Quantification of the Elastic Properties of Soft and Sticky Materials Using AFM

Indentation Type-AFM (IT-AFM) is very useful to analyze the local rheological properties of soft or biological materials. However, analysis of the force-indentation curves is very sensitive to the way the curves are fitted: fits with elastic models such as Hertz or Sneddon's models performed on parts of the curve that indeed correspond to nonlinear elastic regimes, or that result from significant adhesive interactions of the AFM tip with the material lead to results that can be as much as twice larger than fits performed with appropriate models (nonlinear or adhesive). Here, we propose a methodology to address rigidity measurements by fitting parts of the force-indentation curves that correspond to the linear elastic response of the material, even in the presence of adhesion. The major contribution of this methodology is to set up an easy handling criterion to mark out the linear elastic response to indentation, valid either for purely elastic and elasto-adhesive models.