Cell Mechanics Using Atomic Force Microscopy-Based Single-Cell Compression

Abstract

We report herein the establishment of a single-cell compression method based on force measurements in atomic force microscopy (AFM). The high-resolution bright-field or confocal laser scanning microscopy guides the location of the AFM probe and then monitors the deformation of cell shape, while microsphere-modified AFM probes compress the cell and measure the force. Force and deformation profiles of living cells reveal a cubic relationship at small deformation (<30%), multiple peaks at 30-70% compression, and a rapid increase at over 80% deformation. The initial compression may be described qualitatively and quantitatively using a simple model of a nonpermeable balloon filled with incompressible fluid. Stress peaks reflect cell membrane rupture, followed by the deformation and rupture of intracellular components, beyond which the cell responses become irreversible. The Young's modulus and bending constant of living cell membranes are extracted from the balloon models, with 10-30 MPa and 17-52 kT, respectively. The initial compression of dead and fixed cells is modeled using Hertzian contact theory, assuming that the cell is a homogeneous sphere. Dead cells exhibit a cytoskeleton elasticity of 4-7.5 kPa, while fixation treatment leads to a dramatic increase in the cytoskeletal Young's modulus (150-230 kPa) due to protein cross-linking by imine bonds. These results demonstrate the high sensitivity of the single-cell compression method to the molecular-level structural changes of cells, which suggests a new generic platform for investigating cell mechanics in tissue engineering and cancer research.

On the role of the actin cytoskeleton and nucleus in the biomechanical response of spread cells

“…Furthermore, highly contractile cell phenotypes exhibit a higher apparent stiffness when subjected to cell compression. For example, very high compression forces (~2500 nN) have been reported for spread myoblasts [36] whereas lower compression forces (~360 nN) have been reported for less contractile fibroblasts [37]. A recent study by Ronan et al [20] demonstrates that the active SF model used in the in the current study is capable of capturing the relationship between the level of cell contractility and the compression resistance of spread cells.…”

Single-cell mechanics provides a sensitive and quantitative means for probing amyloid-β peptide and neuronal cell interactions

“…The cellular mechanics were measured using our method of single-cell compression (21), from which force versus deformation profiles were acquired as a function of Aβ42 treatment. A schematic shown in Fig.…”

Experimental and Computational Investigation of the Role of Stress Fiber Contractility in the Resistance of Osteoblasts to Compression

“…Such an approach suffers from a number of setbacks: applied deformations are restricted to the upper surface of the cell; measured forces are highly influenced by cell inhomogeneity; large deformations occur in a highly localized region of the cell, making it difficult to characterize the strain field and to interpret measured forces. In an effort to overcome these problems Lulevich et al attached a sphere of diameter 40 µm to the end of the AFM cantilever [11]. In the present study a sphere of diameter 150 µm is attached to an AFM cantilever in order to perform whole cell compression of osteoblasts.…”