Cell Contraction, De-adhesion, and Shape Effects Investigated by Cohesive Model with Finite Element Simulations

Cell adhesion is a complex mechanism, and different factors control this process including surface morphology, chemical, and mechanical interactions. These aspects are usually combined to achieve robust adhesion between surfaces. The later stage in bio-adhesion process involves the formation of molecular bonds through diffusion or interpenetration of molecules at the interface. In order to create contact, cells sense their physical environment by applying mechanical forces or responding to them via traction force. The force is transmitted through cell skeleton. However, how this force is transmitted is mostly unknown. Also, there are still many open questions about fracture mechanism in bio-adhesive contacts. What is the critical shear stress that separates cell from substrate? Which role plays cell contraction in the process of deadhesion? What is the influence of the cell shape effect, the effect of contractile cell strain and fracture energy on the critical stress at separation?

These open questions are addressed by studying cell contraction, de-adhesion, and shape effects investigated by cohesive model with finite element simulations. Cell-substrate system is modeled as a pre-strained elastic disk which is attached to elastic substrate via molecular bonds at the bio-adhesive interface. The effect of fracture energy on the critical stress at separation with constant contractile cell strain; and the effect of contractile cell strain on the critical stress at separation with constant fracture energy have been investigated in this research. Then both effects on the critical stress at separation have been compared. The effect of cell shape on the critical stress at separation has also been studied in this research. It is confirmed that deadhesion is controlled by the transition from small-scale bridging (SSB) behavior to large-scale bridging (LSB) behavior by the dimensionless parameter, the ratio of the crack-bridging zone size to the contact radius, which has important consequences for the design of biomimetic and the achievement of optimized adhesion force.