Modeling of Atomic Force Microscope Contact Experiments on Escherichia coli Bacteria Cellular Systems

We examined common models for atomic force microscope (AFM) nanoindentation of living cells and propose a new methodology for fitting the mechanical properties to the indentation data. By modeling the living cells as fluid-filled spherical membranes, the important parameters become the cell wall thickness, cell wall elastic modulus, and the cell’s turgor pressure. We modeled these parameters in addition to adhesion, plasticity, and viscoelasticity using finite element analysis to better describe the underlying physics and geometry of microbial indentation. This modeling approach applied different scaling laws from the classical Hertz model in order to better explain indentation data found in experiments on living E. coli bacterial cells. Work supported by DARPA Contract No. HR0011-17-2-0037.