Don Nakmali

Mechanical Properties of Stapedial Annular Ligament

Stapedial annular ligament (SAL) provides a sealed but mobile boundary between the stapes footplate and oval window bony wall. Mechanical properties of the SAL affect the transmission of ossicular movement into the cochlea in sound conduction. However, the mechanical properties of this tissue have never been investigated due to its complexity. In this paper, we report measurement of the viscoelastic properties of SAL on human cadaver temporal bones using a micro-material testing system with digital image correlation analysis. The measured load-deformation relations of SAL samples were converted into shear stress-shear strain relationship, stress relaxation function, and ultimate shear stress and shear strain of the SAL. The hyperelastic Ogden model was used to describe constitutive behavior of the SAL and a 3D finite element model of the experimental setup with SAL was created for assessing the effects of loading variation and measurement errors on results. The study demonstrates that the human SAL is a typical viscoelastic material with hysteresis, nonlinear stress-strain relationship and stress relaxation function. The shear modulus changes from 3.6 to 220 kPa when the shear stress increases from 2 to 140 kPa. These results provide useful information on quasi-static behavior of the SAL.

A totally implantable hearing system – Design and function characterization in 3D computational model and temporal bones ☆

Implantable middle ear hearing devices are emerging as an effective technology for patients with mild to moderately severe sensorineural hearing loss. Several devices with electromagnetic or piezoelectric transducers have been investigated or developed in the US and Europe since 1990. This paper reports a totally implantable hearing system (TIHS) currently under investigation in Oklahoma. The TIHS consists of implant transducer (magnet), implantable coil and microphone, DSP-audio signal processor, rechargeable battery, and remote control unit. The design of TIHS is based on a 3D finite element model of the human ear and the analysis of electromagnetic coupling of the transducer. Function of the TIHS is characterized over the auditory frequency range in three aspects: (1) mass loading effect on residual hearing with a passive implant, (2) efficiency of electromagnetic coupling between the implanted coil and magnet, and (3) functional gain of whole unit in response to acoustic input across the human skin. This paper focuses on mass loading effect and the efficiency of electromagnetic coupling of TIHS determined from the FE model of the human ear and the cadaver ears or temporal bones. Some preliminary data of whole unit function are also presented in the paper.

Mechanical Properties of a Human Eardrum at High Strain Rates After Exposure to Blast Waves

The mechanical properties of a human tympanic membrane (TM) or eardrum were characterized at high strain rates after multiple exposures to blast waves. Human cadaveric temporal bones were subjected to blast waves at first, then TM strip specimens were prepared either along the radial or the circumferential direction. A highly sensitive miniature split Hopkinson tension bar was used for tensile experiments on the human eardrum strip specimens at high strain rates. The mechanical properties of the human TMs before and after exposure to blast waves were compared and discussed. The mechanical properties in the time-domain were subsequently converted to the corresponding properties in the frequency domain to investigate the effect of blast waves on the viscoelastic properties. The results indicate that the blast waves have different effects on the mechanical properties in the radial and circumferential directions. After exposure to the overpressure induced by the blast waves, the mechanical behavior in the radial direction in general becomes stiffened, while it is weakened in the circumferential direction. The results could be analyzed further in an ear simulation model to develop understanding of the effect of blast waves on hearing loss.

Complex modulus of round window membrane over auditory frequencies in normal and otitis media chinchilla ears

To better reveal the mechanical properties of round window membrane (RWM) in normal and pathological ears, the complex modulus of chinchilla RWM was determined by measuring its dynamic behaviour together with the finite element simulation. The acute otitis media (AOM) was created by transbullar injection of Haemophilus influenzae in chinchillas and RWM specimens in AOM ears were prepared four days post inoculation. Vibration of the RWM induced by coil-magnet force stimulation was measured by laser Doppler vibrometry over frequencies of 0.2–8 kHz. A finite element model-based inverse-problem solving method was used to determine the complex modulus of each RWM specimen in the frequency domain. Experimental results of the AOM ears indicated that the resonance frequency decreased by 13.94% compared with the normal ears and the mean storage modulus and loss modulus were decreased by 65% and 32%, respectively.

EFFECTS OF MIDDLE EAR SUSPENSORY LIGAMENTS ON ACOUSTIC-MECHANICAL TRANSMISSION IN HUMAN EAR

Two laser vibrometers were used to measure simultaneously the movement of the tympanic membrane and stapes footplate in human temporal bones. After control study of the normal ear, the stapedial tendon, posterior incudal ligament, tensor tympani tendon, and superior malleus/incus ligament were sectioned sequentially. The displacements of the umbo and footplate were measured repeatedly for each section. A 3-D finite element model of human ear which has accurate anatomic structure was used to mimic the middle ear structure changes and to derive the umbo and footplate vibrations in response to those alterations. The results show that the effects of ligaments on transfer function of the middle ear are frequency sensitive and vary with individual ligament.

Biomechanical Measurement and Modeling of Human Eardrum Injury in Relation to Blast Wave Direction

Rupture of the eardrum or tympanic membrane (TM) is one of the most frequent injuries of the ear after blast exposure. To understand how the TM damage is related to blast wave direction, human cadaver ears were exposed to blast waves along three directions: vertical, horizontal, and front with respect to the head. Blast overpressure waveforms were recorded at the ear canal entrance (P0), near the TM (P1), and inside the middle ear (P2). Thirteen to fourteen cadaver ears were tested in each wave direction and the TM rupture thresholds were identified. Results show that blast wave direction affected the peak P1/P0 ratio, TM rupture threshold, and energy flux distribution over frequencies. The front wave resulted in lowest TM rupture threshold and the horizontal wave resulted in highest P1/P0 ratio. To investigate the mechanisms of TM injury in relation to blast wave direction, the recorded P1 waveforms were applied onto the surface of the TM in a three-dimensional finite element model of the human ear and distributions of the stress in TM were calculated. Modeling results indicate that the sensitivity of TM stress change with respect to P1 pressure (dσ/dP1) may characterize mechanical damage of the TM in relation to blast waves.

Computational Modeling of Blast Wave Transmission Through Human Ear

Hearing loss has become the most common disability among veterans. Understanding how blast waves propagate through the human ear is a necessary step in the development of effective hearing protection devices (HPDs). This article presents the first 3D finite element (FE) model of the human ear to simulate blast wave transmission through the ear. The 3D FE model of the human ear consisting of the ear canal, tympanic membrane, ossicular chain, and middle ear cavity was imported into ANSYS Workbench for coupled fluid-structure interaction analysis in the time domain. Blast pressure waveforms recorded external to the ear in human cadaver temporal bone tests were applied at the entrance of the ear canal in the model. The pressure waveforms near the tympanic membrane (TM) in the canal (P1) and behind the TM in the middle ear cavity (P2) were calculated. The model-predicted results were then compared with measured P1 and P2 waveforms recorded in human cadaver ears during blast tests. Results show that the model-derived P1 waveforms were in an agreement with the experimentally recorded waveforms with statistic Kurtosis analysis. The FE model will be used for the evaluation of HPDs in future studies.

A Totally Implantable Hearing Device for Restoration of Hearing

Middle ear implantable hearing devices as an emerging and ffective technology can offer advantages to the individuals with ild to moderately severe sensorineural hearing loss. Several deices with piezoelectric or electromagnetic transducers have been eveloped. A totally implantable hearing system TIHS consistng of a subcutaneous microphone, sound processor, and electroagnetic transducer has been investigated. The design of the IHS has incorporated the bioengineering approaches based on a D finite element FE computational model of the human ear and