  Understanding cellular response to mechanical forces is immensely important
for a plethora of biological processes. Focal adhesions are multi-molecular
protein assemblies that connect the cell to the extracellular matrix and play a
pivotal role in cell mechanosensing. Under time varying stretches, focal
adhesions dynamically reorganize and reorient and as a result, regulate the
response of cells in tissues. Here, I present a simple theoretical model based
on, to my knowledge, a novel approach in the understanding of stretch sensitive
bond association and dissociation processes together with the elasticity of the
cell-substrate system to predict the growth, stability and the orientation of
focal adhesions in the presence of static as well as cyclically varying
stretches. The model agrees well with several experimental observations; most
importantly, it explains the puzzling observations of parallel orientation of
focal adhesions under static stretch and nearly perpendicular orientation in
response to fast varying cyclic stretch.
