13 - Mechanics of interactions of F-actin and vimentin networks

Abstract

The mechanical scaffolding of the cell, called cytoskeleton, is formed by biopolymeric structures such as F-actin, microtubules, and intermediate filaments (IF) that create networks, which are critical in determining the mechanical properties of the cells. This is essential for many mechanical duties such as mechano-sensing, or motility and can be found with a variety of assemblies. An ideal system for such kind of studies is the use of synthetic in vitro network, that allows a well-controlled and simplified environment to mimic biological scaffolding structures, which can contribute to a better understanding of the cytoskeleton-like structural building blocks and soft nanotechnology. Whereas the mechanics of F-actin networks or IF has already been characterised individually, the interaction between these two networks is largely unknown. In particular, composite networks made by semiflexible F-actin and vimentin – IF form complex networks, and are key regulators of cellular stiffness. Recent experimental studies using large deformations rheology show that the copolymerisation of F-actin and vimentin can produce composite networks either stronger or weaker than pure F-actin networks. Here, we develop a mesoscopic model that couples nonlinear elasticity with phase transitions that can describe the emergent properties of the composite network. In order to build it, we defined a free energy functional for the entropic elasticity of the semiflexible networks with transient crosslinks, and an interaction energy term to describe the coupling among the two networks with the formalism of Landau of phenomenological phase transition. Finally, we validated the proposed theory with measurements performed in a previous work on large deformations rheological experiments with different concentrations of actin and vimentin. Then, the proposed mesoscopic model can help to predict the susceptibility of the emergent network due to alterations of the concentrations of the constituents. This kind of studies will provide a very relevant ability to predict mechanical properties for these sorts of synthetic networks, cells, and tissues.