Determination of the elastic moduli of thin samples and adherent cells using conical atomic force microscope tips


The atomic force microscope can detect the mechanical fingerprints of normal and diseased cells at the single-cell level under physiological conditions1,2. However, atomic force microscopy studies of cell mechanics are limited by the ‘bottom effect’ artefact that arises from the stiff substrates used to culture cells. Because cells adhered to substrates are very thin3, this artefact makes cells appear stiffer than they really are4. Here, we show an analytical correction that accounts for this artefact when conical tips are used for atomic force microscope measurements of thin samples. Our bottom effect cone correction (BECC) corrects the Sneddon's model5, which is widely used to measure Young's modulus, E. Comparing the performance of BECC and Sneddon's model on thin polyacrylamide gels, we find that although Sneddon's model overestimates E, BECC yields E values that are thickness-independent and similar to those obtained on thick regions of the gel. The application of BECC to measurements on live adherent fibroblasts demonstrates a significant improvement on the estimation of their local mechanical properties.

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Figure 1: BECC removes the bottom-effect artefact in measurements performed on thin gel samples.
Figure 2: Indentations larger than 10% of the sample thickness result in a very large overestimaton of the elastic modulus.
Figure 3: BECC allows non-artefactual measurement of the local elastic moduli of adherent cells.
Figure 4: NIH3T3 cells display the greatest variability in E in regions that are <4 µm thick.


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The authors thank R. Sunyer, V. Luo and K.M. Yamada for critical input. This work was supported by the Intramural Program of the US National Institute of Deafness and Other Communication Disorders.

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N.G. conceived, designed and performed the experiments and analysed the data. R.S.C. developed the BECC correction. N.G. and R.S.C. co-wrote the paper.

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Correspondence to Richard S. Chadwick.

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The authors declare no competing financial interests.

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Gavara, N., Chadwick, R. Determination of the elastic moduli of thin samples and adherent cells using conical atomic force microscope tips. Nature Nanotech 7, 733–736 (2012).

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