In-plane mechanics of soft architectured fibre-reinforced silicone rubber membranes.

Silicone rubber membranes reinforced with architectured fibre networks were processed with a dedicated apparatus, allowing a control of the fibre content and orientation. The membranes were subjected to tensile loadings combined with continuous and discrete kinematical field measurements (DIC and particle tracking). These tests show that the mechanical behaviour of the membranes is hyperelastic at the first order. They highlight the influence of the fibre content and orientation on both the membrane in-plane deformation and stress levels. They also prove that for the considered fibrous architectures and mechanical loadings, the motion and deformation of fibres is an affine function of the macroscale transformation. These trends are fairly well described by the micromechanical model proposed recently in Bailly et al. (JMBBM, 2012). This result proves that these materials are very good candidates for new biomimetic membranes, e.g. to improve aortic analogues used for in vitro experiments, or existing textiles used for vascular (endo)prostheses.

Application of synchrotron X-ray microtomography for visualizing bacterial biofilms 3D microstructure in porous media.

The development of reliable models to accurately predict biofilm growth in porous media relies on a good knowledge of the temporal evolution of biofilms structure within the porous network. Since little is known on the true 3D structure of biofilms developed in porous media, this work aimed at developing a new experimental protocol to visualize the 3D microstructure of bacterial biofilms in porous media. The main originality of the proposed procedure lies on the combination of the more recent advances in synchrotron microtomography (Paganin mode) and of a new contrast agent (1-chloronaphtalene) that has never been applied to biofilm visualization. It is shown that the proposed methodology takes advantage of the contrasting properties of 1-chloronaphtalene to prevent some limitations observed with more classical contrast agents. A quantitative analysis of the microstructural properties (volume fractions and specific surface area) of bacterial biofilms developed in columns of clay beads is also proposed on the basis of the obtained 3D images.

Towards a biomimetism of abdominal healthy and aneurysmal arterial tissues.

The aim of this work is to develop a new hyperelastic and anisotropic material mimicking histological and mechanical features of healthy and aneurysmal arterial tissues. The material is constituted by rhombic periodic lattices of hyperelastic fibres embedded into a soft elastomer membrane. To fit bi-axial experimental data obtained from the literature, with normal or pathologic human abdominal aortic tissues, the microstructure of the periodic lattices (fibre length, angle between fibres) together with the mechanical behaviour of the fibres (fibre tension-elongation curve) were optimised by using theoretical results arising from a multi-scale homogenisation process. It is shown that (i) a material constituted by only one periodic lattice of fibres is clearly not sufficient to describe all the experimental data set, (ii) a quantitative agreement between measurements and theoretical predictions is obtained by using a material with two fibre lattices, (iii) the optimised microstructures and mechanical properties of the fibrous lattices are strongly different for the abdominal healthy and aneurysmal arterial tissues, (iv) the anisotropic mechanical behaviour of the optimised material is described by only five parameters and (v) the optimal angles between fibres in the case of the healthy aorta are consistent with histological data. Several technical solutions of fibres can be considered as relevant candidates: this is illustrated in the particular cases of straight and wavy fibres.