  Conductive hearing loss, due to middle ear pathologies or traumas, affects
more than 5% of the population worldwide. Passive prostheses to replace the
ossicular chain mainly rely on piston-like titanium and/or hydroxyapatite
devices, which in the long term suffer from extrusion. Although the basic shape
of such devices always consists of a base for contact with the eardrum and a
stem to have mechanical connection with the residual bony structures, a
plethora of topologies have been proposed, mainly to help surgical positioning.
In this work, we optimize the topology of a total ossicular replacement
prosthesis, by maximizing the global stiffness and under the smallest possible
volume constraint that ensures material continuity. This investigation
optimizes the prosthesis topology in response to static displacement loads with
amplitudes that normally occur during sound stimulation in a frequency range
between 100 Hz and 10 kHz. Following earlier studies, we discuss how the
presence and arrangement of holes on the surface of the prosthesis plate in
contact with the umbo affect the overall geometry. Finally, we validate the
designs through a finite-element model, in which we assess the prosthesis
performance upon dynamic sound pressure loads by considering four different
constitutive materials: titanium, cortical bone, silk, and
collagen/hydroxyapatite. The results show that the selected prostheses present,
almost independently of their constitutive material, a vibroacustic behavior
close to that of the native ossicular chain, with a slight almost constant
positive shift that reaches a maximum of 5 dB close to 1 kHz. This work
represents a reference for the development of a new generation of middle ear
prostheses with non-conventional topologies for fabrication via additive
manufacturing technologies or ultraprecision machining in order to create
patient-specific devices.
