Modeling of the Mechanical Deformation of Living Cells in Atomic Force Microscopy

Robert E. Rudd, Michael McElfresh, Eveline Baesu, Rod Balhorn, Michael Allen and James Belak
Lawrence Livermore National Laboratory, US

Keywords: membrane, cell mechanics, atomic force microscopy, recognitition force microscopy

Abstract:
One challenge with using Atomic Force Microscopy (AFM) for recognition microscopy on living cells is the fact that the cell is not rigid, and as the force is applied to a receptor site, it is not just the receptor site that is affected. The whole cell deforms under the applied force, and the measured binding force is a convolution of the local, intrinsic binding force of the receptor site and the gross elastic response of the cell. We have developed a model of the elastic deformation of the cell in order to separate the two effects, based on a continuum level analysis of the elastic deformation, including the incompressible interior and the tension and curvature of the membrane. A novel feature of this formalism are the treatment of the Canham-Helfrich curvature strain for finite deformations under load. As a validation, the model has been compared with force-displacement curves coming from AFM nanoindentation experiments on both membrane vesicles and cells. The model allows site-specific mechanical properties to be deconvoluted from the gross cell deformation in recognition microscopy experiments. Eventually, it may be possible to use concurrent multiscale modeling to provide a model of the atomistic interactions at the receptor site too.

NSTI Nanotech 2003 Conference Technical Program Abstract