Frequency response analysis and in vitro verification of 3D-printed ossicular replacement materials

Abstract

As a bridge that transmits airborne sound signals to the auditory receptors of the inner ear, the eardrum and ossicular chain of the middle ear convert sound through two types of conversions: gas–solid (airborne sound signal–eardrum and ossicular chain) and solid–liquid (eardrum and ossicular chain–internal and external lymphatic fluid in the cochlea). This process concentrates and amplifies the sound to the inner ear through the lever principle structure formed by the three ossicles. However, diseases, hereditary factors, or trauma can reduce the sound transmission function of the middle ear. The effectiveness of middle ear replacement prostheses depends on their vibration response to the human auditory perception frequency, from the eardrum to the stapes plate. This response is influenced by the materials, geometry, and design of the replacement prosthesis and eardrum. This study explores the effects of different materials on hearing after artificial ossicular replacement. Usually, human temporal bone models are used for testing and validating numerical results. However, obtaining specimens from living humans is not always feasible. Therefore, we used three-dimensional printing technology to build a model of the middle ear to test the ossicular bone. Titanium alloy TC4, stainless steel 316L, and composite HA/PCL are chosen as materials for ossicular replacement. Using f‍inite element analysis and an in vitro verification experiment, individual replacements of the ossicles and three bone material replacements were conducted for frequency response analysis. The combination of the malleus made of TC4, the incus made of TC4, and the stapes made of HA/PCL were found to bear higher resemblance to a real normal ear ossicular model.