PhD DEFENSE BY THIBAUD COCHEREAU

The human vocal fold owns exceptional vibratory properties. It is capable of withstanding large deformations, for different types of loading, in a repeated and reversible manner. These particular vibro-mechanical properties are closely linked to its microstructure: a multi-layer complex structure composed of highly heterogeneous protein fibre networks. However, it is still difficult today to describe precisely the implication of the microstructural specificities of the fold in its biomechanical behaviour.In order to clarify this link and to move towards a better understanding of the behaviour of the vocal tissue, this study proposes to approach the problem under three complementary approaches, combining microstructural characterization, mechanical characterization and numerical modelling. First, the microstructure of the fold was studied emph{ex vivo} using an original technique based on X-ray tomography. The use of synchrotron tomography in phase retrieval mode has revealed the structure of the tissue at different scales. In particular, high-resolution 3D images of the fibrous structure of the upper and muscular layers of the tissue were acquired. These images gave rise to a quantitative 3D analysis of the fibrous arrangement, allowing the determination of descriptors of orientation and 3D geometry of the fibers.In a second step, the mechanical behaviour of the fabric under different loading conditions was studied. A protocol has been proposed to characterize the same sample in tension, compression and shear. These tests have complemented existing knowledge on fold biomechanics, and constitute important reference data for the construction and validation of digital models.Finally, based on the data acquired experimentally, a micro-mechanical model was developed. This model has the specificity to take into account the 3D arrangement of the tissue through an idealized but relevant representation of its fibrous microstructure. The macroscopic responses predicted for different loading conditionds could be compared to the experiment for validation. At the microscopic scale, the kinematics of the fibres during the loading could be simulated. The micromechanisms that occur during the deformation of the fibrous network could thus be identified, opening new perspectives in the understanding of the multi-scale properties of the tissue.