The effect of shear on lyotropic lamellar phase shows an interesting instability between a lamellar phase and a phase of close-packed multilamellar vesicles (the so called "onion phase"). These multilamellar vesicles can then be dispersed in excess water. This is shown to be a new process to make biological vectors in order to control the biological activity of bio-polymers such as DNA or proteins.

Several applications will be presented in cosmetics, vaccines and gene therapy. We will particularly developed the structure and the stability of a non cationic DNA vectors which can be used for gene therapy. The stability of DNA in a neutral lamellar phase is studied both experimentally and theoretically. The interaction between these vectors and cells shows some promising results.