Résumé
Elastic materials surface tension effects are characterized by a length scale. They must be taken into account as soon as this level is not microscopic, which is exactly the case of "soft" materials such as gels, elastomers, and several biological materials.We have highlighted a series of new physical phenomena, as the absence of edges and angles in this "soft matter", existence of a Rayleigh-Plateau instability in a elastic cylinder of sufficiently small diameter, presence of a zone reversible elastic very stretched fracture head by masked area plastic deformations for harder materials. We have alsostudied the effect of elastic energy in the unstable Saffman-Taylor, and showed that the surface tension allows to regularize the Biot instability of a compressed solid. The field of applications of this work extends mechanics biological media to the design and construction of objects microscopic controlled geometry.