Expriments in soft condensed matter

Membranes (natural or artificial) are ubiquitous. They ensure compartmentalization, in living organisms at all scales (nucleus, mitochondria, cell, organ, organism), but also in all artificial electrochemical devices (batteries, power cells). Basically, the role of this compartmentalization is to slow down the chemical reactions between constituents of each compartment. But these chemical reactions are nevertheless necessary for the device to operate. A membrane plays thus a double and contradictory role : it must separate, but not too much.

The interaction of cell membranes with the molecules adsorbed on their surface and the way in which the incorporation of these molecules takes place is still poorly understood. We are interested in antimicrobial peptides that form the keystone of the innate immune system of multicellular organisms. Basically, these peptides make membranes permeable by forming pores in them. Their universal presence in the animal and plant kingdoms, their non-specific and broad-spectrum action as well as their very elementary structure suggest a mode of action according to physical mechanisms that are also very general and universal.

The extracellular matrix is a gel. That is to say a solid network of macromolecuiles linked together, here mainly proteins like collagen. This matrix surrounds and delimits organs. So that, cell invasion and tumor vascularization necessarily imply its crossing by cells, which for this produce proteolytic enzymes (proteinases) which break the links of this network. Uderstanding how they work is therefore important to fight against the spread of cancer cells.

Associative polymers assemble into supramolecular structures whose formation and arrangement result from the delicate balance between contradictory forces. Among these, the entropic forces related to the loss of degrees of freedom of molecules, for example freedom of translation or freedom of conformation etc. They perfectly illustrate the various problems encountered in the study of soft matter. Mainly studied from the 1980s in the absence of solvent, my contributions in the field relate to the structures obtained in solution.

A theory is an economy of thought (read E. Mach , P. Duhem , A. Einstein ). We make a representation of reality by establishing unlikely links between things or phenomena that are a priori very different. In the 1970s, P.G. de Gennes achieves a major advance of this type by noting that polymers were critical objects whose self-similarity makes it possible to establish universal laws of behavior (called scaling laws) for observable macroscopic quantities such as osmotic pressure, viscosity or elasticity when expressed as a function of carefully chosen variables (called reduced variables).