Fig. 3.

Measurement of micro-elasticity of matrices by AFM. A) A cantilever with a pyramidal tip (opening angle α) is translated down (Δz) into the sample causing a deflection d monitored by the photodiode, yielding the indentation δ=Δz–d. The required force F=k Δd is defined by the spring constant k multiplied by the deflection d. B) The Young's modulus E is determined by analyzing the resulting force-indentation curves with a modified Hertz model. Black curve denotes data points; red solid line is the best fit resulting from the modified Hertz model. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)