Auteurs : N. Bochud1 , M. Gattin1 , G. Rosi1 , Q. Grossman2 , D. Ruffoni2 & S. Naili1
1. Univ Paris Est Creteil, Univ Gustave Eiffel, CNRS, UMR 8208, MSME, F-94010 Créteil, France
2. Mechanics of Biological and Bioinspired Materials Laboratory, Department of Aerospace and Mechanical Engineering, University of Liège, Quartier Polytech 1, Allée de la Découverte 9, B-4000 Liège, Belgium

Biological tissues have mechanical and functional properties that are extremely difficult to replicate. They are intrinsically multi-scaled, architectured and heterogeneous materials [1], whose outstanding features are the result of a smart arrangement of the basic constituents at different length scales. From a mechanical viewpoint, their unique properties at the tissue scale are hypothesized to result from the combination of two main factors [2], namely (i) the contribution of material ingredients (i.e., soft and hard viscoelastic constituent materials) and (ii) the presence of mechanistic ingredients (i.e., spatial organization of the constituents including periodic microstructure and functional gradients of mechanical properties). In this context, the rational design of architectured orthopedic implants that display an acoustic signature reflecting the microstructure could open the way towards the development of ultrasound characterization methods for the monitoring of their integration to the surrounding biological environment. To this end, it is necessary to have a precise knowledge of the acoustic properties of the constituent materials in the ultrasonic regime, as well as to accurately model the effect of the microstructure, in particular when the size of the unit cell is comparable to the wavelength.

In this seminar, I will discuss the capability of a multi-material additive manufacturing technique to design and fabricate micro-architectured periodic media with programmable ultrasonic responses, with the aim of replicating such multiphasic periodic structures formed by sub-millimeter unit cells in a laboratory-controlled environment. In a first part, the viscoelastic properties of the constituent materials will be assessed by characterizing macroscopically homogeneous samples, which exhibit dispersive losses that are described using a frequency power law model [3]. In a second part, the retrieved properties will be used to feed models of the transmission of longitudinal ultrasound waves propagating through 1D-periodic biphasic samples [4]. Towards this goal, Bloch- Floquet analysis is first applied in the frame of viscoelasticity, with the aim of disentangling the relative contributions of viscoelasticity and periodicity on ultrasound signatures such as dispersion, attenuation, and bandgaps localization. Second, the impact of the finite size nature of these structures is assessed by using a modeling approach based on the transfer matrix formalism. Finally, the modeling outcomes, i.e., apparent phase velocity and attenuation, are confronted with experiments conducted on 3D-printed samples, which exhibit a 1D periodicity at length scales of a few hundreds of micrometers. Altogether, the obtained results shed light on the modeling characteristics to be considered when predicting the complex acoustic behavior of periodic media in the ultrasonic regime.

[1] P. Fratzl, and R. Weinkamer. Nature’s hierarchical materials. Prog. Mater. Sci., 52(8), 1263–1334, 2007.
[2] A. A. Zadpoor. Meta-biomaterials. Biomater. Sci., 8(1), 18–38, 2020.
[3] M. Gattin, N. Bochud, G. Rosi, Q. Grossman, D. Ruffoni, and S. Naili. Ultrasound characterization of the viscoelastic properties of additively manufactured photopolymer materials. J. Acoust. Soc. Am., 152(3), 1901–1912, 2022.
[4] M. Gattin, N. Bochud, G. Rosi, Q. Grossman, D. Ruffoni, and S. Naili. Ultrasonic bandgaps in viscoelastic 1D-periodic media : Mechanical modeling and experimental validation. Ultrasonics, 2022 (under review).