Application of the Johnson–Kendall–Roberts model in AFM-based mechanical measurements on cells and gel.

•The JKR model was applied for analysis of the AFM force curves with adhesion.•The approach and retraction curves obtained on cells and PA gels were compared.•Loading rate, holding time and indentation depth affected the measured parameters.•Observed effects were caused by both bulk and interfacial viscoelasticity.•BSA addition decreased adhesion of the probe to gels but increased adhesion to cells.

The force-distance curves (FCs) obtained by the atomic force microscope (AFM) with colloid probes contain information about both the viscoelastic properties and adhesion of a sample. Here, we processed both the approach and retraction parts of FCs obtained on polyacrylamide gels (in water or PBS) and Vero cells (in a culture medium). The Johnson–Kendall–Roberts model was applied to the retraction curves to account for the adhesion. The effects of loading rate, holding time and indentation depth on adhesion force and Young’s modulus, calculated from approach and retraction curves, were studied. It was shown that both bulk and local interfacial viscoelasticity can affect the observed approach-retraction hysteresis and measured parameters. The addition of 1% bovine serum albumin (BSA) decreased adhesion of the probe to the PAA gel surface, so interfacial viscoelasticity effects were diminished. On the contrary, the adhesiveness of Vero cells increased after BSA addition, indicating the complex nature of the cell-probe interaction.

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