequencies. The results of these measurements were similar, but not identical to measurements made in intact ears. The holography measurements were complemented by laser-Doppler vibrometer measurements of sound-induced umbo velocity, which were made with fine-frequency resolution. Comparisons of these measurements to predictions from a new anatomically accurate FE model with varied membrane characteristics suggest the TM contains viscous elements, which provide relatively low damping, and that the epithelial fold that connects the central section of the human manubrium to the TM only loosely couples the TM to the manubrium. The laser-Doppler measurements in two preparations also suggested the presence of significant variation in the complex modulus of the TM between specimens. Some animations illustrating the model results are available at our website (www.uantwerp.be/en/rg/bimef/downloads/tympanic-membrane-motion).Hearing research 01/2014; · 2.18 Impact Factor