Wavelength-specific optoacoustic-induced vibrations of the guinea pig tympanic membrane

Abstract

Significance: Optoacoustic-induced vibrations of the hearing organ can potentially be used for a hearing device. To increase the efficiency of such a hearing device, the conversion of the light energy into vibration energy within each type of irradiated tissue has to be optimized. Aim: To analyze the wavelength-dependency of optoacoustic-induced vibrations within the tympanic membrane (TM), and to define the most efficient and best-suited optical stimulation parameters for a novel auditory prosthesis. Approach: Single nanosecond laser pulses, continuously tunable in a range of visible to nearinfrared, were used to excite the guinea pig TM. The induced vibrations of the hearing organ were recorded at the malleus using a laser Doppler vibrometer. Results: Our results indicate a strong wavelength-dependency of the vibration's amplitude correlating with the superposition of the absorption spectra of the different specific tissue components. Conclusions: We investigated the spectrum of the vibrations of the hearing organ that were induced optoacoustically within a biological membrane embedded in air, in an animal model. First applications for these results can be envisioned for the optical stimulation of the peripheral hearing organ as well as for research purposes.

Safety margin evaluations for transtympanic laser stimulation of the cochlea from the outer ear in Mongolian gerbils (Meriones unguiculatus)

“…This indicates that the laser irradiation of 27.9 W/cm 2 or above at 532 nm could cause thermal damage. Although these results are not directly comparable to our data because of the difference in wavelength-dependent absorbance in the tympanic membrane and auditory ossicles, as some studies described (Carr, Valdez, Bruns, & Bawendi, 2016; Goblet, Matin, Lenarz, & Paasche, 2021; Heimann et al, 2021), thermal damage to the tympanic membrane and auditory ossicles might be one reason why continuous laser exposure affects the auditory-evoked response more than the laser-evoked response.…”

Feasibility evaluation of transtympanic laser stimulation of the cochlea from the outer ear

“…This study evaluated the feasibility of the use of laser stimulation of the cochlea from the outer ear to compensate for auditory deficits. Since the tissue component of the tympanic membrane does not tend to absorb infrared light (Heimann et al, 2021;Sordillo et al, 2014), laser irradiation projected from the outer ear could penetrate the tympanic preprint (which was not certified by peer review) is the author/funder. All rights reserved.…”

Optoacoustically induced auditory brainstem responses in the mouse model enhanced through an absorbing film

“… 28 These ultrasound-induced mechanical vibrations can be used to stimulate the hearing organ at different loci. 5 – 9 Therefore, the idea to work with this stimulation method to specifically influence the auditory activation suggests the design of a new generation of hearing prosthesis. A stimulation strategy based on a single laser wavelength for frequency-specific stimulation has already been demonstrated by Stahn et al.…”

“… 8 Recently, we demonstrated that the effectiveness of optoacoustically induced vibrations of the guinea pig TM depends on the laser wavelength, most probably through dissimilar absorption characteristics of the TM tissues for different wavelengths. 9 However, one main work package that needs to be performed, before considering the design of a hearing device, is the optimization of the stimulation method to achieve higher activation intensities within biocompatibility margins. We, therefore, sought to assess if the induced vibrations can be amplified by the application of highly absorbing material on the target-irradiated structure in an animal model.…”