ABSTRACT

Nature provides a great source of inspiration regarding the development of biomimetic strategies in engineering, such as the attachment of dissimilar materials through complex and heterogeneous interphases. This talk aims at presenting two studies currently underway at the MSME laboratory, with emphasis on the mechanical characterization of functionally graded and architectured interphases.
A first part concerns the interphase joining tendon to bone, called enthesis, which plays the crucial role of integrating soft to hard tissues, by effectively transferring stresses across two tissues with a mismatch in mechanical properties of at least two orders of magnitude. The excellent mechanical properties of the enthesis are attributed to its complex hierarchical structure, which is hypothesized to arise from a tradeoff between the disorganization of the collagen fibers orientation and a gradient in mineral content at lower scales. The mechanical characterization and mimicking process of this heterogeneous medium at the tissue scale is of particular interest, because the natural tissue is not regenerated following healing or surgical repair, and post-surgical failure rates reach 94%. To better understand the mechanisms behind the robustness of this interfacial region, a multiscale modeling approach is proposed to predict the effective stiffness properties of the enthesis at the tissue level, as well as studying the individual impact of lower-scale components on its overall mechanical behavior at higher scales. As a prospect, this research will help designing multimaterial samples possessing interphases with bioinspired mechanical features using additive manufacturing.
A second part addresses the characterization of architectured materials (e.g., hexagonal lattices) using elastic guided waves, as an attempt to obtain optimized interphases in the context of orthopedic bone-implant stability. Elastic guided waves offer several advantages for the assessment of complex materials owing to their dispersive and multimodal nature. Dispersion curves reflect the dependence of the guided modes with the frequency and thus allow inferring the effective properties of the waveguide. An overview of recent advances on the guided waves characterization of complex media that inherently possess a kind of « architecture », such as cortical bone and nanoporous silicon membranes, will be presented. A methodological framework combining experimental measurements, modeling approaches, and model parameters identification will be introduced. I will then discuss how generalized continuum models typically used for describing architectured media could benefit from this framework.

For more information, contact Davide Ruffoni