SAMBA

This project takes its source in an array of works aiming at designing highly deformable anisotropic membranes for medical applications. The silicone rubbers (polydimethylsiloxane or PDMS) are highly deformable biomaterials widely used by surgeons for their mechanical properties controlled by their crosslinking rate. In current medical applications, the properties of silicones are homogeneous and isotropic. In the present biomimetic approach, our researches aim to provide the clinician elastomeric membranes whose local properties can possibly be non-uniform and will be fully controlled during their elaboration, both in rigidity and anisotropy. The main scientific and technological challenges of this project is to create a controlled anisotropy in every point of the membrane at the scale of the Representative Elementary Volume (REV), to drive the overall mechanical behaviour of the medical application (wide medical application = structure). For applications like artificial muscles, it means for example inducing contraction in specific directions. The proposed solution is based on the creation of local heterogeneities in the elastomeric membrane slightly cross-linked at room temperature by hydrosilylation; the topology of the heterogeneity is controlled by the use of masks during the over-crosslinking reaction by U.V. irradiation. Compared to solutions as fibre incorporation into the matrix, our proposal avoids the inherent difficulties due to the existence of interfaces (debonding, fatigue) and allows a very flexible distribution and perfect control of local properties in the structure. Overall, the project is built in four stages which will be addressed by means of the complementary skills of the three partners. In a first step, the silicone formulation will be optimised in order to control as well as possible the two ways of crosslinking, which must be totally sequenced. In a second step, the different formulations will be characterised in terms of their microstructure and their mechanical properties depending on the crosslinking parameters, and particularly the UV exposure time. The third step consists in the development and the validation of a design process of the local microstructure of the architected membrane in order to obtain the local properties referred to throughout the VER. The aim is to have a modelling approach based on numerical up-scaling by finite element calculations performed on a VER. The needed constitutive equation of the silicone will be determined by taking into account the relationship between microstructure and mechanical properties studied in step 2. Predictions of this model will be experimentally validated on architected membranes for which a target anisotropy and mechanical behaviour are sought. The fourth step will focus on a medical application using such highly deformable architected membranes. The final objective will be to design an artificial muscle activated by pressure, using the macroscopic characteristics of the muscle, especially its form, and the local characteristics of the architected membranes.