A computational modeling for micropipette-manipulated cell detachment from a substrate mediated by receptor-ligand binding

We perform computer simulations of using a micropipette to attach and then detach a red blood cell on a flat substrate mediated by receptor-ligand binding. The cell is initially swollen with osmotic pressure, coated with a specific kind of bio-molecular receptor, sucked into the micropipette and then allowed to approach a substrate coated with the corresponding ligand. Binding interactions between the membrane-bound receptors and the substrate-anchored ligands cause the cell to spread onto the substrate surface. While the specific interaction between a pair of receptor and ligand is described by a chemical reaction equation, a traction-separation law is adopted to describe the non-specific interactions between the receptors and the substrate. A surface diffusion model is introduced to describe the mobility of the receptors within the cell membrane. After the equilibrium state of adhesion is achieved, a pulling force is applied on the micropipette to detach the cell from the substrate. The governing equations of cell-substrate interactions and receptor diffusion are implemented in a finite element scheme to simulate the entire process of cell suction, cell spreading, receptor diffusion, and cell detachment, and to investigate the effects of membrane stiffness, cohesive parameters, micropipette size, and suction pressure on the unbinding kinetics of the cell. The simulation results are shown to agree qualitatively with existing experimental data. (c) 2008 Elsevier Ltd. All rights reserved.