| dc.description.abstract | The tympanic membrane (TM) or eardrum of the ear transfers sound waves into mechanical vibrations in the ossicular chain and into the cochlea. The mechanical properties of the TM play an important role in the sound transmission through the ear. Currently, the mechanical properties for the adult human and animal TM’s are well published. However, it is unclear how age effects the mechanical properties of the TM from young to adult, and there are no published studies on pediatric models of the TM. The goal of this study is to provide the mechanical data of the baboon TM in four different age groups: less than 1 year, 1 – 3 years, 3 – 5 years, and older than 5 years of age or adult. The baboon age can be correlated to human age with a scaling factor of 1:3. With this factor the baboons that are in the first 3 groups correspond to the human pediatric age range of birth to 18 years of age, and the last group corresponds to the adult human population.
The TM specimens were prepared from baboon temporal bones, and cut into rectangle strips before mounting into the dynamic mechanical analyzer (DMA) for quasi-static and dynamic testing. The mechanical properties were obtained by measuring the stress-strain relationship, relaxation function, complex modulus at low frequencies from 1 to 80 Hz, and the failure stress and stretch ratio from young to adult baboon TMs. The adult baboon group, was additionally tested from 1 to 40 Hz at three different temperature levels: 5°C, 25°C, and 37°C. The frequency-temperature superposition (FTS) principle was used to determine complex modulus in the auditory frequency range for the adult baboon TM.
The experimental quasi-static results were further analyzed using the 1st-order hyperelastic Ogden model to derive the constitutive equations and parameters. These parameters were then used to estimate the tangent modulus for each age group of the baboon. The experimental dynamic results were used to obtain the storage and loss moduli for each age group for a frequency range from 1 to 80 Hz, and the adult baboon was obtained for a frequency range from 1 to 8000 Hz. Each baboon age group was compared to each other, and found that as the baboon ages, the stress-strain and the stiffness decreased with age. There was no change in the stress relaxation time for any age group, and there was a slight decrease in the storage and loss moduli for the low frequency range. ANOVA with Tukey-Kraemer statistical analysis was used to detect differences between the age groups, and determined that the mechanical properties of the adults were significantly lower than the younger baboons.
The quasi-static and dynamic experimental data obtained for the adult baboon TM was compared to the published human TM. The baboon average stress-strain relationship was higher than human. The stress relaxation test showed that the baboon relaxed to a higher normalized stress than the human TM. However, the complex modulus over the auditory frequency range determined by the FTS principle showed that the adult baboon’s storage and loss moduli were much lower than the published human data.
The results reported in this study provide a first step towards understanding the age effect on the baboon TM’s mechanical properties from young to adult. | en_US |
