Theory of soft and living matter

Nonlinear mechanics of biopolymer networks.

Principal investigator: P. Ronceray
PhD Student: Andonis Gerardos, Arthur Coët
Postdoc: Yuri Zhang

Networks of stiff, entangled biopolymers play a central role in the mechanical properties of biological matter, from the cell cytoskeleton to the extracellular matrix. Such networks contribute to the mechanical integrity of living matter, and permit force transmission from the motor protein to the tissue scale. Importantly, at the stress levels relevant to biology, the mechanical properties of these disordered assemblies of fibrous, quasi-one-dimensional objects are very different from usual elastic materials. Indeed, they tend to respond nonlinearly to stresses, due both to single filament properties and to emergent, collective deformation modes controlled by the connectivity and disorder of the network. Through simulations and collaborations with experimentalists, we study the fundamental nonlinear mechanical properties of biopolymer networks and their interplay with cell behavior. We aim to address the following question: When probing their complex environment, what do cells actually “feel”?

Inferring the dynamics of living matter.

Principal investigator: P. Ronceray
PhD Student: Andonis Gerardos, Arthur Coët
Postdoc: Yuri Zhang

Networks of stiff, entangled biopolymers play a central role in the mechanical properties of biological matter, from the cell cytoskeleton to the extracellular matrix. Such networks contribute to the mechanical integrity of living matter, and permit force transmission from the motor protein to the tissue scale. Importantly, at the stress levels relevant to biology, the mechanical properties of these disordered assemblies of fibrous, quasi-one-dimensional objects are very different from usual elastic materials. Indeed, they tend to respond nonlinearly to stresses, due both to single filament properties and to emergent, collective deformation modes controlled by the connectivity and disorder of the network. Through simulations and collaborations with experimentalists, we study the fundamental nonlinear mechanical properties of biopolymer networks and their interplay with cell behavior. We aim to address the following question: When probing their complex environment, what do cells actually “feel”?

Encapsulation

Principal investigateur: M. Leonetti

A - dynamics, shape, wrinkling and rupture of an elastic capsule

Doctorant: P. Regazzi

Funding: CNES

Encapsulation is a simple way of protecting, transporting and delivering internalized principles, but also of structuring space. This concerns very diverse fields such as food, cosmetics, new materials for construction or medicine. The capsules studied are droplets bounded by a thin polymer film (shell) and immersed in a liquid. The structural and mechanical properties of such objects are still poorly known: behaviour laws, elastic and viscous moduli, rupture, dynamics, etc. Indeed, there are few experimental results. The behavior of this closed elastic system is governed by the coupling at the interface between the viscous stress jump and the elastic response of the shell (also called skin or membrane depending on the domain).

We are interested in the rupture of capsules as a function of the nature of its membrane, the winkling/folding instabilities and the spatiotemporal dynamics of the shape by a multiscale analysis.

B – Interactions between capsules, collective behaviors

The strong deformation of capsules in flow induces more complex hydrodynamic interactions than between rigid particles. To this, it is necessary to add colloidal interactions as well as friction, key ingredients for the understanding of the rheology of rigid particle suspensions. We propose to study the implication of all these contributions to the case of binary interactions and more broadly in suspension.

Forme et dynamique de vésicules sous écoulement : théorie et simulation

Principal investigateur: M. Leonetti

Collaboration : P. G. Chen, M. Jaeger (M2P2, Marseille)

Souvent, l'objectif principal de la recherche sur l'adhésion cellulaire est d'identifier les protéines d'adhésion et les voies de signalisation pertinentes. Cependant, pour une description complète, il est essentiel de comprendre également la physique et la physico-chimie des processus qui régissent l'adhésion – ce qui n’est pas facile dans le contexte des complexités associées à une cellule vivante. Une façon de résoudre ce problème est d’utiliser des membranes modèles fonctionnalisées pour imiter la membrane cellulaire. Une percée importante a été l'intégration réussie de l’intégrine, protéine transmembranaire d’adhésion, dans des membranes lipidiques synthétiques. Nous sommes en train d'explorer de nouveaux protocoles pour fabriquer des vésicules dérivées de cellules qui contiennent les protéines d'adhésion transmembranaires endogènes.