WP1 aims at developing a multiscale model of COL/HA composite to assess the capability of the material of transmitting and dissipating transient loads.
A first study was carried on wave propagation and energy dissipation in COL peptides. The results showed a strong dependency on the viscoelastic behavior based on loading direction and hydration state. This work suggested distinct roles of collagen in terms of wave transmission in macro-tissues with different percentages of water, such as tendon and eardrum.
In a second study, the ER investigated wave transmission and energy dissipation along dry/hydrated mineralized fibrils, studying the influence of the mineral percentage, water content, and input velocity on the mechanical response of the material. Results showed decreasing trends for both wave speeds and Young’s Moduli over input velocity with a marked strengthening effect in the region where HA is accumulated. In contrast, the dissipative behavior is not affected by either loading conditions or mineral percentage, showing a stronger damping effect upon faster inputs compatible with the bone behavior at the macroscale.
A third study concerned the optimization of middle ear prostheses by maximizing the global stiffness and using the smallest possible volume constraint that ensured material continuity. This investigation optimized the prosthesis topology in response to static displacement loads with amplitudes that normally occur during sound stimulation. Following earlier studies, the ER discussed how the presence and arrangement of holes on the surface of the prosthesis plate in contact with the umbo affect the overall geometry. Finally, the achieved designs were validated through a finite-element model, in which the prosthesis performance was assessed upon dynamic sound pressure loads by considering four different constitutive materials: titanium, cortical bone, silk, and COL/HA.
WP2 concerns the strategies for printing micro-prostheses. The activities started with an extended review of the methodologies currently employed to 3D print HA-reinforced materials.
After the training sessions, the ER followed two parallel research avenues: • Optimization study on the topology of the 3D printing nozzle. This activity exploits the synergies of finite-element models with machine learning (ML) algorithms and the mechanical characterization of materials. The results showed the capability of the developed algorithm to predict the shear stress on the ink based on the geometry of the nozzle. Moreover, it was found that conical nozzles with angles less than 10° and diameters smaller than 400 microns are suitable for 3D-printing prostheses. • Printing the micro-prostheses. The ER was able to 3D print the micro-prostheses made of HA, Silk/HA, and COL/HA with a composition equal to 10/90 (w/w).
WP3 relates to the acousto-mechanical characterization of the micro-prostheses. The ER worked on experimental measurements on human temporal bones and tested the micro-prostheses against acoustic inputs in the acoustic range. The results showed the good suitability of the prostheses to transmit the acoustic energy towards the inner ear.
WP4 relates to the biological assessment of the prostheses. Two main studies were carried out. The first concerned the culture of epithelial cells on the prostheses while, in contrast, the second related to a dynamic study with a dedicated bioreactor to assess the capability of hMSCs to migrate on the prostheses when loaded by a simultaneous mechanical and acoustic input. In both cases the prostheses were successfully covered by cells, demonstrating the capability of the device of being integrated into the host tissues.
