Floppy modes and non-affine deformations in biopolymer networks

Fibrous materials are ubiquitous in nature. They form the cytoskeleton of cells and are essential components of the extracellular matrix. Its building blocks are stiff protein filaments and a myriad of associated crosslinking proteins. The interplay between the elasticity of the biopolymers and the binding and elastic properties of the crosslinkers lead to a variety of network architectures [1]. We review recent advances in understanding the elastic properties of these networks in terms of ``floppy modes'' [2], which are the relevant low-energy excitations characterizing non-affine deformations. This approach might very well serve as a novel paradigm to understand the elasticity of microstructured materials. The theoretical concepts are applied to recent experimental studies of F-actin networks crosslinked with fascin. [1] C. Heussinger and E. Frey, Stiff Polymers, Foams and Fiber Networks, Phys. Rev. Lett. 96, 017802 (2006). [2] C. Heussinger and E. Frey, Floppy Modes and Non-Affine Deformations in Random Fiber Networks, Phys. Rev. Lett. 97, 105501 (2006)