Durotaxis as an elastic stability phenomenon.

It is well documented that directed motion of cells is influenced by substrate stiffness. When cells are cultured on a substrate of graded stiffness, they tend to move from softer to stiffer regions--a process known as durotaxis. In this study, we propose a mathematical model of durotaxis described as an elastic stability phenomenon. We model the cytoskeleton (CSK) as a planar system of prestressed elastic line elements representing actin stress fibers (SFs), which are anchored via focal adhesions (FAs) at their end points to an elastic substrate of variable stiffness. The prestress in the SFs exerts a pulling force on FAs reducing thereby their chemical potential. Using Maxwell's global stability criterion, we obtain that the model stability increases as it is moved from a softer towards a stiffer region of the substrate. Numerical simulations reveal that elastic stability of SFs has a predominantly stabilizing effect, greater than the stabilizing effect of decreasing chemical potential of FAs. This is a novel finding which indicates that elasticity of the CSK plays an important role in cell migration and mechanosensing in general.