Biomechanical Changes of Tympanic Membrane to Blast Waves

Eardrum or tympanic membrane (TM) is a multilayer soft tissue membrane located at the end of the ear canal to receive sound pressure and transport the sound into the middle ear and cochlea. Rupture of the TM is one of the most frequent injuries of the ear after blast exposure in military service members. The TM mechanical property changes induced by blast waves also affect progressive hearing loss in veterans. This chapter describes the biomechanical measurements and modeling of blast wave transduction through the ear and the TM mechanical property changes after blast exposure. The human TM rupture thresholds were determined with a relationship to blast wave direction. It is found that the sensitivity of TM stress change with respect to the pressure reaching on TM surface characterizes the mechanical damage of the TM in relation to blast waves. Mechanical properties of the human TM after exposure to blasts were measured using acoustic loading and laser Doppler vibrometry with the inverse problem-solving method. The complex modulus of the TM exposed to blast waves had significant reduction compared to normal tissue. The SEM images of post-blast TM showed obvious microstructural changes from the normal TM which indicate the tissue damage caused by blast exposures. This chapter provides important data on human TM damage and mechanical changes induced by blast overpressure waves.