The tympanic membrane (TM) transfers sound waves from the air into mechanical motion for the ossicular chain. This requires a high sensitivity to small dynamic pressure changes and resistance to large quasi-static pressure differences. The TM achieves this by providing a layered structure of about 100µm in thickness, a low flexural stiffness, and a high tensile strength. Chronically infected middle ears require reconstruction of a large area of the TM. However, current clinical treatment can cause a reduction in hearing. With the novel additive manufacturing technique of melt electrowriting (MEW), it is for the first time possible to fabricate highly organized and biodegradable membranes within the dimensions of the TM. Scaffold designs of various fiber composition are analyzed mechanically and acoustically. It can be demonstrated that by customizing fiber orientation, fiber diameter, and number of layers the desired properties of the TM can be met. An applied thin collagen layer seals the micropores of the MEW-printed membrane while keeping the favorable mechanical and acoustical characteristics. The determined properties are beneficial for implantation, closely match those of the human TM, and support the growth of a neo-epithelial layer. This proves the possibilities to create a biomimimetic TM replacement using MEW. IntroductionDefects of the tympanic membrane (TM) have many causes, ranging from injuries to chronic otitis media (COM). In the

The human tympanic membrane (TM) captures sound waves from the environment and transforms them into mechanical motion. The successful transmission of these acoustic vibrations is attributed to the unique architecture of the TM. However, a limited knowledge is available on the contribution of its discrete anatomical features, which is important for fabricating functional TM replacements. This work synergizes theoretical and experimental approaches toward understanding the significance of geometry in tissue-engineered TM scaffolds. Three test designs along with a plain control are chosen to decouple some of the dominant structural elements, such as the radial and circumferential alignment of the collagen fibrils. In silico models suggest a geometrical dependency of their mechanical and acoustical responses, where the presence of radially aligned fibers is observed to have a more prominent effect compared to their circumferential counterparts. Following which, a hybrid fabrication strategy combining electrospinning and additive manufacturing has been optimized to manufacture biomimetic scaffolds within the dimensions of the native TM. The experimental characterizations conducted using macroindentation and laser Doppler vibrometry corroborate the computational findings. Finally, biological studies with human dermal fibroblasts and human mesenchymal stromal cells reveal a favorable influence of scaffold hierarchy on cellular alignment and subsequent collagen deposition.

The findings may be considered preliminary as this experimental study was limited to just one of the many different possible situations of tympanoplasty and it involved a small sample size. Nevertheless, the results with the flexible TORP were promising and could encourage further investigations on such prostheses.

The treatment of otitis media requires classifying the effusion in the tympanic cavity for choosing appropriate therapeutic strategies. Otoscopic examination of the middle ear depends on the expertise of the physician and is often hampered in case of inflammatory alterations of the tympanic membrane. In otologic research, optical coherence tomography is an innovative non-invasive imaging technique utilized for visualizing the tympanic membrane. This ex vivo study presents the possibility of OCT and Doppler-OCT for the detection of effusions in the tympanic cavity. Structural OCT imaging allows the direct visualization of scattering fluids behind the tympanic membrane. In addition, the measurement of the reduced oscillation amplitude by means of Doppler-OCT permits the indirect detection of scattering and transparent fluids.

Abstract:The middle ear plays a crucial role in the quality of hearing. This complex construct performs different tasks like the protection against large air pressure input, the transmission of sound and its adaption to the inner ear impedance. Traumas, erosion by chronic otitis media or cholesteatoma, as well as other degenerative or damaging diseases, are reasons for a necessary reconstruction of specific middle ear structures. The reconstruction of the ossicular chain is very often performed by using rigid ossicular replacement prostheses made out of titanium, ceramics or bone. Tilting and dislocation of these passive implants are some of the known complications after middle ear surgery. They are related to loads at the implant coupling points in response to a tension change in the middle ear. The healing process, scar tension and ventilation problems are possible causes.To increase the sound transmission quality of total reconstructions and safety in case of pressure dependent movement of the tympanic membrane, a novel flexible total ossicular replacement prosthesis (TORP) with a silicone coated ball joint prototype was developed and investigated. Besides measurements of first middle ear transfer functions of temporal bones, the mechanical properties of the flexible TORP were examined with stress relaxation investigations.The novel silicone coated ball and socket joint TORP provides a sound transfer equivalent to the intact human middle ear at normal pressure and negative pressure in the middle ear. Together with the low stiffness values at an anatomically typical deflection of about 500 µm the prevention of a stiffening of the stapes annular ligament could be approved. Thus, improved acoustic transmission quality and reconstruction stability in comparison to common rigid titanium TORP could be determined. Nevertheless, further design improvements should be accomplished. The demonstrated flexible TORP can solve some common problems in middle ear reconstruction.

Electrospun membranes have a great potential in myringoplasty, as the special microstructure of fibers could be comparable to the fiber structure of the tympanic membrane (TM), thus, making it an potential implant for tympanic membrane reconstruction. In this work, the microscale parameters of the fiber structure were studied in a numerical homogenization procedure. The aim of the investigations was to obtain an implant that has a compromise between acoustic and mechanical properties and which at macroscale is comparable with the human TM. The numerical results were verified with experiments on first samples.

A fully implantable hearing aid is introduced which is a combined sensor-actuator-transducer designed for insertion into the incudostapedial joint gap (ISJ). The active elements each consist of a thin titanium membrane with an applied piezoelectric single crystal. The effectiveness of the operating principle is verified in a temporal bone study. We also take a closer look at the influence of an implantation-induced increase in middle ear stiffness on the transducer's output. An assembly of the transducer with 1 mm thickness is built and inserted into six temporal bones. At this thickness, the stiffness of the annular ligament is considerably increased, which leads to a loss in functional gain for the transducer. It is assumed that a thinner transducer would reduce this effect. In order to examine the performance for a prospective reduced pretension, we increased the gap size at the ISJ by 0.5 mm by removing the capitulum of the stapes in four temporal bones. The TM is stimulated with a broadband multisine sound signal in the audiological frequency range. The movement of the stapes footplate is measured with a laser Doppler vibrometer. The sensor signal is digitally processed and the amplified signal drives the actuator. The resulting feedback is minimized by an active noise control least mean square (LMS) algorithm which is implemented on a field programmable gate array. The dynamic range and the functional gain of the transducer in the temporal bones are determined. The results are compared to measurements from temporal bones without ISJ extension and to the results of Finite Elements Model (FE model) simulations. In the frequency range above 2 kHz a functional gain of 30 dB and more is achieved. This proposes the transducer as a potential treatment for high frequency hearing loss, e.g. for patients with noise-induced hearing loss. The transducer offers sufficient results for a comprehensive application. Adaptations in the transducer design or surgical approach are necessary to cope with ligament stiffening issues. These cause insufficient performance for low frequencies under 1 kHz.

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