Atomic Force Microscopy for Live-Cell and Hydrogel Measurement

Abstract

Atomic force microscopy (AFM) has emerged as a popular method for determining the mechanical properties of cells, their components, and biomaterials. Here, we describe AFM setup and application to obtain stiffness measurements from single indentations for hydrogels and myofibroblasts.

Keywords: Atomic force microscopy; Fibroblast; Force-curve; Hydrogels; Live-cell measurement; Stiffness; Young’s modulus.

Fig. 1. Schematic of atomic force microscopy principle.

Precise indentation can be made apically on cells or biomaterials. A laser directed onto the cantilever is deflected and detected by a photodiode so that the cantilever deflection at the surface can be measured

Fig. 2. Measurement of surface stiffness.

Force-curve generated on (a) glass, (b) cellular region, and (c) Force curve generated Hertz fit for calculating Young’s Modulus. (d) Cardiac fibroblasts cultured on glass coverslips, imaged live with phase contrast (left) and fixed, confocal (right) imaging. Right panel, cells are stained with DAPI (blue), Fibronectin (purple), alpha-SMA (red), TE-7 (green). The purple and blue arrows refer to the cell periphery and above nucleus, respectively, that upon AFM would generate force-curves as shown in panels b–c and cell stiffness measurements as in panel e. The black arrow refers to the glass substrate that when measured with AFM would generate curves as in panel a. (e) Example of cell stiffness measurements for cardiac fibroblast cellular regions. Each point represents average Young’s Modulus for a 5 × 4 force map covering a 3–5 μm² area. n = 8 (cell periphery) and 7 (above nucleus) cells. For independent t-test, p = 0.3316