University of Antwerp, Laboratory of Biophysics and Biomedical Physics, Groenenborgerlaan 171, 2020, Antwerp, Belgium.
Hear Res. 2020 Mar 1;387:107877. doi: 10.1016/j.heares.2019.107877. Epub 2020 Jan 7.
The eardrum is the primary component of the middle ear and has been extensively investigated in humans. Measuring the displacement and deformation of the eardrum under different quasi-static loading conditions gives insight in its mechanical behavior and is fundamental in determining the material properties of the eardrum. Currently, little is known about the behavior and material properties of eardrums in non-mammals. To explore the mechanical properties of the eardrum in non-mammalian ears, we investigated the quasi-static response of the eardrum of a common lizard: the Tokay gecko (Gekko gecko). The middle ear cavity was pressurized using repetitive linear pressure cycles ranging from -1.5 to 1.5 kPa with pressure change rates of 0.05, 0.1 and 0.2 kPa/s. The resulting shape, displacement and in-plane strain of the eardrum surface were measured using 3D digital image correlation. When middle-ear pressure is negative, the medial displacement of the eardrum is much larger than the displacement observed in mammals; when middle-ear pressure is positive, the lateral displacement is much larger than in mammals, which is not observed in bird single-ossicle ears. Peak-to-peak displacements are about 2.8 mm, which is larger than in any other species measured up to date. The peak-to-peak displacements are at least five times larger than observed in mammals. The pressure-displacement curves show hysteresis, and the energy loss within one pressure cycle increases with increasing pressure rate, contrary to what is observed in rabbit eardrums. The energy lost during a pressure cycle is not constant over the eardrum. Most energy is lost at the region where the eardrum connects to the hearing ossicle. Around this eardrum-ossicle region, a 5% increase in energy loss was observed when pressure change rate was increased from 0.05 kPa/s to 0.2 kPa/s. Other parts of the eardrum showed little increase in the energy loss. The orientation of the in-plane strain on the eardrum was mainly circumferential with strain amplitudes of about +1.5%. The periphery of the measured eardrum surface showed compression instead of stretching and had a different strain orientation. The TM of Gekko gecko shows the highest displacements of all species measured up till now. Our data show the first shape, displacement and deformation measurements on the surface of the eardrum of the gecko and indicate that there could exist a different hysteresis behavior in different species.
鼓膜是中耳的主要组成部分，在人类中耳膜的研究已经非常广泛。测量鼓膜在不同准静态加载条件下的位移和变形，可以深入了解其力学行为，并为确定鼓膜的材料特性提供基础。目前，对于非哺乳动物中耳膜的行为和材料特性知之甚少。为了探索非哺乳动物中耳膜的力学特性，我们研究了常见蜥蜴——蛤蚧（Gekko gecko）的鼓膜的准静态响应。使用重复的线性压力循环，从中耳腔施加压力，范围从-1.5 到 1.5kPa，压力变化率为 0.05、0.1 和 0.2kPa/s。使用 3D 数字图像相关技术测量鼓膜表面的形状、位移和平面内应变。当中耳压力为负时，鼓膜的内侧位移比哺乳动物观察到的位移大得多；当中耳压力为正时，鼓膜的侧向位移比哺乳动物大得多，而鸟类单骨耳则没有观察到这种情况。峰峰值位移约为 2.8mm，比迄今为止测量的任何其他物种都大。峰峰值位移至少是哺乳动物观察到的五倍。压力-位移曲线显示滞后，并且一个压力循环内的能量损失随压力率的增加而增加，这与兔鼓膜的情况相反。在一个压力循环内，能量损失在鼓膜上不是恒定的。大部分能量损失在鼓膜与听小骨连接的区域。在这个鼓膜-听小骨区域，当压力变化率从 0.05kPa/s 增加到 0.2kPa/s 时，能量损失增加了 5%。鼓膜的其他部分能量损失增加很少。鼓膜上平面内应变的方向主要是周向，应变幅度约为+1.5%。测量的鼓膜表面的周边显示压缩而不是拉伸，并且具有不同的应变方向。Gekko gecko 的 TM 显示出迄今为止所有测量物种中最大的位移。我们的数据显示了蛤蚧鼓膜表面的首次形状、位移和变形测量，并表明不同物种可能存在不同的滞后行为。
