Connecting cell structure to local mechanical properties by combining multi-harmonic AFM methods with fluorescence microscopy

Leyla Yamin, Purdue University

Abstract

The Atomic Force Microscope (AFM) is a key instrument for mapping quantitatively the local mechanical properties of cells in solutions. Both quasi-static AFM methods and a new multi-harmonic dynamic AFM method [1] have been recently proposed for this purpose. However, the relationship between the mapped mechanical properties and the underlying cytoskeletal structure are poorly understood. Moreover, the relationship between the mechanical property maps acquired using static vs. dynamic AFM methods remains unclear. In this work we combine fluorescence microscopy (FM) with static force volume and dynamic multi-harmonic AFM methods using magnetically excited cantilever to compare cytoskeletal structure (F-actin, microtubules, nucleus and possibly some other proteins in the cell structure) to low frequency (force volume) and high frequency (dynamic multi-harmonic AFM) mechanical property maps such as storage and loss moduli of fixed rat fibroblast cells in buffer solution. Correlations between the fluorescent and mechanical property maps acquired using the multi-harmonic method show that the nuclear region and thick actin bundles are associated with greater local stiffness and damping. On the other hand the local storage modulus maps using the multi-harmonic and force volume maps show an inversion of contrast between the nuclear region of the cell and the peripheral region. The origin of this apparent inversion in properties depending on AFM method used is clarified by studying the modulus of the cells at different locations at different force levels. The development of combined multi-harmonic AFM at Birck Nanotechnology Center and fluorescence microscopy should open an important biomechanical assay capability in cell biomechanics.

Degree

M.S.M.E.

Advisors

Raman, Purdue University.

Subject Area

Mechanical engineering|Nanotechnology

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