Application of tensile load at the tympanic membrane by an eardrum-contact transducer.

Safety of hearing devices attached to the tympanic membrane depends on applied forces and resulting movements of the ossicles when pulling off the device. A robotized temporal bone measurement setup was designed to apply and measure defined pull-off forces and as well as the corresponding displacements of the round-window membrane via Laser-Doppler-vibrometry. Here, we investigate in five temporal bones the pull-off dynamics of the Vibrosonic Hearing Contact Lens® the silicone membrane of which being formed to match the tympanic-membrane shape of individual temporal bones. The devices were pulled off with a linear stage actuator in a defined manner. We here show that the time courses of stapes displacement and pull-off force follow a consistent characteristic. Mean geometrical maximum stapes displacements were determined to be 5.4 µm ± 6.9 dB, and the geometrical mean maximum force 0.14 N ± 3.8 dB. The acoustical middle-ear transfer function of the temporal bones, expressed as stapes head displacement vs. ear-canal sound pressure, did not change significantly over up to 7 repeated pull-off procedures, as assessed by a low-frequency displacement average. Based on these results, the detachment of the hearing contact lens appears to be tolerable.