A finite elements study on the role of primary cilia in sensing mechanical stimuli to cells by calculating their response to the fluid flow

The primary cilium which is an organelle in nearly every cell in the vertebrate body extends out of the cell surface like an antenna and is known as cell sensor of mechanical and chemical stimuli. In previous numerical simulations, researchers modeled this organelle as a cantilevered beam attached to the cell surface. In the present study, however, we present a novel model that accommodates for both pivoting and bending of primary cilium in response to the fluid flow. In this model, primary cilium is attached to the cell using a thin elastic layer. This layer, which comprises the bottom boundary of the cilium, provides the possibility of pivoting of the cilium around its base so that we are able to analyze the other part of ciliary response to the fluid flow. In this study, we have used finite element method and fluid-structure interaction techniques to simulate the problem. Domains of solid cilium and the surrounding fluid were meshed using triangular elements. The governing equations in this problem were fully coupled and were solved by the direct method. Graphs of maximum stress in the cilium base versus elastic constant of the thin layer depict two different trends. By scrutinizing colored plots of stress distribution in the cilium base it is construed that these trends represent two different mechanisms in ciliary deformation due to the flow of the fluid. In case of low elasticity constants, for which attachment of the cilium to the cell is soft, pivoting mechanism is essential, while in case of harder attachments, bending mechanism dominates.